Sample Reqs

A  (diagnostic and carrier testing) ; CVS or Amnio (prenatal samples)

Turnaround

10 days

Special instructions

Clinical history must be provided.

Test information

Spinal Muscular Atrophy (SMA) is a rare autosomal recessive neuromuscular disorder characterised by progressive muscle weakness and atrophy due to degeneration of lower motor neurons in the spinal cord. Cognitive function is unaffected.

Severity varies widely and is commonly classified by age of onset and motor milestones achieved (types 1–4). Earlier onset generally correlates with more severe disease.

The most common form, SMA 1, results from pathogenic variants in the SMN1 (Survival Motor Neuron 1) gene. Approximately 95% of individuals with SMA have a homozygous deletion of exon 7 of SMN1. Approximately 1 in 50 individuals are carriers.

Testing is carried out by Multiplex Ligation-Dependent Probe Amplification (MLPA) to determine the copy number of exons 7 and 8 of the SMN1 gene on 5q13. MLPA does not detect point mutations within the SMN1 gene.

• Individuals with SMA typically have deletions in both SMN1 copies.
• Carriers have one functional copy of SMN1.

Testing can be carried out on blood samples for diagnostic or carrier status tests, or on CVS or amniocentesis samples for prenatal tests.

Additional testing available:

• Sequence analysis: This can be arranged if MLPA does not identify SMN1 deletions but suspicion of SMA remains. It can identify point mutations in the SMN1 gene.
• SMN2 copy number analysis: Disease severity is modified by the copy number of SMN2, a paralog gene producing small amounts of functional SMN protein. SMN2 copy number is reported when a homozygous deletion of SMN1 exon 7 is identified.

Additional information

• How to order a test
• HSL Genetics specimens
• HSL Genetics specialties
• HSL Genetics request procedures
• Guidance on specimen collection
• Specimen transport
• Sample rejection criteria
• Request Forms

Last-updated: 20/05/26

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