Through extensive genetic studies on a large cohort of clinically diagnosed DC and DCL cases, we identified several novel pathogenic variants within known genetic loci and discovered a new X-linked gene, POLA1. Functional curation of novel variants identified in POLA1, POT1 and ZCCHC8 genes expand the genetic and molecular basis associated with these conditions. Here, POLA1 is linked to dyskeratosis congenita.