AR (Spinal and Bulbar Muscular Atrophy) Repeat Expansion Testing

Description

Pathogenic CAG repeat expansions in the AR gene have been associated with X-linked spinal and bulbar muscular atrophy (SBMA) in males. The pathogenic repeat expansions lead to expanded polyglutamine tracts that alter the conformation of AR protein and confer a toxic gain-of-function.

Pathogenicity is dependent upon CAG repeat length according to the following ranges ^1-3:

*An older age of onset is also associated with reduced penetrance. A younger onset of muscle weakness may be correlated with expansions of more than 40 repeats ².