Patients with DC or HHS carry mutations in genes encoding proteins of the telomerase complex (DKC1, NHP2, NOP10, TERC, TERT) or required for its assembly (WRAP53), components of the shelterin complex (ACD, TINF2) as well as other telomere regulators (CTC1, PARN, RTEL1, and possibly NAF1 and STN1) [47]. The gene discussed is RTEL1; the disease is hypotrichosis 1.