Definition

Huntington disease results from pathological expansion (generally 40 or more repeats) of the CAG trinucleotide repeat in exon 1 of the HTT gene; the resulting abnormally long polyglutamine tract in the huntingtin protein causes neuronal dysfunction and death in the basal ganglia and cortex. The clinical picture typically begins between the ages of 30 and 50 with choreiform movements, progressive cognitive decline and psychiatric symptoms; as the repeat number increases, disease onset occurs earlier (anticipation), an effect that is especially pronounced with paternal transmission.

Gene/region examined

HTT - CAG repeat

Method

Fragment analysis

Accepted sample types

EDTA blood, AF, CVS

Inheritance

Hereditary, autosomal dominant, with full penetrance (40 or more repeats).

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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