Whole Genome Sequencing Uncovers a Rare Germline Variant in ATM Associated with Familial Myeloproliferative Neoplasms

Introduction: Myeloproliferative neoplasms (MPN) are sporadic diseases characterized by a somatic driver mutation in the JAK2, CALR or MPL gene. Although it is generally considered a sporadic disease, approximately 10% of MPN cases display familial clustering, and there is a 5 to 7-fold increased risk of developing an MPN among first degree relatives of MPN patients. In contrast to other myeloid malignancies, investigation of large pedigrees with familial clustering of MPN has failed to identify high-risk predisposition genes relevant to the general MPN population. Genome wide association studies (GWAS) have identified common, low penetrance risk alleles for MPN predisposition in multiple genes including JAK2, TERT, TET2, ATM and SH2B3. In order to identify novel germline predisposition variants in MPN, an unbiased whole genome sequencing (WGS) approach was utilized to examine genomic structure and germline variations in a cohort of individuals with familial MPN. Methods: The study cohort was comprised of 67 individuals with familial MPN enrolled in a prospective research registry at Johns Hopkins Hospital. Familial MPN was defined as a diagnosis of MPN in an individual with a family history of MPN or related myeloid malignancy (myelodysplastic syndrome and chronic myelomonocytic leukemia) in a first or second degree relative. Neutrophil genomic DNA was subjected to WGS using Illumina HiSeq platform and sequenced to 60x depth. We performed germline variant calling using HaplotypeCaller and following the GATK best practices. The variants detected were further enriched for germline by allele frequency 40-60% or >90% and presence in the gnomAD database. Non-synonymous coding variants that occurred in the study cohort at a statistically higher frequency that in the general population (gnomAD) were selected for further analysis. Prediction of variant deleteriousness was assessed by 4 algorithms (Provean, SIFT, Polyphen-2, CADD). Results: Filtering of 32,788 non-synonymous, likely germline variants produced 148 that occurred at a higher frequency in our cohort than in the general population (p < 0.01, Fisher's exact test). Of these, 29 were predicted to be pathogenic in 3 out of 4 algorithms. Five unrelated individuals were found to harbor a heterozygous p.Leu2307Phe variant in the ATM gene (chr11:108326169 C>T). The clinical characteristics of these individuals are presented in Table 1. The structure prediction of ATM indicates that Ser2306 is a potential phosphorylation site of protein kinase A, suggesting that the methionine-aromatic bond between M2026 and the mutated F2307 may block the phosphorylation of S2306 (Figure 1). Conclusions: We identified a rare ATM germline variant (chr11:108326169 C>T; p.Leu2307Phe) present in 5 individuals with familial MPN. ATM is involved in DNA damage repair and important in the maintenance of genomic integrity. Heterozygous germline variants in ATM are known to predispose to multiple cancer types, including breast, prostate, pancreatic and melanoma. Further, common polymorphisms in ATM have been found to be associated with the MPN phenotype via GWAS. Our data suggests that this variant may impact ATM activation and its function in DNA damage repair, and functional studies are in progress. These data implicate a rare germline ATM variant as a novel risk factor for development of MPN. Figure 1 Figure 1. Disclosures Hourigan: Sellas: Research Funding.