Mapping and Characterization of Novel (CAG)nRepeat cDNAs from Adult Human Brain Derived by the Oligo Capture Method

The expansion of a (CAG)ntrinucleotide repeat has been associated with at least eight neurological disorders in which the repeats code for polyglutamine in the protein. To identify additional genes that possess (CAG)nrepeats, single-stranded cDNA clones derived from adult human brain were screened using biotinylated oligonucleotide (CAG)8, and the hybridizing complexes were isolated with strepavidin-coated paramagnetic beads. A total of 119 cDNA clones were isolated and initially characterized by end sequencing. BLAST homology searches were used to reduce redundancies with overlapping clones and to eliminate those that show sequence identity with previously published cDNAs with triplet repeats. Only cDNA clones with more than five CAG repeats were pursued for analysis. A total of 19 novel cDNAs were further characterized by determining chromosomal assignments using the Stanford G3 and Genebridge radiation-reduced hybrid mapping panels. Transcript sizes and tissue expression patterns were determined by Northern blot analysis. Two of 19 clones showed specific or high expression in brain. These cDNAs are ideal candidate genes for other neurodegenerative disorders, such as spinocerebellar ataxia types 5 and 7, and may also be implicated in psychiatric diseases such as bipolar affected disorder and schizophrenia.