A fine integrated map of the SPG4 locus excludes an expanded CAG repeat in chromosome 2p-linked autosomal dominant spastic paraplegia

Autosomal dominant hereditary spastic paraplegia (AD-HSP) is a genetically heterogeneous disorder characterized by progressive spasticity of the lower limbs. A major locus (SPG4) causing AD-HSP in about 40% of the families was mapped to chromosome 2p. The analysis of six SPG4-linked AD-HSP families using the RED procedure previously showed the expansion of a CAG repeat in affected individuals. To identify the gene responsible for this form of HSP, we have constructed a 3.5-Mb YAC contig flanked by loci D2S400 and D2S367, have subcloned five of these YACs spanning the candidate region into cosmids, and screened these cosmid libraries for the presence of GAG; repeat sequences. Four CAG repeats have been identified but none of them is expanded in 26 patients from 13 SPG4-linked AD-HSP families. A gene map comprising 21 transcripts was established using expressed sequence tags (ESTs) assigned previously to this region of 2p21p22 with radiation hybrid panels GeneBridge 4 and G3. Full-length cDNAs corresponding to the 14 ESTs mapping to the SPG4 interval flanked by loci D2S352 and D2S2347 were isolated and sequenced. None contains a CAG repeat in its coding sequence. Finally, we have assembled a BAC contig composed of 37 clones that were also screened for the presence of CAG repeats; this failed to detect additional repeats to those identified on YACs. (C) 1999 Academic Press.