Macular Degeneration: Gao YQ

Piri N, Gao YQ, Danciger M, Mendoza E, Fishman GA, Farber DB. · Department of Ophthalmology, Jules Stein Eye Institute, UCLA, Los Angeles, California 90095, USA. · Ophthalmology. · Pubmed #15629837 No free full text.

Abstract: OBJECTIVE: To identify genes responsible for cone dystrophies and determine the functional consequences of their underlying mutations. DESIGN: Case-control study. PARTICIPANTS: Two hundred forty unrelated patients diagnosed with cone dystrophy, cone-rod dystrophy, macular dystrophy, macular degeneration, or Stargardt disease, 95 control individuals, and 2 unrelated families with a distinctive type of cone dystrophy. METHODS: The DNAs of the 240 probands were screened for sequence variants in the PDE6H gene (that encodes the inhibitory gamma-subunit of cone cyclic guanosine monophosphate [cGMP]-phosphodiesterase [PDE]) by single-strand conformation polymorphism electrophoresis. The effect of a nucleotide substitution in the DNA of a patient on gene expression efficiency was analyzed by in vitro transcription/translation. MAIN OUTCOME MEASURES: Cone-specific gene variants, fundus, visual field and electroretinogram (ERG) findings, and protein synthesis efficiency. RESULTS: We found a heterozygous G to C substitution in the 5' untranslated region (UTR) of the PDE6H gene in the DNA of a patient with a distinctive form of cone dystrophy, her sibling, and their father. This rare form of disease is very different in manifestation from other cone dystrophies and has been described as "cone dystrophy with nyctalopia and supernormal rod responses," "cone dystrophy with supernormal scotopic ERGs" and "supernormal and delayed rod ERG syndrome." Among the 240 patients that we studied, only 1 proband had the G to C variant. Furthermore, none of the 95 controls used in this study had this nucleotide change. We also determined that the PDE6H variant was not present in another family affected with this particular type of cone dystrophy. Because the 5' UTR of mRNAs plays a critical role in the regulation of protein synthesis, we determined the effect of the G to C change in this process. By use of in vitro transcription/translation experiments, we demonstrated that this substitution could lead to an increase in PDE6H gene expression. CONCLUSIONS: Our results indicate that mutations in the PDE6H gene are not common, because only 1 of 240 patients with cone dystrophy showed a single nucleotide substitution in the 5' UTR of PDE6H mRNA that could be associated with the disease. If the effect of the G to C substitution we observed in vitro also occurs in vivo, it will lead to PDE6H overexpression in the photoreceptors. Excess of PDEgamma may affect normal cone cGMP-PDE function by inhibiting the catalytic PDEalpha,beta activity and lead to pathogenic elevation of cGMP and eventual degeneration of cone photoreceptors.

Gao YQ, Danciger M, Longmuir R, Piriev NI, Zhao DY, Heckenlively JR, Fishman GA, Weleber RG, Jacobson SG, Stone EM, Farber DB. · Jules Stein Eye Institute, University of California Los Angeles School of Medicine, CA 90095-7008, USA. · Invest Ophthalmol Vis Sci. · Pubmed #10393054 links to  free full text

Abstract: PURPOSE: To screen the exons of the gene encoding the alpha'-subunit of cone cyclic guanosine monophosphate (cGMP>phosphodiesterase (PDE6C) for mutations in a group of 456 unrelated patients with various forms of inherited retinal disease, including cone dystrophy, cone-rod dystrophy, macular dystrophy, and simplex/multiplex and autosomal recessive retinitis pigmentosa. METHODS: The 22 exons of the PDE6C gene were screened for mutations either by denaturing gradient gel electrophoresis and single-strand conformation polymorphism electrophoresis (SSCP) or by SSCP alone; variants were sequenced directly. RESULTS: Although many sequence variants were found, none could be associated with disease. CONCLUSIONS: The results show that PDE6C was not the site of the amutations responsible for the types of inherited retinal degenerations analyzed in the large population of patients 'in the present study. The types of degeneration included those that predominantly affect cone-mediated function (cone and cone-rod dystrophies) or rod-mediated function (retinitis pigmentosa) or that have a predilection for disease in the macula (macular dystrophies).