Consistent linkage of dominantly inherited osteogenesis imperfecta to the type I collagen loci: COL1A1 and COL1A2

The segregation of COL1A1 and COL1A2, the two genes which encode the chains of type I collagen, was analyzed in 38 dominant osteogenesis imperfecta (OI) pedigrees by using polymorphic markers within or close to the genes. This was done in order to estimate the consistency of linkage of OI genes to these two loci. None of the 38 pedigrees showed evidence of recombination between the OI gene and both collagen loci, suggesting that the frequency of unlinked loci in the population must be low. From these results, approximate 95% confidence limits for the proportion of families linked to the type I collagen genes can be set between .91 and 1.00. This is high enough to base prenatal diagnosis of dominantly inherited OI on linkage to these genes even in families which are too small for the linkage to be independently confirmed to high levels of significance. When phenotypic features were compared with the concordant collagen locus, all eight pedigrees with Sillence OI type IV segregated with COL1A2. On the other hand, Sillence OI type I segregated with both COL1A1 (17 pedigrees) and COL1A2 (7 pedigrees). The concordant locus was uncertain in the remaining six OI type I pedigrees. Of several other features, the presence or absence of presenile hearing loss was the best predictor of the mutant locus in OI type I families, with 13 of the 17 COL1A1 segregants and none of the 7 COL1A2 segregants showing this feature.     

Mapping autosomal recessive vitamin D dependency type I to chromosome 12q14 by linkage analysis.

Linkage analysis in French-Canadian families with vitamin D dependency type I (VDD1) demonstrated that the gene responsible for the disease is linked to polymorphic RFLP markers in the 12q14 region. We studied 76 subjects in 14 sibships which included 17 affected individuals and 17 obligate heterozygotes. Significant results for linkage were obtained with the D12S17 locus at the male recombination fraction (theta m) .018 (Z[theta m theta f] = 3.20) and with D126 at (theta m = .025 (Z[theta m theta f] = 3.07). Multipoint linkage analysis and studies of haplotypes and recombinants strongly suggest the localization of the VDD1 locus between the collagen type II alpha 1 (COL2A1) locus and clustered loci D12S14, D12S17, and D12S6, which segregate as a three-marker haplotype. Linkage disequilibrium between VDD1 and this three-marker haplotype supports the notion of a founder effect in the studied population. The current status of the localization of the disease allows for carrier detection in the families at risk.     

A gene for Usher syndrome type I (USH1A) maps to chromosome 14q.

Usher syndrome (US) is an autosomal recessive disease characterized by congenital hearing impairment and retinitis pigmentosa. It is the most frequent cause of deaf-blindness in adults and accounts for 3 to 6% of deaf children. Here, we report the genetic mapping of a gene for US type I (USH1A), the most severe form of the disease, to the long arm of chromosome 14, by linkage to probe MLJ14 at the D14S13 locus in 10 families of Western France ancestry (Z = 4.13 at theta = 0). Among them, 8 families originated from a small area of the Poitou-Charentes region (Z = 3.78 at theta = 0), suggesting that a founder effect could be involved. However, since not all US type I families were found to be linked to this locus, the present study provides evidence for genetic heterogeneity of this condition (heterogeneity versus homogeneity test HOMOG, P < 0.05; heterogeneity versus no linkage, P < 0.01).     

Molecular heterogeneity in the mild autosomal dominant forms of osteogenesis imperfecta.

Mild osteogenesis imperfecta (OI type I and OI type IV) is characterized by postnatal onset of fractures, absence of skeletal deformity, presenile hearing loss with or without blue sclerae, and dentinogenesis imperfecta. Using one common DNA polymorphism associated with the pro alpha 2(I) human collagen gene, we found genetic heterogeneity in this disorder. In three families, the OI phenotype segregated independently of the DNA polymorphism, whereas in one family, the OI phenotype cosegregated with a DNA polymorphism in a manner suggesting linkage. Use of DNA polymorphisms associated with both type I procollagen genes should provide a tool to unravel the molecular heterogeneity of various heritable disorders of the connective tissue.     

Confirmation and refinement of the genetic localization of the Coffin-Lowry syndrome locus in Xp22.1-p22.2

The Coffin-Lowry syndrome (CLS) is an X-linked inherited disease of unknown pathogenesis characterized by severe mental retardation, typical facial and digital anomalies, and progressive skeletal deformations. Our previous linkage analysis, based on four pedigrees with the disease, suggested a localization for the CLS locus in Xp22.1-p22.2, with the most likely position between the marker loci DXS41 and DXS43. We have now extended the study to 16 families by using seven RFLP marker loci spanning the Xp22.1-p22.2 region. Linkage has been established with five markers from this part of the X chromosome: DXS274 (lod score [Z] (theta) = 3.53 at theta = .08), DXS43 (Z(theta) = 3.16 at theta = .08), DXS197 (Z(theta) = 3.03 at theta = .05), DXS41 (Z(theta) = 2.89 at theta = .08), and DXS207 (Z(theta) = 2.73 at theta = .13). A multipoint linkage analysis further placed, with a maximum multipoint Z of 7.30, the mutation-causing CLS within a 7-cM interval defined by the cluster of tightly linked markers (DXS207-DXS43-DXS197) on the distal side and by DXS274 on the proximal side. Thus, these further linkage data confirm and refine the map location for the gene responsible for CLS in Xp22.1-p22.2. As no linkage heterogeneity was detected, this validates the use of the Xp22.1-p22.2 markers for carrier detection and prenatal diagnosis in CLS families.     

Detection of a high frequency RsaI polymorphism in the human pro alpha 2(I) collagen gene which is linked to an autosomal dominant form of osteogenesis imperfecta.

Screening of the pro alpha 2(I) collagen genes of Southern African populations for restriction fragment length polymorphisms (RFLPs) has revealed a locus polymorphic for the restriction enzyme RsaI. The frequency of the RFLP was 0.38 in Afrikaners, but much lower in indigenous Southern African populations, which suggests that it is of European origin. The polymorphism was used to study 19 affected and non-affected individuals in a four generation family with the autosomal dominant disorder, osteogenesis imperfecta (OI) type I. Co-inheritance of the loss of the RsaI site and the OI phenotype was observed with a lod score of 3.91 at a recombination fraction (theta) of zero, indicating strong linkage. This suggests that the defect in this family is caused by a structural mutation within or close to the pro alpha 2(I) collagen gene. The use of this high frequency RFLP together with other recently described polymorphisms at this locus will facilitate the analysis of the role of this gene in OI and other inherited disorders of connective tissue.     

Identification and molecular characterization of two novel mutations in COL1A2 in two Chinese families with osteogenesis imperfecta

Osteogenesis imperfecta (OI, also known as brittle bone disease) is caused mostly by mutations in two type Ⅰ collagen genes, COL1A1 and COL1A2 encoding the pro-α1 (Ⅰ) and pro-α2 (Ⅰ) chains of type Ⅰ collagen, respectively. Two Chinese families with autosomal dominant OI were identified and characterized. Linkage analysis revealed linkage of both families to COL1A2 on chromosome 7q21.3-q22.1. Mutational analysis was carried out using direct DNA sequence analysis. Two novel missense mutations, c.3350A＞G and c.3305G＞C, were identified in exon 49 of COL1A2 in the two families, respectively. The c.3305G＞C mutation resulted in substitution of a glycine residue (G) by an alanine residue (A) at codon 1102 (p.G1102A), which was found to be mutated into serine (S), argine (R), aspartic acid (D), or valine (V) in other families. The c.3350A＞G variant may be a de novo mutation resulting in p.Y1117C. Both mutations co-segregated with OI in respective families, and were not found in 100 normal controls. The G1102 and Y1117 residues were evolutionarily highly conserved from zebrafish to humans. Mutational analysis did not identify any mutation in the COX-2 gene (a modifier gene of OI). This study identifies two novel mutations p.G1102A and p.Y1117C that cause OI, significantly expands the spectrum of COL1A2 mutations causing OI, and has a significant implication in prenatal diagnosis of OI.     

Exclusion of linkage between the human apolipoprotein B gene and abetalipoproteinemia

Abetalipoproteinemia (ABLP) is a rare autosomal recessive disease characterized by a lack of plasma apolipoprotein B (apo B). In this report, the hypothesis that ABLP is due to rare mutations in the apo B gene was tested. A total of eight ABLP families were studied. Apo B gene RFLPs were used to establish the haplotypes of the apo B alleles in family members. LOD score analysis was used to study the linkage between the apo B alleles and ABLP. These families were categorized arbitrarily as class I, II, III, or IV because of differences in the results derived from both haplotyping and LOD score analysis. In a class I family, affected siblings, who on the basis of the hypothesis would be expected to have the same apo B alleles, had different ones. LOD score analysis of this family gave an infinite negative number at a recombination fraction (theta) of zero. In two class II families, probands who were the result of consanguineous marriages and who, on the basis of the hypothesis, should be homozygotes for a defective apo B allele, were heterozygotes at this locus. The sum of the LOD scores from these two families was -1.7 at theta = 0. In one class III family, a parent was apparently homozygous for a particular apo B allele and yet not affected. This also contributed negatively to the LOD score. In four class IV families, disease inheritance was compatible with segregation of the apo B alleles. This, however, was not statistically significant (LOD score = 0.97 at theta = 0).(ABSTRACT TRUNCATED AT 250 WORDS)     

The gene for X-linked hydrocephalus maps to Xq28, distal to DXS52.

We report the study of five independent X-linked hydrocephalus (HSAS1) families with polymorphic DNA markers of the Xq28 region. A total of 58 individuals, including 7 living affected males and 22 obligate carriers, have been studied. Maximum lod score was 7.21 at theta = 2.40% for DXS52 (St14-1). A single recombination event was observed between this marker and the HSAS1 locus. Other markers studied were DXS296 (Z = 2.02 at theta = 2.5%), DXS304 (Z = 4.37 at theta = 7.8%), DXS74 (Z = 3.50 at theta = 0%), DXS15 (Z = 1.96 at theta = 5.7%), DXS134 (Z = 3.31 at theta = 0%), and F8C (Z = 5.79 at theta = 0%). These data confirm the localization of the HSAS1 gene to Xq28 and provide evidence for genetic homogeneity of this syndrome. In addition, examination of two obligate recombinant meioses along with multipoint linkage analysis supports the distal localization of the HSAS1 locus with respect to the DXS52 cluster. These observations are of potential interest for future studies aimed at HSAS1 gene characterization.     

Two pregnancies after preimplantation genetic diagnosis for osteogenesis imperfecta type I and type IV

Osteogenesis imperfecta (OI) is an autosomal dominant genetic disorder characterized by the presence of brittle bones and decreased bone mass (osteopenia), as a result of mutations in the genes that encode the chains of type I collagen, the major protein of bone. The clinical features of the disease range from death in the perinatal period to normal life span with minimal increase in fractures. The present report describes two polymerase chain reaction (PCR)-based assays allowing preimplantation genetic diagnosis (PGD) on the one hand for OI type I, the mildest form, and on the other hand for OI type IV, which is intermediate in severity between OI type I and OI type III. In the couple referred for PGD for OI type I, the female partner carried a 1-bp deletion in exon 43 of the COL1A1 gene, resulting in a premature stop codon in exon 46. The synthesis of too little type I procollagen results from such a non-functional or COL1A1 null allele. In the other couple, referred for PGD for OI type IV, the male partner carried a G to A substitution in exon 19 of the COL1A2 gene, which results in an abnormal gene product due to an alphaGly247 (GGT) to Ser (AGT) substitution (G247S). Both mutations result in the loss of a specific restriction enzyme recognition site and can therefore be detected by PCR amplification followed by restriction fragment analysis. PCR amplification of genomic DNA of the parents-to-be with one of the two primers fluorescently labelled, followed by automated laser fluorescence (ALF) gel electrophoresis of the amplified and restricted fragments, allowed a distinction between the healthy and affected genotypes. PCR on single Epstein-Barr-virus (EBV)-transformed lymphoblasts resulted in acceptable amplification efficiencies (87% and 85% for OI type I and OI type IV respectively) and the allele drop-out (ADO) rate was assessed at 11.5% and 11.1% for OI type I and OI type IV respectively. With research blastomeres, 100% amplification rates were obtained and no contamination was observed in the blank controls, which validated the tests for clinical application. Embryos obtained after intracytoplasmic sperm injection (ICSI) were evaluated for the presence of the normal genotype of the non-affected parent. For OI type I, two frozen-thawed ICSI-PGD cycles and two fresh ICSI-PGD cycles were carried out for the same couple. The transfer of two unaffected embryos in the last cycle resulted in a twin pregnancy. A twin pregnancy was also achieved in one clinical ICSI-PGD cycle for OI type IV.     

A gene locus responsible for dyschromatosis symmetrica hereditaria (DSH) maps to chromosome 6q24.2-q25.2

Dyschromatosis symmetrica hereditaria (DSH) is a hereditary skin disease characterized by the presence of hyperpigmented and hypopigmented macules on extremities and face. The gene, or even its chromosomal location, for DSH has not yet been identified. In this study, two Chinese families with DSH were identified and subjected to a genomewide screen for linkage analysis. Two-point linkage analysis for pedigree A (maximum LOD score [Z(max)] = 7.28 at recombination fraction [theta] = 0.00) and pedigree B (Z(max) = 2.41 at theta = 0.00) mapped the locus for DSH in the two families to chromosome 6q. Subsequent multipoint analysis of the two families also provided additional support for the DSH gene being located within the region 6q24.2-q25.2, with Z(max) = 10.64. Haplotype analysis confined the locus within an interval of 10.2 Mbp, flanked by markers D6S1703 and D6S1708. The two families had no identical haplotype within the defined region, which suggests that the two families were different in origin. Further work on identification of the gene for DSH will open new avenues to exploration of the genetics of pigmentation.     

Resolution of the two loci for autosomal dominant aniridia, AN1 and AN2, to a single locus on chromosome 11p13.

Two distinct loci have been proposed for aniridia; AN1 for autosomal dominant aniridia on chromosome 2p and AN2 for the aniridia in the WAGR contiguous gene syndrome on chromosome 11p13. In this report, the kindred segregating for autosomal dominant aniridia, which suggested linkage to acid phosphatase-1 (ACP1) and led to the assignment of the AN1 locus on chromosome 2p, has been updated and expanded. Linkage analysis between the aniridia phenotype and ACP1 does not support the original linkage results, excluding linkage up to theta = 0.17 with Z = -2. Tests for linkage to other chromosome 2p markers. APOB, D2S71, D2S5, and D2S1, also excluded linkage to aniridia. Markers that have been isolated from the chromosome 11p13 region were then analyzed in this aniridia family. Two RFLPs at the D11S323 locus give significant evidence for linkage. The PvuII polymorphism detected by probe p5S1.6 detects no recombinants, with a maximum lod score of Z = 6.97 at theta = 0.00. The HaeIII polymorphism detected by the probe p5BE1.2 gives a maximum lod score of Z = 2.57 at theta = 0.00. Locus D11S325 gives a lod score of Z = 1.53 at theta = 0.00. These data suggest that a locus for aniridia (AN1) on chromosome 2p has been misassigned and that this autosomal dominant aniridia family is segregating for an aniridia mutation linked to markers in the 11p13 region.     

A genetic study of Gardner syndrome and congenital hypertrophy of the retinal pigment epithelium.

Gardner Syndrome (GS) is an autosomal dominant variant of colorectal polyposis with essentially complete penetrance. It is distinguished from the other polyposis syndromes by its delayed age at onset, the number of polyps, and its extracolonic manifestations. The presence of epidermal cysts, bony osteomata, desmoid tumors, and dental anomalies are distinguishing features of this syndrome. Recently, multiple and bilateral patches of congenital hypertrophy of the retinal pigment epithelium (CHRPE) have been described in three families with classical GS. Tight linkage of the GS and CHRPE phenotypes (Z = 9.752; theta = 0) suggested that CHRPE is a pleiotropic effect of the Gardner mutation within the families in which the ophthalmic trait occurs and is thus a useful marker for the early detection of GS gene carriers. We have analyzed six new families segregating for classic GS and CHRPE. Linkage was tested between GS and CHRPE and between these two phenotypes and a battery of 22 informative biochemical and serological markers. We have extended the linkage analysis on two GS-CHRPE families originally reported elsewhere. Linkage between GS and CHRPE at theta = 0 was observed in all families, a result supporting our original suggestion that CHRPE is a congenital manifestation of the GS mutation. Exclusionary linkage data presented confirm that, for linkage analysis in these families, the CHRPE phenotype is a more powerful marker than other phenotypic features of GS.     

Genetic analysis of multiply-affected families of insulin-dependent diabetes mellitus (IDDM) probands

The present study combines segregation and linkage information on 30 families ascertained through a proband and a first degree relative affected with insulin-dependent diabetes mellitus (IDDM). An autosomal dominant model with incomplete penetrance was much more likely to fit the family data than a recessive model, whether or not linkage to HLA was assumed. The lod scores for linkage to HLA were 2.46 at theta M = theta F = 0.00 for dominant and 1.45 at theta M = theta F = 0.22 for a recessive model. The results are discussed in light of heterogeneity in likelihood and lod scores when the families are grouped by familial types, which indicate that the increase in likelihood of a dominant hypothesis can be attributed to the parent-child families and not the sib-sib families.     

Microsatellite-based fine mapping of the Van der Woude syndrome locus to an interval of 4.1 cM between D1S245 and D1S414.

Van der Woude syndrome (VWS) is an autosomal dominant craniofacial disorder characterized by lip pits, clefting of the primary or secondary palate, and hypodontia. The gene has been localized, by RFLP-based linkage studies, to region 1q32-41 between D1S65-REN and D1S65-TGFB2. In this study we report the linkage analysis of 15 VWS families, using 18 microsatellite markers. Multipoint linkage analysis places the gene, with significant odds of 2,344:1, in a 4.1-cM interval flanked by D1S245 and D1S414. Two-point linkage analysis demonstrates close linkage of VWS with D1S205 (lod score [Z] = 24.41 at theta = .00) and with D1S491 (Z = 21.23 at theta = .00). The results revise the previous assignment of the VWS locus and show in an integrated map of the region 1q32-42 that the VWS gene resides more distally than previously suggested. When information about heterozygosity of the closely linked marker D1S491 in the affected members of the VWS family with a microdeletion is taken into account, the VWS critical region can be further narrowed, to the 3.6-cM interval between D1S491 and D1S414.     

The mutation for medullary thyroid carcinoma with parathyroid tumors (MTC with PTs) is closely linked to the centromeric region of chromosome 10.

Two new morphs (F and G) detected by the centromeric alpha satellite probe p alpha 10RP8 and D10Z1 in HinfI digests are linked to the PstI polymorphisms of D10Z1, confirming their chromosome 10 location. The F and G morphs were in strong linkage disequilibrium with each other but were in weak linkage disequilibrium with the A and B morphs defined in PstI digests. Data for haplotypes formed by using the A and F morphs improved the lod score for linkage between the disease locus for multiple endocrine neoplasia type 2A (MEN2A) and D10Z1 (Z = 14.06 at theta = 0) in the six large families studied by Wu et al. Furthermore, the locus that codes for a distinct phenotype, medullary thyroid carcinoma (MTC) with parathyroid tumors (PTs) and no pheochromocytomas (PHEOs) (referred to as MTC with PTs), in one of the families was closely linked to two markers, D10Z1 and RBP3, with lodscores of 2.86 and 3.54, respectively, at theta = 0. A possible allelic association was noted between disease phenotypes and centromeric haplotypes. The phenotype MTC and PHEOs with and without PTs was associated with the same relatively common centromeric haplotype (A + B-F-G-) in the four families in which all four morphs could be determined, while the phenotype MTC with PTs was associated with the rare centromeric haplotype (A-B-F-G+) in one family.     

Genetic linkage of Francois-Neetens fleck (mouchetée) corneal dystrophy to chromosome 2q35

Francois-Neetens fleck (mouchetée) corneal dystrophy is an autosomal dominant corneal dystrophy characterized by scattered small white flecks occurring at all levels of the corneal stroma. We report linkage of the CFD locus to D2S2289 (Z(max)=4.46, theta=0), D2S325 (Z(max)=3.28, theta=0), D2S317 (Z(max)=3.1, theta=0), D2S143 (Z(max)=3.8, theta=0.03), and D2S2382 (Z(max)=5.0, theta=0) on chromosome 2q35. Multipoint analysis confirmed linkage to the region between D2S117 and D2S126 with a maximum multipoint lod score of 5.0 located midway between D2S2289 and D2S325. Analysis of CFD in these same families assuming a 90% penetrance increased the maximum lod score to 6.28 at D2S157.     

Heterogeneity in X-linked recessive Charcot-Marie-Tooth neuropathy.

Three families presenting with X-linked recessive Charcot-Marie-Tooth neuropathies (CMT) were studied both clinically and genetically. The disease phenotype in family 1 was typical of CMT type 1, except for an infantile onset; two of five affected individuals were mentally retarded, and obligate-carrier females were unaffected. Families 2 and 3 showed distal atrophy with weakness, juvenile onset, and normal intelligence. Motor-nerve conduction velocities were significantly slowed, and electromyography data were consistent with denervation in affected CMT males in all three families. Thirty X-linked RFLPs were tested for linkage studies against the CMT disease loci. Family 1 showed tight linkage (recombination fraction [theta] = 0) to Xp22.2 markers DXS16, DXS143, and DXS43, with peak lod scores of 1.75, 1.78, and 2.04, respectively. A maximum lod score of 3.48 at DXS16 (theta = 0) was obtained by multipoint linkage analysis of the map DXS143-DXS16-DXS43. In families 2 and 3 there was suggestion of tight linkage (theta = 0) to Xq26 markers DXS86, DXS144, and DXS105, with peak lod scores of 2.29, 1.33, and 2.32, respectively. The combined maximum multipoint lod score of 1.81 at DXS144 (theta = 0) for these two families occurred in the map DXS10-DXS144-DXS51-DXS105-DXS15-DXS52++ +. A joint homogeneity analysis including both regions (Xp22.2 and Xq26-28) provided evidence against homogeneity (chi 2 = 9.12, P less than .005). No linkage to Xp11.12-q22 markers was observed, as was reported for X-linked dominant CMT and the Cowchock CMT variant. Also, the chromosomes 1 and 17 CMT loci were excluded by pairwise linkage analysis in all three families.     

Evidence for the localization of a malignant hyperthermia susceptibility locus (MHS2) to human chromosome 17q.

Malignant hyperthermia susceptibility is a lethal autosomal dominant disorder of skeletal muscle metabolism that is triggered by all potent inhalation anesthetic gases. Recent linkage studies suggest a genetic locus for this disorder on 19q13.1. We have previously reported three unrelated families diagnosed with MHS that are unlinked to markers surrounding this locus on 19q13.1. In this report we extend these observations and present linkage studies on 16 MHS families. Four families (25%) were found linked to the region 19q12-q13.2 (Zmax = 2.96 with the ryanodine receptor at theta = 0.0). Five families (31%) were found closely linked to the anonymous marker NME1 (previously designated NM23) on chromosome 17q11.2-q24 (Zmax = 3.26 at theta = 0.0). Two families (13%) were clearly unlinked to either of these chromosomal regions. In five additional families, data were insufficient to determine their linkage status (they were potentially linked to two or more sites). The results of our heterogeneity analyses are consistent with the hypothesis that MHS can be caused in humans by any one of at least three distinct genetic loci. Furthermore, we provide preliminary linkage data suggesting the localization of a gene in human MHS to 17q11.2-q24 (MHS2), with a gene frequency of this putative locus approximately equal to that of the MHS1 locus on 19q.     

Dental findings in osteogenesis imperfecta: I. Occurrence and expression of type I dentinogenesis imperfecta

Sixty-eight patients with osteogenesis imperfecta (OI) classified according to Sillence were evaluated for dentinogenesis imperfecta (DI). Orthopantomograms of 51 of the 68 were examined. Type I DI was recognized in 22 patients from 16 families. DI was observed in 4/45 patients with type I OI, in one of two patients with type III, and in 13/16 patients with type IV OI. Four of the five patients with an unidentified type of OI had DI. The expression of type I DI was variable. Discoloration and pulpal obliteration were the major manifestations. Teeth from 14 patients from 12 families were studied histologically. Eight of the 14 patients were from six families who had clinical and/or radiographic evidence of DI. Irregularity of the dentin matrix and tubular pattern in the circumpulpal dentin and normal mantle dentin were observed. Interfamilial variability was greater than intrafamilial variability. The expression of DI was mild in one family with type I OI. There was no further relation between the type of OI and the severity of DI.