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Spinal Muscular Atrophy

Other Names

SMA

SMA type I

SMA type II

SMA type III

SMA type IV

Diagnosis Coding

G12.9, Spinal muscular atrophy, unspecified

Disorder Category

A musculoskeletal disease

Screening

Finding

Homozygous deletion of the SMN1 gene

Tested By

Real-time PCR

Overview

Spinal muscular atrophy (SMA) is a group of inherited conditions that affects the motor neurons of the spinal cord causing muscle weakness. Symptoms include difficulty crawling, walking, breathing, swallowing, and controlling the head and neck. There are several types of SMA; classification is based on the severity of the condition and the age at which symptoms begin. Early detection and treatment are most effective when started early.

The long-term outlook varies significantly based on the type, symptoms, and response to treatment. The more severe types of SMA are associated with a shortened lifespan. Newer therapies may improve survival. In general, infants with SMA type I die in early childhood. Those affected by SMA type II live into adolescence and early adulthood. Most people with type III have a normal lifespan but are more susceptible to respiratory infections. SMA type IV is associated with a normal life expectancy.

Incidence

Approximately 1 in 12,500 [Verhaart: 2017]

Inheritance

Autosomal recessive

Prenatal Testing

DNA testing by amniocentesis or chorionic villus sampling (CVS) if both disease causing mutations of an affected family member have been identified

Clinical Characteristics

Newborns with SMA will usually be asymptomatic. Those with Type 1 may develop apparent hypotonia within weeks of birth. Newborns with the rare Type 0 will be severely hypotonic at birth and have contractures, swallowing problems, and respiratory failure.

Follow-up Testing after Positive Screen

SMN1 and SMN2 genetic testing

Primary Care Management

Upon Notification of the + Screen

  • Contact pediatric neurology to coordinate URGENT evaluation and additional testing; Pediatric Neurology (see NW providers [0]). FDA-approved treatments are available and should be started within days of identification.
  • Contact family regarding the need for evaluation and additional testing.

If the Diagnosis is Confirmed

  • Educate the family regarding signs, symptoms, and the need for specialized care.
  • Urgent treatment and follow-up should be continued as indicated by pediatric neurology.
  • For those identified after onset of symptoms, therapy is still beneficial and should be started.

Specialty Care Collaboration

Initial consultation with Pediatric Neurology (see NW providers [0]) and ongoing collaboration if the child is affected. Genetic Testing and Counseling (see NW providers [6]) for the family.

Resources

Information & Support

For further assessment and management information, see The Portal's Spinal Muscular Atrophy.

For Professionals

Spinal Muscular Atrophy (GeneReviews)
An expert-authored, peer-reviewed, current disease description that applies genetic testing to diagnosis and management information; U.S. National Library of Medicine.

Spinal Muscular Atrophy Type I (OMIM)
Information about clinical features, diagnosis, management, and molecular and population genetics; Online Mendelian Inheritance in Man, authored and edited at the McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine

Spinal Muscular Atrophy Type II (OMIM)
Information about clinical features, diagnosis, management, and molecular and population genetics; Online Mendelian Inheritance in Man, authored and edited at the McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine

Spinal Muscular Atrophy Type III (OMIM)
Information about clinical features, diagnosis, management, and molecular and population genetics; Online Mendelian Inheritance in Man, authored and edited at the McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine

For Parents and Patients

Genetic Conditions: Spinal Muscular Atrophy (MedlinePlus)
Excellent, detailed review of condition for patients and families; National Library of Medicine and National Institutes of Health.

Baby's First Test (Genetic Alliance)
Clearinghouse for local, state, and national newborn screening education, programs, policies, and resources. Also, provides many ways for people to connect and share their viewpoints and questions about newborn screening; supported by the U.S. Department of Health and Human Services.

Services for Patients & Families Nationwide (NW)

Genetics-related clinical services throughout the world can be found through Genetics Clinic Directory (GeneTests).

For services not listed above, browse our Services categories or search our database.

* number of provider listings may vary by how states categorize services, whether providers are listed by organization or individual, how services are organized in the state, and other factors; Nationwide (NW) providers are generally limited to web-based services, provider locator services, and organizations that serve children from across the nation.

Authors & Reviewers

Initial publication: June 2019
Current Authors and Reviewers:
Author: Kimberly Hart, MS, LCGC
Reviewer: Russell Butterfield, MD, Ph.D.

Page Bibliography

Verhaart IEC, Robertson A, Wilson IJ, Aartsma-Rus A, Cameron S, Jones CC, Cook SF, Lochmüller H.
Prevalence, incidence and carrier frequency of 5q-linked spinal muscular atrophy - a literature review.
Orphanet J Rare Dis. 2017;12(1):124. PubMed abstract / Full Text