Background and objectives: Androgen insensitivity syndrome (AIS) is an X-linked disorder of XY males characterized by varying degrees of impaired masculinization. In many AIS cases, mutations have been identified in the coding sequence of the human androgen receptor (AR) gene which impair receptor function. Cases have also been reported in which reduced AR mRNA expression may contribute to AIS in association with AR gene mutations. The purpose of this study was to define the molecular basis of AIS in members of a family with clinical and laboratory features of partial androgen insensitivity (PAIS).
Design: Genital skin fibroblast (GSF) cultures were established from foreskin tissue for androgen receptor binding analysis. Genomic DNA was obtained from blood leucocytes for AR gene nucleotide sequence analysis. AR mRNA levels were determined in total RNA extracted from GSF cultures.
Patients: Three related subjects with perineo-scrotal hypospadias, bifid scrotum and microphallus were studied. The family pedigree of these subjects suggested an X-linked pattern of inheritance. Hormone assay results were consistent with AIS.
Measurements: AR binding capacity and affinity were determined in three subjects and compared with unaffected male controls. The coding sequence and 1.4 kb of promoter region of the AR gene were amplified in overlapping fragments by polymerase chain reaction from genomic DNA and sequenced. GSF AR mRNA was measured by a competitive PCR technique.
Results: In the PAIS subjects, AR affinity in cultured GSF was normal (Kd = 0.24, 0.30, 0.48 vs 0.27 +/- 0.07 (SD) nmol/l) but binding capacity was reduced (Bmax = 0.31, 0.36, 0.27 vs 1.26 +/- 0.37 (SD) fmol/microgram DNA). Sequence analysis of the CAG repeat polymorphism within exon 1 of the AR gene showed that both mothers were heterozygous at this locus, and that the three subjects had inherited the same allele. GSF AR mRNA levels were reduced in all three patients compared with controls (0.25, 0.74 and 0.74 vs 3.8 +/- 0.9 (SEM), range 1.8-7.3 amol/microgram total RNA). The nucleotide sequences of the entire AR coding region and of a 1.4 kb segment containing the promoter region were normal.
Conclusion: Members of this family with clinical and biochemical evidence of X-linked partial androgen insensitivity syndrome demonstrated normal androgen receptor binding affinity and androgen receptor gene nucleotide sequence but reduced androgen receptor binding capacity and reduced androgen receptor mRNA. These results suggest that partial androgen insensitivity syndrome in this family may be caused by reduced expression of a normal androgen receptor gene.