Myotonic dystrophy (DM1) is an inherited disease, affecting males and females approximately equally. About 30,000 people in the United States are affected. Symptoms may appear at any time from infancy to adulthood. DM causes general weakness, usually beginning in the muscles of the hands, feet, neck, or face. It slowly progresses to involve other muscle groups, including the heart. DM1 affects a wide variety of other organ systems as well.
Myotonic dystrophy is inherited in an autosomal dominant pattern and thus will be passed along to 50% of a carrier's offspring, on average.In DM1, the affected gene is called DMPK, which codes for myotonic dystrophy protein kinase, a protein expressed predominantly in skeletal muscle. The gene is located on the long arm of chromosome 19.
In DM1, there is an expansion of the cytosine-thymine-guanine (CTG) triplet repeat in the DMPK gene. Between 5 and 37 repeats is considered normal, while individuals with between 38 and 49 repeats are considered to have a pre-mutation and are at risk of having children with further expanded repeats and, therefore, symptomatic disease. Individuals with greater than 50 repeats are almost invariably symptomatic, with some noted exceptions.
Methodology: PCR, Fragment analysis DMPK gene
Purpose: Confirmation of Clinical Diagnosis
ICD-10 Code G71.11
Test Requisition: Molecular Requisition
CPT Code: 81401 Cost: $407.00 (Oklahoma Medicaid requires preauthorization for this test)
Turn-around-time: 28 days
Turner, C; Hilton-Jones D. (2010). "The myotonic dystrophies: diagnosis and management". J Neurol Neurosurg Psychiatry 81: 358–367