New MD Gene Discovered

by Dan Roberts
August, 2002
Researchers at the University of Michigan Kellogg Eye Center have discovered a genetic link to a form of macular degeneration. In an article published in August 2002 in Genome (“X-Linked Recessive Atrophic Macular Degeneration from RPGR Mutation,” pp. 166-171, doi:10.1006/geno.2002.6815, Radha Ayyagari, et al) the gene RPGR (associated until now with retinitis pigmentosa) is also been found to be responsible for an X-linked form of early-onset MD. This is the first time that a gene has been mapped to the X chromosome. Females have two X chromosomes, and males have only one paired with a Y chromosome. Women with the mutated RPGR gene, therefore, can only be carriers of this form of the disease, while men stand a 50% chance of inheriting it from their mothers.
The scientists studied ten related males who had early-onset MD in its dry form. They all showed mutations of the RPGR gene, while only one of them showed symptoms of retinitis pigmentosa. This indicates that the single RPGR gene may be responsible for at least two different types of retinal degeneration. In the same study, twelve related females were found to carry the RPGR gene, but none of them had significant vision loss.
According to the authors of the study, “Identification of an RPGR mutation in atrophic [dry] macular degeneration expands the phenotypic range associated with this gene and provides a new tool for the dissection of the relationship between clinically different retinal pathologies.”
The next step is to learn more about the cause of the mutation, and then to look for ways to correct this form of the disease.