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Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is an autosomal recessive disorder characterized by symmetric and progressive muscle weakness and atrophy resulting from degeneration of anterior horn cells in the brainstem and spinal cord. Symptom onset may occur prenatally or later in life during adolescence or adulthood. SMA occurs in 1 in 10,000 live births with a carrier frequency of 1/35 to 1/117 depending on ethnicity.

The two genes associated with SMA are known as survival motor neuron (SMN) genes. Normally, individuals have two copies of the SMN gene arranged in tandem on each chromosome, known as SMN1 (telomeric copy), and SMN2 (centromeric copy). SMA arises with the loss of function of the SMN1 gene. The remaining functional SMN2 genes cannot compensate without expression of SMN1SMN1 is homozygously deleted in approximately 95% of SMA patients. The remaining 5% of patients have point mutations within the gene.

Reasons for Referral

Child or adult with unexplained symmetric and progressive muscle weakness.

Carrier testing for at-risk relatives.

Prenatal carrier testing for couples with a prior child with SMA.

Testing Methods

PCR and gel electrophoresis

Turn Around Time

5 days or fewer

Specimen Requirements and Shipping/Handling

Blood: A single tube with 1-5 mL whole blood in EDTA (lavender top).

Saliva: To request a DNA Mouthwash Collection Kit please contact Genetics Center at (714)288-3500.


Store blood at 4°C until shipment. Ship at ambient temperature in an insulated container via overnight delivery within 96 hours of collection.

Send Specimen(s) to:

Genetics Center
211. S Main Street
Suite AA
Orange, CA 92868
Tel: (714)288-3500


Test Limitations

This analysis will not detect germline mosaicism or mutations in genes other than SMN1. Results of this test are recommended to be interpreted in the context of relevant pathology and clinical data

CPT Codes

SMA Carrier Testing:

CPT’s: 81401, G0452

SMA Diagnostic Testing:

CPT;s: 81401, G0452

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