Complexgenetic predisposition to cancer inan extended HNPCC family withan ancestral hMLH1 mutation

Hereditary non-polyposis colorectal cancer(HNPCC)ischaracterised byagenetic predisposition todevelop colorectal canceratanearly ageand,toalesser degree, canceroftheendometrium, ovaries, urinarytract, andorgansofthegastrointestinaltractotherthanthecolon.Inthe majority offamilies thedisease islinked to mutations inoneofthetwomismatch repair genes, hMSH2 orhMLH1.We have foundanovelhMLH1 nonsense mutation ina SwissfamilywithLynchsyndrome, whichhasbeentransmitted throughat least ninegenerations. A different tumour spectrumofneoplasmsoftheskin,soft palate, breast, duodenum,andpancreas wasobserved inthreebranchesofthis family, wheretherewasavirtual absence ofcolonic tumours. ThehMLH1 mutation couldnotbedetected inmembersofthese branches suggesting thatatleast asecond genetic defectpredisposing tocanceris segregating inpartofthekindred. (JMed Genet1996;33:636-640)