Mutations in the gene encoding the alpha-subunit of rod phosphodiesterase in consanguineous Pakistani families.

Purpose: To localize and identify the gene and mutations causing autosomal recessive retinitis pigmentosa (RP) in consanguineous Pakistani families.

Methods: Families were ascertained and patients underwent complete ophthalmological examinations. Blood samples were collected and DNA was extracted. A genome-wide scan was performed using 382 polymorphic microsatellite markers on genomic DNA from affected and unaffected family members, and lod scores were calculated.

Results: A genome-wide scan of 50 families gave a lod score of 7.4172 with D5S2015 using HOMOG1. RP in all 4 linked families mapped to a 13.85 cM (14.87 Mb) region on chromosome 5q31-33 flanked by D5S2090 and D5S422. This region harbors the PDE6A gene, which is known to cause autosomal recessive RP. Sequencing of PDE6A showed a homozygous single base pair change; c.889C->T, single base pair insertion; c.2218-2219insT, and single base pair substitution in the splice acceptor site; IVS10-2A->G in each of three families. In the fourth family linked to this region, no disease-causing mutation was identified in the PDE6A gene.

Conclusions: These results provide strong evidence that mutations in PDE6A result in recessive RP in three consanguineous Pakistani families. Although a fourth family was linked to markers in the 5q31-33 interval, no mutation was identified in PDE6A.