CAG/CTG and CGG/GCC repeats in human brain reference cDNAs: outcome in searching for new dynamic mutations.

CAG and CGG expansion is associated with 10 inherited neurological diseases and is thought to be involved in other human genetic diseases. To identify new candidate genes, we have undertaken a large-scale screening project for CAG/CTG ([CAG]n) and CGG/GCC ([CGG]n) repeats in human brain reference cDNAs. Here, we present the final classification for 597 cDNAs selected by CAG and CGG hybridization from two libraries (100,128 clones) and the updated characterization of [CAG]n- and [CGG]n-positive cDNAs (repeat polymorphism and cDNA localization). We have selected 124 CAG and 83 CGG hybridization-positive clones representing new genes, from which 49 CAG and 7 CGG repeats could be identified. New [CAG]n and [CGG]n with more than seven to nine units were rare (1/2000), and perfect [CAG]n 9 were more likely polymorphic. Overall, highly polymorphic to monomorphic new [CAG]n > 9 and [CGG]n > 7 were characterized. The comparison of our data with other [CAG]n and [CGG]n resources suggests that the screening of reference cDNAs leads to unique sources of new [CAG]n and [CGG]n and will enhance the study of enlarged triplet repeats in human genetic diseases.