Fine localisation of the gene for central areolar choroidal dystrophy on chromosome 17p.

Central areolar choroidal dystrophy (CACD) is a retinal disease which causes progressive profound loss of vision in patients during middle age. The disease is inherited as an autosomal dominant trait and shows genetic heterogeneity. Mutations in the peripherin-RDS gene on chromosome 6 have been reported in affected members of families transmitting the disease. A new locus at chromosome 17p13 was identified recently by a genome wide linkage search in members of a large Northern Irish family. We now report the refinement of the critical region for this gene to an interval of approximately 5 cM flanked by polymorphic markers D17S1810 and CHLC GATA7B03.     

Homozygosity mapping of lethal congenital contractural syndrome type 2 (LCCS2) to a 6 cM interval on chromosome 12q13

We have recently described a novel autosomal recessive disorder, lethal congenital contractural syndrome type 2 (LCCS2) (OMIM 607598), in a large Israeli Bedouin kindred. The phenotype, which is lethal in the neonatal period, is distinguished by the presence of a markedly distended urinary bladder. Association of LCCS2 to the known loci associated with arthogryposis was excluded. In the present study, we set out to determine the genetic locus harboring the gene defective in this disease. We performed genome-wide linkage analysis, demonstrating linkage to a approximately 6 cM (corresponding to approximately 7.2 Mb) homozygosity region on chromosome 12q13 between markers D12S1604 and D12S83. Based on recombination events, the interval harboring the disease-associated locus was further narrowed to a region spanning approximately 6 cM ( approximately 6.4 Mb) between D12S325 and D12S1072. Linkage of LCCS2 to that locus was established, with two significant maximum peaks at markers D12S1604 (Z(max) = 10.56 at theta = 0.01) and D12S1700 (Z(max) = 9.23 at theta = 0.00).     

Refinement of the laminin alpha2 chain locus to human chromosome 6q2 in severe and mild merosin deficient congenital muscular dystrophy.

About half of the children with classical congenital muscular dystrophy (CMD) show an absence in their skeletal muscle of laminin alpha2 chain, one of the components of the extracellular matrix protein, merosin. Linkage analysis implicated the laminin alpha2 chain gene (LAMA2) on chromosome 6q2, now confirmed by the discovery of mutations in the laminin alpha2 chain gene. We have further investigated the location of the LAMA2 locus on chromosome 6q2, using both linkage analysis in nine informative families and homozygosity mapping in 13 consanguineous families. Four of these families only had mild or moderate down regulation of laminin alpha2 chain expression and a milder phenotype; the rest had no protein or only a trace. Haplotype analysis in all the informative families, including those with partial laminin alpha2 expression, was compatible with linkage to chromosome 6q2. This observation expands the spectrum of the phenotype secondary to laminin alpha2 chain deficiency. Our results suggest that the LAMA2 locus is more centromeric than previously proposed. Recombinant events place the locus between markers D6S470 and D6S1620 in an interval of less than 3 cM.     

Fine mapping of a schizophrenia susceptibility locus at chromosome 6q23: increased evidence for linkage and reduced linkage interval

We previously reported an autosomal scan for schizophrenia susceptibility loci in a systematically recruited sample of Arab Israeli families. The scan detected significant evidence for linkage at chromosome 6q23 with a nonparametric LOD score (NPL) of 4.60 (P=0.000004) and a multipoint parametric LOD score of 4.16. In order to refine this finding we typed 42 additional microsatellite markers on chromosome 6q between D6S1570 (99.01 cM from the pter) and D6S281 (190.14 from the pter) in the same sample (average intermarker distance approximately 1.7 cM). In the 23 cM region between D6S1715 and D6S311, markers were more closely spaced ( approximately 1.1 cM). Multipoint nonparametric and parametric and single point linkage analyses were performed. The peak NPL rose to 4.98 (P=0.00000058) at D6S1626 (136.97 cM), immediately adjacent to D6S292 (NPL 4.98, P=0.00000068), the marker that gave the highest NPL in the original genome scan, under the broad diagnostic category. The putative susceptibility region (NPL-1) was reduced from 12.0 to 4.96 cM. The peak multipoint parametric LOD score was 4.63 at D6S1626 under a dominant genetic model, core diagnostic category and the LOD-1 interval was 2.10 cM. The maximum single point LOD score (3.55, theta=0.01) was also at D6S1626 (dominant model, core diagnostic category). Increased evidence for linkage in the same sample as in the original genome scan and consistent localization of the linkage peak add further support for the presence of a schizophrenia susceptibility locus at chromosome 6q23. Moreover, the markedly reduced linkage interval greatly improves prospects for identifying a schizophrenia susceptibility gene within the implicated region.     

Replication and refinement of linkage of posterior polymorphous corneal dystrophy to the posterior polymorphous corneal dystrophy 1 locus on chromosome 20.

PURPOSE: The study purpose was to identify the genetic basis of posterior polymorphous corneal dystrophy, an autosomal dominant disorder of the corneal endothelium that is associated with the development of corneal edema, necessitating corneal transplantation for visual rehabilitation. Glaucoma also develops in up to 40% of patients with posterior polymorphous corneal dystrophy. METHODS: Linkage analysis, using microsatellite markers previously used to demonstrate linkage of posterior polymorphous corneal dystrophy to the chromosome 20 candidate region known as posterior polymorphous corneal dystrophy 1, was performed in 29 members of a family with posterior polymorphous corneal dystrophy. Thirty-four microsatellite markers were used to refine the posterior polymorphous corneal dystrophy 1 interval. TCF8, located on chromosome 10, was screened in an affected family member to exclude posterior polymorphous corneal dystrophy 3. RESULTS: Significant evidence of linkage to the posterior polymorphous corneal dystrophy 1 interval was obtained with both single-point and multipoint analyses. The largest single-point log odds ratio score obtained was 4.38 (theta=0) at marker D20S471; within 4.7 Mbp (7.2 cM) of D20S471 eight markers provided single-point log odds ratio scores of greater than 3.00 and three markers provided single-point log odds ratio scores greater than 4.00. The largest multipoint log odds ratio score obtained was 4.83, found across the adjacent markers D20S844, D20S191, D20S484, and D20S111. The support interval for posterior polymorphous corneal dystrophy 1 in the family we report is approximately 13.5 Mbp (10 cM) long and lies between the markers D20S182 and D20S195. Eleven markers have multipoint log odds ratio scores greater than 4.0 within this region. No coding region mutations were identified in TCF8 in an affected member of the family, effectively excluding posterior polymorphous corneal dystrophy 3. CONCLUSIONS: The originally described 19.8 cM posterior polymorphous corneal dystrophy 1 candidate disease interval has been refined to a 10 cM interval between markers D20S182 and D20S195. A portion of this refined interval overlaps a more recently reported posterior polymorphous corneal dystrophy 1 interval, with only 20 known and predicted genes mapped to the 2.4 cM common interval.     

Localizaion of the gene for dominant cystoid macular dystrophy on chromosome 7p

In a family with autosomal dominant cystoid macular dystrophy(DCMD) lInkage was detected with the dinucleotide marker D7S435on the short arm of chromosome 7. With markers flanking D7S435,the DCMD locus could be asigned to the interval D7S493-D7S526at 7p15-p21, which spans approximately 20 cM. Three-points lInkageyIelded a maximal lod score of 9.46 and location score of 43.5and suggested that DCMD is 5, 5 cM proximal to D7S493. Recently,a retinitis plgmentosa (RP7) locus has been mapped in roughlythe same area of chromosome 7. Genetic data of both studiesdescribed below, allow a region of overlap between the locationof the DCMD and the RP7 gene between D7S435 and D7S526. Bothgenes being one and the same will further substantiate the closerelationship between macular degeneration and retinitis pIgmentosa.     

Genomewide linkage scan in a multigeneration Caucasian pedigree identifies a novel locus for keratoconus on chromosome 5q14.3-q21.1.

PURPOSE: Keratoconus is a corneal dystrophy with an incidence of 1 in 2000 and a leading cause for cornea transplantation in Western developed countries. Both clinical observations and segregation analyses suggest a major role for genes in its pathogenesis. It is genetically heterogeneous, most commonly sporadic, but inherited patterns with recessive or dominant modes have also been reported. We studied a four-generation autosomal-dominant pedigree to identify disease loci for keratoconus. METHODS: A two-stage genome-wide scan was applied to 27 family members. First linkage analysis was performed with 343 microsatellite markers along the 22 autosomal chromosomes at approximately 10 cM density. This was followed by fine mapping at approximately 2 cM density, in regions suggestive of linkage. Multipoint linkage analysis was performed using GeneHunter2. RESULTS: Evidence of suggestive linkage from the initial scan was observed at the 82 to 112 cM region of chromosome 5q14.1-q21.3 with a maximum lod score (LOD) of 3.48 (penetrance = 0.5). Fine mapping by testing an additional 11 microsatellite markers at 1 to 3 cM intervals revealed a narrower and higher peak (99-119 cM) with LOD 3.53. By analysis of the recombination of haplotypes, the putative locus of keratoconus was further narrowed to a 6 cM region (8.2 Mbp physical distance) between markers D5S2499 and D5S495. CONCLUSION: These results indicate a promising new locus for keratoconus in this pedigree. Because of the heterogeneous nature of keratoconus, this locus may be specific to familial autosomal-dominant keratoconus. Nevertheless, the identification of this locus may provide new insights into the pathogenesis of keratoconus.     

Fifth finger camptodactyly maps to chromosome 3q11.2-q13.12 in a large German kindred

Camptodactyly (MIM 114200) is a digit deformity characterised by permanent flexion contracture of fifth fingers at the proximal interphalangeal (PIP) joints. The sporadic cases are common but a familial occurrence is not much appreciated. In an attempt to identify the genetic basis of camptodactyly, we have analysed a large German family with camptodactyly segregating in an autosomal dominant fashion. The affected family members exhibited clinical features of fifth finger camptodactyly and knuckle pads on the crooked fifth finger and on fingers 2-3. Typically, women were more severely affected than men. Microsatellite analyses of five candidate loci known to be associated with camptodactyly-like phenotypes did not show co-segregation with the phenotype in our family. A genome-wide linkage scan using a total of 414 microsatellite markers gave significant evidence of linkage between the familial phenotype and chromosomal locus 3q11.2-q13.12 (maximum two-point LOD score 3.04). The key recombination events showed that the phenotype localises between markers D3S2465 and D3S3044, spanning an interval of approximately 15 cM. This study reports the first genetic locus linked to isolated autosomal dominant fifth finger camptodactyly with knuckle pads and proves the hypothesis that camptodactyly is distinct from camptodactyly-associated phenotypes including Dupuytren contracture. Additional studies of other families will be necessary to determine the existence of genetic homogeneity or heterogeneity of the anomaly and to narrow down the genetic interval to identify the responsible gene. Since genetic heterogeneity for isolated camptodactyly is likely, we propose to designate the 3q11.2-q13.12 locus as CAMPD1 (ie, camptodactyly 1).     

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.      

NRL S50T mutation and the importance of 'founder effects' in inherited retinal dystrophies

The aim of this work was to identify NRL mutations in a panel of 200 autosomal dominant retinitis pigmentosa (adRP) families. All samples were subjected to heteroduplex analysis of the three exons of the NRL gene, and HphI restriction digest analysis of exon 2 (to identify the S50T mutation). Families found to have the S50T mutation, and six additional larger pedigrees (which had previously been excluded from the other nine adRP loci) underwent linkage analysis using polymorphic markers located in the region of 14q11. HphI restriction analysis followed by direct sequencing of the amplified NRL exon 2 product demonstrated the presence of the NRL S50T sequence change in three adRP families. Comparison of marker haplotypes in affected individuals from these families with those of affected members of the original 14q11 linked family revealed a common disease haplotype for markers within the adRP locus. Recombination events observed in these families define an adRP critical interval of 14.9 cM between D13S72 and D14S1041. Linkage analysis enabled all six of the larger adRP pedigrees to be excluded from the 14q11 locus. The NRL S50T mutation represents another example of a 'founder effect' in a dominantly inherited retinal dystrophy. Identification of such 'founder effects' may greatly simplify diagnostic genetic screening and lead to better prognostic counselling. The exclusion of several adRP families from all ten adRP loci indicates that at least one further adRP locus remains to be found.     

Finer linkage mapping of a primary hip osteoarthritis susceptibility locus on chromosome 6

Primary osteoarthritis (OA) is a common late-onset disease that exhibits complex genetic transmittance. A previous genome-wide linkage scan of OA affected sibling pair families (ascertained by total joint replacement surgery) identified a region of suggestive linkage on chromosome 6, with a maximum multipoint-LOD score (MLS) of 2.9 in 194 families containing sibling pairs concordant for total hip replacement (THR-families). However, up to 50 cM of the chromosome had a multipoint-LOD score >2.0, indicating that the susceptibility locus was poorly mapped. We have now genotyped chromosome 6 to a higher density in an expanded cohort of 378 THR-families. We obtained an MLS of 2.8 to an 11.4 cM interval defined by markers D6S452 and 509-8B2, which map between 70.5 to 81.9 cM from the 6p-telomere. Stratification by gender revealed that this linkage was completely accounted for by female THR-families (n=146), with an MLS of 4.0 and with the highest two-point LOD score being 4.6 for marker D6S1573 (75.9 cM). The 11.4 cM interval just encompasses the candidate gene COL9A1 (81.9 cM). We identified and then genotyped twenty common single nucleotide polymorphisms (SNPs) from within COL9A1 in the 146 probands from our female THR-families and in 215 age-matched female controls. No SNP allele, genotype or haplotype demonstrated association to disease. Overall, we have narrowed the chromosome 6 OA susceptibility locus to a point at which linkage disequilibrium/association analysis is feasible, we have demonstrated that this locus is female specific, and found no evidence that COL9A1 encodes for the susceptibility.     

Linkage disequilibrium in inbred North African families allows fine genetic and physical mapping of triple A syndrome

Triple A syndrome (Allgrove syndrome, MIM No. 231550) is a rare autosomal recessive disorder characterised by ACTH-resistant adrenal insufficiency, achalasia of the cardia, and alacrimia. The triple A gene has been previously mapped to chromosome 12q13 in a maximum interval of 6 cM between loci D12S1629 and D12S312. Using linkage analysis in 12 triple A families, mostly originating from North Africa, we confirm that the disease locus maps to the 12q13 region (Zmax = 10.89 at theta = 0 for D12S1604) and suggest that triple A is a genetically homogeneous disorder. Recombination events as well as homozygosity for polymorphic markers enabled us to reduce the genetic interval to a 3.9 cM region. Moreover, total linkage disequilibrium was found at the D12S1604 locus between a rare allele and the mutant chromosomes in North African patients. Analysis of markers at five contiguous loci showed that most of the triple A chromosomes are derived from a single founder chromosome. As all markers are located in a 0 cM genetic interval and only allele 5 at the D12S1604 locus was conserved in mutant chromosomes, we speculate that the triple A mutation is due to an ancient Arabian founder effect that occurred before migration to North Africa. Since we also found linkage disequilibrium at D12S1604 in two patients from Southern Europe (France and Spain), the founder effect might well extend to other Mediterranean countries. Taking advantage of a YAC contig encompassing the triple A minimal physical region, the triple A gene was mapped to a 1.7 Mb DNA fragment accessible to gene cloning.     

Clouston hidrotic ectodermal dysplasia (HED): genetic homogeneity, presence of a founder effect in the French Canadian population and fine genetic mapping

HED is an autosomal dominant skin disorder that is particularly common in the French Canadian population of south-west Quebec. We previously mapped the HED gene to the pericentromeric region of chromosome 13q using linkage analysis in eight French Canadian families. In this study, we extend our genetic analysis to include a multiethnic group of 29 families with 10 polymorphic markers spanning 5.1 cM in the candidate region. Two-point linkage analysis strongly suggests absence of genetic heterogeneity in HED in four families of French, Spanish, African and Malaysian origins. Multipoint linkage analysis in all 29 families generated a peak lod score of 53.5 at D13S1835 with a 1 lod unit support interval spanning 1.8 cM. Recombination mapping placed the HED gene in a 2.4 cM region flanked by D13S1828 proximally and D13S1830 distally. We next show evidence for a strong founder effect in families of French Canadian origin thereby representing the first example of a founder disease in the south-west part of the province of Quebec. Significant association was found between HED in these families and all markers analysed (Fisher's exact test, P < 0.001). Complete allelic association was detected at D13S1828, D13S1827, D13S1835, D13S141 and D13S175 (P(excess) = 1) spanning 1.3 cM. A major haplotype including all 10 associated alleles was present on 65% of affected chromosomes. This haplotype most likely represents the founder haplotype that introduced the HED mutation into the French Canadian population. Luria-Delbrück equations and multipoint likelihood linkage disequilibrium analysis positioned the gene at the D13S1828 locus (likely range estimate: 1.75 cM) and 0.58 cM telomeric to this marker (support interval: 3.27 cM) respectively.     

Further refinement of Pendred syndrome locus by homozygosity analysis to a 0.8 cM interval flanked by D7S496 and D7S2425.

Pendred syndrome is an autosomal recessive disease characterised by congenital sensorineural deafness and goitre. The gene responsible for Pendred syndrome has been mapped to chromosome 7q31 in a 5.5 centimorgan (cM) interval flanked by D7S501 and D7S523. This interval was recently refined a to 1.7 cM interval located between D7S501 and D7S692. In the present study, we report linkage analysis data on a large consanguineous family genotyped with eight microsatellite markers located between D7S501 and D7S523. Complete cosegregation with the disease locus was observed with the loci analysed, which further supports locus homogeneity for Pendred syndrome and close linkage to this region. Haplotype analysis placed the Pendred syndrome gene between D7S496 and D7S2425 in a 0.8 cM interval. This additional refinement of the Pendred syndrome region will facilitate the construction of a physical map of the region and will help the identification of candidate genes.     

The gene for schnyder's crystalline corneal dystrophy maps to human chromosome 1p34.1-p36

Schnyder's crystalline corneal dystrophy (SCCD) is an autosomal dominant eye disease characterized by a bilateral clouding of the central cornea, arcus lipoides and/or visible crystalline deposits of cholesterol in the stroma. There is accumulation of phospholipid, unesterified cholesterol and cholesterol ester in the corneal stroma; this is believed to be due to an imbalance in the local factors affecting lipid/cholesterol transport or metabolism. The cellular mechanism of abnormal lipid transport and metabolism in SCCD is of interest due to its potential involvement in atherosclerosis, and its implications for the pathogenesis of cerebrovascular, coronary and peripheral vascular disease as well as corneal opacification. To determine the chromosomal location of the SCCD locus, genome-wide linkage analysis has been performed in two large Swede-Finn kindreds recently identified in central Massachusetts. After analysing 300 microsatellite markers > 90% of the genome was excluded from linkage to the SCCD locus. We now report the chromosomal assignment of the gene for SCCD in both families to be 1p34.1-p36; the maximum multipoint lod- score was 8.48 in the interval between D1S214 and D1S503. From haplotype analysis, the SCCD locus lies in the 16 cM interval between markers D1S2663 and D1S228. Several candidate genes for SCCD have been localized to the 1p34.1-p36 interval.      

Detailed genetic mapping of the von Hippel-Lindau disease tumour suppressor gene.

Von Hippel-Lindau (VHL) disease is an autosomal dominant inherited familial cancer syndrome characterised by a predisposition to the development of retinal, cerebellar, and spinal haemangioblastomas, renal cell carcinoma, and phaeochromocytoma. The gene for VHL disease has been mapped to chromosome 3p25-p26 and flanking markers identified. We report the detailed genetic mapping of the VHL disease locus in 38 families. Significant linkage was detected between VHL disease and D3S601 (Zmax = 18.86 at theta = 0.0, CI 0.0-0.025), D3S18 (Zmax = 11.42 at theta = 0.03, CI 0.005-0.08), RAF1 (Zmax = 11.02 at theta = 0.04, CI 0.007-0.01), and D3S1250 (Zmax = 4.73 at theta = 0.05, CI 0.005-0.15). Multipoint linkage analysis mapped the VHL disease locus between D3S1250 and D3S18 close to D3S601. There was no evidence of locus heterogeneity. This study has (1) confirmed the tight linkage between VHL disease and D3S601, (2) identified D3S1250 as the first marker telomeric to RAF1 which maps centromeric to the VHL disease gene, and (3) narrowed the target region for isolation of the VHL disease gene by positional cloning techniques to a 4 cM interval between D3S1250 and D3S18. These findings will improve the clinical management of families with VHL disease by improving the accuracy of presymptomatic diagnosis using linked DNA markers, and will enhance progress towards isolating the VHL disease gene.     

Spastic paraplegia 5: Locus refinement, candidate gene analysis and clinical description.

Thirty-three different loci for hereditary spastic paraplegias (HSP) have been mapped, and 15 responsible genes have been identified. Autosomal recessive spastic paraplegias (ARHSPs) usually have clinically complex phenotypes but the SPG5, SPG24, and SPG28 loci are considered to be associated with pure forms of the disease. We performed a genome-wide scan in a large French family. Fine mapping of the refined SPG5 region on chromosome 8q12 was performed in another 17 ARHSP families with additional microsatellite markers. After exclusion of known ARHSP loci, the genome-wide screen provided evidence of linkage with a maximal multipoint lod score of 2.6 in the D8S1113-D8S1699 interval. This interval partially overlapped SPG5 and reduced it to a 5.9 megabase (Mb)-region between D8S1113 and D8S544. In a family of Algerian origin from a series of 17 other ARHSP kindreds, linkage to the SPG5 locus was supported by a multipoint lod score of 2.3. The direct sequencing of the coding exons of seven candidate genes did not detect mutations/polymorphisms in the index cases of both linked families. The phenotype of the two SPG5-linked families consisted of spastic paraparesis associated with deep sensory loss. In several patients with long disease durations, there were also mild cerebellar signs. The frequency of SPG5 was approximately 10% (2/18) in our series of ARHSP families with pure or complex forms. We have refined the SPG5 locus to a 3.8 cM interval and extended the phenotype of this form of ARHSP to include slight cerebellar signs.     

Unique noncoding variants upstream of PRDM13 are associated with a spectrum of developmental retinal dystrophies including progressive bifocal chorioretinal atrophy

The autosomal dominant progressive bifocal chorioretinal atrophy (PBCRA) disease locus has been mapped to chromosome 6q14–16.2 that overlaps the North Carolina macular dystrophy (NCMD) locus MCDR1. NCMD is a nonprogressive developmental macular dystrophy, in which variants upstream of PRDM13 have been implicated. Whole genome sequencing was performed to interrogate structural variants (SVs) and single nucleotide variants (SNVs) in eight individuals, six affected individuals from two families with PBCRA, and two individuals from an additional family with a related developmental macular dystrophy. A SNV (chr6:100,046,804T>C), located 7.8 kb upstream of the PRDM13 gene, was shared by all PBCRA‐affected individuals in the disease locus. Haplotype analysis suggested that the variant arose independently in the two families. The two affected individuals from Family 3 were screened for rare variants in the PBCRA and NCMD loci. This revealed a de novo variant in the proband, 21 bp from the first SNV (chr6:100,046,783A>C). This study expands the noncoding variant spectrum upstream of PRDM13 and suggests altered spatio‐temporal expression of PRDM13 as a candidate disease mechanism in the phenotypically distinct but related conditions, NCMD and PBCRA.     

Refinement of the RP17 locus for autosomal dominant retinitis pigmentosa, construction of a YAC contig and investigation of the candidate gene retinal fascin

The RP17 locus for autosomal dominant retinitis pigmentosa has previously been mapped to chromosome 17q by linkage analysis. Two unrelated South African families are linked to this locus and the identification of key recombination events assigned the RP17 locus to a 10 cM interval on 17q22. The work reported here refines the mapping of the locus from a 10 cM to a 1 cM interval between the microsatellite markers D17S1604 and D17S948. A physical map of this interval was constructed using information from the Whitehead/MIT YAC contig WC 17.8. Sequence-tagged site (STS) content mapping of seven overlapping YACs from this contig was employed in order to build the map. A BAC library was screened to cover a gap in the YAC contig and two positive BACs were identified. Intragenic polymorphisms in the retinal fascin gene provided evidence for the exclusion of this candidate as the RP17 disease gene.     

Exclusion of the Ellis-van Creveld region on chromosome 4p16 in some families with asphyxiating thoracic dystrophy and short-rib polydactyly syndromes

Ellis-van Creveld syndrome (EVC) is a relatively rare, usually non-lethal, autosomal recessive skeletal dysplasia characterized by short stature, polydactyly, cardiac and renal anomalies. Linkage analysis has localized the disease gene to chromosome 4p16, with the markers at loci D4S827 and D4S3135 defining the centromeric and telomeric limits of the linked interval, respectively. There has been long-term speculation that asphyxiating thoracic dystrophy (ATD) and the short-rib polydactyly syndromes (SRP) represent the severe end of the EVC disease spectrum. We performed linkage analysis using markers from the EVC region in seven families manifesting either ATD or SRP type III. In two of the families, one segregating ATD and one SRP kindred, linkage of the phenotype to the EVC region was excluded. In the other five families linkage of the phenotype to the EVC region could not be excluded, but the families were too small for linkage to the region to be established. The exclusion of the EVC region in ATD and SRP III families suggests that locus heterogeneity exists within the short-rib dysplasia (with and without polydactyly) group of disorders.