Retinitis pigmentosa (RP) is the most prevalent hereditary retinal degenerative disease. To date, approximately 40 loci and mutations in more than 25 genes have been identified as the cause of various types of RP.¹ The gene for human oxygen regulated photoreceptor protein (RP1) encodes a protein of 2156 amino acids that is localised in the connecting cilia of both rod and cone photoreceptors.² The RP1 protein is required for the morphogenesis of the outer segments of the photoreceptor cells.^3,4 Several laboratories have found mutations in the RP1 gene to be the cause of autosomal dominant retinitis pigmentosa (adRP).^5–7 However, to our knowledge, association of the RP1 gene with recessive RP has never been reported.

The aim of the present study was to map the disease locus for three consanguineous Pakistani families suffering from RP. We present mapping of these autosomal recessive RP families to the 8q11 locus. The results show, for the first time, that in these families a form of arRP is caused by homozygous mutations of the RP1 gene. Although these mutations were found in the parents and some of the siblings who had normal vision (carriers) in a heterozygous state, they were not found in any of a panel of 100 normal controls.

PATIENTS AND METHODS

We studied three consanguineous Pakistani families (442RP, 452RP, and 336RP) suffering from autosomal recessive RP (fig 1). The patients had night blindness since early childhood and progressive deterioration of vision with age. All the patients were completely blind by the age of 12–15 years in the case of the 442RP and 452RP families and 17–18 years in the 336RP family. Fundoscopic examination and electroretinographic (ERG) analyses were carried out on all the patients, their heterozygous parents and siblings, and unaffected normal siblings.