ANALYSIS OF THE SRY GENE IN 22 SEX-REVERSED XY FEMALES IDENTIFIES 4 NEW POINT MUTATIONS IN THE CONSERVED DNA-BINDING DOMAIN

The open reading frame of the SRY gene has been examined in a series o f 22 XY females with clinically defined pure gonadal dysgenesis by dir ect sequencing of biotinylated PCR product bound to streptavidin coate d beads. Amongst the 22 XY females examined, rive (two of whom are sis ters) were found to have single base changes all within the highly con served DNA binding (or HMG box) domain. In the remaining 17 cases, the SRY gene sequence was indistinguishable from that found in normal mal es. In three of the XY females with point mutations, the altered amino acids occur in highly conserved positions leading to non-conservative changes (Arg to Gly at position 5, Met to Thr at position 21 and Arg to Trp at position 76). Examination of the SRY gene from the father's Y chromosome has shown that the mutations at position 5 in patient SHM 60 and position 21 in patient HN31 have arisen de novo. In the case of the two sibs, both have identical mutations where a C to T transition in codon 17 has created a TAG termination signal, thus suggesting tha t the deceased father is likely to be a gonadal mosaic for the mutatio n. In the case of the mutations at positions 17 and 76, the fathers ar e not available for investigation and so it has not been possible to d etermine whether the changes are de novo. These data indicate that the majority of XY females with pure gonadal dysgenesis owe their sex-rev ersed phenotype to mutations in as yet uncharacterised segments of the SRY gene, or, at other loci acting early in the sex-determining pathw ay.