Candidate genes for chromosomes 6 and 10 quantitative trait loci for age-related retinal degeneration in mice.

Purpose: In a previous study, several quantitative trait loci (QTL) that influence age-related degeneration (ageRD) were identified in a cross between the albino strains B6(Cg)-Tyr(c-2J)/J (B6a) and BALB/cByJ (C). The Chromosome (Chr) 6 and Chr 10 QTL were the strongest and most highly significant loci and both involved B6a protective alleles. The QTL were responsible for 21% and 9% of the variance in phenotypes, respectively.

Loss of the metalloprotease ADAM9 leads to cone-rod dystrophy in humans and retinal degeneration in mice.

Cone-rod dystrophy (CRD) is an inherited progressive retinal dystrophy affecting the function of cone and rod photoreceptors. By autozygosity mapping, we identified null mutations in the ADAM metallopeptidase domain 9 (ADAM9) gene in four consanguineous families with recessively inherited early-onset CRD. We also found reduced photoreceptor responses in Adam9 knockout mice, previously reported to be asymptomatic.

A missense mutation in the nuclear localization signal sequence of CERKL (p.R106S) causes autosomal recessive retinal degeneration.

Purpose: To investigate the genetic basis of autosomal recessive retinal degeneration in a large consanguineous family from Pakistan.

Methods: Ophthalmic examinations were conducted on family members to establish their diagnosis. Genomic DNA extracted from peripheral blood was used for homozygosity mapping to discover the chromosomal region that harbors the defective gene.

Influence of a quantitative trait locus on mouse chromosome 19 to the light-adapted electroretinogram.

Purpose: Both implicit time and amplitude of the cone-mediated electroretinographic (ERG) b-wave differ significantly between the C57BL/6JOlaHsd and 129S2/SvHsd inbred mouse strains. The purpose of this work was to undertake a quantitative genetics study to localize the gene or genes involved.

Methods: Implicit time and amplitude of the a- and b-waves of the single-flash and flicker cone-mediated ERG were recorded as the quantitative traits in reciprocal backcrossed populations.

Genetic modifiers of retinal degeneration in the rd3 mouse.

Purpose: In previous studies of light-induced (LRD) and age-related (ageRD) retinal degeneration (RD) between the BALB/cByJ (BALB) and B6(Cg)-Tyr(c-2J)/J (B6a) albino mouse strains, RD-modifying quantitative trait loci (QTLs) were identified. After breeding BALB- and B6a-rd3/rd3 congenic strains and finding significant differences in RD, an F1 intercross to determine rd3 QTLs that influence this inherited RD was performed.

Methods: N10, F2 BALB- and B6a-rd3/rd3 strains were measured for retinal outer nuclear layer (ONL) thickness from 5 to 12 weeks of age.

Association of the Asn306Ser variant of the SP4 transcription factor and an intronic variant in the beta-subunit of transducin with digenic disease.

Purpose: SP4 is a transcription factor abundantly expressed in retina that binds to the GC promoter region of photoreceptor signal transduction genes. We have previously shown that SP4 may be involved in the transcriptional activation of these genes alone or together with other transcription factors such as SP1, neural retina leucine zipper protein (NRL), and cone-rod homeobox gene (CRX). Since mutations in NRL and CRX are involved in inherited retinal degenerations, SP4 was considered a good candidate for mutation screening in patients with this type of diseases.

Quantitative genetics of age-related retinal degeneration: a second F1 intercross between the A/J and C57BL/6 strains.

Purpose: Previously, several quantitative trait loci (QTL) that influence age-related retinal degeneration (ageRD) were demonstrated in a cross between the C57BL/6J-c(2J) and BALB/cByJ strains (B x C). In this study, as a complementary approach to ongoing recombinant progeny testing for the purpose of identifying candidate quantitative trait genes (QTG), a second test cross using the A/J and the pigmented C57BL/6J strains (A x B) was carried out. The albino A/J strain was selected because it had the most amount of ageRD among several inbred strains tested, and the pigmented C57BL/6J strain was selected because along with its coisogenic counterpart C57BL/6J-c(2J) it had the least amount of ageRD.

Disruption of the gene encoding the beta1-subunit of transducin in the Rd4/+ mouse.

Purpose: The Rd4/+ mouse inherits an autosomal dominant retinal degeneration that cosegregates with a large inversion spanning nearly all of mouse chromosome 4 (Chr 4). This inversion is homozygous lethal. The hypothesis for the study was that disruption of a gene at one of the two breakpoints in the Rd4 chromosome is responsible for the retinal degeneration.

Constant light-induced retinal damage and the RPE65-MET450 variant: assessment of the NZW/LacJ mouse.

Purpose: In a previous constant light-induced retinal damage (CLD) quantitative genetics study between the albino C57BL/6J-c2J (B6al) and BALB/c mouse strains, we identified a very strong and highly significant quantitative trait locus (QTL) on distal Chr 3 that we associated with a variant of the Rpe65 gene. The B6al strain carries the MET450 variant of RPE65 and is resistant to CLD while the BALB/c strain carries the LEU450 variant and is sensitive. Since then, we have discovered that the NZW/LacJ (NZW) albino mouse strain is sensitive to CLD but carries the MET450 variant of RPE65.

A substitution of G to C in the cone cGMP-phosphodiesterase gamma subunit gene found in a distinctive form of cone dystrophy.

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.

New retinal light damage QTL in mice with the light-sensitive RPE65 LEU variant.

The purpose of this study was to determine the QTL that influence acute, light-induced retinal degeneration differences between the BALB/cByJ and 129S1/SvImJ mouse strains. Five- to 6-week-old F(2) progeny of an intercross between the two strains were exposed to 15,000 LUX of white light for 1 h after their pupils were dilated, placed in the dark for 16 h, and kept for 10-12 days in dim cyclic light before retinal rhodopsin was measured spectrophotometrically. This was used as the quantitative trait for retinal degeneration.

Electroretinographic evidence for altered phototransduction gain and slowed recovery from photobleaches in albino mice with a MET450 variant in RPE65.

Our purpose was to investigate the physiological phenotype of albino mice with a variation in the Rpe65 gene encoding either methionine or leucine at amino acid #450. Full-field electroretinograms (ERGs) were recorded from C57BL/6J-c(2J) albino mice with MET450 and BALB/cByJ albino mice with LEU450. Recordings from pigmented mice (C57BL/6J) served as controls.

A strong and highly significant QTL on chromosome 6 that protects the mouse from age-related retinal degeneration.

Purpose: BALB/cByJ (C) albino mice have significantly more retinal degeneration as they age than C57BL/6J-c(2J) (B6) albinos. To discover the genetic loci that influence age-related retinal degeneration (ARD), a quantitative genetics study was performed with 8-month-old progeny from an intercross between these two strains.

Methods: The thickness of the outer nuclear layer of the retina was used as the quantitative trait.

CORD9 a new locus for arCRD: mapping to 8p11, estimation of frequency, evaluation of a candidate gene.

Purpose: To determine the locus of the mutant gene causing autosomal recessive cone-rod dystrophy (arCRD) in a consanguineous pedigree, to evaluate a candidate gene expressed in retina that maps to this locus, and to estimate the percentage of arCRD cases caused by mutations in this gene.

Methods: DNAs from family members were genotyped for markers covering the entire genome at an average spacing of approximately 9 centimorgans (cM). The data were input into a pedigree computer program to produce output files used to calculate lod scores.

Mutation analysis of ocular genes.

The RHO gene, which encodes rhodopsin, was the first gene in which mutations were found that were associated with an inherited retinal disease (1). RHO was examined by exon screening in a large population of patients with autosomal dominant retinitis pigmentosa (adRP), because a linkage study in an Irish family showed one locus of adRP to be on human chromosome 3q (2)-where RHO had been previously mapped (3). Since that time, over 100 different diseasecausing mutations have been found in RHO, and many other mutations in at least 55 additional genes.

A homozygous deletion in RPE65 in a small Sardinian family with autosomal recessive retinal dystrophy.

Purpose: We have been engaged in an ongoing study to screen candidate genes for mutations in small families with various forms of autosomal recessive retinal dystrophy. Here we report the screening of a cohort of 14 families from Sardinia for mutations in the genes encoding the alpha- and beta-subunits of cGMP-phosphodiesterase and RPE65 (PDE6A, PDE6B, and RPE65).

Methods: Haplotype analysis was performed on each family using simple sequence repeat markers closely flanking or within each of the three gene candidates.

Disease expression of RP1 mutations causing autosomal dominant retinitis pigmentosa.

Purpose: To determine the disease expression in heterozygotes for mutations in the RP1 gene, a newly identified cause of autosomal dominant retinitis pigmentosa (adRP).

Methods: Screening strategies were used to detect disease-causing mutations in the RP1 gene, and detailed studies of phenotype were performed in a subset of the detected RP1 heterozygotes using electroretinography (ERG), psychophysics, and optical coherence tomography (OCT).

Results: Seventeen adRP families had heterozygous RP1 changes.

A QTL on distal chromosome 3 that influences the severity of light-induced damage to mouse photoreceptors.

C57BL/6J-c(2J) (c2J) albino mice showed much less damage to their photoreceptors after exposure to prolonged light than BALB/c mice and seven other albino strains tested. There were no gender differences, and preliminary studies suggested that the c2J relative protective effect was a complex trait. A genome-wide scan using dinucleotide repeat markers was carried out for the analysis of 194 progeny of the backcross (c2J x BALB/c)F(1) x c2J and the thickness of the outer nuclear layer (ONL) of the retina was the quantitative trait reflecting retinal damage.

A deletion in a photoreceptor-specific nuclear receptor mRNA causes retinal degeneration in the rd7 mouse.

The rd7 mouse, an animal model for hereditary retinal degeneration, has some characteristics similar to human flecked retinal disorders. Here we report the identification of a deletion in a photoreceptor-specific nuclear receptor (mPNR) mRNA that is responsible for hereditary retinal dysplasia and degeneration in the rd7 mouse. mPNR was isolated from a pool of photoreceptor-specific cDNAs originally created by subtractive hybridization of mRNAs from normal and photoreceptorless rd mouse retinas.

A nonsense mutation in a novel gene is associated with retinitis pigmentosa in a family linked to the RP1 locus.

Retinitis pigmentosa (RP) represents a group of inherited human retinal diseases which involve degeneration of photoreceptor cells resulting in visual loss and often leading to blindness. In order to identify candidate genes for the causes of these diseases, we have been studying a pool of photoreceptor-specific cDNAs isolated by subtractive hybridization of mRNAs from normal and photoreceptorless rd mouse retinas. One of these cDNAs was of interest because it mapped to proximal mouse chromosome 1 in a region homo-logous to human 8q11-q13, the locus of autosomal dominant RP1.

Screening of the gene encoding the alpha'-subunit of cone cGMP-PDE in patients with retinal degenerations.

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.

Genetic and physical maps of the mouse rd3 locus; exclusion of the ortholog of USH2A.

The rd3 retinal degeneration gene was previously mapped 10 +/- 2.5 cM distal to Akp1 on mouse Chromosome (Chr) 1 (Chang et al., 1993), a region that may be homologous to the locus of the human USH2A gene, which carries mutations responsible for Usher IIa retinal degeneration/hearing loss syndrome.

The mouse X-linked juvenile retinoschisis cDNA: expression in photoreceptors.

Retinal photoreceptor cells are particularly vulnerable to degenerations that can eventually lead to blindness. Our purpose is to identify and characterize genes expressed specifically in photoreceptors in order to increase our understanding of the biochemistry and function of these cells, and then to use these genes as candidates for the sites of mutations responsible for degenerative retinal diseases. We have characterized a cDNA, a fragment of which (SR3.

Exon screening of the genes encoding the beta- and gamma-subunits of cone transducin in patients with inherited retinal disease.

Purpose: To screen the exons of the genes encoding the beta3-subunit (GNB3) and gammac-subunit (GNGT2) of cone transducin for mutations in a large number of unrelated patients with various forms of inherited retinal disease including cone dystrophy, cone-rod dystrophy and macular dystrophy.

Methods: Exons of the two genes were screened for mutations by denaturing gradient gel electrophoresis (DGGE) and/or single strand conformation polymorphism electrophoresis (SSCP); any variants were sequenced directly.

Results: Although many sequence variants were found in both genes, none could be associated with disease.