Novel and reported APC germline mutations in Chinese patients with familial adenomatous polyposis

Objective: Familial adenomatous polyposis (FAP) is mainly caused by germline mutations in the adenomatous polyposis coli (APC) gene. This study aimed to detect pathogenic variants in five Chinese FAP families and review all previously reported pathogenic variants of APC gene in Chinese population.

Methods: Five non-consanguineous FAP families and 100 unrelated ethnicity-matched controls were included in the study. Sanger sequencing was performed to screen for APC coding and splicing variants. Chinese and English literature on APC germline mutations were reviewed to compile the mutation spectrum of APC gene in Chinese FAP patients.

Results: One pathogenic variant was detected in each family for the five pedigrees we tested. Three variants (c.3183_3187delACAAA, c.2626C>T and c.1312+1G>A) were previously reported as pathogenic. The other two variants were novel: c.794_795insG/p.Val266SerfsTer11 and c.2142_2143insG/p.His715AlafsTer19. They are absent from public databases (1000 Genomes, dbSNP, ESP and ExAC) and 100 normal controls, and are classified as pathogenic based on the new ACMG/AMP variant classification guidelines. Literature review and current study revealed a total of 82 different pathogenic variants from 127 Chinese FAP families. Among these families, 83 families had frameshift variants (65.35%), 26 with nonsense variants (20.47%), six with splice site variants (4.72%), three with missense variants (2.36%) and nine with large deletion or duplication variants (7.09%). Apart from the two previously reported mutation hotspots c.3927_3931delAAAGA (20.47%) and c.3183_3187delACAAA (7.09%), c.847C>T/p.Arg283Ter variant occurred with a frequency of 3.15% (4 out of 127) in Chinese FAP patients.

Conclusions: We reported two novel pathogenic variants. The comprehensive compilation of variants and comparison revealed largely similar mutation spectrum between Chinese and Western patient populations. Some unique features noticed in Chinese patient population may help to better understand the pathogenesis of FAP.