Myotonic Dystrophy Type 1 Repeat Expansion Analysis

Casandra

Casandra Test Code BG29049Version 1 (DRAFT)

Performing Lab

Lab Baylor GeneticsLab Test ID 6041CPT Code 81234

Myotonic Dystrophy Type 1 Repeat Expansion Analysis

Clinical Use

Use

The Myotonic Dystrophy Type 1 Repeat Expansion Analysis is designed to determine the number of CTG repeats in the DMPK gene. Myotonic dystrophy type 1 is a prevalent adult muscular dystrophy, with symptoms manifesting variably, from infantile hypotonia to adult muscle wasting and weakness. Common signs include myotonia, cataracts, and other systems affected may include the heart and endocrine systems. With typical repeat counts, unaffected individuals show 5-34 repeats, premutation carriers between 35-49 repeats, and full mutations indicate 50 or more repeats. Genetic counseling and testing are essential for families, especially those considering pregnancy.

Special Instructions

Testing is recommended for individuals with clinical or suspected myotonic dystrophy, those with a family history, and prospective parents for carrier screening. Pre-pregnancy testing is crucial for identifying risks associated with congenital myotonic dystrophy. Collecting samples must follow specific protocols, including using a sterile medium when necessary. Consultation with healthcare providers is encouraged. Testing may inform treatment planning and supportive care options.

Limitations

There may be limitations in repeat size detection, particularly with alleles outside the sensitivity range of the PCR assay. Larger repeat sizes may be reflected in Southern blot results but can also face inconsistency. The test does not account for all genetic variations, and clinical correlation is necessary for an accurate diagnosis. This assay is not recommended for symptomatic patients without a confirmed clinical diagnosis or strong family history. Misinterpretation can occur if the clinical context is not considered.

Test Details