PARN and dyskeratosis congenita: To date, ACD, CTC1, DKC1, NHP2, NOP10, PARN, RTEL1, TERC, TERT, TINF2, and WRAP53 are the genes in which pathogenic variants are known to cause dyskeratosis congenita (DC) and result in very short telomeres (Savage and Alter, 2009).