in patients with juvenile polyposis syndrome jps the frequency of large genomic deletions in the smad4 and bmpr1a genes was unknown mutation and phenotype analysis was used in 80 unrelated patients of whom 65 met the clinical criteria for jps typical jps and 15 were suspected to have jps by direct sequencing of the two genes point mutations were identified in 30 patients 46 of typical jps using mlpa large genomic deletions were found in 14 of all patients with typical jps six deletions in smad4 and three deletions in bmpr1a mutation analysis of the pten gene in the remaining 41 mutation negative cases uncovered a point mutation in two patients 5 smad4 mutation carriers had a significantly higher frequency of gastric polyposis 73 than did patients with bmpr1a mutations 8 p 0 001 all seven cases of gastric cancer occurred in families with smad4 mutations smad4 mutation carriers with gastric polyps were significantly older at gastroscopy than those without p 0 001 in 22 of the 23 unrelated smad4 mutation carriers hereditary hemorrhagic telangiectasia hht was also diagnosed clinically the documented histologic findings encompassed a wide distribution of different polyp types comparable with that described in hereditary mixed polyposis syndromes hmps screening for large deletions raised the mutation detection rate to 60 in the 65 patients with typical jps a strong genotype phenotype correlation for gastric polyposis gastric cancer and hht was identified which should have implications for counselling and surveillance histopathological results in hamartomatous polyposis syndromes must be critically interpreted.