High throughput sequencing analysis for the molecular diagnosis of Inherited Thrombocytopenias

Inherited thrombocytopenias are a heterogenous group of rare genetic disorders characterized by reduced platelet count sometimes combined with bleeding tendency and/or other clinical defects. The molecular diagnosis of ITs is essential to make clinical decision and infer personalized prognosis and risks. More than 30 genes have been identified that harbor mutations responsible for ITs (Balduini et al., 2017). In addition, ITs often show phenotypic overlaps that hamper the correct diagnosis with the traditional diagnostic algorithm based on step-wise specialized investigations. However, the advent of next generation sequencing has changed the diagnostic approach of diseases characterized by high genetic heterogeneity like ITs. In order to improve the diagnosis of IT, we designed a targeted next generation sequencing panel (IT-NGS) to screen the 28 genes more commonly mutated in ITs. Ninety-seven consecutive probands with a suspicious of ITs had been sequenced. The analysis led us to reach a definite diagnosis for 37 probands. In these probands we identified known or novel likely pathogenic mutations causing specific diseases, including monoallelic Bernard Soulier syndrome (N=14), biallelic Bernard Soulier syndrome (N=4), ACTN1-related thrombocytopenia (N=4), MYH9-related disease (N=7), ANKRD26-related thrombocytopenia (N=4), congenital amegakaryocytic thrombocytopenia (N=1), grey platelet syndrome (N=1), Wiskott-Aldrich syndrome (N=1) and Acute Myelogenous Leukemia (N=1). In another 34 cases we identified variants of uncertain significance (VUS) whose pathogenic role has to be supported by segregation analysis and in-depth functional studies. Since 17 probands had no potential candidate variant impacting IT-NGS genes, they are eligible for whole exome sequencing (WES) to clone novel genes involved in ITs. In conclusion, since some IT forms predispose to additional acquired disease during life, an accurate diagnosis is essential to infer personalized prognosis and define proper treatments and follow-up. Because of clinical and genetic heterogeneity, the molecular diagnosis of ITs represents a lengthy and expensive challenge using conventional technologies. The use of IT-NGS in clinical practice aided by specific investigations clarifying the role of variant of uncertain significance, overcomes these issues facilitating a definite diagnosis in patients with a suspicious of known ITs forms.