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Paediatric Laboratory Medicine

Spinal Muscular Atrophy: SMN1 and SMN2 Deletion/Duplication Analysis

Clinical Significance

Spinal muscular atrophy (SMA) is a recessively inherited neuromuscular disorder caused by the progressive degeneration of cells in the spinal cord and brainstem. The onset of weakness ranges from before birth to young adulthood, and progresses with age. SMA affects children with varying severity, ranging from the severe and usually fatal SMA type 1 (Werdnig-Hoffman disease) to milder forms that are associated with longer survival but significant morbidity.

Spinal muscular atrophy is caused by a mutation in the survival motor neuron (SMN) gene on chromosome 5. People normally have two copies of the SMNtel gene. Molecular studies have shown that approximately 95 per cent of SMA patients have deletions in both of the SMNtel genes (homozygous deletions). The remaining SMA patients do not have a homozygous deletion of SMNtel , but carry a deletion of the SMNtel gene on one chromosome and a point mutation of the SMNt gene on the other chromosome.

If one chromosome carries a deletion in the SMNtel gene and the other copy is normal, the individual will be a carrier of SMA. Carriers do not have, and will not develop, spinal muscular atrophy. However, carriers may pass the mutation on to their children. If two individuals are carriers, there is a 25 per cent chance they will have an affected child. There is a 75 per cent chance their children will be unaffected. De novo mutational events occur in two per cent of patients with SMA, meaning that only one parent is a carrier and a new mutation in the offspring resulted in SMA.

Test Name

Spinal Muscular Atrophy: SMN1 and SMN2 Deletion/Duplication Analysis

Alternate Name/ Synonym

  • SMA

Gene Name

  • SMN1
  • SMN2

Alternate Gene Name

SMNC, SMNT

Test Code

SMA

Division

Molecular Genetics

Method

Deletion/duplication analysis via MLPA

External Proficiency Testing

CAP

Turn Around Time

2 weeks (Prenatal samples), 2-3 weeks (Pregnancy/Urgent samples), 4-6 weeks (Routine)

Protein

Survival of motor neuron 1

Disease/Condition

Spinal Muscular Atrophy

Specimen Type

Blood; extracted DNA is not accepted for this test.

For details about specimen requirements, please refer to: Specimen Type & Requirements (PDF).

Minimum Specimen Requirements

5-10 mL EDTA or ACD
0.5 mL EDTA (neonate)

Storage/Transportation

Room Temperature

Special Requirements

Special Instructions for Genome Diagnostics Samples

If sample shipment >48 hours, ship on ice.

Approval is not required

CPT Codes

81400

Shipping and Contact Information

The Hospital for Sick Children
Rapid Response Laboratory
170 Elizabeth Street, Room 3642
Toronto, ON
M5G 2G3
Canada
Phone: 416-813-7200
Phone: 1-855-381-3212

Interpretation

Interpretation is provided in report

Information Sheet: Spinal Muscular Atrophy