Juvenile polyposis in a family with «familial adenomatous polyposis» - an accidental find or a natural phenomenon?

Aim: based on literature data and our own experience, to demonstrate the need for a meticulous family history harvesting in patients with suspected hereditary polyposis syndrome, as well as the importance of conducting a complex molecular genetic study. Materials and methods: the most known among hereditary polyposis syndromes is familial adenomatous polyposis (FAP).At the same time, according to the literature, one of the hamartomatous polyposis syndromes- juvenile polyposis - may mimic endoscopic picture of adenomatous polyposis. The article presents a clinical observation of a family whose members have been suspected of having FAP for several years, and only whole-exome sequencing helped to establish the diagnosis of juvenile polyposis syndrome. Results: based on the family history, as well as the clinical picture of the disease, which was somewhat unusual for FAP, the patient underwent whole-exome sequencing, which revealed a previously undescribed pathogenic variant in the SMAD4 gene - c.705dupA (p.Gly236ArgfsTer28). The presence of a similar mutation was also confirmed in 3 close relatives of the patient. Conclusion: taking into account the wide phenotypic variability of manifestations of juvenile polyposis, molecular genetic study of the SMAD4 and BMPR1A genes is of particular importancein patients with a clinic of adenomatous polyposis syndrome and the absence of mutations in the APC and MutYH genes.