NTHL1 biallelic mutations seldom cause colorectal cancer, serrated polyposis or a multi-tumor phenotype, in absence of colorectal adenomas

Abstract

In 2015 Weren et al. described a hereditary cancer syndrome caused by biallelic mutations in the DNA base excision repair gene NTHL1, characterized by attenuated adenomatous polyposis and increased colorectal cancer (CRC) risk, largely resembling the recessive syndrome caused by MUTYH mutations1. To date, 33 homozygous or compound heterozygous NTHL1 mutation carriers have been reported (21 families)1,2,3,4,5,6,7,8. More than 5 colonic adenomas (range: 6 to >50) were identified in 24 of the 28 (85%) mutation carriers who underwent colonoscopy screening, and CRC was diagnosed in 19 (68%) of them. Noteworthy, 17 carriers (57%) were diagnosed with multiple primary malignant tumors in extracolonic locations, being the most recurrently found breast and endometrial tumors, head neck squamous cell carcimomas, meningiomas, and bladder and basal cell carcinomas, suggesting that the NTHL1-associated syndrome is a multi-tumor disease rather than a solely CRC syndrome. On the other hand, the fact that at least ¼ (7/28) of the reported biallelic mutation carriers who underwent colonoscopy screening had ≤10 adenomas, and that ≥5 hyperplastic polyps were detected in five carriers (polyp number range: 5->30), lead us to suspect a possible association of NTHL1 mutations with nonpolyposis CRC and serrated/hyperplastic polyposis. Based on previous evidence and with the aim of refining the phenotypic characteristics of the NTHL1-associated syndrome, here we evaluated the implication of NTHL1 biallelic mutations in the predisposition to personal or familial history of multiple tumor types, familial/early-onset nonpolyposis CRC, and serrated/hyperplastic polyposis.