Familial adenomatous polyposis (FAP) is an inherited disorder, which can develop into cancer and is a result of germline mutations in the adenomatous polyposis coli gene (APC).

The diagnosis was made based on clinical and pathological examination. We screened the APC gene for mutation and evaluated the genotype-phenotype correlation in 21 classical unrelated FAP patients with autosomal dominant pattern in pedigree chart.

Mean age at onset of 27.90 years and males to female ratio was 13/8. Nine patients had a coexisting colorectal cancer, of which 6 had APC mutations .Congenital hypertrophy of the retinal pigment epithelium was the most common extra colonic manifestation. The most common symptom was abdominal pain (43%). Genomic DNA sequencing of codon 999 to 1410 of the APC gene was identified in 14 of the 21 patients, with a mutation rate of 66.66%.including one novel frame shift mutation, three nonsense mutations and 10 novel missense mutations (71%). The most frequent mutations were in codon 1308 and 1350.

In conclusion, our study results indicate that the APC gene has a high mutation detection rate (66.66%) between codons 999 and 1410, and codons 1308 and 1350 are two mutation hotspot regions.