Definition

It results from a pathological expansion of the CTG trinucleotide repeat in the 3' untranslated region of the DMPK gene; the expanded RNA transcripts sequester RNA-binding proteins, disrupting the alternative splicing of multiple genes. The clinical picture is a slowly progressive multisystem disease involving myotonia, progressive muscle weakness, cataracts, cardiac conduction defects, and central nervous system involvement; there is a strong correlation between repeat number and age of onset/severity (anticipation).

Gene/region examined

DMPK - CTG Repeat Number Analysis

Method

Fragment Analysis

Accepted sample types

EDTA blood, AF, CVS

Inheritance

Hereditary, autosomal dominant (CTG repeat expansion is unstable across generations).

Related Tests

Inheritance Patterns

Describes how a genetic condition is passed on within a family. There are five main patterns

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Carrier (Heterozygous / Homozygous)

Why it matters: In autosomal recessive inheritance, when each parent is a carrier (while both appear healthy), the chance of their child being born with the disease is 25% in each

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VUS (Variant of Uncertain Significance)

This is the situation where the test has detected a change in the DNA, but the role of this change in the development of disease is unconfirmed.

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How to Read a Genetic Test Result (Positive / Negative / VUS)

A genetic test result falls into three main categories

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Types of Genetic Tests

A genetic test is a type of medical test that detects changes in genes, chromosomes or proteins. Today there are more than 77,000 genetic tests available.

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