Identification of GUCY2D gene mutations in CORD5 families and evidence of incomplete penetrance

Cone rod dystrophy 5 (CORD5) is an autosomal dominant retinal disease that primarily affects cone function. The locus has previously been mapped to human chromosome 17p12-p13 between the markers D17S926/D17S849 and D17S945/D17S804. One of our "unaffected" recombinant individual from family 1175 was subsequently found to cross through this interval. Reexamination revealed that he was in fact mildly affected. This expanded the minimum candidate region. Direct sequencing of the GUCY2D and other candidate genes within this interval was carried out on 2 American families affected with CORD5. There was an R838C missense mutation within the GUCY2D gene in one and a R838H missense mutation in another families. The previously reported mutations for CORD6 are clustered at the same position within the gene. These results indicate that both CORD5 (MIM# 600977) and CORD6 (MIM# 601777) are actually the same disease. We conclude that significant variability in expression and incomplete penetrance exists even within one family.     

Localisation of a gene for dominant cone-rod dystrophy (CORD6) to chromosome 17p

We have performed genetic linkage analysis on a four generation British family with cone-rod dystrophy. Significant linkage to the disease gene was obtained with eight marker loci situated on chromosome 17p12-p13. A maximum two-point lod score of 5.93 with no recombination was obtained with marker locus D17S1844. Critical recombinants identified with flanking marker loci placed the disease gene between D17S796/D17S938 and D17S954, an interval estimated to be 8 cM in size. This new localisation for autosomal dominant cone-rod dystrophy (CORD6) overlaps with regions attributed previously to Leber's congenital amaurosis, central areolar choroidal dystrophy and dominant cone dystrophy. Given their differences in phenotype, the most plausible explanation would be that these different retinal disorders are caused by mutations in different genes mapping close together within the genome.      

A mutation in guanylate cyclase activator 1A (GUCA1A) in an autosomal dominant cone dystrophy pedigree mapping to a new locus on chromosome 6p21.1

We report a mutation (Y99C) in guanylate cyclase activator 1A (GUCA1A), the gene for guanylate cyclase activating protein (GCAP1), in a family with autosomal dominant cone dystrophy. Linkage analysis excluded all the known cone and cone-rod dystrophy loci, except the chromosome 6p21.1 region. This is known to contain the RDS gene, which is associated with dominant cone-rod dystrophy. Screening of the RDS gene by heteroduplex analysis and direct sequencing failed to demonstrate sequence changes in the coding region of this gene. The gene for GCAP1, a calcium binding protein which is highly expressed in photoreceptor outer segments, is also located in 6p21.1. It was screened for mutations, and all affected individuals showed a single base pair missense mutation (A-->G) at codon 99 in exon 2 of this gene generating a tyrosine-to-cysteine change in the GCAP1 protein. This change was absent from 206 unrelated normal controls. We propose that this change would at least disrupt the EF3handof GCAP1 thereby preventing calcium binding and consequently interfere with activation. The resulting effect on cGMP production would predictably modify the number of open cGMP gated cation channels, and could explain the ultimate demise of cone photoreceptor cells.      

Prevalence of mutations causing retinitis pigmentosa and other inherited retinopathies

Inherited retinopathies are a genetically and phenotypically heterogeneous group of diseases affecting approximately one in 2000 individuals worldwide. For the past 10 years, the Laboratory for Molecular Diagnosis of Inherited Eye Diseases (LMDIED) at the University of Texas-Houston Health Science Center has screened subjects ascertained in the United States and Canada for mutations in genes causing dominant and recessive autosomal retinopathies. A combination of single strand conformational analysis (SSCA) and direct sequencing of five genes (rhodopsin, peripherin/RDS, RP1, CRX, and AIPL1) identified the disease-causing mutation in approximately one-third of subjects with autosomal dominant retinitis pigmentosa (adRP) or with autosomal dominant cone-rod dystrophy (adCORD). In addition, the causative mutation was identified in 15% of subjects with Leber congenital amaurosis (LCA). Overall, we report identification of the causative mutation in 105 of 506 (21%) of unrelated subjects (probands) tested; we report five previously unreported mutations in rhodopsin, two in peripherin/RDS, and one previously unreported mutation in the cone-rod homeobox gene, CRX. Based on this large survey, the prevalence of disease-causing mutations in each of these genes within specific disease categories is estimated. These data are useful in estimating the frequency of specific mutations and in selecting individuals and families for mutation-specific studies.     

A novel locus for autosomal dominant cone-rod dystrophy maps to chromosome 10q

Here we report recruitment of a three-generation Romani (Gypsy) family with autosomal dominant cone-rod dystrophy (adCORD). Involvement of known adCORD genes was excluded by microsatellite (STR) genotyping and linkage analysis. Subsequently, two independent total-genome scans using STR markers and single-nucleotide polymorphisms (SNPs) were performed. Haplotype analysis revealed a single 6.7-Mb novel locus between markers D10S1757 and D10S1782 linked to the disease phenotype on chromosome 10q26. Linkage analysis gave a maximum LOD score of 3.31 for five fully informative STR markers within the linked interval corresponding to the expected maximum in the family. Multipoint linkage analysis of SNP genotypes yielded a maximum parametric linkage score of 2.71 with markers located in the same chromosomal interval. There is no previously mapped CORD locus in this interval, and therefore the data reported here is novel and likely to identify a new gene that may eventually contribute to new knowledge on the pathogenesis of this condition. Sequencing of several candidate genes within the mapped interval led to negative findings in terms of the underlying molecular pathogenesis of the disease in the family. Analysis by comparative genomic hybridization excluded large chromosomal aberrations as causative of adCORD in the pedigree.     

Three different ABCA4 mutations in the same large family with several consanguineous loops affected with autosomal recessive cone-rod dystrophy

A large multiplex family presumably affected with autosomal recessive cone-rod dystrophy (CRD) was ascertained from Israel. In this family of Christian Arab ancestry with six consanguineous loops, linkage analysis failed to identify homozygosity in all six nuclear families at any of the three arCORD loci hitherto reported. However, homozygosity was found at the CORD3 locus for two nuclear families and the segregation of three distinct haplotypes at this locus in the whole pedigree suggested the alteration of the ABCA4 gene. This hypothesis was confirmed by the identification of three distinct mutations. Subsequently, with regard to the wide spectrum of autosomal recessive retinal dystrophies related to ABCA4 mutations, the natural history of the disease was revisited in all patients. Although the diagnosis of CRD was confirmed in 8/9 patients, the last one, aged of 34, displayed typical signs of Stargardt disease without extension to the peripheral retina. The results of this study emphasize the pitfalls of homozygosity mapping in highly inbred families when the heterozygote carrier frequency is particularly high in the general population.     

Low frequency of BRCA1 germline mutations in 45 German breast/ovarian cancer families.

In this study we investigated 45 German breast/ovarian cancer families for germline mutations in the BRCA1 gene. We identified four germline mutations in three breast cancer families and in one breast-ovarian cancer family. among these were one frameshift mutation, one nonsense mutation, one novel splice site mutation, and one missense mutation. The missense mutation was also found in 2.8% of the general population, suggesting that it is not disease associated. The average age of disease onset in those families harbouring causative mutations was between 32.3 and 37.4 years, whereas the family harbouring the missense mutation had an average age of onset of 51.2 years. These findings show that BRCA1 is implicated in a small fraction of breast/ovarian cancer families suggesting the involvement of another susceptibility gene(s).     

Mutation in the PYK2-binding domain of PITPNM3 causes autosomal dominant cone dystrophy (CORD5) in two Swedish families

Autosomal dominant cone dystrophy (CORD5) (MIM 600977) is a rare disease predominantly affecting cone photoreceptors. Here we refine the CORD5 locus previously mapped to 17p13 from 27 to 14.3 cM and identified a missense mutation, Q626H in the phosphatidylinositol transfer (PIT) membrane-associated protein (PITPNM3) (MIM 608921) in two Swedish families. PITPNM3, known as a human homologue of the Drosophila retinal degeneration B (rdgB), lacks the N-terminal PIT domain needed for transport of phospholipids, renewal of photoreceptors membrane and providing the electroretinogram (ERG) response to light. In our study, the mutation causing CORD5 is located in the C-terminal region interacting with a member of nonreceptor protein tyrosine kinases, PYK2. Our finding on the first mutation in the human homologue of Drosophila rdgB indicates novel pathways and a potential important role of the PITPNM3 in mammalian phototransduction.     

Missense mutations in the rod domain of the lamin A/C gene as causes of dilated cardiomyopathy and conduction-system disease

BACKGROUND: Inherited mutations cause approximately 35 percent of cases of dilated cardiomyopathy; however, few genes associated with this disease have been identified. Previously, we located a gene defect that was responsible for autosomal dominant dilated cardiomyopathy and conduction-system disease on chromosome 1p1-q21, where nuclear-envelope proteins lamin A and lamin C are encoded by the LMNA (lamin A/C) gene. Mutations in the head or tail domain of this gene cause Emery-Dreifuss muscular dystrophy, a childhood-onset disease characterized by joint contractures and in some cases by abnormalities of cardiac conduction during adulthood. METHODS: We evaluated 11 families with autosomal dominant dilated cardiomyopathy and conduction-system disease. Sequences of the lamin A/C exons were determined in probands from each family, and variants were confirmed by restriction-enzyme digestion. The genotypes of the family members were ascertained. RESULTS: Five novel missense mutations were identified: four in the alpha-helical-rod domain of the lamin A/C gene, and one in the lamin C tail domain. Each mutation caused heritable, progressive conduction-system disease (sinus bradycardia, atrioventricular conduction block, or atrial arrhythmias) and dilated cardiomyopathy. Heart failure and sudden death occurred frequently within these families. No family members with mutations had either joint contractures or skeletal myopathy. Serum creatine kinase levels were normal in family members with mutations of the lamin rod but mildly elevated in some family members with a defect in the tail domain of lamin C. CONCLUSIONS: Genetic defects in distinct domains of the nuclear-envelope proteins lamin A and lamin C selectively cause dilated cardiomyopathy with conduction-system disease or autosomal dominant Emery-Dreifuss muscular dystrophy. Missense mutations in the rod domain of the lamin A/C gene provide a genetic cause for dilated cardiomyopathy and indicate that this intermediate filament protein has an important role in cardiac conduction and contractility.     

三个角膜营养不良家系的TGFBI基因突变

目的 筛查3个角膜营养不良家系患者TGFBI基因突变.方法 采集患者外周静脉血,提取基因组DNA,采用直接测序对TGFBI基因全部17个外显子以及外显子内含子拼接部进行序列分析.结果 3个家系中两个家系表型为格子样角膜营养不良1型(1attice corneal dystrophy type I,LCD I)和格子样角膜营养不良3A型(lattice corneal dystrophy type ⅢA,LCDⅢA),另外1个家系为Avellino角膜营养不良(avellino corneal dystrophy,ACD).在两个LCD家系中分别检出编码子R124C和H626R突变,而在ACD家系中检出R124H突变.结论 TGFBI基因是引起角膜营养不良的致病基因.R124和H626是角膜营养不良的突变热点.     

Genetic studies of 20 Japanese families of dystrophic epidermolysis bullosa

Dystrophic EB (DEB) is clinically characterized by mucocutaneous blistering in response to minor trauma, followed by scarring and nail dystrophy, and is caused by mutations in the COL7A1 gene encoding type VII collagen. DEB is inherited in either an autosomal dominant (DDEB) or recessive (RDEB) fashion. DDEB basically results from a glycine substitution mutation within the collagenous domain on one COL7A1 allele, while a combination of mutations such as premature stop codon, missense, and splice-site mutations on both alleles causes RDEB. In this study, mutation analysis was performed in 20 distinct Japanese DEB families (16 RDEB and four DDEB). The result demonstrated 30 pathogenic COL7A1 mutations with 16 novel mutations, which included four missense, five nonsense, one deletion, two insertion, one indel, and three splice-site mutations. We confirmed that Japanese COL7A1 mutations were basically family specific, although three mutations, 5818delC, 6573+1G>C, and E2857X, were recurrent based on previous reports. Furthermore, the Q2827X mutation found in two unrelated families would be regarded as a candidate recurrent Japanese COL7A1 mutation. The study furthers our understanding of both the clinical and allelic heterogeneity displayed in Japanese DEB patients. An erratum to this article can be found at     

A new family of Greek origin maps to the CRD locus for autosomal dominant cone-rod dystrophy on 19q.

Retinal photoreceptor dystrophies (RD) are a highly heterogeneous group of genetic disorders of the retina, representing the most frequently inherited form of visual handicap, affecting approximately 1.5 million people world wide. To date, more than 40 genetic loci have been implicated in RD. One of them, the CORD2 locus, for an autosomal dominant form of cone-rod dystrophy (CRD), maps to chromosome 19q and has previously been reported in a single large family of British origin. We now report a new family with severe early onset CRD, phenotypically very similar to the British family, which also maps to 19q, but is of Greek origin. Haplotype data of the Greek family showed no recombination between and including markers D19S219 and D19S246 and linkage analysis gave a lod score of 2.7 (at theta=0) with marker D19S412, confirming the data obtained in the British family.     

Mutations in HPRP3, a third member of pre-mRNA splicing factor genes, implicated in autosomal dominant retinitis pigmentosa.

Retinitis pigmentosa (RP), the commonest form of inherited retinal dystrophies is a clinically and genetically heterogeneous disorder. It is characterized by progressive degeneration of the peripheral retina leading to night blindness and loss of peripheral visual field. RP is inherited either in an autosomal dominant, autosomal recessive or X-linked mode. A locus (RP18) for autosomal dominant RP was previously mapped by linkage analysis in two large pedigrees to chromosome 1p13-q21. The human HPRP3 gene, the orthologue of the yeast pre-mRNA splicing factor (PRP3), localizes within the RP18 disease interval. The recent identification of mutations in human splicing factors, PRPF31 and PRPC8, led us to screen HPRP3 as a candidate in three chromosome 1q-linked families. So far, two different missense mutations in two English, a Danish family and in three RP individuals have been identified. Both mutations are clustered within a two-codon stretch in the 11th exon of the HPRP3 gene. Interestingly, one of the mutations (T494M) is seen repeatedly in apparently unlinked families raising the possibility of a mutation hot spot. This has been confirmed by haplotype analysis using SNPs spanning the HPRP3 gene region supporting multiple origins of the mutation. The altered HPRP3 amino acids, which are highly conserved in all known HPRP3 orthologues, indicate a major function of that domain in the splicing process. The identification of mutations in a third pre-mRNA splicing factor gene further highlights a novel mechanism of photoreceptor degeneration due to defects in the splicing process.     

Refinement of the locus for autosomal recessive cone–rod dystrophy (CORD8) linked to chromosome 1q23–q24 in a Pakistani family and exclusion of candidate genes

Cone–rod retinal dystrophy (CORD) characteristically leads to early impairment of vision due to the simultaneous involvement of both cone and rod photoreceptor cells. Several loci/genes have been identified for CORD, including the cone–rod dystrophy (CORD8) locus [OMIM#605549] identified for a Pakistani family. All members of this family underwent detailed clinical re-examination to determine the nature of the dystrophy. All affected individuals suffered from bilateral CORD8 with an autosomal recessive mode of inheritance. The CORD8 locus, mapped on chromosome 1q12–q24, consisted of a very large critical disease region of 21 cM. Analysis with more recently available microsatellite markers within the reported region showed heterozygosity with some of the new markers, and the crossovers lead to a refinement of the disease region from 21 to 11.53 cM. Mutation screening has excluded some of the candidate genes in the region. The disease phenotype of this family could be due to a mutation in a novel gene located within the refined CORD8 locus.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .Khalid Anwar: Deceased     

Myofibrillogenesis regulator 1 gene (MR-1) mutation in an Omani family with paroxysmal nonkinesigenic dyskinesia

Two recurrent missense mutations (c.20C>T: A7V; c.26C>T: A9V) in the gene encoding the myofibrillogenesis regulator 1 (MR-1) have been shown to cause autosomal dominant paroxysmal nonkinesigenic dyskinesia (PNKD) in 13 families of primarily European ancestry. Here we report an Omani PNKD family with seven affected family members and autosomal dominant inheritance. Our linkage analysis provided consistent positional evidence that the MR-1 gene could be the responsible disease gene. Sequence analysis identified a MR-1 missense mutation (c.20C>T; A7V) in the affected family members, whereas it was not present in five unaffected family members and 129 population controls. Taking into account that previous haplotype analyses did not reveal evidence for common founders among several PNKD families, our present findings strengthen three implications: (1) autosomal dominant PNKD seems to be a homogenous disorder, for which the MR-1 gene is the major disease gene; (2) mainly two recurrent MR-1 missense mutations (57% V7, 43% V9) account for the genetic variance of familial PNKD; (3) it supports current evidence that some of the recurrent MR-1 mutations may have arisen independently by de novo mutation at functionally convergent key sites of the brain-specific MR-1L isoform.     

Mutations in the PCSK9 gene in Norwegian subjects with autosomal dominant hypercholesterolemia

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is at a locus for autosomal dominant hypercholesterolemia, and recent data indicate that the PCSK9 gene is involved in cholesterol biosynthesis. Mutations within this gene have previously been found to segregate with hypercholesterolemia. In this study, DNA sequencing of the 12 exons of the PCSK9 gene has been performed in 51 Norwegian subjects with a clinical diagnosis of familial hypercholesterolemia where mutations in the low-density lipoprotein receptor gene and mutation R3500Q in the apolipoprotein B-100 gene had been excluded. Two novel missense mutations were detected in the catalytic subdomain of the PCSK9 gene. Two patients were heterozygotes for D374Y, and one patient was a double heterozygote for D374Y and N157K. D374Y segregated with hypercholesterolemia in the two former families where family members were available for study. Our findings support the notion that mutations in the PCSK9 gene cause autosomal dominant hypercholesterolemia.     

Prevalence of AIPL1 mutations in inherited retinal degenerative disease

Leber congenital amaurosis (LCA) is the most severe form of inherited retinal dystrophy and the most frequent cause of inherited blindness in children. LCA is usually inherited in an autosomal recessive fashion, although rare dominant cases have been reported. One form of LCA, LCA4, maps to chromosome 17p13 and is genetically distinct from other forms of LCA. We recently identified the gene associated with LCA4, AIPL1 (aryl-hydrocarbon interacting protein-like 1) and identified three mutations that were the cause of blindness in five families with LCA. In this study, AIPL1 was screened for mutations in 512 unrelated probands with a range of retinal degenerative diseases to determine if AIPL1 mutations cause other forms of inherited retinal degeneration and to determine the relative contribution of AIPL1 mutations to inherited retinal disorders in populations worldwide. We identified 11 LCA families whose retinal disorder is caused by homozygous or compound heterozygous AIPL1 mutations. We also identified affected individuals in two apparently dominant families, diagnosed with juvenile retinitis pigmentosa or dominant cone-rod dystrophy, respectively, who are heterozygous for a 12-bp AIPL1 deletion. Our results suggest that AIPL1 mutations cause approximately 7% of LCA worldwide and may cause dominant retinopathy.     

A mutational hot spot in the KCNQ4 gene responsible for autosomal dominant hearing impairment

Several different mutations in the KCNQ4 K+ channel gene are responsible for autosomal dominant nonsyndromic hearing impairment (DFNA2). Here we describe two additional families originating from Europe and Japan with a KCNQ4 missense mutation (W276S) that was previously found in one European family. We compared the disease-associated haplotype of the three W276S-bearing families using closely linked microsatellite markers and intragenic single nucleotide polymorphisms. Differences between the haplotypes were found, excluding a single founder mutation for the families. Therefore, the W276S mutation has occurred three times independently, and most likely represents a hot spot for mutation in the KCNQ4 gene.