Spinal Muscular Atrophy: Genetic Counseling

Spinal Muscular Atrophy (SMA) is an incurable, inherited neuromuscular disease typified by progressive weakness and, in the most severe forms, death due to respiratory failure.1 SMA is the second most common congenital disease with an estimated worldwide incidence of approximately 1 in 10,000 live births.2 Given that the inheritance pattern of SMA is autosomal recessive,1 the high birth incidence rate of SMA means that there are a high number of asymptomatic carriers, on average 1 in 503 though some ethnic populations appear to have higher frequencies.2 The genetics of SMA can present unique challenges,4,5 and thus given its high incidence2 and its biological idiosyncrasies,6 there is a widespread and specific need for genetic counseling in SMA.6,7

Genetic counselors provide many useful services to referred individuals as indicated below:8

  • They discuss family planning options with at-risk families
  • They provide statistical information about the likelihood of having a child with SMA
  • They explain genetic testing results to ensure full understanding of the test’s implications
  • They provide basic information about SMA like symptoms, disease course, and prognosis
  • They identify at-risk individuals
  • They can recommend follow-up testing if needed

Consensus guidelines recommend that genetic counseling be included among multidisciplinary services offered to parents who have children diagnosed with, or suspected of having, SMA.9 The American College of Obstetricians and Gynecologists advises offering genetic counseling to identified all known SMA carriers, anyone who sought SMA genetic testing, and anyone requesting fetal testing.10 Despite these recommendations, genetic counseling and offers of testing to at-risk families are particularly lacking in SMA.4,11 A survey of how parents received their diagnosis and genetic counseling revealed the primary source of information was their child’s neurologist and that the shared information was not optimally matched to families’ needs.12 Trained genetic counselors are ideally suited for conveying the complexities of SMA to families.13 The diagnostic odyssey in SMA can be long in duration14 and ultimately achieving a SMA diagnosis is traumatic for families.15 Genetic counselors should possess SMA-specific knowledge to ensure effective communication with parents and patients.13 A single interaction with a trained counselor is not an assurance of parents being aware of even basic facts such risk of recurrence in future offspring,8 a finding that highlights the need for better parental education before and after genetic testing,16 especially in SMA.12 A follow-up letter after genetic counseling reinforces understanding of topics covered in the counseling session.8 

Prenatal screening,17 universal newborn testing,18,19 and genetic testing of asymptomatic siblings of patients with SMA9 have been controversial topics because of ethical dilemmas given the absence of proven interventions, but these topics may be revisited in the near future with the approval of effective therapies for SMA.19

References

1. D’Amico A, Mercuri E, Tiziano FD, Bertini E. Spinal muscular atrophy. Orphanet journal of rare diseases. 2011;6:71.

2. Verhaart IEC, Robertson A, Wilson IJ, et al. Prevalence, incidence and carrier frequency of 5q-linked spinal muscular atrophy – a literature review. Orphanet journal of rare diseases. 2017;12(1):124.

3. Sugarman EA, Nagan N, Zhu H, et al. Pan-ethnic carrier screening and prenatal diagnosis for spinal muscular atrophy: Clinical laboratory analysis of >72,400 specimens. Eur J Hum Genet. 2012;20(1):27-32.

4. Jedrzejowska M, Szczaluba K, Sielska D. Homozygous deletion in the smn1 gene in asymptomatic individual – genetic counselling issues in sma-risk families. Medycyna wieku rozwojowego. 2011;15(2):126-131.

5. da Silva LR, Colovati ME, Coprerski B, et al. Spinal muscular atrophy due to a “de novo” 1.3 mb deletion: Implication for genetic counseling. Neuromuscular disorders : NMD. 2013;23(5):388-390.

6. Ogino S, Wilson RB. Spinal muscular atrophy: Molecular genetics and diagnostics. Expert review of molecular diagnostics. 2004;4(1):15-29.

7. Alias L, Barcelo MJ, Bernal S, et al. Improving detection and genetic counseling in carriers of spinal muscular atrophy with two copies of the smn1 gene. Clinical genetics. 2014;85(5):470-475.

8. Forrest LE, Delatycki MB, Curnow L, Skene L, Aitken M. Genetic health professionals and the communication of genetic information in families: Practice during and after a genetic consultation. Am J Med Genet A. 2010;152a(6):1458-1466.

9. Wang CH, Finkel RS, Bertini ES, et al. Consensus statement for standard of care in spinal muscular atrophy. J Child Neurol. 2007;22(8):1027-1049.

10. Committee opinion no. 690: Carrier screening in the age of genomic medicine. Obstet Gynecol. 2017;129(3):e35-e40.

11. Forrest L, Delatycki M, Curnow L, Gen Couns M, Skene L, Aitken M. An audit of clinical service examining the uptake of genetic testing by at-risk family members. Genet Med. 2012;14(1):122-128.

12. Meldrum C, Scott C, Swoboda KJ. Spinal muscular atrophy genetic counseling access and genetic knowledge: Parents’ perspectives. J Child Neurol. 2007;22(8):1019-1026.

13. Carre A, Empey C. Review of spinal muscular atrophy (sma) for prenatal and pediatric genetic counselors. Journal of genetic counseling. 2016;25(1):32-43.

14. Lin CW, Kalb SJ, Yeh WS. Delay in diagnosis of spinal muscular atrophy: A systematic literature review. Pediatr Neurol. 2015;53(4):293-300.

15. Lawton S, Hickerton C, Archibald AD, McClaren BJ, Metcalfe SA. A mixed methods exploration of families’ experiences of the diagnosis of childhood spinal muscular atrophy. Eur J Hum Genet. 2015;23(5):575-580.

16. Forrest LE, Delatycki MB, Skene L, Aitken M. Communicating genetic information in families–a review of guidelines and position papers. Eur J Hum Genet. 2007;15(6):612-618.

17. Wood SL, Brewer F, Ellison R, Biggio JR, Edwards RK. Prenatal carrier screening for spinal muscular atrophy. American journal of perinatology. 2016;33(12):1211-1217.

18. Phan HC, Taylor JL, Hannon H, Howell R. Newborn screening for spinal muscular atrophy: Anticipating an imminent need. Seminars in perinatology. 2015;39(3):217-229.

19. Lin PJ, Yeh WS, Neumann PJ. Willingness to pay for a newborn screening test for spinal muscular atrophy. Pediatr Neurol. 2017;66:69-75.

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