Homozygosity mapping of a Weill-Marchesani syndrome locus to chromosome 19p13.3-p13.2

Weill-Marchesani syndrome (WMS) is a rare disease characterized by short stature, brachydactyly, joint stiffness, and characteristic eye abnormalities, including microspherophakia, ectopia lentis, and glaucoma. Both autosomal recessive and autosomal dominant modes of inheritance have been described in association with WMS. We have performed a genome-wide search in two large consanguineous families of Lebanese and Saudian origin consistent with an autosomal recessive mode of inheritance. Here, we report the linkage of the disease gene to chromosome 19p13.3-p13.2 (Zmax=5.99 at theta=0 at locus D19S906). A recombination event between loci D19S905 and D19S901 defines the distal boundary, and a second recombination event between loci D19S221 and D19S840 defines the proximal boundary of the genetic interval encompassing the WMS gene (12.4 cM). We hope that our ongoing studies will lead to the identification of the disease-causing gene.     

Paget disease of bone: mapping of two loci at 5q35-qter and 5q31

Paget disease of bone is characterized by focal increases of the bone-remodeling process. It is the second most common metabolic bone disease after osteoporosis. Genetic factors play a major role in the etiology of Paget disease of bone, and two loci have been mapped for the disorder: PDB1 and PDB2. The gene(s) causing the typical form of the disorder remains to be characterized. To decipher the molecular basis of Paget disease of bone, we performed genetic linkage analysis in 24 large French Canadian families (479 individuals) in which the disorder was segregating as an autosomal dominant trait. After exclusion of PDB2, a genomewide scan was performed on the three most informative family nuclei. LOD scores >1.0 were observed at seven locations. The 24 families were then used to detect strong evidence for linkage to chromosome 5q35-qter. Under heterogeneity, a maximum LOD score of 8.58 was obtained at D5S2073, at straight theta= .1. The same characteristic haplotype was carried by all patients in eight families, suggesting a founder effect. A recombination event in a key family confined the disease region within a 6-cM interval between D5S469 and the telomere. The 16 other families, with very low conditional probability of linkage to 5q35-qter, were further used, to map a second locus at 5q31. Under heterogeneity, a maximum LOD score of 3.70 was detected at D5S500 with straight theta=.00. Recombination events refined the 5q31 region within 12.2 cM, between D5S642 and D5S1972. These observations demonstrate the mapping of two novel loci for Paget disease of bone and provide further evidence for genetic heterogeneity of this highly prevalent disorder. It is proposed that the 5q35-qter and 5q31 loci be named "PDB3" and "PDB4," respectively.     

A new locus for autosomal recessive hereditary spastic paraplegia maps to chromosome 16q24.3.

Hereditary spastic paraplegia is a genetically and phenotypically heterogeneous disorder. Both pure and complicated forms have been described, with autosomal dominant, autosomal recessive, and X-linked inheritance. Various loci (SPG1-SPG6) associated with this disorder have been mapped. Here, we report linkage analysis of a large consanguineous family affected with autosomal recessive spastic paraplegia with age at onset of 25-42 years. Linkage analysis of this family excluded all previously described spastic paraplegia loci. A genomewide linkage analysis showed evidence of linkage to chromosome 16q24.3, with markers D16S413 (maximum LOD score 3.37 at recombination fraction [theta] of .00) and D16S303 (maximum LOD score 3.74 at straight theta=.00). Multipoint analysis localized the disease gene in the most telomeric region, with a LOD score of 4.2. These data indicate the presence of a new locus linked to pure recessive spastic paraplegia, on chromosome 16q24.3, within a candidate region of 6 cM.     

A locus for an autosomal dominant form of progressive renal failure and hypertension at chromosome 1q21

Linkage studies were performed in a large family with an autosomal dominant phenotype characterized by nephropathy and hypertension. In this family of Iraqi Jewish origin, the nephropathy develops into progressive renal failure. By performing a genomewide linkage search, we localized the disease gene to chromosome 1q21; the highest LOD score was obtained for the marker at locus D1S305, which yielded a maximum LOD score of 4.71 at a recombination fraction of 0. Recombination mapping defined an interval of approximately 11.6 cM, between the markers at loci D1S2696 and D1S2635, that contains the disease gene. Localization of the disease-causing gene in this family represents a necessary step toward isolation of the defective gene and toward a deeper understanding of the mechanisms of hypertension and progressive renal failure.     

Mapping of facioscapulohumeral muscular dystrophy gene to chromosome 4q35-qter by multipoint linkage analysis and in situ hybridization

We have recently assigned the facioscapulohumeral muscular dystrophy (FSHD) gene to chromome 4 by linkage to the microsatellite marker Mfd 22 (locus D4S171). We now report that D4S139, a VNTR locus, is much more closely linked to FSHD. Two-point linkage analysis between FSHD and D4S139 in nine informative families showed a maximum combined lod score (Zmax) of 17.28 at a recombination fraction theta of 0.027. Multipoint linkage analysis between FSHD and the loci D4S139 and D4S171 resulted in a peak lod score of 20.21 at 2.7 cM from D4S139. Due to the small number of recombinants found with D4S139, the position of the FSHD gene relative to that of D4S139 could not be established with certainty. D4S139 was mapped to chromosome 4q35-qter by in situ hybridization, thus firmly establishing the location of the FSHD gene in the subtelomeric region of chromosome 4q. One small family yielded a negative lod score for D4S139. In the other families no significant evidence for genetic heterogeneity was obtained. Studies of additional markers and new families will improve the map of the FSHD region, reveal possible genetic heterogeneity, and allow better diagnostic reliability.     

The Friedreich ataxia gene is assigned to chromosome 9q13-q21 by mapping of tightly linked markers and shows linkage disequilibrium with D9S15.

Chamberlain et al. have assigned the gene for Friedreich ataxia (FA), a recessive neurodegenerative disorder, to chromosome 9, and have proposed a regional localization in the proximal short arm (9p22-cen), on the basis of linkage to D9S15 and to interferon-beta (IFNB), the latter being localized in 9p22. We confirmed more recently the close linkage to D9S15 in another set of families but found much looser linkage to IFNB. We also reported another closely linked marker, D9S5. Additional families have now been studied, and our updated lod scores are z = 14.30 at theta = .00 for D9S15-FA linkage and z = 6.30 at theta = .00 for D9S5-FA linkage. Together with the recent data of Chamberlain et al., this shows that D9S15 is very likely within 1 cM of the FA locus. We have found very significant linkage disequilibrium (delta Std = .28, chi 2 = 9.71, P less than .01) between FA and the D9S15 MspI RFLP in French families, which further supports the very close proximity of these two loci. No recombination between D9S5 and D9S15 was found in the FA families or Centre d'Etude du Polymorphisme Humain families (z = 9.30 at theta = .00). Thus D9S5, D9S15, and FA define a cluster of tightly linked loci. We have mapped D9S5 by in situ hybridization to 9q13-q21, and, accordingly, we assign the D9S5, D9S15, and FA cluster to the proximal part of chromosome 9 long arm, close to the heterochromatic region.     

Genome Scan for Predisposing Loci for Distal Interphalangeal Joint Osteoarthritis: Evidence for a Locus on 2q

The genetic contribution to common forms of osteoarthritis (OA) is well established but poorly understood. We performed a genome scan, using 302 markers for loci predisposing to distal interphalangeal joint (DIP) OA. To minimize genetic heterogeneity in our study sample, we identified siblings with a severe, radiologically defined phenotype from the nationwide registers of Finland. In the initial genome scan, linkage analysis in 27 sibships gave a pairwise LOD score (Z) >1.00 with nine of the screening markers. In the second stage, additional markers and family members were genotyped in these chromosomal regions. On 2q12-q13, IL1R1 resulted in Z=2.34 at recombination fraction (theta) 0, allowing a dominant mode of inheritance. Association analysis of markers D2S2264, IL1R1, D2S373, and D2S1789 jointly provided some evidence for a shared haplotype among the affected individuals (P value of.012). Also, multipoint nonparametric linkage analysis yielded a P value of.0001 near the locus IL1R1 and P=.0007 approximately 20 cM telomeric near marker D2S1399, which, in two-point analysis, gave Z=1.48 (straight theta=. 02). This chromosomal region on 2q harbors the interleukin 1 gene cluster and, thus, represents a good candidate region for inflammatory and autoimmune disorders. Three additional chromosomal regions-4q26-q27, 7p15-p21, and Xcen-also provided some evidence for linkage, and further analyses would be justified to clarify their potential involvement in the genetic predisposition to DIP OA.     

Continuous linkage map of human chromosome 14 short tandem repeat polymorphisms.

Nine moderately to highly informative short tandem repeat polymorphisms were assigned to chromosome 14 using somatic cell hybrids and were mapped using linkage analysis. The nine markers formed a continuous linkage map covering almost the entire long arm from 14q11.2 to q32. The markers filled a large gap within previously reported linkage maps for this chromosome. Best order of the new loci from q11.2 to q32 was D14S50, D14S54, D14S49, D14S47, D14S52, D14S53, D14S55, D14S48, and D14S51. The order shown for all adjacent pairs of loci was very strongly favored with the exception of loci pair D14S55 and D14S48, for which the order was moderately favored. Map lengths for the nine loci were 142 cM in females and 72 cM in males. Female recombination frequencies exceeded male recombination frequencies in the middle and distal portions of the map.     

A genome-wide search for genes predisposing to manic-depression, assuming autosomal dominant inheritance.

Manic-depressive illness (MDI), also known as "bipolar affective disorder," is a common and devastating neuropsychiatric illness. Although pivotal biochemical alterations underlying the disease are unknown, results of family, twin, and adoption studies consistently implicate genetic transmission in the pathogenesis of MDI. In order to carry out linkage analysis, we ascertained eight moderately sized pedigrees containing multiple cases of the disease. For a four-allele marker mapping 5 cM from the disease gene, the pedigree sample has > 97% power to detect a dominant allele under genetic homogeneity and has > 73% power under 20% heterogeneity. To date, the eight pedigrees have been genotyped with 328 polymorphic DNA loci throughout the genome. When autosomal dominant inheritance was assumed, 273 DNA markers gave lod scores < -2.0 at recombination fraction (theta) = .0, 174 DNA loci produced lod scores < -2.0 at theta = .05, and 4 DNA marker loci yielded lod scores > 1 (chromosome 5--D5S39, D5S43, and D5S62; chromosome 11--D11S85). Of the markers giving lod scores > 1, only D5S62 continued to show evidence for linkage when the affected-pedigree-member method was used. The D5S62 locus maps to distal 5q, a region containing neurotransmitter-receptor genes for dopamine, norepinephrine, glutamate, and gamma-aminobutyric acid. Although additional work in this region may be warranted, our linkage results should be interpreted as preliminary data, as 68 unaffected individuals are not past the age of risk.     

Mapping of a new locus for autosomal recessive demyelinating Charcot-Marie-Tooth disease to 19q13.1-13.3 in a large consanguineous Lebanese family: exclusion of MAG as a candidate gene

Autosomal recessive Charcot-Marie-Tooth disease (CMT) type 4 (CMT4) is a complex group of demyelinating hereditary motor and sensory neuropathies presenting genetic heterogeneity. Five different subtypes that correspond to six different chromosomal locations have been described. We hereby report a large inbred Lebanese family affected with autosomal recessive CMT4, in whom we have excluded linkage to the already-known loci. The results of a genomewide search demonstrated linkage to a locus on chromosome 19q13.1-13.3, over an 8.5-cM interval between markers D19S220 and D19S412. A maximum pairwise LOD score of 5.37 for marker D19S420, at recombination fraction [theta].00, and a multipoint LOD score of 10.3 for marker D19S881, at straight theta = .00, strongly supported linkage to this locus. Clinical features and the results of histopathologic studies confirm that the disease affecting this family constitutes a previously unknown demyelinating autosomal recessive CMT subtype known as "CMT4F." The myelin-associated glycoprotein (MAG) gene, located on 19q13.1 and specifically expressed in the CNS and the peripheral nervous system, was ruled out as being the gene responsible for this form of CMT.     

Linkage analysis of the human dopamine beta-hydroxylase gene

The human gene for dopamine beta-hydroxylase (D beta H) has been mapped to chromosome 9q34. Using polymerase chain reaction amplification of exon 11 of the D beta H gene followed by digestion of the reaction products with FnuDII (BstUI), we detected a low-frequency restriction fragment length polymorphism (RFLP). The CEPH panel of family DNAs was genotyped for this RFLP, enabling us to determine the linkage relationships between D beta H and four other loci previously mapped to human chromosome 9q. We obtained two-point recombination frequencies (theta) between D beta H and arginosuccinate synthetase (theta = 0, LOD = 7.37), the ABO blood group locus (theta = 0, LOD = 4.5), CRI-P111 (theta = 0, LOD = 2.1), and D9S31 (theta = .06, LOD = 2.81).     

A locus for brachydactyly type A-1 maps to chromosome 2q35-q36

Brachydactyly type A-1 (BDA1) was, in 1903, the first recorded example of a human anomaly with Mendelian autosomal dominant inheritance. Two large families, the affected members of which were radiographed, were recruited in the study we describe here. Two-point linkage analysis for pedigree 1 (maximum LOD score [Zmax] 6.59 at recombination fraction [theta] 0.00) and for pedigree 2 (Zmax=5.53 at straight theta=0.00) mapped the locus for BDA1 in the two families to chromosome 2q. Haplotype analysis of pedigree 1 confined the locus for family 1 within an interval of <8.1 cM flanked by markers D2S2248 and D2S360, which was mapped to chromosome 2q35-q36 on the cytogenetic map. Haplotype analysis of pedigree 2 confined the locus for family 2 within an interval of <28. 8 cM flanked by markers GATA30E06 and D2S427, which was localized to chromosome 2q35-q37. The two families had no identical haplotype within the defined region, which suggests that the two families were not related.     

Localization of the gene for fibrodysplasia ossificans progressiva (FOP) to chromosome 17q21-22

Fibrodysplasia ossificans progressiva (FOP) is a very rare disease characterized by congenital malformation of the great toes and progressive heterotopic ossification of muscles. To identify the chromosomal localization of the FOP gene, we conducted a genomewide linkage analysis using seven affected families. The FOP phenotype is linked to markers located in the 17q21-22 region (LOD score of 3.41 at the recombination fraction theta = 0). Crossover events localize the putative FOP gene within a 12cM interval, bordered proximally by D17S809 and distally by D17S1838. Noggin (NOG) gene, located in 17q22, is an excellent candidate gene for FOP.     

A locus for autosomal dominant colobomatous microphthalmia maps to chromosome 15q12-q15

Congenital microphthalmia is a common developmental ocular disorder characterized by shortened axial length. Isolated microphthalmia is clinically and genetically heterogeneous and may be inherited in an autosomal dominant, autosomal recessive, or X-linked manner. Here, we studied a five-generation family of Sephardic Jewish origin that included 38 members, of whom 7 have either unilateral or bilateral microphthalmia of variable severity inherited as an autosomal dominant trait with incomplete penetrance. After exclusion of several candidate loci, we performed a genome-scan study and demonstrated linkage to chromosome 15q12-q15. Positive LOD scores were obtained with a maximum at the D15S1007 locus (maximum LOD score 3.77, at recombination fraction 0.00). Haplotype analyses supported the location of the disease-causing gene in a 13.8-cM interval between loci D15S1002 and D15S1040.     

A locus for an axonal form of autosomal recessive Charcot-Marie-Tooth disease maps to chromosome 1q21.2-q21.3.

Charcot-Marie-Tooth disease (CMT) is a heterogeneous group of disorders that affect the peripheral nervous system. Three loci are known for the autosomal dominant forms of axonal CMT (CMT2), but none have yet been identified for autosomal recessive axonal CMT (ARCMT2). We have studied a large consanguineous Moroccan ARCMT2 family with nine affected sibs. The onset of CMT was in the 2d decade in all affected individuals who presented with a severe motor and sensory neuropathy, with proximal muscle involvement occurring in some patients. After exclusion of known loci for CMT2 and for demyelinating ARCMT2, a genomewide search was performed. Evidence for linkage was found with markers on chromosome 1q. The maximum pairwise LOD score was above the threshold value of 3.00, for markers D1S514, D1S2715, D1S2777, and D1S2721, and it reached 6.10 at the loci D1S2777, D1S2721, and D1S2624, according to multipoint LOD-score analysis. These markers defined a region of homozygosity that placed the gene in a 4.4-cM interval. Moreover, a recombination event detected in an unaffected 48-year-old individual excludes the D1S506 marker, thereby reducing the interval to 1.7 cM. In addition, the P0 gene, an attractive candidate because of both its location on chromosome 1q and its role in myelin structure, was excluded by physical mapping and direct sequencing.     

Deletion and linkage mapping of eight markers from the proximal short arm of chromosome 6

Eight chromosome 6p markers (MUT, D6S4, D6S5, D6S19, D6S29, PIM, HLA, and F13A) were regionally mapped using somatic cell hybrid deletion cell lines that retained different regions of chromosome 6p. New restriction fragment length polymorphisms were identified at the D6S5 and PIM loci using newly isolated genomic clones at these loci. Genetic linkage among the eight loci was determined using the 40 CEPH reference families. Linkage analyses showed that these loci are in one linkage group spanning 48 cM in males and 128 cM in females. Using both the deletion mapping data and multipoint linkage analyses, chromosomal order for these loci was determined as centromere-(MUT, D6S4)-(D6S5, D6S19)-(D6S29, PIM)-HLA-F13-A-telomere. Analyses of sex-specific recombination frequencies revealed a higher rate of recombination in females in the region between D6S4 and D6S29, while the recombination rate in males was higher for the interval between D6S29 and the HLA loci.     

Further localization of a gene for paroxysmal dystonic choreoathetosis to a 5-cM region on chromosome 2q34

Paroxysmal dystonic choreoathetosis (PDC) is a rare neurological disorder characterized by episodes of involuntary movement, involving the extremities and face, which may occur spontaneously or be precipitated by caffeine, alcohol, anxiety, and fatigue. PDC is transmitted as an autosomal dominant trait with incomplete penetrance. A gene implicated in this paroxysmal disorder has been mapped to a 10–15 cM region on chromosome 2q31–36 in two families. We describe a third family with PDC. Two-point linkage analyses with markers linked to the candidate PDC locus were performed. A maximum two-point LOD score of 4.20 at a recombination fraction of zero was obtained for marker D2S120, confirming linkage to the distal portion of chromosome 2q. The anion exchanger gene, SLC2C, maps to this region, but the family was poorly informative for polymorphic markers within and flanking this candidate gene. Haplotype analysis revealed a critical recombination event that confines the PDC gene to a 5-cM region bounded by the markers D2S164 and D2S377. We compared the haplotype in our family with that in another chromosome 2-linked PDC family, but did not detect a region of shared genotypes. However, identifying a third family whose disease maps to the same region and narrowing the critical region will facilitate identification of the 2q-linked PDC gene. Received: 10 June 1997 / Accepted: 17 September 1997     

Physical mapping of probes within 14q32, a subtelomeric region showing a high recombination frequency

The genetic linkage map of chromosome 14q32 contains 11 loci which span a distance of more than 60 cM. We have assigned 10 of these loci and the AKT1 proto-oncogene to segments of 14q32, using breakpoints derived from four independent chromosomal deletions or rearrangements. The most telomeric breakpoint was found in a proband (HSC 6) carrying a ring-14 chromosome. HSC 6 is monosomic for the distal part of 14q32, which contains the immunoglobulin heavy-chain locus (IGH), and random markers D14S20, D14S19, and D14S23. Two other chromosomal breakpoints, found in probands HSC 121 and HSC 981, could not be distinguished from each other using DNA probes, although the cytogenetic breakpoints appeared to be different at 14q32.32 and 14q32.31, respectively. The region between the breakpoints of HSC 6 and HSC 121 contains AKT1, D14S1, D14S17, and D14S16. The entire telomeric band 14q32 is assumed to contain about 10% of chromosome 14, or approximately 10 Mb. The 8 most telomeric loci, including D14S1, map to 14q32.32-qter, which measures only several megabases. However, these loci span a genetic distance of 23 cM. The high recombination frequency contrasts with the observation that two of the gamma genes in the IGH constant region show a high degree of linkage disequilibrium, though 180 kb apart. This finding suggests that a telomeric localization per se does not lead to a higher recombination frequency and favors the hypothesis that the higher recombination frequency at the telomeres may be due to specific "hot spots" for recombination.     

Confirmation of linkage to 1q21-31 in a Danish autosomal dominant juvenile-onset glaucoma family and evidence of genetic heterogeneity

Autosomal dominant juvenile-onset open-angle glaucoma has been mapped to 1q21-31 in a number of American families. Our study confirms linkage in a Danish five-generation dominant juvenile-onset glaucoma family with a maximum two-point lod score of 6.67 at the D1S210 locus. Multipoint linkage analysis in a nine-generation Swedish family with dominant juvenile-onset glaucoma and iris hypoplasia excludes linkage to the region of approximately 18 cM between loci D1S104 and D1S218, shown to contain the previously mapped glaucoma gene. This study thus provides support for genetic heterogeneity with respect to dominant juvenile-onset glaucoma.