molecular diagnostics of cancer predisposition is very important for the medical treatment of the patient and persons belonging to the high risk group . molecular studies enable the detection of mutation carriers and release from unreasonable stress of persons from the group with increased risk of cancer occurrence . the mutation spectrums in the genes predisposing to colorectal cancer in the polish population have been described [ 1 - 4 ] . in the present work we focused on recurrent mutations of the apc gene causing fap . familial adenomatous polyposis ( fap ) is characterized by the appearance of numerous polyps in the large intestine . the correlation between mutations of the apc gene and the occurrence of familial adenomatous polyposis was described in 1991   and since then , mutations of the apc gene have been investigated in research centres leading to identification of various mutation types . mutations of the apc gene , in most cases , are small deletions or insertions with the most frequent mutations , in the greater part of the described populations , being the aaaga deletion at codon 1309 and the acaaa deletion at codon 1061 . clinical diagnoses of fap patients were conducted in collaborating genetic centres or gastroenterology clinics in the place of residence of patients . so far , samples of dna belonging to 280 polish fap families have been collected in the dna bank of polish fap families established in 1997 at the institute of human genetics , polish academy of science in poznan . dna was extracted from peripheral blood cells by the classical phenol purification method and entire coding sequence of apc gene was screened for mutations by pcr - hd and sscp methods in 280 probands . dna fragments showing heteroduplex or additional pattern in sscp analysis were sequenced by direct pcr product sequencing and analyzed using a megabace 500 sequencer according to the manufacturer 's specifications . we identified 72 mutations in 124 of our 280 fap families and observed eight types of recurrent mutations . the mutations and age of onset two of them were localized in exon 11 and the remaining six in the 3 ' part of exon 15 . the most frequent mutation , 39273931delaaaga , occurred in twenty - eight families ( 10% ) ; the second one was 31833187delacaaa , occurring in eight families ( 2.8% ) ; and the third most frequent mutation was 32023205deltcaa , detected in 5 families ( 1.7% ) . in our fap patients y500x occurred in four families ( 1.4% ) while q978x was detected in three families . each of the remaining four types of mutation occurred in two families and the frequencies of these mutations were below one percent . fifty - four recurrent mutations identified in apc gene and age of onset in a group of 124 diagnosed polish fap families nd  no data available in the human mutations database at the institute of medical genetics in cardiff , considered the most representative population in the world , seven hundred mutations are listed for the apc gene . the mutation reports describe the frequency of this mutation from 0% in northwest spain , 2.4% in the australian population , 5% in dutch , 7% in israeli to 16% in the group of italian fap patients [ 6 - 9 ] . the second most frequent mutation , 31833187delacaaa , is reported with frequency ranging from 0% in northwest spain , 1.5% in israeli populations to 8.4% in australia [ 6 - 9 ] . a study of over 100 dutch families revealed equal frequency of those two most frequent mutations ( 39273931delaaaga and 31833187delacaaa ) . the latest published report in 2005 involved the analysis of over 1000 patients . in comparison to this study , the representative study of mutation frequency in the neighbouring population indicated two times higher frequency of 39273931delaaaga , whereas a difference in frequency of 31833187del - acaaa was not observed ( germany 3.8% , poland 2.7% ) . the frequency of 32023205deltcaa was equal ( 1.7% ) in both populations . in worldwide comparison differences in the frequency of mutations the polish population of fap patients belongs to the group where 39273931delaaaga occurred with higher frequency , whereas the frequency of mutation 31833187del - acaaa occurred with medium frequency in comparison with other populations . the two recurrent mutations localized on exon 11 were observed only in the polish population . in our two unrelated families with 14901491inst brain tumours were observed . another mutation ( q978x ) did not occur with higher frequency as described for other populations . in our fap patient group q283x , which occurs with frequency of 4.5% in uk fap patients , screening for these mutations permitted us to diagnose 19% of all families in our population but eight types of mutations constitute 43.5% of all our diagnosed families . the mutation study in our population should involve these eight mutations to improve molecular diagnostics of the apc gene . the study was financed by grant 2p05a10728 from the ministry of science and higher education .
the molecular diagnostics of genetically conditioned disorders is based on the identification of the mutations in the predisposing genes . 
 hereditary cancer disorders of the gastrointestinal tracts are caused by mutations of the tumour suppressor genes or the dna repair genes . 
 occurrence of recurrent mutation allows improvement of molecular diagnostics . 
 the mutation spectrum in the genes causing hereditary forms of colorectal cancers in the polish population was previously described . in the present work 
 an estimation of the frequency of the recurrent mutations of the apc gene was performed . 
 eight types of mutations occurred in 19.4% of our fap families and these constitute 43% of all polish diagnosed families .