Spinal Muscular Atrophy Carrier Testing and Prenatal Diagnosis

Spinal muscular atrophy (SMA) is a hereditary disease characterized by the progressive degeneration of the lower motor neurons, leading to muscle weakness and, in the most common type, respiratory failure by age two. Muscles responsible for crawling, walking, swallowing and head and neck control are the most severely affected. SMA has been known as congenital axonal neuropathy, arthrogryposis multiplex congenita (prenatal SMA), Werdnig-Hoffman disease (SMA type I), Dubowitz disease (SMA type II) and Kugelberg-Welander disease (SMA type III).

Couples who are planning a pregnancy or who are already pregnant may decide to have testing to find out if they are carriers and at risk of having a baby with SMA. If both parents are found to be carriers, prenatal diagnosis by CVS or amniocentesis is available. Indications for SMA carrier testing and prenatal diagnosis include: Carrier testing for individuals with family history of SMA and prenatal diagnosis for at-risk pregnancies (when both parents are carriers or when severe joint contractures are found on fetal ultrasound). Carrier testing for individuals in the general population may be considered.

Genzyme does not offer pediatric or adult diagnostic testing for SMA.

CPT Codes:

83891, 83892(4), 83900(4), 83912

Specimen Requirements:

1. Blood:

• ACD-A (yellow-top) or EDTA (lavender-top) tube.
• Adult: 10 cc whole blood; 30 cc whole blood if ordering multiple tests.

2. Prenatal:

Please Note: Call a laboratory genetic coordinator prior to obtaining any specimens. In some circumstances, specimens from other family members may be required. All prenatal specimens (including cord blood) must be accompanied by a maternal blood or mouthwash specimen for analysis of the specimen for possible maternal cell contamination. Cultures are required for prenatal SMA testing.

• Amniotic fluid - Discard first 2 cc; then 15 cc amniotic fluid in 15 cc orange-top polypropylene tube. If cultured at another facility, 1 T-25 flask of confluent cells. Please ensure that a back-up culture is maintained.
• CVS - 10-15 mg chorionic villi in laboratory-provided screw-top tubes with sterile transport medium. If cultured at another facility, 1 T-25 flask of confluent cells. Please ensure that a back-up culture is maintained.
• If additional testing is desired, more amniotic fluid is needed. For example, chromosome analysis requires an additional 15-25 cc (see Cytogenetics – Amniotic Fluid Chromosome Analysis test page) and AFAFP requires an additional 2 cc (see Amniotic Fluid Alpha-Fetoprotein - AFAFP test page).

Turnaround Time:

7-11 days (when cell culture is required, add ~2 weeks)