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RP1 gene mutations have been discovered for the first time in autosomal recessive retinitis pigmentosa (RP), according to a study of consanguineous Pakistani families with the condition. They are not a major cause of the disorder in Pakistanis, say the researchers.
All affected members of two families were homozygous at the RP1 locus, whereas their parents and unaffected siblings were heterozygous. A homozygous C→T missense mutation at nucleotide 1118 (thre→isoleu at codon 373) segregated with affected family members. Unaffected members were all heterozygous for the mutation, and 100 ethnically matched, unrelated, healthy controls showed no homozygous mutation. A third family had a homozygous four base pair insertion at 1461–65 TGAA, producing a stop codon and a drastically shortened protein product. Again, the mutation segregated with affected family members; it was present in some other members and parents of affected members as a heterozygous mutation but not in the controls. Affected members of all three families had severe RP and were completely blind by age 18 years. Finally, a new heterozygous G→A missense mutation at nucleotide 2005 (ala→thre at codon 669) was found in one patient in a random panel of 150 patients with RP screened for RP1 mutations, but not in the controls.
All patients, their parents, and some of their unaffected siblings were thoroughly investigated and had electroretinographic examinations. Mutational analysis comprised amplification of DNA from blood samples, heteroduplex analysis, and direct DNA sequencing.
All previously known mutations in the RP1 gene cause autosomal dominant RP.