Abstract 2484: Whole-exome sequencing of a rare case of familial childhood acute lymphoblastic leukemia

Abstract Acute lymphoblastic leukemia (ALL) is the most common cancer in children, accounting for approximately 25% of all pediatric cancer cases. However, familial childhood ALL is extremely rare. Few families with multiple non-twinned siblings diagnosed with childhood ALL have been reported, and to date no highly penetrant leukemia susceptibility gene(s) has been identified to explain this uncommon occurrence. We postulated that pure (nonsyndromic) familial childhood ALL could result from the accumulation of disadvantaging rare DNA variants in predisposing genes or biological pathways. To address this hypothesis, we used next-generation sequencing technologies to capture and re-sequence the whole-exomes of a family comprising the mother, father and two male non-twinned affected siblings (sibling A and sibling B). Both brothers were diagnosed with the identical ALL subtype, pre-B hyperdiploid childhood ALL, three years apart. The similar clinical and molecular characteristics of the siblings suggest shared etiologic factors. Using the Agilent SureSelect All Human Exon 38 Mb Kit and the SOLiD 3 Plus system, we captured and sequenced a total of 17.5 Gb of sequence for the entire family, with a mean coverage of 47X. For each individual, approximately 96% or 36.4 Mb of the targeted bases were covered α1X and 70% of the targeted bases or 26.4 Mb passed our thresholds for variant calling. We identified 52,038 positions at which the called allele(s) differed from the reference genome in at least one of the four family members. In total, we identified 19,096 germline variants in sibling A and 28,061 in sibling B, of which 2,355 (12.3%) and 2,125 (7.6%), respectively, were previously undiscovered in dbSNP. We investigated non-synonymous homozygous variant and compound heterozygous positions shared between the siblings, as well as genes/pathways with increased burden of rare non-synonymous variants. Based on several criteria (PolyPhen annotation, known allele frequency, etc.), we identified variants that are strong functional candidates to explain this case of pure familial childhood ALL. In parallel, high-density genotyping was also performed (Illumina Omni 2.5M) for quality control and structural variant detection, allowing the identification of putatively shared copy number variants that may also be involved in leukemogenesis. Though independent validation and functional assessment is required, this is the first study to identify genetic factors involved in pure familial childhood ALL. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2484. doi:1538-7445.AM2012-2484

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