Congenital thrombocytopenia/platelet disorders are heterogeneous disorders of platelet number and/or function. Pathogenic variants in the genes implicated in megakaryocyte differentiation and platelet formation cause thrombocytopenia in these patients. Recent advances have elucidated several causative genes for these disorders, but identifying the underlying causative genes remains challenging. Patients with these disorders often receive inappropriate treatments, including glucocorticoids and splenectomy, for chronic immune thrombocytopenia (ITP). In Japan, we have developed a diagnostic system using high-throughput DNA sequencing with a multigene panel and established a registry. Between 2018 and 2023, 245 patients were enrolled and analyzed. Pathogenic variants in 17 genes (42 MYH9, 19 ANKRD26, 17 ITGA2B/ITGB3, 8 ACTN1, 8 WAS, 6 ETV6, 6 VWF, 5 CYCS, and 14 others) were identified in 125 patients (51.0%). An additional 29 patients (11.8%) had suspected pathogenic variants under investigation. We also found that immature platelet fraction (IPF%) is useful in the differential diagnosis because the median IPF% in MYH9 disorders, 48.7%, was significantly higher than in all other groups (chronic ITP, 13.4%; controls, 2.6%). The results of this study provide new insight into congenital thrombocytopenia/platelet disorders.

Over the last decade, the implementation of multigene panels for hereditary tumor syndrome has increased at our institution (Inselspital, University Hospital Berne, Switzerland). The aim of this study was to determine the prevalence of variants of unknown significance (VUS) in patients with suspected Lynch syndrome and suspected hereditary breast and ovarian cancer syndrome, the latter in connection with the trend toward ordering larger gene panels.
Retrospectively collected data from 1057 patients at our institution showed at least one VUS in 126 different cases (11.9%). In patients undergoing genetic testing for BRCA1/2, the prevalence of VUS was 6%. When < 10 additional genes were tested in addition to BRCA1/2, the prevalence increased to 13.8%, and 31.8% for > 10 additional genes, respectively. The gene most frequently affected with a VUS was ATM. 6% of our patients who were tested for Lynch syndrome had a VUS result in either MLH1, MSH2 or MSH6.
Our data demonstrate that panel testing statistically significantly increases VUS rates due to variants in non-BRCA genes. Good genetic counseling before and after obtaining results is therefore particularly important when conducting multigene panels to minimize patient uncertainty due to VUS results.