Endocrine Abstracts

While we have made great strides in understanding the developmental molecular and cellular events that underlie gonad development it is far from complete picture. Crucial insights into the regulation of gonad development have come from analysing patients with Differences of Sex Development (DSD). Our gene discovery and functional variant analysis has more than tripled the number of 46,XY DSD patients receiving a diagnosis. This has enhanced prognostic accuracy (cancer risk, adrenal insufficiency) and assisted with their clinical management. However, at least 60% of 46,XY DSD patients remain without a genetic diagnosis. Furthermore, women with ovarian failure have diagnostic rates as low as 20%, leaving a 80% undiagnosed. A subset includes 46,XX Premature Ovarian Insufficiency (POI) affecting up to 1% of young women and is associated with cessation of menstruation and ovarian hormones before the age of 40. These women are infertile and at an elevated risk for cardiovascular disease, diabetes, osteoporosis and earlier mortality. There is often a genetic basis to POI but the known genes only account for about a quarter of cases. Using genomic analysis we have identified 20 novel POI genes which will assist with clinical management. Clearly, additional genes critical for human gonad development and dysfunction remain to be identified before diagnostic rates and clinical care for patients can be improved. One such new gene we discovered was SART3. We showed SART3 gene variants underlie a new spliceosomopathy characterised by failure of testis development and neuronal defects. This implicates the splicesome components in testis development. In addition, we showed that disrupted testis-specific regulatory enhancer sequences impact testis development and cause DSD. We identified SOX9 enhancers that, when duplicated or deleted, result in 46,XX or 46,XY sex reversal, respectively. These enhancers provide the missing link by which SRY activates SOX9 initiation, upregulation and maintenance in human testis development. Finally, we developed a protocol to differentiate human iPSCs into early bipotential gonadal cells, showing these can be aggregated to form testis-like organoids. This testis organoid model will be another powerful tool for understanding human testis development and dysfunction.