CAG repeat contraction in the androgen receptor gene in three brothers with mental retardation

We report on three brothers with mental retardation and a contracted CAG repeat in the androgen receptor (AR) gene. It is known that expansion of the CAG repeat in this gene leads to spinal and bulbar muscular atrophy (SBMA or Kennedy disease); however, contracted repeats have not yet been implicated in disease. As the range of the length of CAG repeats in the AR gene, like those of other genes associated with dynamic mutations, follows a normal distribution, the theoretical possibility of disease at both ends of the distribution should be considered.