Mutations in the RPGR gene cause X-linked cone dystrophy

Area of Science:

• Ophthalmology
• Genetics
• Molecular Biology

Background:

• X-linked cone dystrophy is a hereditary retinal degeneration affecting photopic (cone) vision.
• It is characterized by photophobia, color vision loss, and reduced central vision, distinct from retinitis pigmentosa.
• This disorder is genetically heterogeneous, with known loci at Xp11.4–Xp21.1 (COD1) and Xq27 (COD2).

Purpose of the Study:

• To investigate the genetic basis of X-linked cone dystrophy.
• To identify specific mutations within the RPGR gene associated with the COD1 locus.
• To understand the molecular mechanisms underlying cone-specific degeneration.

Main Methods:

• Genetic linkage analysis was performed on two families with X-linked cone dystrophy.
• The RPGR gene, particularly the ORF15 exon, was sequenced to identify mutations.
• The identified mutations were analyzed for their potential to cause frame-shifts and premature termination of translation.

Main Results:

• Two distinct mutations in the ORF15 exon of the RPGR gene were identified in the studied families.
• One mutation (ORF15+1343_1344delGG) resulted in a frame-shift and premature termination.
• The other mutation (ORF15+694_708del15) led to the deletion of five amino acids.

Conclusions:

• Mutations in the RPGR gene, specifically within ORF15, can cause X-linked cone dystrophy.
• These findings expand the known spectrum of RPGR-associated retinal disorders beyond X-linked retinitis pigmentosa.
• The expression of RPGR in both rods and cones supports its role in cone-specific degeneration.