Spinal Muscular Atrophy : SMN1/SMN2 Deletion/Duplication (MLPA)

Test Information

SMN1/SMN2 Deletion/Duplication (MLPA) is a molecular test used to identify copy number variants in the gene associated with Spinal Muscular Atrophy.

Turnaround Time

2 weeks

CPT Code(s)

81329

Cost

$600

Genes

Clinical Information

Spinal Muscular Atrophy (SMA) is a neuromuscular disorder characterized by progressive muscle weakness resulting from the degeneration of motor neurons in the brain and spinal cord. The incidence of SMA is 1 in 10,000 births, and the age of onset and severity are variable. While specific types of SMA have been historically described, phenotypic overlap does occur from one type to another. Congenital SMA (SMA 0) may present prenatally with reduced fetal movement or at birth and is characterized by severe hypotonia, respiratory failure, and absent developmental milestones. Feeding difficulties are common, and death typically occurs by the age of 6 months. SMA I, also known as Werdnig-Hoffman disease, presents in individuals less than six months of age, and associated symptoms include proximal muscle weakness, swallowing issues, and labored breathing. Tongue fasciculations are present in a majority of affected individuals, and death typically occurs by 2 years of age. SMA II appears at 6-12 months of age, and it is characterized by delayed motor development due to muscle weakness, scoliosis, and lung disease. Affected individuals are unable to walk without assistance, but most patients survive to adulthood. Individuals SMA II show delayed motor development due to muscle weakness, scoliosis, and lung disease, and are unable to walk without assistance; however, most patients survive to adulthood. In individuals with onset at greater than 18 months of age (SMA III, or Kugelberg-Welander disease), the majority maintain the ability to walk and have a normal lifespan. The onset of muscle weakness in adulthood (SMA IV) commonly occurs with a course similar to type III. These forms of spinal muscular atrophy are inherited in an autosomal recessive pattern, and most are due to homozygous deletions of at least exon 7 of the SMN1 gene. Typically, the number of copies of SMN2 can modify the phenotype of SMA.

Indications

Molecular testing is useful to confirm the diagnosis and to identify the disease causing mutations within a family to allow for carrier testing and prenatal diagnosis.

Methodology

multiplex ligation-dependent probe amplification (MLPA)

Detection

MLPA analysis is used to detect copy number of exons 7 and 8 of the SMN1 and SMN2 genes, and this test is designed for diagnosis and carrier screening. Please note that while approximately 95% of individuals with spinal muscular atrophy have homozygous deletions of at least exon 7 of the SMN1 gene, up to 5% of patients may have a sequence variant that will not be detected by MLPA analysis.

Specimen Requirements

5 to 7 ml of peripheral blood collected in an EDTA (lavender top) tube is the preferred specimen type. The minimal blood needed for reliable DNA isolation is 3 ml. Extracted DNA, dried blood spots, and saliva are also accepted for this test.

Transport Instructions

The specimen should be kept at room temperature and delivered via overnight shipping. If shipment is delayed by one or two days, the specimen should be refrigerated and shipped at room temperature. Do not freeze the specimen. Samples collected on Friday can be safely designated for Monday delivery.

Prenatal Testing Information

Prenatal diagnosis is available if the familial mutations are known. Additional fees for cell culture and maternal cell contamination may apply. Maternal cell contamination studies are required for all prenatal molecular tests. Contact the laboratory prior to sending a prenatal specimen.

Have Questions Need Support?

Call our laboratory at 1-800-473-9411 or contact one of our Laboratory Genetic Counselors for assistance.
Robin Fletcher, MS, CGC
Kellie Walden, MS, CGC

Deletion/Duplication, MLPA, Molecular Testing
Meet Makayla Gunn

Meet Makayla Gunn

Makayla was diagnosed with Rett Syndrome in April of 2015 at the age of two.   At about 18 months, we noticed she had started some repetitive hand motions, and her pediatrician was a little concerned that she did not have many words.  She had learned some sign language, and was saying ‘mama’ and ‘dada’, but that was it.  Then she suddenly stopped all of that.  At her 2 year old check-up, the pediatrician referred us to BabyNet, ...

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