Editor—Familial adenomatous polyposis (FAP) is an autosomal dominant condition characterised by the presence of more than 100 adenomatous polyps in the colon and rectum. Polyps generally first appear in the second or third decade of life and are usually most numerous distally. Left untreated, colorectal cancer is virtually inevitable and generally arises in the fourth or fifth decade.1 Adenocarcinoma of the appendix is an uncommon neoplasm and has only rarely been reported in association with FAP.2

The gene responsible for FAP, APC, was initially localised to the long arm of chromosome five (5q) by linkage.3 4 This followed a case report describing carcinomas of the rectum and ascending colon, adenomatous polyposis, mental retardation, and various dysmorphic features in a 42 year old man with a constitutional deletion of 5q.5 Most patients with FAP have normal karyotypes.6 Mental retardation and dysmorphic features are unusual in such people but characterise those rare patients with cytogenetically visible 5q deletions and FAP.5-12 The few reports detailing the clinical findings in patients with submicroscopic deletions ofAPC suggest that such people may be mentally normal.13 14

In this report we describe a patient with adenomatous polyposis, mental retardation, and an apparently balanced translocation t(5;8)(q22;p23.1) causing submicroscopic deletion of APC andMCC.

Clinical data were obtained by review of medical records. In addition, the patient was interviewed and examined by two of the authors (JF and AS) before her death. Cytogenetic studies were performed using standard techniques on a 72 hour peripheral blood culture with GTG banding, as previously reported.6

Slides for fluorescence in situ hybridisation (FISH) were obtained using the cell suspension retained after routine cytogenetic harvest. RNAse treatment, probe and chromosomal denaturation, and hybridisation conditions were as previously described15 with the …