Spinal Muscular Atrophy

Alternate test name

SMA

Gene name / Alternate gene name

SMN1
SMN2
SMNC, SMNT

Protein

Survival of motor neuron 1

Lab area

Genome Diagnostics - Molecular Genetics

Method and equipment

Deletion/duplication analysis via MLPA

Expected turn-around time

Prenatal samples: 2 weeks Pregnancy/STAT: 2-3 weeks Routine: 4-6 weeks

Specimen type

Blood; extracted DNA is not accepted for this test.

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

Specimen requirements

Blood: 5-10 mL in EDTA, 0.5 mL in EDTA (neonate);
DNA-minimum 10 ug in 100 uL low TE (pH8.0)

Storage and transportation

Room Temperature

For details about specimen requirements, please refer to: Specimen Type and Requirements

DNA extracted at an external lab is not accepted for MLPA testing.

Special requirements

Special Instructions for Genome Diagnostics Samples

If sample shipment >48 hours, ship on ice.

Shipping information

The Hospital for Sick Children

Division of Genome Diagnostics

555 University Avenue, Black Wing, Room 3416

Toronto, ON

Canada

M5G 1X8

Phone: 416-813-7200 ext. 2

Hours: Monday to Friday, 8 a.m. to 4:30 p.m.

Off hours: Please send to Rapid Response Laboratory, 555 University Avenue, Room 3642

Email Molecular Lab: molecular.lab@sickkids.ca

Email Cytogenetics: cytogenetics.requests@sickkids.ca

Requisition

Spinal Muscular Atrophy - requisition

Background and 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 SMN_tel gene. Molecular studies have shown that approximately 95 per cent of SMA patients have deletions in both of the SMN_tel genes (homozygous deletions). The remaining SMA patients do not have a homozygous deletion of SMN_tel , but carry a deletion of the SMN_tel gene on one chromosome and a point mutation of the SMN_t gene on the other chromosome.

If one chromosome carries a deletion in the SMN_tel 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.

See related information sheet: Spinal muscular atrophy

Disease condition

Spinal Muscular Atrophy