P818: NEXT GENERATION TARGETED SEQUENCING FOR ENHANCED GENOTYPING OF DIAMOND BLACKFAN ANEMIA IN ISRAEL

Background: Diamond Blackfan anemia (DBA), an erythroid-specific congenital bone marrow failure syndrome, is predominantly driven by mutations in one of several genes encoding ribosomal proteins (RP), leading to protein haploinsufficiency. In recent years, a number of patients with “DBA-like” syndrome were found to have mutations in non-RP genes including CECR1. Next generation sequencing (NGS) is rapidly replacing conventional Sanger sequencing approaches in the molecular diagnosis of patients with DBA and other inherited bone marrow failure syndromes. Targeted NGS panels enable high-resolution deep sequencing of all known genes associated with a specific clinical presentation such as congenital anemias. Aims: This study aims to use a targeted NGS panel specific for inherited anemias to genotype previously undiagnosed patients with clinical DBA in Israel. Enhanced genotyping efficiency provided by NGS may provide an opportunity to evaluate for genotype-phenotype correlations. Methods: A targeted NGS panel including over 260 genes was used as an adjunct to Sanger sequencing and multiplex ligation-dependent probe amplification for genotyping patients from the Israeli inherited bone marrow failure registry (I-IBMFR) with a clinical diagnosis of DBA. Over 90% of 48 patients with DBA from the Israeli registry had available DNA for genotyping. Results: Forty-eight patients with clinical DBA, registered to the I-IBMFR, have been followed for a median of 12.1 years. The majority of patients presented with anemia in the first year of life, with a median age at presentation of 3 months. Forty-four of these patients underwent genotyping. Pathogenic RP gene alterations were detected in 31 patients in 9 different RP genes; homozygous CECR1 mutations were found in 8 separate patients. Forty percent of these molecular diagnoses were detected by targeted NGS panel technology. More than half of the patients exhibited at least one congenital malformation. Cardiac anomalies were observed broadly in patients with small and large subunit RP gene mutations. Thumb anomalies were found exclusively in patients with RPL5 mutations; cleft lip and palate were reported only in patients with RPS10 and RPL11 mutations. Fewer than half of the patients given a steroid trial were responsive; patients with RPS19 mutations responded significantly better to steroid treatment than patients with RPL5 mutations. Just under half of the patients with RP gene mutations became red blood cell (RBC) transfusion dependent, while almost all of the patients with CECR1 mutations required RBC transfusions. Three patients, including two genetically undiagnosed patients, went into spontaneous remission after receiving chronic treatment. Summary/Conclusion: Use of targeted NGS has dramatically enhanced the efficiency of genotyping for patients with DBA and other inherited bone marrow failure syndromes, allowing for focused management of patients and discovery of novel genotype-phenotype correlations. Ongoing investment in registries and comprehensive genotyping are crucial in increasing our understanding of this rare disease and optimizing patient care.