Type II -gonadal germ cell tumours (GCT) (seminoma/non-seminoma/dysgerminoma) occur with high frequency in dysgenetic gonads of individuals who have differences of sex development (DSD). GCT in DSD do not result from somatic driver mutations but have a developmental origin. The aim of this long term project is to unravel the earliest steps in the pathogenesis of these GCT, specifically in dysgenetic gonads. The primary objective is to provide a full-depth biological characterization of Undifferentiated Gonadal Tissue (UGT), the major precursor for these GCT, in order to develop diagnostic markers for the presence of germ cells (GC) that have malignant potential, and that can readily  be applied in a diagnostic setting. Our limited understanding of the pathobiology of GCT in DSD hinders individualized management of patients, with regard to e.g. prophylactic gonadectomy, surveillance of gonads at risk, and development of fertility preservation protocols. The overall aim of this research is to better understand and diagnose DSD-related GCT development, with the aim of developing evidence-based guidelines for clinical management of gonads at risk.