Definition

Kennedy disease is a slowly progressive neuromuscular disorder characterized by muscle weakness, atrophy, and fasciculations due to degeneration of lower motor neurons; affected men also show gynecomastia and reduced fertility related to mild androgen insensitivity. It results from a pathologic expansion of the CAG repeat in the first exon of the AR gene; healthy individuals have 5 to 34 repeats, while 38 or more repeats lead to fully penetrant disease.

Gene/region examined

AR - CAG repeat

Method

Fragment analysis

Accepted sample types

EDTA blood

Inheritance

X-linked inheritance. Fertile affected men pass the expanded repeat to all their daughters (usually asymptomatic carriers) and to none of their sons; daughters are usually unaffected due to low circulating androgen levels.

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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