DIRECT IDENTIFICATION AND CLONING OF UNST ABLE EXPANDED (CCG)N AND (CTG)N TRINUCLEOTIDE REPEAT LOCI FROM COMPLEX GENOMES

We describe a simple method for the identification of pathologically e xpanded (CCG)n and (CTG)n threenucleotides repeat arrays in the human genome and for the recovery of flanking sequences. We were able to det ect the presence of novel high-molecular-weight alleles in at least tw o of three subjects known to have expanded (CCG)n tracts at the FRAXA locus. The above method may be used for testing of small families or e ven single affected individuals with disease thought to display clinic al evidence of anticipation. The (CCG)(n>200) and (CTG)(n>250) probes may also be useful for individual ''DNA fingerprint'' identifications.