Clinical features and skewed X-chromosome inactivation in female carriers of X-linked recessive spinal and bulbar muscular atrophy.

In X-linked recessive disorders, a few female gene carriers become symptomatic. Recent evidence implicates skewed X-chromosome inactivation in such female carriers. We studied the clinical features of eight female gene carriers of X-linked recessive spinal and bulbar muscular atrophy (SBMA), and evaluated the relationship between phenotype and genotype from the viewpoint of X-chromosome inactivation. Seven of eight cases were symptomatic, showing mild muscle weakness, frequent muscle cramps, slight elevation of the serum creatinine kinase level, or neurogenic changes on the electromyogram. Only one carrier was asymptomatic clinically. For the estimation of X-chromosome inactivation, the methylation status of the androgen receptor (AR) gene was determined by polymerase chain reaction-based assay. Highly skewed inactivation of the affected AR gene was found in the asymptomatic carrier, while symptomatic carriers had a random or lower inactivation pattern of the affected AR gene. These findings suggest that most female carriers of SBMA show some clinical abnormalities, and highly skewed inactivation of the affected X-chromosome seems to closely relate with escape of the manifestation in female carriers of SBMA.