Comparison of Fluorescence in Situ Hybridization and Flow Cytometry (Flow-FISH) with Monochrome Multiplex Quantitative Polymerase Chain Reaction (MM-qPCR) for Telomere Length Screening in Adult Patients with Suspected Cryptic Dyskeratosis Congenita (DKC)

Introduction: Dyskeratosis Congenita (DKC) is caused by defective telomere maintenance, mostly due to mutations impacting on the functional activity of telomerase. Classical DKC is characterized by mucocutaneous features and bone marrow failure diagnosed during childhood. In contrast, the cryptic form of DKC often first manifests itself in adulthood and presents clinically with less characteristic manifestations. Correct identification of DKC patients is of utmost importance because of significant implications for the affected patients (treatment, toxicities) and her/his family (donor selection, genetic counselling). Accelerated shortening of telomere length (TL) in peripheral blood leucocytes (PBL) represents the functional read-out and consequently, clinically useful screening parameter of altered telomere function. Consequently, in cases without distinct genetics or clinical presentation, significantly shortened TL is frequently used as a disease-defining marker. TL in PBL of pediatric DKC patients typically is below the first percentile (