Analysis of Familial Tylosis with Oesophageal Cancer Genes on 17q25

Tylosis has been associated with oral leukokeratosis and squamous cell oesophageal cancer in three families. The causative locus, the tylosis oesophageal cancer (TOC) gene, is also important in sporadic squamous cell oesophageal cancer. The minimal genomic region that contains the TOC gene has been located by us to approximately 500kb on chromosome 17q25. Objectives: The aims of this project were to reduce the minimal region further and to identify candidate genes for further analysis. Methods: Novel microsatellite markers were identified using bioinformatics analysis of the sequence data. PCR amplification of these markers in two of the tylosis-affected families was followed by haplotype analysis. Results: Twenty novel microsatellites were identified in the 500kb region, but only 9 of the repeats were polymorphic in the UK and/or US families. After haplotype analysis, two of the new markers, D17S2239 and D17S2244, redefined the TOC minimal region in the UK family and have narrowed the critical region to just over 65kb. Sequencing of family members identified 63 single nucleotide polymorphisms in this 65kb, none of which were in coding regions of genes, but these allowed the reduction of the minimal region to 38kb. Computer analysis of sequence data from this minimal region identified 1 known and 1 poorly characterised candidate genes. Characterisation and expression analysis of these genes is ongoing. Conclusion: Bioinformatic analysis of sequence data can identifying molecular markers for use in mapping studies. Markers have been typed in two pedigrees suffering from familial tylosis with oesophageal cancer and the results have led to the reduction of the region containing the gene from 500kb (containing over 100 genes) to 38kb (containing 2 genes). Analysis of these 2 genes is continuing in order to identify the causative gene and investigate its function.

Funded by the North West Cancer Research Fund and Cancer Research UK.