Complete androgen insensitivity syndrome caused by the R855H mutation in the androgen receptor gene.

Complete androgen insensitivity syndrome (CAIS) is characterized by a completely female phenotype in a 46,XY individual and is caused by mutations in the androgen receptor (AR) gene. A 5 year-old girl presented with bilateral hernia and was noted to have bilateral testes. She had a 46,XY karyotype and was diagnosed with CAIS. To identify the underlying mutation, the exons 2 to 8 of the AR gene were amplified by PCR using sets of known primers and reaction conditions. The results of the mutational analysis for the AR showed the presence of the R855H mutation; her mother was found to be heterozygous and both her 46,XX sister and her aunt had a normal AR gene. This mutation, is the result of a guanine to adenine transition in codon 855 at position 2926 in exon 7 of the AR gene, which causes an alteration of the coding nucleotide triad from CGC to CAC, which subsequently causes the substitution from arginine to histidine in the amino acid sequence of the receptor protein molecule. The same mutation has been reported to cause variable phenotypic expression, which could be explained by the presence of additional co-activating factors modifying the biological activity of the AR. The identification of an AR mutation in a girl with CAIS provides important information, because of the syndrome's genetic heterogeneity. This report emphasizes the fact that genetic determinants outside the coding sequence of the AR can influence the function of the AR protein molecule. Phenotypic expression of the mutation may be used for the construction of maps of functional domains of the AR.