Analysis of 15 primary open-angle glaucoma families from Australia identifies a founder effect for the Q368STOP mutation of myocilin

Primary open-angle glaucoma (POAG) is a leading cause of blindness in the world. A number of mutations in the myocilin gene have been identified that predispose to glaucoma. The most frequent of these is the Glutamine368STOP (Q368STOP) mutation. It has been postulated that individuals with the Q368STOP mutation are derived from a common founder. To clarify this situation, we studied 15 unrelated POAG families who carried the Q368STOP mutation, from south eastern Australia. In one large family, nine affected and ten unaffected individuals were identified with the Q368STOP mutation. Closely linked polymorphic microsatellite markers were used to establish a disease haplotype in this family. Additional genotyping of markers in another 14 unrelated Q368STOP families revealed the presence of the same disease haplotype. These findings indicate that the Q368STOP mutation in all 15 families shared a common origin prior to the European settlement of Australia in the early 1800s.     

Low prevalence of <Emphasis Type="Italic">MYOC</Emphasis> mutations in UK primary open-angle glaucoma patients limits the utility of genetic testing

Primary open angle glaucoma (POAG) affects 1% of people over age 40. Early detection and treatment can prevent blindness, but the disease is often asymptomatic until a late stage. Positive family history is an important risk factor and previous studies indicate that approximately 5% of POAG results from mutations in the myocilin (MYOC) gene, raising the possibility of identifying individuals genetically predisposed to glaucoma. We collected DNA samples from 426 unselected UK POAG patients and analyzed them for MYOC mutations. The Q368X mutation was found in six patients (1.4%). No other mutations were identified, suggesting that amongst patients unselected for family history, the prevalence of MYOC mutations in the UK is lower than in other populations. Genetic and glaucoma screening was offered to first-degree relatives of these six probands (group 1) and of age/sex-matched mutation-negative controls (group 2). Of 11 group-1 relatives, three carried Q368X, one of whom already had glaucoma. Notably, of the 13 relatives in both groups who were mutation negative, one was already being treated for ocular hypertension. We therefore caution against changing glaucoma surveillance regimens in such individuals and suggest that routine untargeted genetic testing for MYOC mutations in patients with POAG would be of limited value until additional significant genetic risk factors are identified.     

Mapping a gene for adult-onset primary open-angle glaucoma to chromosome 3q.

Glaucoma is the third-leading cause of blindness in the world, affecting >13.5 million people. Adult-onset primary open-angle glaucoma (POAG) is the most common form of glaucoma in the United States. We present a family in which adult-onset POAG is inherited as an autosomal dominant trait. Twelve affected family members were identified from 44 at-risk individuals. The disease-causing gene was mapped to chromosome 3q21-24, with analysis of recombinant haplotypes suggesting a total inclusion region of 11.1 cM between markers D3S3637 and D3S1744. This is the first report of mapping of an adult-onset POAG gene to chromosome 3q, gene symbol GLC1C.     

A common gene for juvenile and adult-onset primary open-angle glaucomas confined on chromosome 1q.

Primary open-angle glaucoma (POAG), which causes progressive loss of the visual fields, was subdivided into two groups according to age at onset: (1) chronic open-angle glaucoma (COAG) diagnosed after age 40 years and (2) juvenile open-angle glaucoma (JOAG) diagnosed between 3 years of age and early adulthood. A JOAG gene (GLC1A) was recently mapped to chromosome 1q. We studied 142 members of a huge multigenerational French Canadian family affected with autosomal dominant POAG. Either JOAG or COAG was diagnosed in 40 patients. Six subjects were also diagnosed with ocular hypertension (OHT), which may lead to POAG. To localize a common disease gene that might be responsible for both glaucoma subsets, we performed linkage analysis considering JOAG and COAG under the same phenotypic category. JOAG/COAG was tightly linked to seven microsatellite markers on chromosome 1q23-q25; a maximum lod score of 6.62 was obtained with AF-M278ye5. To refine the disease locus, we exploited a recombination mapping strategy based on a unique founder effect. The same characteristic haplotype, composed of 14 markers spanning 12 cM between loci D1S196 and D1S212, was recognized in all persons affected by JOAG, COAG, or OHT, but it did not occur in unaffected spouses and in normal family members > 35 years of age, except for three obligatory carriers. Key recombination events confined the disease region within a 9-cM interval between loci D1S445 and D1S416/D1S480. These observations demonstrate that the GLC1A gene is responsible for both adult-onset and juvenile glaucomas and suggest that the JOAG and COAG categories within this family may be part of a clinical continuum artificially divided at age 40 years.     

Genetic variants of <Emphasis Type="Italic">CYP1B1</Emphasis> and <Emphasis Type="Italic">WDR36</Emphasis> in the patients with primary congenital glaucoma and primary open angle glaucoma from saint-Petersburg

In 32 unrelated patients with primary congenital glaucoma (PCG), a search for mutations in the myocilin (MYOC), cytochrome P450B1 (CYP1B1), and WDR36 genes was performed. The Q368X mutation in myocilin gene, typical of the patients with adult-onset primary open-angle glaucoma (POAG), was not detected in the PCG patients. Screening of the CYP1B1 introns 2 and 3 for the presence of mutations in PCG patients revealed only six DNA polymorphisms, including IVS1-12ntT>C (g.3793 T>C), A119S (g.4160 G>T; GCC>TCC), G188G (g.4369 C>A; GGC>GGA), L432V (g.8131 C>G; CTG>GTG), D449D (g.8184 C>T; GAC>GAT), and N453S (g.8195 A>G; AAC>AGC) (nucleotide numbering is given in accordance with the GenBank sequence U56438). In the groups of PCG patients and donors without eye diseases, the frequencies of these variants were not statistically significantly different, pointing to the neutrality of these polymorphisms. Furthermore, the CYP1B1 polymorphism L432V, considered to be associated with POAG in some world populations, was not associated with this disease in the patients from St. Petersburg. DNA collections obtained from the POAG and PCG patients and from the control group were tested for the carriage of the worldwide distributed mutations of the WRD36 gene, D658G, R529Q, A449T, and N355S. D658G variant was found with equally low frequencies in the groups of POAG and PCG patients, as well as in the control group. Mutations A449T and R529Q were found only once each, while mutation N355S was not detected in any of the groups examined. Our results indicate that the WDR36 variants make no substantial contribution to the development of POAG and PCG in the patients from St. Petersburg and represent normal DNA polymorphism. It is likely that in most of the PCG patients from the population examined the disease is not associated with the CYP1B1 gene defects.     

Allelic and locus heterogeneity in autosomal recessive gelatinous drop-like corneal dystrophy

Gelatinous drop-like corneal dystrophy (GDLD) is a rare autosomal recessive disease characterized by the deposition of amyloid beneath the corneal epithelium and by severely impaired visual acuity leading to blindness. Although gelatinous corneal dystrophy has previously been mapped to chromosome 1p and seems to be associated with mutations in the M1S1 gene, molecular genetic studies have been limited to Japanese patients. To investigate the cause of GDLD in patients with diverse ethnic backgrounds, we performed linkage analyses in eight unrelated GDLD families from India, USA, Europe, and Tunisia. In seven of these families, the disease locus mapped to a 16-cM interval on the short arm of chromosome 1 between markers D1S519 and D1S2835, a region including the M1S1 gene. In addition, a 1.2-kb fragment containing the entire coding region of M1S1 gene was sequenced in affected individuals. Seven novel mutations (M1R, 8-bp ins., Q118 E, V194 E, C119 S, 870delC, and 1117delA) were identified in six families and two unrelated individuals. No sequence abnormalities were detected in a single family in which the GDLD locus was also excluded from the M1S1 region by linkage analysis. These findings demonstrate allelic and locus heterogeneity for GDLD.     

Age-dependent penetrance and mapping of the locus for juvenile and early-onset open-angle glaucoma on chromosome 1q (GLC1A) in a French family

The GLC1A locus for autosomal dominant primary open-angle glaucoma (POAG) with juvenile onset (before 20 years) has been mapped to chromosome 1q21– q31. Recently, a French-Canadian family was described in which both juvenile-onset and middle-age or early-onset POAG were observed and linked to GLC1A. We now describe a second POAG family with variable age of onset (range 11–51, median 36 years of age). Linkage to GLC1A was established with a maximum lod score of 6.21 at the D1S452 locus. A recombination event in a severely glaucomatous patient restricted the distal boundary of the GLC1A interval proximal to the AFM154xc9 marker. This study strengthens the idea that early-onset POAG may also be determined by the GLC1A genetic region. Received: 6 May 1996 / Revised: 21 June 1996     

Juvenile open angle glaucoma: fine mapping of the TIGR gene to 1q24.3–q25.2 and mutation analysis

Autosomal dominant juvenile open angle glaucoma (JOAG) is an early-onset form of primary open angle glaucoma (POAG), which has been linked to chromosome 1q21–q31. Recently, mutations in the trabecular meshwork inducible glucocorticoid response gene (TIGR), one of the candidate genes mapped in this region, were identified in glaucoma patients of several families. We screened for mutations of the TIGR gene in two German families with JOAG and in 100 unselected sporadic cases of POAG. In the first family we identified a Pro370Leu mutation and in the second family a Gly367Arg mutation cosegregating with the glaucoma phenotype. No pathogenic mutation was found in 100 sporadic cases but a Tyr347Tyr polymorphism was found in two patients. Furthermore, fluorescence in situ hybridization (FISH) analysis was used to map a TIGR-specific yeast artificial chromosome to 1q24.3–q25.2. Received: 19 June 1997 / Accepted: 12 August 1997     

Homozygosity Mapping of Autosomal Recessive Retinitis Pigmentosa Locus (RP22) on Chromosome 16p12.1–p12.3

Autosomal recessive retinitis pigmentosa (arRP) is a genetically and clinically heterogeneous and progressive degenerative disorder of the retina, leading usually to severe visual handicap in adulthood. To date, disease loci/genes have been mapped/identified only in a minority of cases. DNA samples were collected from 20 large consanguineous Indian families, in which arRP segregated and that were suitable for homozygosity mapping of the disease locus. After excluding linkage to all known arRP loci, a genome-wide scan was initiated. In two families, homozygosity mapping, haplotype analysis, and linkage data mapped the disease locus (RP22) in an approximately 16-cM region between D16S287 and D16S420 on the proximal short arm of chromosome 16. No mutation has been found by direct sequencing in the gene (CRYM) encoding μ crystallin, which maps in the critical region.     

Myocilin Polymorphisms and Primary Open-Angle Glaucoma: A Systematic Review and Meta-Analysis

Background

Glaucoma is the leading cause of irreversible blindness in the world. Recent evidence indicates a role for genetic susceptibility to primary open-angle glaucoma (POAG). The relation between myocilin polymorphisms and POAG susceptibility has been studied in different populations.

Methods

A meta-analysis of 32 published genetic association case-control studies, which examined the relation between POAG and the R46X, R76K, Y347Y, T353I, and Q368X polymorphisms of the myocilin gene, was carried out.

Results

In meta-analysis, significant associations were observed between POAG risk and two myocilin polymorphisms with summarized odds ratio of 4.68 (95%CI, 2.02–10.85) for Q368X and 2.17 (95% CI, 1.32–3.57) for T353I. Both Q368X and T353I were significantly associated with high-tension glaucoma, with summarized odds ratio of 4.26 (1.69, 10.73) and 2.26 (1.37–3.72). In Westerners, significant association was observed for Q368X mutation (odds ratio, 5.17; 95% CI, 2.16–12.40). However, in Asians it was for T353I (odds ratio, 2.17; 95% CI, 1.32–3.57).

Conclusions

There is strong evidence that myocilin polymorphisms are associated with POAG susceptibility, and the prevalence of myocilin mutations might be ethnicity-dependent in Caucasians for Q368X and in Asians for T353I.     

Mapping of a gene for autosomal dominant juvenile-onset open-angle glaucoma to chromosome Iq.

A large Caucasian family is presented, in which a juvenile-onset form of open-angle glaucoma is transmitted in an autosomal dominant fashion. Sixteen affected family members were identified from 31 at-risk individuals descended from the affected founder. Affected patients developed high intraocular pressures (sometimes > 40 mm Hg) within the first 2 decades of life. Linkage analysis between the disease phenotype and 12 microsatellite repeat markers located on chromosome 1q gave a maximum lod score of 8.38 at a recombination fraction of zero for marker D1S210. Analysis of recombinant haplotypes suggests a total inclusion region of about 14 cM between markers D1S194 and D1S218 at 1q21-q31. This represents the second juvenile-glaucoma family, in which the disease has been mapped to the long arm of chromosome 1.     

Exclusion analysis of Charcot-Marie-Tooth neuropathy (CMT1) with chromosome 1p markers

We previously described a large five-generation family with autosomal dominant inheritance of hereditary motor and sensory neuropathy type I, or Charcot-Marie-Tooth disease (CMT1). The genetic defect in this family was not linked to the Duffy blood group. We investigated the possibility of a disease locus on the short arm of chromosome 1 using 12 anonymous DNA markers. Two markers, D1S2 and D1S22, showed positive linkage, suggesting the existence of a CMT1 locus on 1p. D1S2 and D1S22 are clustered in the 1p31----p22 region. However, multipoint linkage analysis, including additional DNA markers from this chromosome region, excluded a possible CMT1 locus in this part of chromosome 1.     

A genome-wide scan for primary open-angle glaucoma (POAG): the Barbados Family Study of Open-Angle Glaucoma

Primary open-angle glaucoma (POAG) is characterized by damage to the optic nerve with associated loss of vision. Six named genetic loci have been identified as contributing to POAG susceptibility by genetic linkage analysis of mostly Caucasian families, and two of the six causative genes have been identified. The Barbados Family Study of Open-Angle Glaucoma (BFSG) was designed to evaluate the genetic component of POAG in a population of African descent. A genome-wide scan was performed on 1327 individuals from 146 families in Barbados, West Indies. Linkage results were based on models and parameter estimates derived from a segregation analysis of these families, and on model-free analyses. Two-point LOD scores >1.0 were identified on chromosomes 1, 2, 9, 10, 11, and 14, with increased multipoint LOD scores being found on chromosomes 2, 10, and 14. Fine mapping was subsequently carried out and indicated that POAG may be linked to intervals on chromosome 2q between D2S2188 and D2S2178 and chromosome 10p between D10S1477 and D10S601. Heterogeneity testing strongly supports linkage for glaucoma to at least one of these regions and suggests possible linkages to both. Although TIGR/myocilin and optineurin mutations have been shown to be causally linked to POAG in other populations, findings from this study do not support either of these as causative genes in an Afro-Caribbean population known to have relatively high rates of POAG.     

A novel genetic locus for familial febrile seizures and epilepsy on chromosome 3q26.2–q26.33

Febrile seizures (FS) are common in children, and the incidence is 2–5% before the age of 5 years. A four-generation Chinese family with autosomal dominant febrile seizure and epilepsy was studied by genome-wide linkage analysis. Significant linkage was identified with markers on chromosome 3q26.2–26.33 with a maximum pairwise LOD score of >3.00. Fine mapping defined the new genetic locus within a 10.7-Mb region between markers D3S3656 and D3S1232. A maximum multipoint LOD score of 5.27 was detected at marker D3S1565. A previously reported CLCN2 gene for epilepsy was excluded as the disease-causing gene in the family by mutational analysis of all exons and exon–intron boundaries of CLCN2 and by haplotype analysis. Mutation analysis of KCNMB2 and KCNMB3, which were two potassium-channel genes in this linkage region, did not reveal a disease causing mutation. Our results identified another novel locus on chromosome 3q26.2–26.33, and future studies of the candidate genes at the locus will identify a new gene for combined FS and idiopathic epilepsies. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. X.-H. Dai, W.-W. Chen, and X. Wang contributed equally to this work.     

Homozygous WNT3 mutation causes tetra-amelia in a large consanguineous family

Tetra-amelia is a rare human genetic disorder characterized by complete absence of all four limbs and other anomalies. We studied a consanguineous family with four affected fetuses displaying autosomal recessive tetra-amelia and craniofacial and urogenital defects. By homozygosity mapping, the disease locus was assigned to chromosome 17q21, with a maximum multipoint LOD score of 2.9 at markers D17S931, D17S1785, D17SS1827, and D17S1868. Further fine mapping defined a critical interval of approximately 8.9 Mb between D17S1299 and D17S797. We identified a homozygous nonsense mutation (Q83X) in the WNT3 gene in affected fetuses of the family. WNT3, a human homologue of the Drosophila wingless gene, encodes a member of the WNT family known to play key roles in embryonic development. The Q83X mutation truncates WNT3 at its amino terminus, suggesting that loss of function is the most likely cause of the disorder. Our findings contrast with the observation of early lethality in mice homozygous for null alleles of Wnt3. To our knowledge, this is the first report of a mutation in a WNT gene associated with a Mendelian disorder. The identification of a WNT3 mutation in tetra-amelia indicates that WNT3 is required at the earliest stages of human limb formation and for craniofacial and urogenital development.     

Genetic mapping of RP1 on 8q11-q21 in an Australian family with autosomal dominant retinitis pigmentosa reduces the critical region to 4 cM between D8S601 and D8S285

The locus (RP1) for one form of autosomal dominant retinitis pigmentosa (adRP) was mapped on chromosome 8q11-q22 between D8S589 and D8S285, which are about 8 cM apart, by linkage analysis in an extended family ascertained in the USA. We have studied a multigeneration Australian family with adRP and found close linkage without recombination between the disease locus and D8S591, D8S566, and D8S166 (Z_max = 1.137– 4.650 at θ = 0.00), all mapped in the region known to harbor RP1. Assuming that the mutation of the same gene is responsible for the disease in both families, the analysis of multiply informative meioses in the American and Australian families places the adRP locus between D8S601 and D8S285, which reduces the critical region to about 4 cM, corresponding to approximately 4 Mb, which is completely covered by a yeast artificial chromosome contig assembled recently. Received: 23 April 1996 / Accepted: 3 July 1996     

Identification of a modifier gene locus on chromosome 1p35-36 in familial adenomatous polyposis

Phenotypic variability based on nonallelic heterogeneity is a characteristic feature of the dominantly inherited disease, familial adenomatous polyposis (FAP). A modifying locus, called Mom-1, which strongly influences disease expression has been mapped in the mouse model of FAP to the region of murine chromosome 4, which has synteny to human chromosome 1p35-36. In the present study, this chromosomal region was investigated by using 14 microsatellite markers within a large FAP kindred in which patients harbor the same germ-line mutation but show markedly different disease characteristics. The linkage program MLINK was used to determine whether any correlation exists between these markers and the development of extracolonic symptoms in polyposis coli patients. Depending on the mode of inheritance of the affected locus, a maximum lod score was observed for markers D1S211 and D1S197, reaching 2.08 and 1.77, respectively. The observed values obtained within one large FAP family are supportive of a phenotype-modifying locus within this chromosomal region. Received: 6 December 1996 / Revised: 23 December 1996     

Recombination of 4p16 DNA markers in an unusual family with Huntington disease

The Huntington disease (HD) mutation has been localized to human chromosome 4p16, in a 6-Mb region between the D4S10 locus and the 4p telomere. In a report by Robbins et al., a family was identified in which an affected individual failed to inherit three alleles within the 6-Mb region originating from the parental HD chromosome. To explain these results, it was suggested that the HD locus (HD) lies close to the telomere and that a recombination event took place between HD and the most telomeric marker examined, D4S90. As a test of this telomere hypothesis, we examined six members of this family, five of whom are affected with HD, for the segregation of 12 polymorphic markers from 4p16, including D4S169, which lies within 80 kb of the 4p telomere. We separated, in somatic cell hybrids, the chromosomes 4 from each family member, to determine the phase of marker alleles on each chromosome. We excluded nonpaternity by performing DNA fingerprint analyses on all six family members, and we found no evidence for chromosomal rearrangements when we used high-resolution karyotype analysis. We found that two affected siblings, including one of the patients originally described by Robbins et al., inherited alleles from the non-HD chromosome 4 of their affected parents, throughout the 6-Mb region. We found that a third affected sibling, also studied by Robbins et al., inherited alleles from the HD chromosome 4 of the affected parent, throughout the 6-Mb region. Finally, we found that a fourth sibling, who is likely affected with HD, has both a recombination event within the 6-Mb region and an additional recombination event in a more centromeric region of the short arm of chromosome 4. Our results argue against a telomeric location for HD and suggest that the HD mutation in this family is either associated with DNA predisposed to double recombination and/or gene conversion within the 6-Mb region or is in a gene that is outside this region and that is different from that mutated in most other families with HD.     

Exclusion of linkage to the pericentromeric region of chromosome 21 in the Canadian pedigree with familial Alzheimer disease

Summary Alzheimer disease (AD) is a devastating neurodegenerative disease leading to global dementia. The familial form (FAD) has been linked to markers on chromosome 21 in some families, most tightly to the loci D21S16 and D21S13 located close to the centromere of the long arm. In other families the FAD mutation has been excluded from the more telomeric D21S1/S11 region, but not from the centromeric region of chromosome 21. We identified two new restriction fragment length polymorphisms (RFLPs) for the locus D21S13 and have used these RFLPs for the analysis of one of the largest known early-onset FAD pedigrees. We calculated pairwise and multipoint lod scores for the loci D21S13, D21S110, and D21S11. Linkage to this region of chromosome 21 was excluded with maximum negative lod scores of -6.4 at D21S13 and D21S110. Thus, it is unlikely that the FAD mutation in this family is located in the region that has shown linkage in other FAD pedigrees. This result provides evidence for genetic heterogeneity of early-onset FAD or a location of FAD centromeric to D21S13.     

Localization of a novel locus for alopecia with mental retardation syndrome to chromosome 3q26.33–q27.3

Alopecia with mental retardation syndrome is a rare autosomal recessive disorder characterized clinically by total or partial alopecia and mental retardation. In an effort to understand the molecular bases of this form of alopecia syndrome, large Pakistani consanguineous kindred with multiple affected individuals has been ascertained from a remote region in Pakistan. Genome wide scan mapped the disease locus on chromosome 3q26.33–q27.3. A maximum two-point LOD score of 3.05 (θ=0.0) was obtained at marker D3S3583. Maximum multipoint LOD score exceeding 5.0, obtained with several markers, supported the linkage. Recombination events observed in affected individuals localized the disease locus between markers D3S1232 and D3S2436, spanning 11.49-cM region on chromosome 3q26.33–q27.3. Sequence analysis of a candidate gene ETS variant gene 5 from DNA samples of two affected individuals of the family revealed no mutation.