Evaluation of human diacylglycerol kinaset, DGKI, a homolog of Drosophila rdgA, in inherited retinopathy mapping to 7q

Purpose: To determine the genomic organization of diacylglycerol kinaset and to test whether defects in this gene are present in individuals affected with autosomal dominant retinitis pigmentosa (adRP). Diacylglycerol kinaset has been mapped to the RP10 locus on 7q and shows 49% sequence similarity to the DrosophilaDGK2 rdgA gene. Since mutations in the DGK2 rdgA gene cause photoreceptor degeneration in Drosophila, it is possible that mutations in diacylglycerol kinaset could be responsible for human retinal degeneration. Methods: DNA sequence from genomic clones containing diacylglycerol kinaset was compared with the cDNA sequence to identify intron/exon boundaries. Single-strand conformational analysis and PCR product sequencing were used to screen members of one family previously mapped to the RP10 locus and 47 small unmapped families with autosomal dominant retinitis pigmentosa. Results: Diacylglycerol kinaset is divided into 35 exons with the initiation codon being present in exon 2. Mutational analysis found a missense change (Lys153Phe) in three adRP families; however, it did not segregate with disease in one of the families. Silent substitutions were seen in codons 865 and 875. Intronic variation was detected in the amplifications of exons 3,5,18, 28, and 32; these do not affect splice site consensus sequences. Typing of a polymorphic variant detected in intron 31 in members of the RP10 family gave a LOD score of -4.2 at 0% recombination. Conclusions: No evidence of disease-associated mutations was found in any of the samples tested. Based on the linkage data and mutation screening, diacylglycerol kinaset is excluded as a candidate for the RP10 form of adRP and cannot be a frequent cause of other forms of adRP. Mutations in diacylglycerol kinaset may yet be the cause of recessive forms of retinal degeneration in humans, either in homozygous or compound heterozygous forms. The data provided here will permit testing of this hypothesis.