Familial X/Y translocations associated with variable sexual phenotype.

T rue hermaphroditism, defined clinically as the presence of both male and female gonadal tissue in the same individual usually accompanied by ambiguous genitalia, is a genetically heterogeneous condition. Less than 10% of true hermaphrodites with an apparent 46,XX constitution are SRY-positive, usually resulting from translocation between Xp and Yp. Previously we described two true hermaphrodites (AK and PG) of Polish origin, both of whom carry X/Y translocations with SRY translocated onto distal Xp. Here, we show that the same X/Y translocation is also carried by fertile male and female relatives of the hermaphrodite probands, and identify varying sexual phenotype in individuals with the same chromosome abnormality. AK was ascertained aged 17 with ambiguous internal and external genitalia. Biopsy revealed a left ovary and a right testis with no signs of spermatogenesis. PG was ascertained at 6 months of age with ambiguous internal and external genitalia. She was found to have a right ovary and a left ovotestis, which was removed and upon microscopical examination showed signs of dysgenesis in the testicular part. Circulating testosterone levels were ,0.1 ng/ml, rising to 0.2 ng/ml following hCG stimulation. Now aged 15, her remaining ovary has developed apparently normally, she menstruates regularly, and thus may be fertile. There was no family history of sex discrepancy in either pedigree, with no indication of abnormalities of sexual development in any of the relatives examined. By PCR of STS markers, breakpoints on the Y chromosome were localised 6–7 kb proximal to SRY in both AK and PG (data not shown). In order to map breakpoints on the X chromosome we obtained parental blood samples, extracted DNA, and amplified microsatellite markers located in distal Xp. Results for DXYS228X, located within the proximal region of the Xp/Yp pseudo-autosomal region (PAR1) approximately 80 kb from the pseudo-autosomal boundary (http://genome.cse.ucsc.edu/), are shown in fig 1. Both AK and PG have three alleles, indicating that the X chromosome breakpoint lies distal to this locus, resulting in a der(X) chromosome carrying two copies of the proximal part of PAR1. Because individuals with an SRY-positive 46,XX constitution are almost invariably infertile, and, by definition, translocations involving the Y chromosome must be of paternal origin, we expected the der(X) in AK and PG to be paternal and de novo in origin. Much to our surprise however, results for DXYS228X show that both the father of AK and the mother of PG also possess three copies of this locus, suggesting that they also carry the der(X). In order to confirm both the presence and inheritance of the der(X) in these individuals, we performed SSCP analysis of a single nucleotide polymorphism 1.5 kb 59 of SRY (rs2534636 in dbSNP, http://www.ncbi.nlm.nih.gov/SNP/). Results are shown in fig 2, and demonstrate that both the hermaphrodites AK and PG possess a single SRY allele, while the mother of AK is SRY-negative, as expected. However, the father of AK has two SRY alleles, suggesting he possesses a normal Y chromosome and the der(X). This was confirmed by positive amplification of several STS markers mapping to proximal Yp and Yq (data not shown). In addition, the mother of PG also carries SRY. As her SRY allele is identical to that in PG but different from that in PG’s father, this verifies both the presence of the der(X) in the mother of PG and its maternal transmission. Furthermore, use of STS markers in the mother of PG localised the Yp breakpoint to the same interval 6–7 kb proximal to SRY as observed in PG, suggesting that there was no gain or loss of Yp material between generations (data not shown). Analysis of DNA obtained from the maternal aunt of PG also yielded identical results, indicating that she has the same 46,X,der(X) karyotype. The presence of the der(X) in both the mother and maternal aunt of PG indicates that it must also be carried by one of the maternal grandparents. Similarly, as the father of AK carries a normal Y chromosome which was presumably paternally inherited, the der(X) must therefore also be present in the paternal grandmother of AK, although we were unable to formally prove this. Unfortunately no further family members were available for analysis. Pedigrees of AK and PG are shown in fig 3. These data demonstrate the presence of an SRY-positive X/Y translocation associated with male, female, and hermaphrodite development in different individuals within the same pedigree. Despite possessing an intact copy of SRY, both the mother and maternal aunt of PG have developed as normal, fertile females. This same X/Y translocation has then been inherited by PG, causing hermaphroditism and ambiguous genitalia. Similarly, the hermaphrodite AK carries the same der(X) that is present in his father, a normal fertile male. As AK’s father also possesses an intact Y chromosome, the paternal grandmother of AK (a fertile and reputedly normal female) must also carry the der(X). Thus, our observations Key points