MYH Gene Status in Polish FAP Patients without APC Gene Mutations.

Familial Adenomatous Polyposis (FAP) is an inheritable predisposition for the occurrence of numerous polyps in the large intestine. In about 50% of all patients, the occurrence of the disease is conditioned by heterozygotic mutations of the APC gene. Screening for genetic factors in persons without mutations in the APC gene led to the identification of homozygotic mutations of the MYH gene as the cause of the appearance of the polyposis form which is characterized by recessive heritability and a milder course than in the case of the classic form of the disease. The authors examined 90 persons from the DNA bank of patients with FAP from the Institute of Human Genetics of the Polish Academy of Sciences in Poznań in whom no mutations in the APC gene were detected. Two of the most frequent mutations of the MYH gene (Y165C and G382D) were found to be heterozygous in 13% of patients and no other mutations in this gene coding sequence were observed. In the group with heterozygotic occurrence of the mutation in the MYH gene, the disease phenotype was not milder in comparison with the entire examined group and the mean age of the disease manifestation was even lower. This observation allows one to conclude that the employed methods of mutation screening were correct and, in the case of the examined group, the mutation ratio of the MYH gene does not precondition the occurrence of the disease, but it cannot be excluded that it may modify its phenotype. The obtained results indicate that the criteria applied during the process of FAP qualification are more rigorous than those applied in other countries.