Physical Therapist test for muscular dystrophy in pediatrics patients

REVIEW PAPER Review of Spinal Muscular Atrophy (SMA) for Prenatal and Pediatric Genetic Counselors Amanda Carré 1&Candice Empey 2 Received: 6 May 2014 / Accepted: 30 June 2015 / Published online: 8 August 2015 #National Society of Genetic Counselors, Inc. 2015 Abstract Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular condition with degeneration of the anterior horn cells in the spinal column. Five SMA subtypes exist with classification dependent upon the motor milestones achieved. Study of the SMN1(survival motor neuron) and SMN2 genes as well as the concepts of the B2+0 ^carriers, gene conversion, de novo mutations and intragenic mutations allow for a better understanding of SMA. Detailing the carrier and diagnostic testing options further deepens the genetic counselor ’s knowledge of SMA. A review of care guidelines and research options is included as this information gives a patient a well-rounded view of SMA. Although SMA is most commonly associated with the SMN1gene, a number of spinal muscular atrophies not caused by genetic changes in this gene may be included as differential diagnoses until confirmatory testing can be completed. SMA is a complex condition requir- ing a detailed knowledge on the genetic counselor ’spartin order to explain the disorder to the patient with clarity thus facilitating increased communication and decision making guidance with the patient. Keywords Spinal muscular atrophy .

Carrier screening .

Diagnostic testing .

Genetic counseling .

Prenatal .

Pediatric Introduction Spinal muscular atrophy (SMA) may present in various forms, affecting every stage of life from the affected fetus with joint contractures, to the young child who never sits independently, to the young adult who loses the ability to ambulate on his or her own. Although classified as an autosomal recessive condi- tion, the genetics of SMA are not straightforward and thus, counseling for the preconception, prenatal and pediatric setting can be confusing for both the patient and health care provider.

Genetic counselors are tasked with explaining the natural his- tory, genetics, testing options, and potential outcomes of ge- netic disorders, such as SMA, to their patients. The goals for this paper are to elucidate the complex genetics of SMA and to expound on the carrier and diagnostic testing options available for SMA to aid genetic counselors in their discussions with patients and other healthcare providers. The majority of litera- ture written on SMA concerns the disorder associated with genetic changes on chromosome 5. However, other spinal muscular atrophies with similar physical findings but hetero- geneous causes are often included in the differential diagnoses until confirmatory testing can be completed for the patient.

Background Clinical Description The first part of this paper will focus on spinal muscular atro- phy (SMA) as caused by genetic changes of the SMN1(sur- vival motor neuron 1) gene. Please refer to the end of the paper Electronic supplementary material The online version of this article (doi:10.1007/s10897-015-9859-z) contains supplementary material, which is available to authorized users.

* Amanda Carré [email protected] 1 Department of Obstetrics and Gynecology, Drexel University College of Medicine, 216 N. Broad St, Feinstein Building 4th Floor, MS 990, Philadelphia, PA 19102, USA 2 Integrated Genetics, Laboratory Corporation of America® Holdings, Philadelphia, PA, USA J Genet Counsel (2016) 25:32 –43 DOI 10.1007/s10897-015-9859-z for discussion of spinal muscular atrophies not associated with theSMN1 gene.

SMA has an estimated incidence of 1 in 10,000 live births (Prior 2008; Smith et al. 2007). It is the most common genetic cause of mortality in children under the age of two. It is the second most common fatal autosomal recessive condition af- ter cystic fibrosis in the United States (Bürglen et al. 1996; Prior 2008; Wirth 2000). SMA as associated with chromo- some 5 is typically split into five subtypes, based on the age of onset and the clinical course of the disorder. Even with the degree of separation of symptoms between the sub-types, SMA is a disorder that can be categorized as a spectrum or continuum. The five subtypes are now commonly differenti- ated by numbers (0, I, II, III, IV) (Table 1). Patients are cate- gorized into their subtype by the motor milestones they achieve. All individuals with SMA have neuromuscular find- ings due to the degeneration of anterior horn cells in the spinal cord (Bürglen et al. 1996; Prior et al. 2004; Smith et al. 2007).

This loss of cells leads to symmetrical loss of muscle control and atrophy in the body, with proximal muscles most commonly being affected. The level of severity differs from the loss of muscular control needed for breathing and swallowing in Type I to loss of ambulation later in life in Types III and IV (Wirth 2000). Individuals with SMA may also experience poor weight gain, sleep difficulties, sco- liosis and joint contractures as well as restrictive lung disease, dysphasia, and constipation (Iannaccone 2007). While neuro- muscular findings are universal with SMA, intelligence levels and emotional development are not affected (von Gontard et al. 2002).

Type 0 SMA is often referred to as prenatal SMA, as this type presents in utero with arthrogryposis and joint contrac- tures. There is also a lack of fetal movement (MacLeod et al.

1999 ; Prior and Russman 2013; Russman 2007). Type I SMA, also known as Werdnig-Hoffman, is the most common sub- type of SMA occurring in about 60– 70 % of SMA cases (Ogino and Wilson 2004; Ogino et al. 2004;Prior 2008).

Often severe muscle weakness and hypotonia lead to fatal respiratory failure by 2 years of age. With the use of respira- tory support, life expectancy can be extended. These children never gain the ability to sit or walk independently. Sabine Rudnik-Schöneborn et al. ( 2008) reported atrial or ventricular defects occur in 75 % of type I SMA patients who only had a single SMN2 copy. Type II SMA, also called intermediate form, has an onset before 18 months of age. These children can learn to sit upright but do not walk unaided. The risk for pulmonary issues remains and life expectancy is unknown, with some affected individuals surviving to adulthood. Type III SMA is diagnosed with the onset of proximal muscle weakness after 2 years of age and was previously referred to as Kugelberg-Welander disease. Individuals with Type III of- ten have the ability to walk independently until the disease progresses. Life expectancy extends into adulthood. Finally, Type IV SMA is rarely diagnosed and is not apparent in an affected individual until adolescence or adulthood. Types 0 and I are the most severe forms of SMA, while Types III and IV lead to a later onset and a milder diagnosis.

Genetics Using linkage analysis, Lefebvre et al. ( 1995) first suggested the candidate gene for SMA was located at the SMN1(survival motor neuron 1) gene on chromosome 5q13. The SMN1gene is close to the telomere of chromosome five and contains nine exons about 20 kb in length (Bürglen et al. 1996; Wirth 2000).

SMA is an autosomal recessive condition most commonly ca used by a homozygous deletion of the SMN1gene.

Ninety-four percent of SMA cases are caused by the homozy- gous deletion of the SMN1gene, while the other 6 % of cases are compound heterozygotes with one deleted copy of the SMN1 gene and a point mutation in the other copy (Wirth 2000 ) or patients with de novo mutations. Downstream of the SMN1 gene and nearer to the centromere of chromosome 5istheSMN2 (survival motor neuron 2) gene. The SMN2 gene differs in functionality from SMN1by a single change at position 840 which leads to an alteration in splicing, reduc- ing the amount of full protein production. SMN2contains a thymine at position 840 in exon 7, whereas SMN1contains a cytosine (Bürglen et al. 1996). Individuals in the general pop- ulation typically have two SMN1gene copies, but may have Ta b l e 1 Subtypes of SMA Age of onset Clinical presentation Type 0 prenatal most severe; presents with lack of fetal movement, arthrogryposis, joint contractures; fatal at birth unless respiratory/medical support available Type I birth to 6 months severe generalized muscle weakness and hypotonia at birth; death from respiratory failure in less than 2 years Ty p e I I 6 –12 months able to sit; unable to walk or stand without aid, life expectancy unknown Type III after 18 months of age milder form; patients learn to walk unaided but lose ambulation as disease progresses Type IV adolescence to adulthood like Type III, but rarely diagnosed Compiled from Ogino et al. 2004; Prior et al. 2004; Prior 2008; Prior and Russman 2013;Russman 2007; Wirth et al. 1999 Review of SMA for Prenatal and Pediatric Genetic Counselors 33 up to four (Smith et al.2007). Prior et al. ( 2004)reportthe SMN2 copy number in the general population typically varies from zero (10 –15 %) to three SMN2gene copies. Some indi- viduals have been found to have as many as four to five SMN2 gene copies (Prior et al. 2004; Wirth 2000).

Due to the nucleotide difference between the SMN1and SMN2 genes, there is a potential for gene conversion making the SMN1 gene into a SMN2gene and vice versa (Burghes 1997; Campbell et al. 1997; Lefebvre et al.1995). For example, with gene conversion, the SMN1gene is altered so it now has a thymine at position 840. Thus it becomes a SMN2gene; how- ever, the location of the newly altered SMN2gene does not change from where the original SMN1gene was positioned near the telomere. Conversion mutation rates are the same in paternal and maternal settings at 2.07 × 10 5 (Ogino et al. 2004).

The SMN1 gene is responsible for producing 80 –90 % of the SMN protein while 10 –20 % of the SMN protein is de- rived from the SMN2gene. Individuals with a homozygous deletion of the SMN1gene still have the potential for making some functional protein through the SMN2gene, although the SMN2 gene produces an abbreviated protein 90 % of the time.

Therefore, this is not a disorder complicated by the complete absence of the protein, but instead it is a disorder with a critical reduction of available functional protein. The SMN protein is an omnipresent protein; however, it has increased levels in the spinal motor neurons (Wirth 2000).

Additionally, homozygous deletion of the SMN2gene does not lead to a diagnosis of SMA when at least one copy of the SMN1 gene is present in an individual. However, the copy number of the SMN2gene is thought to affect the genotype/ phenotype correlation when there is a homozygous deletion of the SMN1 genes (Feldkötter et al. 2002; Wirth et al. 1999; Wirth 2000). Some studies have indicated a more severe phe- notype for SMA when an individual has homozygous SMN1 mutations and less than three copies of the SMN2gene. A milder phenotype may correlate with those who have three or more copies of the SMN2gene. Prior et al. ( 2004)suggested five or more SMN2gene copies may partially compensate for the loss of the SMN1genes, although other modifying factors are most likely present. In a study published by Prior in 2009, three milder cases of SMA did not show the expected pheno- type correlation of increased SMN2copy number. Instead a c.859G>C substitution was found possibly modifying the phe- notype. SMN2copy number alone is not diagnostic of the type of SMA an individual will have.

Carrier Frequency for SMA Due to SMN1 Carrier frequency differs based on ethnicity, with the highest risk of 1 in 47 for Caucasians to the lowest risk of 1 in 72 for African-Americans (Table 2). Dependent upon ethnicity, risks of being a carrier for SMA are similar to the risks of being a carrier for cystic fibrosis. For individuals of mixed ethnicity, the ethnic background with the highest risk estimate is usually used when calculating risks for a fetus to be affected by SMA.

Most carriers of SMA have a heterozygous deletion of the SMN1 gene (Wirth 2000). These carriers have no medical concerns due to their carrier status. If both parents are carriers, the risk to have an affected child is 25 % based on straightfor- ward autosomal recessive inheritance. If the carrier ’s partner has two copies of SMN1, the risk to have an affected child is less than 1 %. The risk is not zero due to four situations in which a parent can be a SMA carrier even with two SMN1copies. First, the parent may have a B2+0 ^ ca rrier status. These individuals are found to have two SMN1 copies on one chromosome and no copies of the SMN1gene on the second chromosome. B2+0 ^carriers do not exhibit symptoms of SMA as they have two SMN1copies, but they have the potential to have an affected child if they pass on the chromosome with no copies of the SMN1 gene. Approximately 3.8 –4 % of the general popula- tion is thought to be a carrier of the B2+0 ^formation (McAndrew et al. 1997; Ogino et al. 2002a). Second, gene conversion between the SMN1andSMN2 genes may random- ly occur in a gamete, thus lowering the SMN1gene count and increasing the SMN2gene count passed on to a pregnancy.

This conversion would not be identified as an SMN1deletion in the parental blood. Third, there are individuals who are carriers of an intragenic mutation for SMA (Ogino et al.

2004 ; Smith et al. 2007). Finally, SMA has a de novo mutation rate with a paternal and maternal rate of 2.11 × 10 4and 4.15 × 10 5 respectively (Ogino et al. 2004).

An individual with two copies of SMN1is usually consid- ered a Bnon-carrier. ^The approximate 1 % residual risk may be difficult for a Bnon-carrier ^to process. While the risk may be perceived as low by the health provider, the risk may be perceived as high by the Bnon-carrier. ^Individuals may not act on the basis of the ‘actual ’risk presented to them, but act on the basis of their perception of the risk (Marteau 1999; Meiser et al. 2000;O’Doherty and Suthers 2007; Slovic et al. 1982;Slovic 1987).

For examples of various scenarios illustrating SMA carrier risk calculations, please refer to Shuji Ogino and Robert Wilson ’s 2002 paper entitled BGenetic testing and risk Ta b l e 2 Carrier frequency and detection rate by ethnicity Ethnicity Carrier frequency Detection rate Caucasian 1/47 94.8 % Ashkenazi Jewish 1/67 90.5 % Asian 1/59 93.3 % African American 1/72 70.5 % Hispanic 1/68 90.0 % Overall 1/54 91.2 % Adapted from Sugarman et al. 2012 34 Carré and Empey assessment for spinal muscular atrophy (SMA)^(located in the journal of Human Genetics) or Melanie Smith and col- leagues ’2007 paper on BPopulation screening and cascade testing for carrier of SMA ^(located in the European Journal of Human Genetics).

Genetic Testing Options Carrier Screening As the most common type of carrier of SMA has only one copy of SMN1, determining the copy number of SMN1is essential to carrier screening. Dosage analysis, also called copy number analysis, is used for carrier screening. Dosage analysis determines the number of SMN1genes an individual has in total. The detection rate for carrier screening is 94 % in individuals of Caucasian descent; however, it is lower for individuals of other ethnicities (see Table 2) (Sugarman et al.

2012). Specificity of carrier screening approaches 100 % (Scheffer et al. 2000). The residual carrier risk decreases with increasing number of SMN1copies found. Limitations of using dosage analysis for carrier screening include the follow- ing: cannot distinguish between B2+0 ^carriers and B1+1 ^ non-carriers, plus it cannot detect point mutations.

Additionally, the de novo germline mutation rate cannot be accounted for in carrier screening (Prior and Russman 2013).

Luo et al. ( 2014) recently completed analysis on carrier screening in the Ashkenazi Jewish population. They attempted to identify deletion and duplication founder alleles in the Ashkenazi Jewish population through microsatellite analysis and next-generation sequencing. The team ’saim was to improve the accuracy of residual risk estimates and increase the number of B2+0 ^carriers detected through carrier screening. Their findings are reported in BAn Ashkenazi Jewish SMN1haplotype specific to duplication alleles im- proves pan-ethnic carrier screening for spinal muscular atrophy^ (located in the journal Genetics in Medicine).

Further data is needed to help determine if Luo ’ssuggested method for expanded carrier screening for potential B2+0 ^ carriers should be included as part of the initial carrier screen or if it should be ordered as a reflex test when dosage analysis does not determine the patient to be a carrier for SMA. Please refer to appendix A for a flowchart illustrating possible testing routes seen with carrier screening for SMA in the general population when the individual being tested has no family history of SMA. Over 50 laboratories throughout the world offer carrier screening for SMA. In the past, carrier testing through labo- ratories consisted of ordering SMA carrier screening as a stand-alone screen. Clinicians now have the opportunity to order SMA carrier screening as part of a multi-disorder carrier panel. These multi-disorder panels allow for a patient to be screened for numerous genetic disorders simultaneously with one sample collection instead of multiple blood draws. The process of testing with multi-disorder panels for SMA carrier status may be through dosage analysis or via sequencing of the SMN1 gene. If ordering SMA carrier screening through a multi-disorder panel, it is important to distinguish which method the laboratory utilizes. Not all laboratories offer com- plete SMA testing, such as reflex sequencing for intragenic mutations or SMN2copy number analysis. Depending upon previously completed carrier screening or patient preference, the clinician can aid the patient in selecting stand-alone SMA carrier screening versus a multi-disorder panel. For stand-alone SMA carrier screening, sample require- ments vary between the laboratories; however, many request 4 – 10 cc of whole blood in lavender top tubes (EDTA) or yellow top tubes (ACDA). Samples are sent overnight at room temperature to the laboratory completing the testing. Turn- around time may range from 5 to 28 days, depending on the la boratory. For multi-disorder panels, sample requirements al- so vary between the laboratories. Acceptable samples may include saliva samples or approximately 10 –20 cc of whole blood in lavender top tubes (EDTA). As with stand-alone testing, samples are sent overnight at room temperature to the laboratory. Turn-around time typically is 2 weeks. Many times carrier screening occurs in a consecutive man- ner, meaning the female partner of the couple is screened first and if she is found to be a carrier for SMA, then her male partner is screened. Carrier screening can occur concurrently, with both partners of the couple having blood drawn at the same time. Concurrent testing may be advisable when there is limited time to perform screening on both members of the couple, e.g., a pregnant woman has a family history of SMA and she is close to the gestational age limitation for complet- ing a fetal diagnostic procedure such as amniocentesis. Reproductive options for carrier couples include prenatal diagnosis (see further description later in this article), gamete donation, preimplantation genetic diagnosis, termination of an affected pregnancy, placing an affected individual for adop- tion and adoption of an unaffected individual. Appropriate follow-up should be offered to additional family members when an individual is found to be a carrier for SMA. This may include offering genetic counseling and carrier screening to extended family members.

Approach to Prenatal Carrier Screening Current recommendations by the American College of Medical Genetics (ACMG) include offering SMA carrier screening to all couples, regardless of race or ethnicity, before conception or early in pregnancy. The ACMG also suggests educational materials be made available to all couples, while formal genetic counseling services be made available to any- one requesting this screening. The ACMG proposes all Review of SMA for Prenatal and Pediatric Genetic Counselors 35 identified carriers should be referred for follow-up genetic counseling and offered prenatal and preimplantation diagnosis (Prior2008). Current recommendations by the American Congress of Obstetricians and Gynecologists (ACOG) do not advise preconception and prenatal screening for SMA be offered to the general population. ACOG advocates testing be offered to couples with a family history of SMA or SMA-like disease and those who request SMA carrier screening after completing genetic counseling. ACOG recommends all iden- tified carriers for SMA be referred for follow-up genetic counseling to discuss prenatal and preimplantation diagnosis, including gamete donations. ACOG suggests referral to a ge- netic counselor for patients requesting fetal testing for SMA (ACOG Committee Opinion 2009).

Prenatal Diagnosis Prenatal diagnosis to determine if a fetus is affected with SMA utilizes dosage analysis of the SMN1gene from fetal DNA obtained by chorionic villi sampling or amniocentesis.

Invasive prenatal diagnosis by chorionic villi sampling or am- niocentesis is most appropriate if both parents are known car- riers or if the patient is a carrier and the partner ’s status is unavailable. In most situations the mutations found in the patient and her partner will be known and proper testing for these specific mutations in the fetus can be arranged.

Limitations of prenatal testing utilizing dosage analysis in- clude the following: it cannot identify intragenic mutations and the partner ’s genotypic information is necessary for a more informative result. If a patient or partner has a known intragenic mutation, sequencing analysis may be utilized on the fetal DNA sample. Laboratories performing preimplanta- tion diagnosis for SMA will also use dosage and sequencing analysis to produce embryos without SMN1mutations, an option for couples who are known carriers.

Postnatal Diagnostic Testing Clinically the diagnosis of SMA is suspected in individuals with a personal history of motor difficulties and evidence of motor neuron disease on a p hysical examination. The clinical classification of SMA is based on age of onset and maximum function attained (Prior and Russman 2013).

Electromyography, nerve conduction velocities, muscle en- zyme creatine kinase, and muscle histology were used more so in the past to establish a diagnosis of SMA (Hausmanowa- Petrusewicz and Karwa ńska 1986 ;Russman 2007;Wang et al. 2007).

After linkage analysis was used to identify the SMN1gene, deletion analysis of the SMN1gene was used as the basis for a SMA diagnosis. Deletion analysis consists of the detection of the complete absence of exon 7 in the SMN1gene. The detec- tion rate of this diagnostic testing for an affected individual is 94– 95 % (Lefebvre et al. 1998;OginoandWilson 2002; Wang et al. 2007) with almost 100 % specificity (Rodrigues et al. 1995; Wang et al. 2007). With deletion analysis, the polymerase chain reaction-RFLP assay utilizes restriction en- zymes to cut only the SMN2exon 7 polymerase chain reaction products. In patients with spinal muscular atrophy, the uncut SMN1 exon 7 is found to be absent (Prior 2007). This type of deletion analysis is also called RFLP analysis.

Currently, over 60 laboratories worldwide perform diagnos- tic testing for SMA. Deletion analysis may often be first tier testing due to cost prohibitions for the other technologies uti- lized for SMA diagnostic testing. Deletion analysis, however, cannot detect the copy number of SMN1(thus it cannot detect individuals who are carriers for SMA or compound heterozy- gotes), point mutations, and small intragenic insertions or de- letions. To address the limitations of this older technology, clinicians may choose to begin testing their patients through dosage analysis and then reflex to sequence analysis of the entire coding region, which increases the ability to identify compound heterozygote patients with intragenic mutations. Dosage analysis is a quantitative test for the number of SMN1 gene copies, while sequence analysis of the SMN1gene may be especially useful for those who are suspected of being compound heterozygotes with an intragenic mutation and de- letion of one copy of the SMN1gene (Prior et al. 2011).

Sequence analysis can be performed for the detection of cer- tain intragenic mutations such as small intragenic deletions/ insertions and missense, nonsense, and splice site mutations.

Whole-gene deletions/duplications may not be detected, while variants of uncertain significance may be detected. Additional testing by a method facilitating SMN1-specific and SMN2- specific amplification and sequence analysis (Prior et al.

2011 ) is necessary to verify an intragenic mutation has oc- curred in SMN1and not SMN2.

McAndrew et al. ( 1997) developed the first assay for dos- age analysis of the SMN1gene. The assay uses quantitative PCR analysis. The copy number of SMN1is determined by the coamplification of SMN1,SMN2 and other gene standards.

Since then, other assays of dosage have been developed.

Dosage analysis allows for the detection of duplication as well as deletion of the SMN1gene, as determined by the copy number present (Ogino and Wilson 2004). This technology is most utilized for carrier status, although it can be used for diagnostic purposes, including prenatal diagnosis.

Finally, some laboratories also use linkage analysis in con- junction with dosage analysis. Linkage analysis can be uti- lized when two copies of SMN1are found in the parents of an affected child who lacks both copies of SMN1(Ogino and Wilson 2002; Ogino et al. 2002b). If an intragenic mutation is found in an affected individual, linkage analysis can help track which unaffected or undiagnosed family members may have the same intragenic mutation. Chen et al. ( 1999)reportthat linkage analysis can also be useful in differentiating between 36 Carré and Empey theB1+1 ^genotype and the B2+0 ^genotype, as well as find- ing crossover events associated with de novo SMN1deletions.

Appendix B includes a flowchart illustrating possible test- ing routes that may occur with diagnostic testing for SMA.

For more in depth reviews of the diagnostic testing method- ology for SMA please refer to Shuji Ogino and Robert Wilson ’s 2004 paper entitled BSpinal Muscular Atrophy:

Molecular Genetics and Diagnostics ^(located in the journal of Expert Review of Molecular Diagnostics) or Thomas Prior and colleagues ’2011 paper on BTechnical Standards and Guidelines for Spinal Muscular Atrophy Testing ^(located in Genetics in Medicine). When an individual has been found to have SMA through diagnostic testing, appropriate follow-up should be offered to additional family members. This includes carrier screen- ing for the parents of the affected child so reproductive options and recurrence risks for subsequent pregnancies can be established. Siblings of reproductive age also benefit from carrier screening; however, parents of siblings who are not yet of reproductive age may wish to wait until those siblings are older to pursue this testing. Diagnostic testing in siblings who may not yet be exhibiting symptoms of SMA is controversial and the implications of such testing should be discussed thor- oughly with the family before pursuing testing. The American Society of Human Genetics (ASHG) and the American College of Medical Genetics ’(ACMG) Boards of Directors in 1995 discussed numerous points to consider when testing minors for genetic disorders, including the impact of potential benefits and harms on decisions about testing, the family ’s involvement in decision making, and considerations for future research. For example, medical benefit to the child should be the main justification for completing genetic testing in minors.

Therefore, some health practitioners may advise delaying test- ing in a child who is not showing signs of SMA if the medical benefits are uncertain or will not be beneficial to the child at the current time. Others contend early testing may lead to earlier treatment and therefore possibly reduce the severity of the disorder in the potentially affected individual. ASHG and ACMG stress the importance of not only focusing on the medical benefits and harms of genetic testing on minors but also the potential psychosocial benefits and harms genetic testing can involve. Extended family members, such as aunts, uncles, and cousins of reproductive age, may also be informed of the risks to be carriers. Genetic counselors can work with primary families to determine the best way to approach ex- tended family members with the information on screening opportunities.

Treatment for Affected Individuals There is no genetic cure for SMA; however, a number of treatments are performed on affected individuals. The International Standard of Care Committee for Spinal Muscular Atrophy was founded in 2005 with the goal of de- veloping guidelines for care of affected individuals. The com- mittee suggests either a pediatric neurologist or geneticist co- ordinate clinical care for the patient and their family. Medical management of individuals with SMA also includes team members from genetic counseling, orthopedics, neurology, pulmonology, general surgery, gastroenterology, neonatology, general pediatrics, and palliative care. Currently treatment for SMA focuses on symptomatic and supportive care for indi- viduals with SMA. The International Committee focused on five areas of care in its guidelines for SMA –diagnostic/new interventions, pulmonary, gastrointestinal/nutrition, orthope- dics/rehabilitation, and palliative care (Wang et al. 2007).

Diana Castro and Susan Iannaccone in their 2014 article B Spinal Muscular Atrophy: Therapeutic Strategies ^(located in the Current Treatment Options in Neurology journal) pro- vide further commentary on medical management for symp- tomatic patients with SMA. Treatments for the physical concerns focus on the symp- toms of the disorder. For the pulmonary concerns, Wang et al.

( 2007 ) listed the key respiratory problems as impaired ability to cough, hypoventilation during sleeping periods, underde- velopment of the chest wall and lungs, and recurrent infec- tions. Respiratory support is designed to aid individuals with breathing at times of wakefulness and sleeping. This support may include the use of ventilators with masks available in numerous sizes and maintaining airway clearance by utilizing me chanical cough assist machinery (Iannaccone 2007).

Patients with SMA type I can survive beyond 2 years of age when offered tracheostomy or noninvasive respiratory support (Bach et al. 2002). Respiratory support is seen as a tool to extend the length of an affected patient ’s life, but it does not slow the progression of the disease. Families may feel respi- ratory support can improve the quality of life for their child. Gastrointestinal problems include feeding and swallowing issues, dysfunction of the gastrointestinal system including constipation, delayed gastric emptying and growth difficulties (Wang et al. 2007). With constipation concerns, dietary man- agement and control of fiber and water content may help min- imize the discomfort for the patient and reduce the risk for bowel impaction (Iannaccone 2007). Other treatments con- centrate on augmenting feeding times and increasing the nu- trients obtained during those feedings. Placement of feeding tubes may be beneficial for some patients; however, the sur- gery to place such tubes comes with risks for individuals with SMA. These risks must be discussed with the family prior to the potential need for surgery so the appropriate plan of care can be made for the patient. Monitoring for and management of gastroesophageal reflux is also important for individuals with SMA as it can increase the mortality and morbidity rates in this population due to risks for aspiration, pneumonias and additional respiratory concerns (Birnkrant et al. 1998; Wang et al. 2007). Review of SMA for Prenatal and Pediatric Genetic Counselors 37 Orthopedic care includes conservative and operative treat- ment options for contractures, hip dysplasia, fractures, scoliosis and pelvic obliquity. One of the major problems in orthopedic therapy is scoliosis in nearly 100 % of nonambulatory SMA patients with type II and III (Haaker and Fujak 2013). Surgical spine correction can result in rest ored sitting ability without arm support and avoidance of impingement of the ribs on the pelvis creating increased sitting comfort and self-confidence in en- hanced appearance (Haaker and Fujak 2013). Treatments also include physical therapy, occupational therapy, orthoses, tech- nical devices, operative treatment, power wheelchairs for mo- bility, and pain management. Finally, palliative care with the use of hospice referrals and availability of medical, social, and spiritual assistance can benefit families (Wang et al. 2007).

A debate exists concerning the current available therapies that may prolong the length of life, but do not increase the quality of life (i.e., do not slow the progression of the disease).

There is little agreement in the literature about the use of available treatments and optimal care for patients with SMA.

Optimal management is achieved through a multidisciplinary approach with consistent communication between the medical team and the patient ’sfamily.

Emerging Medical Therapies Due to the inability to effectively slow the progression of the disorder with current treatments, a number of research teams are exploring methods to treat affected individuals to slow or stop progression of the disorder. In Li-Kai Tsai ’s 2012 review article, therapy development can be divided into two classes; B SMN Dependent ^and BSMN Independent ^targets. In poten- tial SMN dependent therapy the strategies are divided into small molecules, antisense oligonucleotides and viral vector mediated gene therapy. The aim of small molecules, which include histone deacetylase inhibitors such as aclarubicine (Andreassi et al. 2001), sodium butyrate (Chang et al. 2001), and valproic acid (Brichta et al. 2003), is to increase the level of full-length proteins as made by the SMN2gene. Pfizer (234 East 42nd Street, New York, NY 10017) is conducting phase I studies researching the ability of quinazolines to prohibit the breakdown of SMN2RNA (Castro and Iannaccone 2014; Zanetta et al. 2014a). However, most small molecule therapies have not proven to show consistent benefits in clinical trials (Kissel et al. 2011; Swoboda et al. 2009, 2010 ; Tsai 2012).

Antisense oligonucleotides (ASO) are designed to base pair with target RNA. ASO can then elicit effects on the RNA, such as promoting RNA degradation, interfering with pre-mRNA pro- cesses, blocking access to RNA an d disrupting the structure of the RNA (Rigo et al. 2012; Zanetta et al.2014b). The process through which the ASO works is dependent upon the class of RNA, the location on the RNA the ASO binds, and the chemical composition of the ASO itself (Rigo et al. 2012). Rigo et al. ( 2012)showedsystemictreatme nt with ASOs could enhance survival in a mouse model with severe SMA. ISIS Pharmaceuticals Inc. (2855 Gazelle Court, Carlsbad CA 92010) is in the process of testing an ASO therapy (ISIS- SM NRx) that allows the nucleotides to bind to the mRNA se- quence in the SMN2gene. Then exon 7 of the SMN2gene is able to be included in the sequencing instead of being repressed; thus, a full length and more functional SMN protein is created (Castro and Iannaccone 2014; Zanetta et al. 2014a,b). In mice and non- human primates, the use of ISIS-SMNRx, a 2 ′-O-Methoxyethyl- modified antisense drug, has shown the ability to increase the production of fully functional SMN protein (Rigo et al. 2014). In the ISIS clinical trial phase I study, patients with types II and III SMA were injected with an ASO into their intrathecal space, thus allowing for a bypass of the blood brain barrier and ensuring the drug can have an effect in the central nervous system (Castro and Iannaccone 2014). A phase II study is currently underway de- signed to examine the safety, tole rability and pharmacokinetics of multiple dose administration (Zanetta et al. 2014a). Braun ( 2013) describes a possible limitation of ASO use in treating patients with SMA. He notes re-administration of the ASO would be necessary due to the limited half-life of the compound. Viral vector mediated gene therapy in animal trials involves injection of a viral vector carrying SMNinto mice with SMA.

Glascock et al. ( 2011) found when injecting a viral vector with SMN intracerebroventricularly into SMA mice, they gained more weight and displayed fewer early deaths than mice injected intravenously thus demonstrating route of delivery of vector mediated gene replacement is crucial in gene therapy treatment for SMA. In 2014, a phase I clinical trial began at Nationwide Children ’s Hospital in Ohio. The study is investi- gating the ability of an adenovirus vector, AAV9, to cross the blood brain barrier and replace the missing SMN1gene in patients with SMA (Castro and Iannaccone 2014; Zanetta et al. 2014b ). Viral gene therapy has shown an advantage of having a long survival time in preclinical studies with the need for only one delivery (Braun 2013).

Another new SMNdependent therapy being evaluated is the idea of neuroprotection. Trophos, a French pharmaceutical company, recently conducted a phase II study concerning the ability of olesoxime to provide protection for motor neurons.

The therapy was found to be effective in keeping motor neu- rons alive in culture (Zanetta et al. 2014a). Olesoxime was provided orally to patients with SMA II or III. The goal was to determine if the medication, a cholesterol-like molecule, could also aid the survival of motor neurons in human sub- jects. At this time, no results of the phase II study are available for review (Castro and Iannaccone 2014; Zanetta et al. 2014a).

SMN independent potential therapies include but are not limited to myotrophic effects, axonal dynamics, and stem cells. Investigation of albuterol is an example of a potential therapy involving myotrophic effects. A trial with 23 type II SMA patients showed better Hammersmith motor functional 38 Carré and Empey scores after daily treatment for 6 or 12 months (Pane et al.

2008). With reference to axonal dynamics, treatment of SMA model mice with Rho-kinase inhibitor Y-27632 led to signif- icant prolonged survival and improvement in the integrity of neuromuscular junctions (Bowerman et al. 2012; Tsai 2012).

Stem cell therapy includes neural stem cells, embryonic stem cells and induced pluripotent stem cells. Kerr et al.

( 2003 ) researched the ability to use stem cell therapy to estab- lish motor neurons to replace those which degenerated due to the disease. Corti et al. ( 2008) used intrathecal injection of neural stem cells derived from mouse spinal cord into a severe type of SMA mouse model. This therapy showed promoted motor neuron survival, improved motor function and prolonged lifespan. There is much still to be accomplished in cell therapy before clinical application is possible (Tsai 2012).

For more intensive reviews of current and future medical therapies for SMA, please refer to the 2013 article BGene- based therapies of neuromuscular disorders: an update and the pivotal role of patient organizations in their discovery and implementation (Serge Braun, The Journal of Gene Medicine), ^Chiara Zanetta ’s2014article BMolecular thera- peutic strategies for spinal muscular atrophies: current and future clinical trials (Clinical Therapeutics journal), ^and the 2014 article from Journal of Cellular and Molecular Medicine by C. Zanetta BMolecular, genetic, and stem cell-mediated therapeutic strategies for spinal muscular atrophy. ^Through ongoing research, treatments may soon be designed to signif- icantly reduce the severity of symptoms associated with SMA.

For patients wishing to participate in research, an up-to-date list of ongoing trials for spinal muscular atrophy can be found at www.clinicaltrials.gov . At the time of the writing of this paper, there were 160 studies registered for SMA testing.

Other Types of Spinal Muscular Atrophies When an individual with symptoms suggestive for SMA pre- sents for clinical examination with no confirmed genetic di- agnosis, numerous genetic disorders may be considered in the differential diagnosis. Some of these genetic disorders may include forms of SMA unrelated to changes in the SMN1gene.

The following is a short review of a number of different spinal muscular atrophies included in the differential diagnosis list.

This list is not all inclusive. SMA with respiratory distress type 1 (SMARD) is another autosomal recessive condition. It is linked to the IGHMBP2 gene at 11q13.2-q13.4. Affected individuals present in the first 3 months of life with eventration of the right or both hemidiaphragms plus finger and feet abnormalities (Wang et al. 2007).

X-linked infantile SMA with arthrogryposis is also associ- ated with loss of anterior horn cells in the spinal cord (Baumbach-Reardon et al. 2012). X-linked infantile SMA, however, has been linked to a change at Xp11.3-q11.2. For affected children, death can occur at less than 2 years of age (Wang et al.

2007). The disorder is associated prenatally with polyhydramnios and poor fetal movement, which can lead to bone fractures. After delivery, these children face restrictive lung disease (Baumbach-Reardon et al. 2012).

X-linked spinal and bulbar muscular atrophy is a disorder seen in men, with an onset between 20 and 50 years of age.

These affected individuals show muscle weakness, muscle atrophy, fasciculations, gynecomastia, testicular atrophy, and reduced fertility (La Spada 2011; Russman 2007). Carrier fe- males for X-linked spinal and bulbar muscular atrophy may experience muscle cramps or tremors (Mariotti et al. 2000).

Autosomal dominant SMA typically has an onset after 20 years of age; however, there are a few cases of adolescents with autosomal dominant SMA. This slowly progressing disor- der comprises up to 30 % of adult onset SMA (Pearn 1978 ; R ietscheletal. 1992). As a specific example of an autosomal dominant SMA, individuals with scapuloperoneal spinal muscu- lar atrophies experience a loss of ambulation occurring in the fifth decade or later. A linkage analysis of one large affected family suggests a change in the area of 12q24.1 –24.31 to be the causa- tive factor (Isozumi et al. 1996). These disorders are diagnosed through the presence of large motor units on electromyography with normal sensory potentials and normal nerve conduction velocities (Russman 2007). They clinically present with progres- sive weakness of scapuloperoneal and laryngeal muscles (Wang et al. 2007).

Distal spinal muscular atrophies, unlike SMN1-associated SMA which starts in the proximal muscles, are classified as such due to the wasting of the distal muscles with slow pro- gression to the proximal muscles (Russman 2007). There are currently ten subtypes of distal spinal muscular atrophy, with both autosomal dominant and autosomal recessive methods of inheritance noted (Irobi et al. 2004).

Individuals with later-onset autosomal recessive hexosa- minidase A, or G M2 -gangliosidoses, deficiencies have been incorrectly identified as affected by SMA. Case reports have discussed how affected individuals were found to meet the clinical diagnosis of SMA –difficulty in ambulation, progres- sive decline in muscle strength, SMA electromyography find- ings, and SMA muscle biopsy findings. However, when fur- ther tested for hexosaminidase A activity levels, the patients were found to be lacking normal levels of hexosaminidase A and were thus diagnosed with hexosaminidase A deficiencies (Johnson et al. 1982; Karni et al. 1988).

Pontocerebellar hypoplasia with SMA is an autosomal reces- sive condition, caused by a mutation in the VRK1gene, present- ing with cerebellar and brainstem hypoplasia and neuronal loss in the basal ganglia (Renbaum et al. 2009;Wangetal. 2007).

Fazio-londe disease affects the lower cranial nerves and symptoms become apparent in the second decade of life. Death usually occurs within 1 to 5 years of the diag- nosis (Russman 2007). Review of SMA for Prenatal and Pediatric Genetic Counselors 39 Summary There is substantial variability in the natural history of SMA as it is a complex genetic disorder with numerous subtypes and dif- ferential diagnoses. The focus of this paper has been on spinal muscular atrophy as caused by genetic changes in theSMN1gene on chromosome 5q13. This overv iew of the current literature provides a comprehensive summary of the disorder, including the natural history of the disorder, the genetics of SMA, available carrier screening, potential prenatal and pediatric diagnostic test- ing, care management options, pot ential emerging medical treat- ment therapies, and differential diagnoses. Healthcare providers, especially genetic counselors, may routinely be called upon to discuss SMA with their patients as the general public becomes aware of the availability of carri er screening for this disorder.

Genetic counselors are in the ideal position to be educational resources on SMA. They may provide pertinent, factual medical information and support materials to their patients. In relation to the natural history of SMA, there are five subtypes of SMA. They are clinically denoted by the motor milestones achieved by the affected individual. All five sub- types share a main diagnostic feature –degeneration of the anterior horn cells in the spinal column; however, age of onset of the symptoms plays a role in the categorizing of the subtype an individual has.

Numerous items complicate the inheritance pattern and counseling for SMA. The numerical count of SMN1and SMN2 genes an individual carries is one such issue. Prenatal and pediatric genetic counseling for SMA referrals may need to involve discussion of B2+0 carriers, ^gene conversion be- tween the SMN1andSMN2 gene, maternal and paternal de novo mutations, and intragenic mutations. Without a genetic cure for SMA, care has been focused on providing symptom- atic and supportive treatments for patients with SMA. Great advances in clinical research trials have placed potential treat- ments on the horizon which aim to reduce the severity and progression of SMA. Finally, a subset of spinal muscular at- rophies not caused by deletions or intragenic changes in the SMN1 gene exists. These disorders are often included in the differential diagnoses for a suspected affected individual until confirmatory diagnostic testing can be completed.

Resources Healthcare Provider Resources GeneReviews: http://www.genetests.org/resources/ genereviews.php GeneTests: http://www.genetests.org/ OMIM (online Mendelian Inheritance in Man): http:// www.omim.org/ Appendix C : Sample letter for carrier of SMA to share with family members Appendix D : Sample letter for parents of child with SMN1 gene deletions to share with family members Appendix E : Sample letter for parents of child with SMN1 gene deletion and intragenic mutation to share with family members Patient and Family Resources The Claire Altman Heine Foundation, Inc. 1112 Montana Ave, #372, Santa Monica CA 90403 www.clairealtmanheinefoundation.org Cure SMA 925 Busse Road, Elk Grove Village IL 60007 www.curesma.org Fight SMA 1321 Duke Street, Suite 304, Alexandria VA 22314 www.fightsma.org The Jennifer Trust 40 Cygnet Court, Timothy ’s Bridge Road, Stratford upon Avon, Warwickshire CV37 9NW, U.K. www.jtsma.org.uk Muscular Dystrophy Association –USA National Headquarters 3300 E. Sunrise Drive, Tucson AZ 85718 www.mdausa.org Spinal Muscular Foundation 888 Seventh Avenue, Suite 400, New York NY 10019 www.smafoundation.org Acknowledgments We would like to thank Kenny Wong, Meghan Wayne, Patricia Page and Natalie Beck for their help in gathering data for this paper. We also gratefully thank Dr. Alan Donnenfeld and Dr.

Geraldine McDowell for their review of this manuscript.

Compliance with Ethical Standards Please refer to this section which is located on page 33. It contains the conflict of interest statements, re- search involving human/animal participants ’statement, and the informed consent statement.

Conflict of Interest Amanda Carré declares that she has no conflict of interest.

Candice Empey was a past employee of Integrated Genetics, Laboratory Corporation of America® Holdings, which performs Spinal Muscular Atrophy testing.

Research Involving Human Participants and/or Animals This arti- cle does not contain any studies with human participants or animals per- formed by any of the authors.

Informed Consent As this article does not contain any studies with hu- man participants or animals, informe d consent was not necessary to obtain.

Comments This manuscript is submitted solely to the Journal of Genetic Counseling and has not been published elsewhere or submitted to any other journal for publication purposes. 40 Carré and Empey Appendix A Appendix B References ACOG Committee Opinion No. 432. (2009). Spinal muscular atrophy.Obstetrics and Gynecology, 113 , 1194–1196.

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We began our research for this paper by conducting multiple PubMed searches. These searches were completed to locate papers included in the reference section. Keyword combinations utilized during the searches included: spinal muscular atrophy, spinal muscular atrophy carrier screen- ing, and spinal muscular atrophy diagnostic testing. No publishing date limitations were used during the searches. A review of the reference sections in the papers found through the PubMed searches allowed for the collection of additional publications. Finally, a search for spinal mus- cular atrophy on GeneTests ( http://www.genetests.org/ ) demonstrated numerous differential diagnoses for spinal muscular atrophy as caused by changes in the SMN1gene. Review of SMA for Prenatal and Pediatric Genetic Counselors 43 Copyright ofJournal ofGenetic Counseling isthe property ofSpringer Science&Business Media B.V.anditscontent maynotbecopied oremailed tomultiple sitesorposted toa listserv without thecopyright holder'sexpresswrittenpermission. However,usersmayprint, download, oremail articles forindividual use.