Whole Exome Sequencing in Severe Aplastic Anemia Identifies Unrecognized Inherited Subset with Inferior Survival after Hematopoietic Cell Transplant

Background: It is important to identify inherited bone marrow failure syndromes (IBMFS) in patients with aplastic anemia in order to provide appropriate therapy. IBMFS are diagnosed through genetic or other diagnostic testing but can also go unrecognized, particularly in adults who may lack classic IBMFS features. This is particularly critical in light of increasing identification of individuals with variants of uncertain significance (VUS) and those with single pathogenic variants in an autosomal recessive (AR) gene or X-linked recessive (XLR) gene in females (SPVR) (“carriers”) during evaluation. In this study of patients diagnosed with acquired severe aplastic anemia (SAA), we evaluated putatively causal variants in IBMFS genes to determine the frequency of patients with an unrecognized IBMFS or SPVR and assessed their association with outcomes after hematopoietic cell transplant (HCT). Methods: We used pre-HCT blood samples and clinical data from the Transplant Outcomes in Aplastic Anemia study (TOAA; a collaboration between the National Cancer Institute and the Center for International Blood and Marrow Transplant Research). Germline whole exome sequencing was performed on 732 patients with acquired SAA who received HCT between 1991-2015. A total of 104 IBMFS genes, (51 autosomal dominant (AD), 46 AR, 3 both AR and AD, 4 XLR) were evaluated for both single nucleotide (SNV) and copy number variants (CNV). All variants were curated using ACMG/AMP criteria, and a subset were validated by Sanger sequencing. Variants classified as VUS according to ACMG/AMP criteria and with a damaging score prediction in 3 of 5 in silico meta-predictors were categorized as deleterious VUS. Patients were divided into 3 groups based on known inheritance patterns of identified genes into those with 1) unrecognized IBMFS 2) SPVR or 3) neither (presumed acquired SAA). For telomere biology genes with AD/AR inheritance, we used telomeres