NR0B1 and gonadal dysgenesis: If normal levels of NR0B1 are crucial for testicular development and spermatogenesis, an excessive dosage of NR0B1 has been suggested to act as an anti-testicular factor (164) Xp21.1 duplications, which include NR0B1 and testis-specific MAGEB genes, have been identified in some XY patients with gonadal dysgenesis.