APC GENE-MUTATIONS IN FAMILIAL ADENOMATOUS POLYPOSIS-COLI IDENTIFIED AT THE DNA AND PROTEIN LEVEL

Peripheral blood cell DNA of patients suffering from Familial Adenomat ous Polyposis coli (FAP) were subjected to SSCP screening analyses. He re, we report on a patient, who was diagnosed at the age of 31 years s uffering from a severe form of adenomatous polyposis coli. The germlin e mutation was identified to result from a 5-bp germline microdeletion surrounding Adenomatous Polyposis Coli (APC) codon 1309. Examination of DNA derived from pooled adenomas of the same patient confirmed the inherited mutation. Western blot analysis with an APC N-terminus speci fic antiserum (anti-APC123) applied to tumor-derived proteins identifi ed a polypeptide chain of 140 kD corresponding to the truncation induc ed by the APC germline mutation. We further examined DNA isolated indi vidually from eight adenomas of the same patient. The analysis reveale d the surprising observation, that three out of eight tumor samples an alyzed, gave rise to a predominant PCR-amplified band of normal size, implicating that the allele containing the germline deletion had been lost, and instead hemi-/homozygosity for the somatic, not for the germ line mutation had been aquired as a tertiary event. A similar mutation al mechanism has been reported for the Rb-1 tumor suppressor gene in t he retinoblastoma model.