With the confirmation of FIP and short telomeres, we began to search for mutations in telomere-related genes. We first sequenced the proband for mutations in TERT and hTR but did not detect a mutation. We then performed targeted sequencing of additional telomerase related genes TINF2, NHP2, NOP10, and DKC1. No mutations were detected in TINF2, NHP2, or NOP10; however, a previously undescribed A-to-G 1213 transition that is predicted to encode a Thr405Ala amino acid substitution was identified in DKC1 (Fig 4). SIFT analysis, which uses an algorithm using the amino acid sequence to predict whether a mutation is likely to significantly affect function, predicted this to be a deleterious mutation (SIFT score, 0.02). Confirmatory sequencing of the affected sibling’s DNA identified the same Thr405Ala mutation. As DKC1 lies on the X chromosome, each of the female offspring is an obligate carrier of the variant. To prove transmission of this variant, we sequenced DKC1 in each daughter and confirmed heterozygosity for the same Thr405Ala mutation; a maternal aunt with normal length telomeres did not carry this variant.