Digenic Inheritance of Mutations in Homologous Recombination Genes in Cancer Patients

Abstract

Background/objectives: BRCA1, BRCA2, ATM, and CHEK2 are known cancer predisposition genes (CPGs), but tumor risk in patients with simultaneous pathogenic variants (PVs) in CPGs remains largely unknown. In this study, we describe six patients from five families with multiple cancers who coinherited a combination of PVs in these genes.

Methods: PVs were identified using NGS DNA sequencing and were confirmed by Sanger.

Results: Families 1, 2, and 3 presented PVs in BRCA2 and ATM, family 4 in BRCA2 and BRCA1, and family 5 in BRCA2 and CHEK2. PVs were identified using NGS DNA sequencing and were confirmed by Sanger. The first family included patients with kidney, prostate, and breast cancer, in addition to pancreatic adenocarcinomas. In the second family, a female had breast cancer, while a male from the third family had prostate, gastric, and pancreatic cancer. The fourth family included a male with pancreatic cancer, and the fifth family a female with breast cancer.

Conclusions: The early age of diagnosis and the development of multiple cancers in the reported patients indicate a very high risk of cancer in double-heterozygous patients associated with PVs in HR-related CPGs. Therefore, in families with patients who differ from other family members in terms of phenotype, age of diagnosis, or type of cancer, the cascade testing needs to include the study of other CPGs.

Keywords: ATM; BRCA1; BRCA2; CHEK2; digenic inheritance; double heterozygosity; familial cancer.

Figure 1

Pedigree of the five families reported: (a) family 1, (b) family 2, (c) family 3, (d) family 4, and (e) family 5. The probands are marked with arrows. ca., cancer; CRC, colorectal cancer; d., death; dx., diagnosis; y., years; +/−, heterozygous genotype; −/−, homozygous wild type genotype; ?/?, unknown genotype.