The existence of a high FSH/LH ratio prior to any treatment in a significant number of patients with biallelic TAC3/TACR3 mutations, contrary to patients with other genetic causes of CHH, suggests that this ratio could serve as a diagnostic marker to prescreen for TAC3/TACR3 mutations in untreated patients with nCHH. This evidence concerns the gene TAC3 and cartilage-hair hypoplasia.