Context: Testis development is a tightly regulated process that requires an efficient and coordinated spatio-temporal action of many factors and it has been shown that several genes involved in gonadal development exert a dosage effect. Chromosomal imbalances have been reported in several patients presenting with gonadal dysgenesis (gonadal dysgenesis) as part of severe dysmorphic phenotypes.

Results: We screened for submicroscopic DNA copy number variations in two sisters with an apparent normal 46,XY karyotype and female external genitalia due to gonadal dysgenesis and in which mutations in known candidate genes had been excluded. By high resolution tiling BAC array comparative genome hybridization, a submicroscopic duplication at Xp21.2 containing DAX1 (NR0B1) was identified. Using FISH, multiple ligation probe amplification and PCR the rearrangement was further characterized. This revealed a 637 kb tandem duplication that in addition to DAX1 includes the four MAGEB genes, the hypothetical gene CXorf21, GK and part of the MAP3K7IP3 gene. Sequencing and analysis of the breakpoint boundaries and duplication junction suggest that the duplication originated through a coupled homologous and nonhomologous recombination process.

Conclusion: This represents the first duplication on Xp21.2 identified in patients with isolated gonadal dysgenesis, as all previously described XY subjects with Xp21 duplications presented with gonadal dysgenesis as part of a more complex phenotype including mental retardation and/or malformations. Our data thus support DAX1 as a dosage sensitive gene responsible for gonadal dysgenesis, and highlight the importance of considering DAX1 locus duplications in the evaluation of all cases of 46,XY gonadal dysgenesis.