Intragenic Duplication of DMRT1 in a SRY-Negative Boy with 46,XX Disorder of Sex Development

Background: 46,XX disorders of sex development are rare. Approximately, 90% of XX males are SRY-positive, while testicular development in the absence of SRY takes place in a minority. Methods: A boy with 46,XX karyotype (SRY-negative; absence of SOX9 duplications) was investigated by targeted Next Generation Sequencing (NGS), Multiplex ligation-dependent probe amplification (MLPA), and Comparative Genomic Hybridization array (CGH-array). Results: The boy had normal male phenotype and normal prepubertal values of testicular hormones. He presented a heterozygous duplication of 49.626 bp, encompassing exons 2 and 3 of DMRT1. The result was arr[GRCh37] 9p24.3(845893_895518)x3. Since both breakpoints are harbored in the intronic regions, the duplication does not stop or shift the coding frame. Additional known pathogenic or uncertain variants in pro-testis gene cascade were not identified. Conclusions: This study report a boy with 46,XX testicular disorder of sex differentiation, showing a de novo partial intragenic duplication of DMRT1. This intragenic duplication may result in a gain of function, acting as primary pro-testis gene (or anti-ovary gene) in a 46,XX human foetus and permitting normal pre-pubertal endocrine testis function.