Mutation in the guanine nucleotide-binding protein beta-3 causes retinal degeneration and embryonic mortality in chickens

PURPOSE. To identify the gene defect that causes blindness and the predisposition to embryonic death in the retinopathy globe enlarged (rge) chicken. METHODS. Linkage analysis, with previously uncharacterized microsatellite markers from chicken chromosome 1, was performed on 138 progeny of an rge/+ and an rge/rge cross, and candidate genes were sequenced. RESULTS. The rge locus was refined and the gene for guanine nucleotide-binding protein β-3 (GNB3), which encodes a cone transducin β subunit, was found to have a 3-bp deletion (D153del) that segregated with the rge phenotype. This mutation deleted a highly conserved aspartic acid residue in the third of seven WD domains in GNB3. In silico modeling suggested that this mutation destabilized the protein. Furthermore, a 70% reduction was found in immunoreactivity to anti-GNB3 in the rge-affected retina. CONCLUSIONS. These findings implicate the β-subunit of cone transducin as the defective protein underlying the rge phenotype. Furthermore, GNB3 is ubiquitously expressed, and the c.825C→T GNB3 splicing variant (MIM 139130) has been associated with hypertension, obesity, diabetes, low birth weight, coronary heart disease, and stroke in the human population. It therefore seems likely that the defect underlying these human diseases also causes reduced embryonic viability in the rge chicken, making it a powerful model for studying the pathology involved in these associations

Molecular confirmation of the causes of inherited visual impairment in Northern Pakistan

Families with inherited visual impairment were identified and examined from January 2000 to December 2005 and given a clinical diagnosis. Known genes and loci were screened for mutations or linkage at Institute of Ophthalmology and Neurosciences, University of Leeds, in order to provide molecular confirmation. Inherited retinal disease was the most common cause of inherited visual impairment in 38 of 57 families (66.6%) with Leber\u27s congenital amaurosis, rod-cone dystrophy and cone-rod dystrophy being the most common diagnoses in 22, 8 and 3 families respectively. Anterior segment dysgenesis was diagnosed in 8 families (14%). Mutations in known genes or linkage to known loci were identified in 23 of 57 families (40%). All families had molecular confirmation of autosomal recessive inheritance or a pedigree consistent with this mode of inheritance, with evidence of first-cousin marriage. Knowledge of carrier status and genetic counseling may allow families to make an informed decision regarding marriage, and thus begin to plan a way of reducing the incidence of inherited visual impairment

Identification of a novel splice-site mutation in the Lebercilin (LCA5) gene causing Leber congenital amaurosis

Purpose: Leber congenital amaurosis (LCA) is one of the most common causes of hereditary blindness in infants. To date, mutations in 13 known genes and at two other loci have been implicated in LCA causation. An examination of the known genes highlights several processes which, when defective, cause LCA, including photoreceptor development and maintenance, phototransduction, vitamin A metabolism, and protein trafficking. In addition, it has been known for some time that defects in sensory cilia can cause syndromes involving hereditary blindness. More recently evidence has come to light that non-syndromic LCA can also be a “ciliopathy.” Methods: Here we present a homozygosity mapping analysis in a consanguineous sibship that led to the identification of a mutation in the recently discovered LCA5 gene. Homozygosity mapping was done using Affymetrix 10K Xba I Gene Chip and a 24.5cM region on chromosome 6 (6q12- q16.3) was identified to be significantly homozygous. The LCA5 gene on this region was sequenced and cDNA sequencing also done to characterize the mutation. Results: A c.955G>A missense mutation in the last base of exon 6 causing disruption of the splice donor site was identified in both the affected sibs. Since there is a second consensus splice donor sequence 5 bp into the adjacent intron, this mutation results in a transcript with a 5 bp insertion of intronic sequence, leading to a frameshift and premature truncation. Conclusions: We report a missense mutation functionally altering the splice donor site and leading to a truncated protein. This is the second report of LCA5 mutations causing LCA. It may also be significant that one affected child died at eleven months of age due to asphyxia during sleep. To date the only phenotype unambiguously associated with mutations in this gene is LCA. However the LCA5 gene is known to be expressed in nasopharynx, trachea and lungs and was originally identified in the proteome of bronchial epithelium ciliary axonemes. The cause of death in this child may therefore imply that LCA5 mutations can in fact cause a wider spectrum of phenotypes including respiratory disease

Enrichment of pathogenic alleles in the brittle cornea gene, ZNF469, in keratoconus

Keratoconus, a common inherited ocular disorder resulting in progressive corneal thinning, is the leading indication for corneal transplantation in the developed world. Genome-wide association studies have identified common SNPs 100 kb upstream of ZNF469 strongly associated with corneal thickness. Homozygous mutations in ZNF469 and PR domain-containing protein 5 (PRDM5) genes result in brittle cornea syndrome (BCS) Types 1 and 2, respectively. BCS is an autosomal recessive generalized connective tissue disorder associated with extreme corneal thinning and a high risk of corneal rupture. Some individuals with heterozygous PRDM5 mutations demonstrate a carrier ocular phenotype, which includes a mildly reduced corneal thickness, keratoconus and blue sclera. We hypothesized that heterozygous variants in PRDM5 and ZNF469 predispose to the development of isolated keratoconus. We found a significant enrichment of potentially pathologic heterozygous alleles in ZNF469 associated with the development of keratoconus (P = 0.00102) resulting in a relative risk of 12.0. This enrichment of rare potentially pathogenic alleles in ZNF469 in 12.5% of keratoconus patients represents a significant mutational load and highlights ZNF469 as the most significant genetic factor responsible for keratoconus identified to date

Enrichment of pathogenic alleles in the brittle cornea gene, ZNF469, in keratoconus

Keratoconus, a common inherited ocular disorder resulting in progressive corneal thinning, is the leading indication for corneal transplantation in the developed world. Genome-wide association studies have identified common SNPs 100 kb upstream of ZNF469 strongly associated with corneal thickness. Homozygous mutations in ZNF469 and PR domain-containing protein 5 (PRDM5) genes result in brittle cornea syndrome (BCS) Types 1 and 2, respectively. BCS is an autosomal recessive generalized connective tissue disorder associated with extreme corneal thinning and a high risk of corneal rupture. Some individuals with heterozygous PRDM5 mutations demonstrate a carrier ocular phenotype, which includes a mildly reduced corneal thickness, keratoconus and blue sclera. We hypothesized that heterozygous variants in PRDM5 and ZNF469 predispose to the development of isolated keratoconus. We found a significant enrichment of potentially pathologic heterozygous alleles in ZNF469 associated with the development of keratoconus (P = 0.00102) resulting in a relative risk of 12.0. This enrichment of rare potentially pathogenic alleles in ZNF469 in 12.5% of keratoconus patients represents a significant mutational load and highlights ZNF469 as the most significant genetic factor responsible for keratoconus identified to dat

Analysis of candidate genes for macular telangiectasia type 2

Purpose: To find the gene(s) responsible for macular telangiectasia type 2 (MacTel) by a candidate-gene screening approach.Methods: Candidate genes were selected based on the following criteria: those known to cause or be associated with diseases with phenotypes similar to MacTel, genes with known function in the retinal vasculature or macular pigment transport, genes that emerged from expression microarray data from mouse models designed to mimic MacTel phenotype characteristics, and genes expressed in the retina that are also related to diabetes or hypertension, which have increased prevalence in MacTel patients. Probands from eight families with at least two affected individuals were screened by direct sequencing of 27 candidate genes. Identified nonsynonymous variants were analyzed to determine whether they cosegregate with the disease in families. Allele frequencies were determined by TaqMan analysis of the large MacTel and control cohorts.Results: We identified 23 nonsynonymous variants in 27 candidate genes in at least one proband. Of these, eight were known single nucleotide polymorphisms (SNPs) with allele frequencies of >0.05; these variants were excluded from further analyses. Three previously unidentified missense variants, three missense variants with reported disease association, and five rare variants were analyzed for segregation and/or allele frequencies. No variant fulfilled the criteria of being causal for MacTel. A missense mutation, p.Pro33Ser in frizzled homolog (Drosophila) 4 (FZD4), previously suggested as a disease-causing variant in familial exudative vitreoretinopathy, was determined to be a rare benign polymorphism.Conclusions: We have ruled out the exons and flanking intronic regions in 27 candidate genes as harboring causal mutations for MacTel

Defects in the acid phosphatase ACPT cause recessive hypoplastic amelogenesis imperfecta

We identified two homozygous missense variants (c.428C>T, p.(T143M) and c.746C>T, p.(P249L)) in ACPT, the gene encoding Acid Phosphatase, Testicular, which segregate with hypoplastic Amelogenesis imperfecta (AI) in two unrelated families. ACPT is reported to play a role in odontoblast differentiation and mineralisation by supplying phosphate during dentine formation. Analysis by computerised tomography and scanning electron microscopy of a primary molar tooth from an individual homozygous for the c.746C>T variant, revealed an enamel layer that was hypoplastic but mineralised with prismatic architecture. These findings implicate variants in ACPT as a cause of early failure of amelogenesis during the secretory phase