Molecular Test Listing

Molecular Requisition

Myotonic dystrophy (DM) is the most common inherited neuromuscular disease in adults and affects 1 in 8,000 individuals. DM is an autosomal dominant muscle disease which is caused by a defect in the regulation of a gene cluster located on chromosome 19q13.2. Myotonic dystrophy results in prolonged muscle contraction, cardiac arrhythmia, and can cause cataracts. DM is a progressive disease with a marked variability of expression. There is a severe congenital form that is frequently fatal after birth, but more typically the onset is in the second and third decades of life. DM also displays a phenomenon called anticipation, in which the disease becomes progressively more severe with earlier onset in each successive generation.

DM is one of the family of unstable trinucleotide repeat conditions. It is caused by an unstable region of CTG repeats within the DM gene cluster, but not in a protein coding region. Normal sizes range from 5 – 50 rpts. Adult onset ranges from 70 – 1000 rpts, and congenital onset results from expanse greater than 1000. In severely myotonic babies, myotonic dystrophy analysis can be included in a Newborn Hypotonia Panel with SMA and Prader-Willi to expedite diagnosis.

• Individuals with unexplained myotonia and cardiac arrhythmia.

• To determine whether a child with severe myotonia may have DM.

• Individuals with a family history of DM who want to have a better knowledge of their risk.
• Individuals at risk who wish prenatal diagnosis.

• Testing may be combined with testing for SMA and PWS in a Newborn Hypotonia Panel.

• PCR amplification of the variable CTG repeat region and fluorescence size analysis; in conjunction with Southern Blot analysis of the myotonin protein kinase gene.

• Blood EDTA (purple top) tubes:  

            Newborn: minimum 1-2 mL          

            Child/Adult: prefer 2 tubes of 3-5 mL

• Prenatal testing: Please contact the laboratory for instructions.

TURNAROUND TIME:     15 working days

CPT CODES: