Article

Pigmented Paravenous Chorioretinal Atrophy Is Associated with a Mutation within the Crumbs Homolog 1 ( CRB1 ) Gene

Ophthalmic Research Centre, Institute of Clinical Science, Queen's University of Belfast, Belfast, Northern Ireland, United Kingdom.
Investigative Ophthalmology & Visual Science (Impact Factor: 3.4). 02/2005; 46(1):322-8. DOI: 10.1167/iovs.04-0734
Source: PubMed

ABSTRACT

Pigmented paravenous chorioretinal atrophy (PPCRA) is an unusual retinal degeneration characterized by accumulation of pigmentation along retinal veins. The purpose of this study was to describe the phenotype of a family with PPCRA, determine the mode of inheritance, and identify the causal mutation.
Ophthalmic examination was performed on seven family members and serially detailed in the proband over a 3-year period. Blood samples were collected and DNA extracted. All 12 coding exons and the 5' promoter region of the crumbs homologue 1 (CRB1) gene were PCR amplified and DNA sequenced. In silico homology modeling was performed on the mutated protein domain.
Subtle symmetrical chorioretinal atrophy in the inferior quadrant was the earliest clinical sign detectable within this family. Paravenous pigmentation occurred initially in the far periphery, progressing centrally, with atrophy later becoming more widespread, involving the nasal, then the temporal, and finally the upper quadrant. A novel, dominant Val162Met mutation within the fourth EGF-like domain of CRB1 cosegregates with the PPCRA phenotype. It is thought to affect domain structure, because codon 162 is involved in hydrogen bonding between the antiparallel beta-strands of the major beta-sheet, causing sufficient perturbation of the backbone that the domain-stabilizing hydrogen bond does not form or is weakened.
PPCRA was dominantly inherited in this family, but exhibited variable expressivity. Males are more likely to exhibit a severe phenotype, whereas females may remain virtually asymptomatic even in later years. The PPCRA phenotype is associated with a Val162Met mutation in CRB1 which is likely to affect the structure of the CRB1 protein.

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Available from: Gareth J Mckay
    • "SAR is located above adherens junctions and consists of a group of adaptor proteins including CRB1 (Richard et al., 2006). Mutations in the CRB1 gene in humans are implicated in various human retinal degenerative diseases such as Leber's congenital amaurosis (LCA), autosomal recessive retinitis pigmentosa (ArRP), and retinitis pigmentosa with coats-like exudative vasculopathy (den Hollander et al., 2004; McKay et al., 2005; Mehalow et al., 2003). LCA is one of the most severe forms of retinal dystrophies leading to blindness or severe visual damage in humans (den Hollander et al., 2004). "
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    ABSTRACT: Mutations in crumb homologue 1 (CRB1) in humans are associated with Leber's congenital amaurosis (LCA) and retinitis pigmentosa (RP). There is no clear genotype-phenotype correlation for human CRB1 mutations in RP and LCA. The high variability in clinical features observed in CRB1 mutations suggests that environmental factors or genetic modifiers influence severity of CRB1 related retinopathies. Retinal degeneration 8 (rd8) is a spontaneous mutation in the Crb1 gene (Crb1(rdr/rd8)). Crb1(rdr/rd8) mice present with focal disruption in the outer retina manifesting as white spots on fundus examination. Mild retinal dysfunction with decreased b-wave amplitude has been reported in Crb1(rdr/rd8) mice at 18 months. Methylene tetrahydrofolate reductase (MTHFR) is a crucial enzyme of homocysteine metabolism. MTHFR mutations are prevalent in humans and are linked to a broad spectrum of disorders including cardiovascular and neurodegenerative diseases. We recently reported the retinal phenotype in Mthfr-deficient (Mthfr(+/-)) heterozygous mice. At 24 weeks the mice showed decreased RGC function, thinner nerve fiber layer, focal areas of vascular leakage and 20% fewer cells in the ganglion cell layer (GCL). Considering the variability in CRB1-related retinopathies and the high occurrence of human MTHFR mutations we evaluated whether Mthfr deficiency influences rd8 retinal phenotype. Mthfr heterozygous mice with rd8 mutations (Mthfr(+/-)(rd8/rd8)) and Crb(rd8/rd8) mice (Mthfr(+/+)(rd8/rd8)) mice were subjected to comprehensive retinal evaluation using ERG, fundoscopy, fluorescein angiography (FA), morphometric and retinal flat mount immunostaining analyses of isolectin-B4 at 8-54 wks. Assessment of retinal function revealed a significant decrease in the a-, b- and c-wave amplitudes in Mthfr(+/-)(rd8/rd8) mice at 52 wks. Fundoscopic evaluation demonstrated the presence of signature rd8 spots in Mthfr(+/+)(rd8/rd8) mice and an increase in the extent of these rd8 spots in Mthfr(+/-)(rd8/rd8) mice at 24 weeks and beyond. FA revealed marked vascular leakage, ischemia and vascular tortuosity in Mthfr(+/-)(rd8/rd8) mice at 24 and 52 weeks. Retinal dysplasia was observed in ∼14-33% Mthfr(+/-)(rd8/rd8) mice by morphometric analysis. This was accompanied by a ∼20% reduction in cells of the GCL of Mthfr(+/-)(rd8/rd8) mice at 24 and 52 weeks. Retinal flat mount immunostaining with isolectin-B4 showed neovascularization and loss of blood vessel integrity in Mthfr(+/-)(rd8/rd8) mice in contrast to mild vasculopathy in Mthfr(+/+)(rd8/rd8) mice. Taken together, our data support an earlier onset and worsened retinal phenotype when Mthfr and rd8 mutations coexist. Our study sets the stage for future studies to investigate the role of MTHFR deficiency in human CRB1 retinopathies.
    No preview · Article · Dec 2015 · Experimental Eye Research
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    • "Mutations in the Crumbs homolog 1 (CRB1) gene are known to cause retinitis pigmentosa-12 (RP-12) [1] and Leber congenital amaurosis 8 (LCA8) [2]. A CRB1 mutation was also reported in a family with possible autosomal dominant inherited pigmented paravenous chorioretinal atrophy (PPCRA) [3], but this was not verified by other studies. RP is caused by progressive loss of rod and cone photoreceptors. "
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    ABSTRACT: To identify disease-causing mutations in Chinese families who presented with retinitis pigmentosa (RP) and Leber congenital amaurosis (LCA). The pathogenic variant in a Chinese family with autosomal dominant RP was investigated with a specific hereditary eye disease enrichment panel (HEDEP) based on targeted exome capture technology. The identified variant was confirmed with Sanger sequencing. CRB1 mutations in 67 patients with sporadic retinal dystrophy were examined with Sanger sequencing. Compound heterozygous mutations were identified in a family who had undergone HEDEP analysis. After complete sequence analysis of the CRB1 gene was performed in 67 patients with sporadic retinal dystrophy, other compound heterozygous mutations were detected in three families. The mutations included three novel heterozygous mutations: c.3059delT (p.M1020SfsX1), c.3460T>A (p.C1154S), and c.4207G>C (p.E1403Q). The mutation frequency of CRB1 in this study was 5.9% (8/136). Our findings broaden the spectrum of CRB1 mutations and the phenotypic spectrum of the disease in Chinese patients. The results from this study show that patients with LCA carry CRB1 null mutations more frequently than patients with RP.
    Full-text · Article · Mar 2014 · Molecular vision
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    • "Mutations in Crumbs homologue 1 (CRB1; OMIM 600105) have been associated with several visual disorders including retinitis pigmentosa (RP) with [10,11] or without [11,12] preserved para-arteriolar retinal pigment epithelium, paravenous pigmented chorioretinal atrophy [13], and LCA [14,15]. Of these disorders, LCA is the most severe form of inherited retinal dystrophy and is characterized by severe visual impairment from birth or very early in infancy and a decreased or absent electroretinogram (ERG) response [16]. "
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    ABSTRACT: Leber congenital amaurosis (LCA) is one of the most severe inherited retinal dystrophies with the earliest age of onset. Mutations in the Crumbs homologue 1 (CRB1; OMIM 600105) gene explain 10%-24% of cases with LCA depending on the population. The aim of the present work was to study a fetal mutation associated to LCA in maternal plasma by a new methodology in the noninvasive prenatal diagnosis field: the denaturing High Performance Liquid Chromatography (dHPLC). This study presents the case of a compound heterozygous fetus for two mutations in CRB1 (1q3.1-q32.2). dHPLC and automated DNA sequencing were used to detect the paternally inherited fetal mutation in a maternal plasma sample collected at the 12th week of gestation. To test the detection limit of dHPLC, we made serial dilutions of paternal DNA in control DNA. We were able to detect the presence of the paternally inherited fetal CRB1 mutation in maternal plasma by dHPLC. Moreover, by comparing chromatograms of serial dilutions to the plasma sample, we could ascertain that the percentage of fetal DNA in maternal plasma was at least 2%. However, the detection of the fetal mutation was not possible by automated DNA sequencing. dHPLC seems to be sensitive enough to detect small amounts of fetal DNA in maternal plasma samples. It could be a useful tool for the noninvasive prenatal detection of paternally inherited point mutations associated with retinopathies.
    Full-text · Article · Feb 2008 · Molecular vision
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