IGSF10 and hypogonadotropic hypogonadism: Causative mutations were found in the PROP1 transcription factor gene as well as two other genes known to contribute to isolated hypogonadotropic hypogonadism (IHH), namely IGSF10 and SEMA3A. Our results are in agreement with multiple studies reporting the occurrence of common PROP1 founder mutations in sporadic and familial cases (26–29).