Exclusion of CAG repeat expansion as the cause of disease in autosomal dominant retinitis pigmentosa families.

The involvement of genes with expanded tracts of (CAG)n in some neurodegenerative diseases is well established. Whether genes containing these motifs could also have a role in degenerative diseases affecting the retina, which is also neural in origin, is unknown. We investigated (CAG)n expansions as a cause of disease in a panel of eight autosomal dominant retinitis pigmentosa (ADRP) pedigrees, including families known to map to the RP9, RP11, and RP13 loci, using the technique known as "repeat expansion detection" (RED). An expansion was detected in one of the unlinked families, but it did not segregate with the disease and was thus nonpathogenic. Expansions were not detected in any other families. In conclusion, expanded (CAG)n repeats are not the cause of disease in the families we have studied, but given the high level of heterogeneity in RP and in retinal degenerations in general they remain strong candidates for involvement in other forms of retinal dystrophy.