High-resolution physical and transcript map of human chromosome 2p21 containing the sitosterolaemia locus

Sitosterolaemia (phytosterolaemia) is an autosomal recessive disorder characterised by the presence of tendon xanthomas in the face of normal or mildly elevated plasma cholesterol levels, premature atherosclerotic disease and has diagnostically elevated plasma and tissue plant sterol concentrations. Affected individuals show an increased absorption of both cholesterol and sitosterol from the diet, decreased bile clearance of these sterols and their metabolites resulting in markedly expanded whole body cholesterol and sitosterol pools. The defective gene is therefore hypothesised to play a crucial role in regulating dietary cholesterol absorption, and its elucidation may shed light on these molecular processes. We have previously localised the defective gene to human chromosome 2p21, between microsatellite markers D2S1788 and D2S1352, a distance of approximately 15 cM. Recently, the disease locus interval has been narrowed to lie between D2S2294 and D2S2291/D2S2174. We have constructed a high-resolution YAC and BAC contigs by using known STSs and generating novel STSs from the minimal interval. Eight previously identified genes and 60 ESTs were mapped to these contigs. The BAC contig contains 60 BAC clones and 108 STSs and encompasses a physical distance of approximately 2.0 cM between microsatellite markers D2S2294 and D2S2291. These results will not only facilitate cloning of the sitosterolaemia gene, but also other disease genes located in this region, and accelerate sequencing of the corresponding genomic clones.