Evaluation of the G protein coupled receptor-75 (GPR75) in age related macular degeneration

Background - A long term project was initiated to identify and to character ise genes that are expressed exclusively or preferentially in the retina as candidates for a genetic susceptibility to age related macular degeneratio n (AMD). A transcript represented by a cluster of five human expressed sequ ence tags (ESTs) derived exclusively from retinal cDNA libraries was identi fied. Methods - Northern blot and RT-PCR analyses confirmed preferential retinal expression of the gene, which encodes a G protein coupled receptor, GPR75. Following isolation of the full length cDNA and determination of the genomi c organisation, the coding sequence of GPR75 was screened for mutations in 535 AMD patients and 252 controls from Germany, the United States, and Ital y. Employed methods included single stranded conformational polymorphism (S SCP) analysis, denaturing high performance liquid chromatography (DHPLC, an d direct sequencing. Results - Nine different sequence variations were identified in patients an d control individuals. Three of these (-30A >C, 150G >A, and 346G >A) likel y represent polymorphic variants. Each of six alterations (-4G >A, N78K, P9 9L, S108T, T135P, and Q234X) were found once in single AMD patients and wer e considered variants that could affect the protein function and potentiall y cause retinal pathology. Conclusion - The presence of six potential pathogenic variants in a cohort of 535 AMD patients alone does not provide statistically significant eviden ce for the association of sequence variation in GPR75 with genetic predispo sition to AMD. However, a possible connection between the variants and age related retinal pathology cannot be discarded. Functional studies are neede d to clarify the role of GPR75 in retinal physiology.