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. Significant linkage was revealed at 8cen, prompting the genotyping of a number of additional markers. Exons of a candidate gene were sequenced directly by standard fluorescent dideoxy methods. Haplotype analysis was performed with markers in this locus in 13 multiplex and 2 simplex CRD families in which neither parent had disease. RESULTS: Four-point linkage analysis gave a maximum lod score of approximately 7.6 at both D8S1769 and GATA101H09 in the large consanguineous family. Recombination events defined an interval of 8.7 cM between D8S1820 and D8S532 within which the gene must lie. This 8p11 locus (CORD9) is immediately distal to but distinct from the RP1 autosomal dominant RP (adRP) locus. Two islands of homozygosity were found in this locus: The alleles of 6 of 10 markers in one of the islands and 2 of 4 in the other were homozygous. The UniGene cluster Hs.8719 (UniGene System, provided by the National Center for Biotechnology Information and available at http://www.ncbi.nlm.nih.gov/UniGene), which tags a gene with significant homology to Dual Specificity Phosphatase 3, maps within the CORD9 interval and is highly expressed in the retina. To evaluate this gene as a potential disease candidate, intron-exon structure was determined, and exons were screened in the consanguineous family. No variants were found that could be related to disease. Haplotype analysis of 15 other families with CRD, using markers at CORD9, excluded this locus in 9 of 15. CONCLUSIONS: A new arCRD locus (CORD9) has been identified corresponding to a yet unidentified gene in the 8.7-cM interval D8S1820-D8S532. No mutations were found in one candidate gene in affected members of the primary study family. Haplotype analysis of a cohort of 13 multiplex and 2 simplex families with CRD ruled out the CORD9 gene in 9 of 15 of the families. To date, a total of 126 loci carrying gene mutations causing various forms of retinal degeneration have been mapped, and the mutant gene has been identified in 64 of them. However, only 2 loci for arCRD have been documented. This is the report of a third.     

Novel RDH12 mutations associated with Leber congenital amaurosis and cone-rod dystrophy: biochemical and clinical evaluations

The purpose of this study was to determine the role of the retinol dehydrogenase 12 (RDH12) gene in patients affected with Leber congenital amaurosis (LCA), autosomal recessive retinitis pigmentosa (arRP) and autosomal dominant/recessive cone-rod dystrophies (CORD). Changes in the promoter region, coding regions and exon/intron junctions of the RDH12 gene were evaluated using direct DNA sequencing of patients affected with LCA (n=36 cases), RP (n=62) and CORD (n=21). The allele frequency of changes observed was assessed in a multiethnic control population (n=159 individuals). Detailed biochemical and structural modeling analysis of the observed mutations were performed to assess their biological role in the inactivation of Rdh12. A comprehensive clinical assessment of retinal structure and function in LCA patients carrying mutations in the RDH12 gene was completed. Of the six changes identified, three were novel including a homozygous C201R change in a patient affected with LCA, a heterozygous A177V change in patients affected with CORD and a heterozygous G46G change in a patient affected with LCA. A novel compound heterozygote T49M/A269fsX270 mutation was also found in a patient with LCA, and both homozygous and heterozygous R161Q changes were seen in 26 patients affected with LCA, CORD or RP. These R161Q, G46G and the A177V sequence changes were shown to be polymorphic. We found that Rdh12 mutant proteins associated with LCA were inactive or displayed only residual activity when expressed in COS-7 and Sf9 cells, whereas those mutants that were considered polymorphisms were fully active. Thus, impairment of retinal structure and function for patients carrying these mutations correlated with the biochemical properties of the mutants.     

Novel complex GUCY2D mutation in Japanese family with cone-rod dystrophy

PURPOSE: All mutations in the retinal guanylate cyclase gene (GUCY2D) that causes autosomal dominant cone-rod dystrophy (CORD) are associated with an amino acid substitution in codon 838. A novel heterozygous complex missense mutation of I915T and G917R in the GUCY2D gene was found in a Japanese family with autosomal dominant CORD. The clinical features associated with this mutation were described. METHODS: Blood samples were collected from 27 patients with cone-rod or cone dystrophies and from 11 patients with macular dystrophy. Genomic DNA was extracted from peripheral leukocytes. All 18 coding exons of the GUCY2D gene were directly sequenced. The PCR product carrying a novel mutation was subcloned, and each allele was sequenced. A complete ophthalmologic examination was performed in members of the family with the novel mutation. RESULTS: A novel heterozygous complex missense mutation of T2817C and G2822C that would predict I915T and G917R amino acid substitutions, respectively, was found in an autosomal dominant CORD family. The two nucleotide changes were located on the same allele, and segregated with the disease. Two other known missense mutations of R838H and R838C were found in two other CORD families. The clinical phenotype associated with the novel mutation was similar to that with the Arg838 mutations. CONCLUSIONS: A heterozygous complex mutation of I915T and G917R in the GUCY2D gene caused autosomal dominant CORD, indicating that a heterozygous mutation that does not include a codon 838 substitution can lead to this ocular phenotype.     

Novel mutations in the TULP1 gene causing autosomal recessive retinitis pigmentosa

PURPOSE: To assess the contribution of TULP1 to autosomal recessive retinitis pigmentosa (arRP). METHODS: Fifteen exons of the gene were screened by single-strand conformation polymorphism analysis of 7 (of 49) arRP pedigrees showing cosegregation with TULP1 locus markers. RESULTS: In one of the seven families two allelic mutations, IVS4-2delAGA and c.937delC, were found in exons 5 and 10, respectively. CONCLUSIONS: Two novel mutations in TULP1 were found to be associated with arRP. That they both compromise the gene product supports their pathogenicity. This gene was present in no more than 2% of a panel of 49 Spanish families affected by arRP.     

Mutation screening of Pakistani families with congenital eye disorders

To map the disease loci several Pakistani families suffering from autosomal recessive retinitis pigmentosa with preserved para-arteriolar retinal pigment epithelium and Leber congenital amaurosis (LCA) were analyzed. Analysis revealed close genetic linkage between the disease phenotype of some of the families (3330RP, 111RP and 010LCA) and the microsatellite markers on chromosome 1q31. Mutation screening of the candidate gene CRB1 revealed a G to A transversion in exon 7 in arRP family 330RP and a T to C substitution in another arRP family, 111RP. In exon 9 of the CRB1 gene a T to C transversion was found in the family suffering from LCA (010LCA).The LCA phenotype of another family (011LCA) in which the CRB1 locus was excluded, showed linkage with microsatellite markers D17S1294 and D17S796 on chromosome 17p13.1. The association of the candidate gene GUCY2D (17p13.1) with the disease phenotype was excluded as no disease-associated mutation was found in any of its exons. Mutation screening of another candidate gene, AIPL1 located in the same region, showed a novel homozygous C to A substitution in exon 2. These sequence changes are unique for the Pakistani families and some of these have not been reported previously.     

The 208delG mutation in FSCN2 does not associate with retinal degeneration in Chinese individuals

PURPOSE: The 208delG (c.72delG, p.Thr25GlnfsX120) mutation in the FSCN2 gene was reported to cause autosomal dominant retinitis pigmentosa (ADRP) and autosomal dominant macular degeneration (ADMD). The purpose of this study was to detect the 208delG mutation in Chinese individuals, with or without hereditary retinal degeneration. METHODS: DNA fragments encompassing the 208delG mutation were amplified by polymerase chain reaction (PCR). The amplicons were analyzed by sequencing or/and heteroduplex- single-strand conformational polymorphism (SSCP) analysis. An ophthalmic evaluation was conducted in those individuals with the 208delG mutation. RESULTS: The 208delG mutation was detected in 8 of 242 unrelated probands: 175 with retinitis pigmentosa (RP), 20 with Leber congenital amaurosis (LCA), and 47 with cone-rod dystrophy (CORD). Of the eight, the retinal diseases were RP in six probands, LCA in one proband, and CORD in one proband. The disease was transmitted as an autosomal dominant (one family), autosomal recessive (two families), or sporadic (five families) trait. The mutation did not cosegregate with retinal degeneration in three families, whereas five normal family members also had the mutation. In addition, this mutation was also detected in 13 of 521 unrelated control subjects. CONCLUSIONS: The 208delG mutation in FSCN2 is not associated with hereditary retinal degeneration in the Chinese individuals examined, which contradicts the original report about mutation in FSCN2 as a cause of ADRP and ADMD. This finding reminds us that great care is needed in making mutation-disease associations.     

Spectrum of the ABCA4 gene mutations implicated in severe retinopathies in Spanish patients

PURPOSE: The purpose of this study is to describe the spectrum of mutations in the ABCA4 gene found in Spanish patients affected with several retinal dystrophies. METHODS: Sixty Spanish families with different retinal dystrophies were studied. Samples were analyzed for variants in all 50 exons of the ABCA4 gene by screening with the ABCR400 microarray, and results were confirmed by direct sequencing. Haplotype analyses were also performed. For those families with only one mutation detected by the microarray, denaturing (d)HPLC was performed to complete the mutational screening of the ABCA4 gene. RESULTS: The sequence analysis of the ABCA4 gene led to the identification of 33 (27.5%) potential disease-associated alleles among the 60 patients. These comprised 16 distinct sequence variants in 25 of the 60 subjects investigated. For autosomal recessive cone-rod dystrophy (arCRD), we found that 50% of the CRD families with the mutation had two recurrent changes (2888delG and R943Q). For retinitis pigmentosa (RP) and autosomal dominant macular dystrophy (adMD), one putative disease-associated allele was identified in 9 of the 27 and 3 of the 7 families, respectively. CONCLUSIONS: In the population studied, ABCA4 plays an important role in the pathogenesis of arCRD. However, mutations in this gene are less frequently identified in other retinal dystrophies, like RP or adMD, and therefore it is still not clear whether ABCA4 is involved as a modifying factor or the relationship is a fortuitous association.     

The benign concentric annular macular dystrophy locus maps to 6p12.3-q16

PURPOSE: To describe the clinical findings and to identify the genetic locus in a Dutch family with autosomal dominant benign concentric annular macular dystrophy (BCAMD). METHODS: All family members underwent ophthalmic examination. Linkage analysis of candidate retinal dystrophy loci and a whole genome scan were performed. Five candidate genes from the linked locus were analyzed for mutations by direct sequencing. RESULTS: The BCAMD phenotype is initially characterized by parafoveal hypopigmentation and good visual acuity, but progresses to a retinitis pigmentosa-like phenotype. Linkage analysis established complete segregation of the BCAMD phenotype (maximum multipoint LOD score, 3.8) with DNA markers at chromosome 6, region p12.3-q16. Recombination events defined a critical interval spanning 30.7 cM at the long arm of chromosome 6 between markers D6S269 and D6S300. This interval encompasses several retinal dystrophy loci, including the ELOVL4 gene, mutated in autosomal dominant Stargardt disease, and the RIM1 gene, mutated in autosomal dominant cone-rod dystrophy, as well as the retinally expressed GABRR1 and -2 genes. Mutation screening of these four genes revealed no mutations. Sequence analysis of the interphotoreceptor matrix proteoglycan 1 gene IMPG1, also residing in the BCAMD locus, revealed a single base-pair change (T-->C) of nucleotide 1866 in exon 13, resulting in a Leu579Pro amino acid substitution. This mutation was absent in 190 control individuals. CONCLUSIONS: Significant linkage was found for the BCAMD defect with chromosomal 6, region p12.3-q16. A Leu579Pro mutation in the IMPG1 gene may play a causal role.     

Autosomal Dominant Cone-Rod Dystrophy with R838H and R838C Mutations in the <Emphasis Type="Italic">GUCY2D</Emphasis> Gene in Japanese Patients

Purpose To describe the clinical phenotypes of two Japanese families with autosomal dominant cone–rod dystrophy (CORD) caused by an R838H or R838C mutation in the guanylate cyclase 2D gene (GUCY2D).Methods Complete ophthalmological examinations were performed on three affected individuals from two Japanese families with autosomal dominant CORD. One family had an R838H mutation, and the other family had an R838C mutation in the GUCY2D gene. The tests included best-corrected visual acuity, slit-lamp and fundus examinations, fundus photography, electroretinography, Goldmann kinetic perimetry, and automated light- and dark-adapted static perimetry.Results The three patients showed essentially normal fundus or little pigmentary change in the maculae by indirect ophthalmoscopy, and only fluorescein angiography revealed clear atrophy of the retinal pigmented epithelium around the fovea. Central or paracentral scotoma was detected by the Goldmann kinetic visual field test. Electroretinography as well as light-adapted and dark-adapted two-color perimetry showed more severe impairment of cone than of rod function. The clinical features in our patients resembled those in Caucasian families with R838H or R838C mutations.Conclusions The R838H and R838C mutations in GUCY2D cause CORD in the Japanese population. These mutations can cause a similar clinical phenotype in other races. Jpn J Ophthalmol 2004;48:228–235 © Japanese Ophthalmological Society 2004     

Novel C8orf37 Mutations in Patients with Early-onset Retinal Dystrophy,Macular Atrophy,Cataracts, and High Myopia

Purpose: More than 50 genes are reported as causative genes of autosomal recessive (ar) retinitis pigmentosa (RP) and cone-rod dystrophy (CRD). It is challenging to identify causative mutations for arRP and arCRD. The purpose of the present study was to investigate clinical and genetic features of two siblings with early-onset retinal dystrophy.

Methods: Whole-exome sequencing was conducted for the two affected siblings and their unaffected brother and mother from a Japanese family. We performed complete ophthalmic examinations, including visual acuity, funduscopy, visual-field testing, electroretinography and optical coherence tomography.

Results: Whole-exome sequencing analysis identified novel compound heterozygous mutations, a splice site mutation (c.374?+?2T?>?C in intron 4) and a deletion mutation (c.575delC [p.T192MfsX28] in exon 6) of chromosome 8 open reading frame 37 (C8orf37) gene, which encodes a ciliary protein, in both patients. The mother carried the truncating mutation, and the brother carried neither mutation. Ophthalmic examinations revealed diffuse retinal degeneration, macular atrophy, non-recordable electroretinography responses, cataracts, and high myopia in both patients, who could not be diagnosed with either RP or CRD because of the severe retinal degeneration and early onset disease. Longitudinal follow-up of the patients revealed highly progressive retinal degeneration, macular atrophy, and visual field loss.

Conclusions: Recessive C8orf37 mutations have been identified in early to adolescent-onset arRP and arCRD with macular involvement. Our study identified two novel truncating mutations of the C8orf37 gene in siblings with early-onset retinal dystrophy, macular atrophy, cataracts, and high myopia.     

A detailed study of the phenotype of an autosomal dominant cone-rod dystrophy (CORD7) associated with mutation in the gene for RIM1

AIM: To characterise the phenotype of an autosomal dominant cone-rod dystrophy (CORD7) associated with the Arg844His mutation in RIM1. METHODS: Eight members of a four generation, non-consanguineous British family were examined clinically and underwent electrophysiological testing, automated dark adapted perimetry, dark adaptometry, colour vision assessment, colour fundus photography, fundus fluorescein angiography (FFA), and fundus autofluorescence (AF) imaging. RESULTS: The majority of affected individuals described a progressive deterioration of central vision, night vision, and peripheral visual field usually between the third and fourth decades. The visual acuity ranged from 6/6 to 3/60. Colour vision testing showed mild to moderate dyschromatopsia in the majority of individuals. Fundus changes comprised a range of macular appearances varying from mild retinal pigment epithelial (RPE) disturbance to extensive atrophy and pigmentation. In some individuals retinal vessels were attenuated and in two subjects peripheral areas of retinal atrophy were present. An absent or severely reduced PERG was detected in all subjects, indicative of marked macular dysfunction. Full field ERG showed abnormal rod and cone responses. AF imaging revealed decreased macular AF centrally surrounded by a ring of increased AF in the majority of individuals. "Bull's eye" lesions were present in two individuals, comprising of a ring of decreased perifoveal AF bordered peripherally and centrally by increased AF. Photopic sensitivity testing demonstrated elevated central visual field thresholds with additional superior greater than inferior peripheral field loss. There were rod and cone sensitivity reductions in the central and peripheral visual fields, with the inferior retina being more affected than the superior. CONCLUSIONS: The detailed phenotype is described of the autosomal dominant cone-rod dystrophy, CORD7, which is associated with a point mutation in RIM1, a gene encoding a photoreceptor synaptic protein. The pattern of disease progression and long term visual outcome facilitates improved genetic counselling and advice on prognosis. Such phenotypic data will be invaluable in the event of future therapy.     

视网膜色素变性和视锥-视杆细胞营养不良患者基因突变频谱分析

目的：分析中国宁夏地区常染色体隐性遗传视网膜色素变性(ARRP)及视锥-视杆细胞营养不良(CORD)的基因突变频谱。

方法：纳入2016-09/2020-02在宁夏人民医院眼科医院就诊的35例ARRP患者和18例常染色体隐性CORD患者,行详细的眼科检查。抽取外周静脉血,对先证者应用包含232个致病基因的遗传性视网膜疾病捕获芯片进行靶向捕获富集高通量测序。利用在线分析软件对可疑基因变异致病性进行预测,利用Sanger测序对家系成员进行共分离分析。

结果：ARRP患者35例中,检测到致病基因16个,以RP1基因突变率最高,占14%(5/35),其次为ABCA4、CRB1和EYS基因,均占11%(4/35); 18例常染色体隐性CORD患者中,检测到致病基因10个,以ABCA4基因突变率最高,占28%(5/18),其次为ALMS1、PROM1、RPE65、USH2A基因,均占11%(2/18); ARRP和CORD患者中,共同致病基因有ABCA4、CLN3、CRB1、PROM1、NRL共5个,占42%(22/53)。

结论：ARRP及CORD两种疾病在表型之间具有一定程度的相似性和交叉性,致病基因突变谱上存在一定重叠性。宁夏地区最常见的重叠基因为ABCA4。     

Spectrum and frequency of mutations in IMPDH1 associated with autosomal dominant retinitis pigmentosa and leber congenital amaurosis

PURPOSE: The purpose of this study was to determine the frequency and spectrum of inosine monophosphate dehydrogenase type I (IMPDH1) mutations associated with autosomal dominant retinitis pigmentosa (RP), to determine whether mutations in IMPDH1 cause other forms of inherited retinal degeneration, and to analyze IMPDH1 mutations for alterations in enzyme activity and nucleic acid binding. METHODS: The coding sequence and flanking intron/exon junctions of IMPDH1 were analyzed in 203 patients with autosomal dominant RP (adRP), 55 patients with autosomal recessive RP (arRP), 7 patients with isolated RP, 17 patients with macular degeneration (MD), and 24 patients with Leber congenital amaurosis (LCA). DNA samples were tested for mutations by sequencing only or by a combination of single-stranded conformational analysis and by sequencing. Production of fluorescent reduced nicotinamide adenine dinucleotide (NADH) was used to measure enzymatic activity of mutant IMPDH1 proteins. The affinity and the specificity of mutant IMPDH1 proteins for single-stranded nucleic acids were determined by filter-binding assays. RESULTS: Five different IMPDH1 variants, Thr116Met, Asp226Asn, Val268Ile, Gly324Asp, and His 372Pro, were identified in eight autosomal dominant RP families. Two additional IMPDH1 variants, Arg105Trp and Asn198Lys, were found in two patients with isolated LCA. None of the novel IMPDH1 mutants identified in this study altered the enzymatic activity of the corresponding proteins. In contrast, the affinity and/or the specificity of single-stranded nucleic acid binding were altered for each IMPDH1 mutant except the Gly324Asp variant. CONCLUSIONS: Mutations in IMPDH1 account for approximately 2% of families with adRP, and de novo IMPDH1 mutations are also rare causes of isolated LCA. This analysis of the novel IMPDH1 mutants substantiates previous reports that IMPDH1 mutations do not alter enzyme activity and demonstrates that these mutants alter the recently identified single-stranded nucleic acid binding property of IMPDH. Studies are needed to further characterize the functional significance of IMPDH1 nucleic acid binding and its potential relationship to retinal degeneration.     

Molecular genetic analysis of two functional candidate genes in the autosomal recessive retinitis pigmentosa, RP25, locus

PURPOSE: To identify the disease gene in five Spanish families with autosomal recessive retinitis pigmentosa (arRP) linked to the RP25 locus. Two candidate genes, EEF1A1 and IMPG1, were selected from the region between D6S280 and D6S1644 markers where the families are linked. The genes were selected as good candidates on the basis of their function, tissue expression pattern, and/or genetic data. METHODS: A molecular genetic study was performed on DNA extracted from one parent and one affected member of each studied family. The coding exons, splice sites, and the 5' UTR of the genes were amplified by polymerase chain reaction (PCR). For mutation detection, direct sequence analysis was performed using the ABI 3100 automated sequencer. Segregation of an IMPG1 single nucleotide polymorphism (SNP) in all the families studied was analyzed by restriction enzyme digest of the amplified gene fragments. RESULTS: In total, 15 SNPs were identified of which 7 were novel. Of the identified SNPs, one was insertion, two were deletions, five were intronic, six were missense, and one was located in the 5' UTR. These changes, however, were also identified in unaffected members of the families and/or 50 control Caucasians. The examined known IMPG1 SNP was not segregating with the disease phenotype but was correlating with the genetic data in all families studied. CONCLUSIONS: Our results indicate that neither EEF1A1 nor IMPG1 could be responsible for RP25 in the studied families due to absence of any pathogenic variants. However, it is important to notice that the methodology used in this study cannot detect larger deletions that lie outside the screened regions or primer site mutations that exist in the heterozygous state. A role of both genes in other inherited forms of RP and/or retinal degenerations needs to be elucidated.     

CRB1 mutations may result in retinitis pigmentosa without para-arteriolar RPE preservation

Purpose: To report a new phenotype in retinitis pigmenotosa (RP) patients with CRB1 mutations at the RP12 locus. Patients: Thirty-seven patients from two Pakistani families with severe retinitis pigmentosa. Methods: Samples were screened with single-strand conformation polymorphism analysis followed by DNA sequencing of the coding sequence of the CRB1 gene. Results: Two novel CRB1 mutations were discovered. No patients had evidence of preservation of the para-arteriolar retinal pigment epithelium (PPRPE) that has been previously reported in all cases of RP associated with CRB1 mutations. Conclusions: Patients with severe autosomal recessive (or simplex) RP who lack the finding of PPRPE should not be excluded from molecular analysis of CRB1 purely because they lack the clinical feature of PPRPE. This report illustrates that RP at the RP12 locus is not clinically uniform. The absence of PPRPE cannot be used to exclude CRB1 as a potential molecular explanation for RP.     

Extensive intrafamilial and interfamilial phenotypic variation among patients with autosomal dominant retinal dystrophy and mutations in the human RDS/peripherin gene.

Clinical phenotypes of patients with mutations in the human RDS/peripherin gene are described. A 67-year-old woman, who carried a 1 base pair deletion in codon 307, presented with typical late onset autosomal dominant retinitis pigmentosa (RP). In another autosomal dominant pedigree, a nonsense mutation at codon 46 caused 'inverse' retinitis pigmentosa-like fundus changes associated with progressive cone-rod degeneration in a 58-year-old man, whereas his 40-year-old son presented with yellow deposits in the retinal pigment epithelial layer resembling a pattern dystrophy, and with moderately reduced rod and cone function, as determined by two colour dark adapted threshold perimetry and electroretinography. It is suggested that both clinical pictures within this latter family may represent manifestations of fundus flavimaculatus. The clinical data of the three patients provide further evidence for the remarkable variety of disease expression within and between families with mutations in the RDS/peripherin gene. Currently, the most comprehensive statement could be that RDS/peripherin mutations are associated either with typical RP or with various forms of flecked retinal disease.     

Autosomal dominant macular atrophy at 6q14 excludes CORD7 and MCDR1/PBCRA loci

PURPOSE: Localization of the gene responsible for autosomal dominant atrophic macular degeneration (adMD) in a large pedigree UM:H785. METHODS: Standard ophthalmologic examinations were performed. Microsatellite markers were used to map the disease gene by linkage and haplotype analyses. RESULTS: The macular degeneration in this family is characterized by progressive retinal pigment epithelial atrophy in the macula without apparent peripheral involvement by ophthalmoscopy or functional studies. Acuity loss progressed with age and generally was worse in the older affected individuals. The rod and cone function remained normal or nearly normal in all tested affected members up to 61 years of age. The phenotype in our family has characteristics similar to Stargardt-like macular degeneration with some differences. Haplotype analysis localized the disease gene in our adMD family to an 8-cM region at 6q14, which is within the 18-cM interval of STGD3 but excludes cone-rod dystrophy 7 (CORD7; centromeric) and North Carolina macular degeneration and progressive bifocal chorioretinal atrophy (MCDR1/PBCRA; telomeric). The mapping interval overlaps with that of recessive retinitis pigmentosa (RP25). CONCLUSIONS: These results implicate at least three genetically distinct loci for forms of macular degeneration that lie within a 30-cM interval on chromosome 6p11-6q16: CORD7, adMD, and MCDR1/PBCRA. Because the critical interval for the adMD family studied overlaps with STGD3 and RP25, these loci could be allelic.     

Exclusion of four candidate genes, KHDRBS2, PTP4A1, KIAA1411 and OGFRL1, as causative of autosomal recessive retinitis pigmentosa

To identify the disease gene in 6 Spanish families with autosomal recessive retinitis pigmentosa linked to the RP25 locus, mutation screening of 4 candidate genes, KHDRBS2, PTP4A1, KIAA1411 and OGFRL1, was undertaken based on their expression or functional relevance to the retina. Twenty-six single nucleotide polymorphisms were identified, of which 14 were novel. Even though no pathological mutations were detected, these genes however remain as good candidates for other retinal degenerations mapping to the same chromosomal region.     

Three families displaying the combination of Stargardt's disease with cone-rod dystrophy or retinitis pigmentosa

OBJECTIVE: To investigate the clinical spectrum and molecular causes of retinal dystrophies in 3 families. DESIGN: Family molecular genetics study. PARTICIPANTS: Sixteen patients and 15 relatives in 3 families. METHODS: Members of 3 families with multiple ABCA4-associated retinal disorders were clinically evaluated. Deoxyribonucleic acid samples of all affected individuals and their family members were analyzed for variants in all 50 exons of the ABCA4 gene. MAIN OUTCOME MEASURES: ABCA4-associated retinal phenotypes and mutations in the ABCA4 gene. RESULTS: In family A, 2 sisters were diagnosed with Stargardt's disease (STGD); the eldest sister was compound heterozygous for the mild 2588G-->C and the severe 768G-->T mutation. Another patient in this family with a severe type of retinitis pigmentosa (RP) carried the 768G-->T mutation homozygously. In family B, 2 siblings presented with an RP of severity similar to that encountered in family A. Both were homozygous for the severe IVS33+1G-->A mutation. Two other family members with STGD were compound heterozygous for the 2588G-->C and IVS33+1G-->A mutations. In family C, all 5 siblings of generation II demonstrated age-related macular degeneration (AMD). In generations III and IV, 2 STGD patients and 1 cone-rod dystrophy (CRD) patient were present. In 1 STGD patient we identified a heterozygous 768G-->T mutation. Sequence analysis of the entire ABCA4 gene did not reveal the remaining 2 mutations. Nevertheless, the 2 patients with STGD, the patient with CRD, and 2 of the AMD patients shared a common haplotype spanning the ABCA4 gene. CONCLUSIONS: Different mutations in the ABCA4 gene are the cause of STGD and RP or CRD in at least 2 and, possibly, 3 families. Patients with RP caused by ABCA4 mutations are characterized by an early onset and rapid progression of their retinal dystrophy, with extensive chorioretinal atrophy resulting in a very low visual acuity. Various combinations of relatively rare retinal disorders such as STGD, CRD, and RP in one family may not be as uncommon as once believed, in view of the relatively high carrier frequency of ABCA4 mutations (about 5%) in the general population.     

Homozygous null mutations in the ABCA4 gene in two families with autosomal recessive retinal dystrophy

PURPOSE: To identify the genes causing autosomal recessive retinal dystrophy in Indian families and to characterize the associated phenotypes. DESIGN: Experimental and observational. METHODS: Families with autosomal recessive nonsyndromic retinal dystrophies were recruited. Complete ophthalmic evaluation, including visual acuity, visual fields, fundus examinations, and electroretinography, was performed on all members. Genotyping of 14 families for two or more microsatellite markers flanking each of 21 different genes causing retinal dystrophy was done by standard methods to screen for the presence of homozygosity by descent. Mutational screening of the ABCA4 gene was carried out on 18 members (five affected) of two families by amplification and direct automated sequencing of exons and flanking sequences. Sequence alterations identified were tested for cosegregation with disease in the families and for presence in 100 unrelated normal controls. RESULTS: Two of 14 families showed homozygosity shared by affected individuals for markers flanking the ABCA4 locus. A homozygous nonsense mutation in the ABCA4 gene of Arg2030Stop was found in one family and a homozygous single base deletion leading to frameshift at Arg409 was found in the second family. Both of these mutations were found to cosegregate with disease. Five affected individuals from the two families had early-onset visual loss, diminished rod and cone electroretinographic responses, and widespread atrophy of the retinal pigment epithelium. CONCLUSION: Homozygous null mutations in ABCA4 produced a severe widespread retinal degeneration that showed marked central retinal involvement.