Exclusion of COL2A1 as a candidate gene in a family with Wagner-Stickler syndrome

Multimodal Retinal Imaging Findings in Two Cousins With VCAN-Related Vitreoretinopathy or Wagner Disease

Wagner disease is a rare, nonsyndromic vitreoretinopathy caused by autosomal dominant variants in the versican (VCAN) gene. It is associated with abnormalities of the vitreoretinal interface that can lead to peripheral traction and retinal detachments, which also occur in other vitreoretinopathies such as X-linked retinoschisis (XLRS), familial exudative vitreoretinopathy (FEVR) and Stickler syndrome. There is variability in the clinical phenotype in Wagner disease potentially due to variants in VCAN gene variants. In this article, we report a family harboring the VCAN c.9265+1G>C variant and describe the clinical and retinal findings in two members. [Ophthalmic Surg Lasers Imaging Retina 2022;53:639-643.].

Spectral-Domain Optical Coherence Tomography in Wagner Syndrome: Characterization of Vitreoretinal Interface and Foveal Changes

PURPOSE

To evaluate the spectrum of morphologic abnormalities in patients with Wagner syndrome by spectral-domain optical coherence tomography (SD OCT).

DESIGN

Retrospective comparative case study.

METHODS

Institutional study of patients entered into the French Vitreoretinopathy Study Group database. Twelve eyes of 9 patients from 3 unrelated families with genetically confirmed Wagner syndrome and 28 eyes from 15 age- and sex-matched healthy family controls were scanned by SD OCT. Morphology and layer thickness of the total retina, inner retinal layers, outer retinal layers, and photoreceptor layer at different degrees of eccentricity from the fovea were compared between the 2 groups.

RESULTS

A thick multilayered membrane adherent to the perifovea but completely detached from the fovea, thus forming a bridge over the foveal pit, was observed in 84% of eyes from patients with Wagner syndrome. At the equatorial area, SD OCT imaging allowed visualization of the architecture of an avascular vitreous veil with localized retinal traction. Most retinal layers were significantly thinner in patients with Wagner syndrome compared to the control group, except at the foveal center where abnormal persistence of 1 or more inner retinal layers could be observed.

CONCLUSION

SD OCT provides better structural insight into the range of retinal defects at the vitreoretinal interface and fovea, which is not only useful for improving diagnosis and management, but also for understanding the pathogenesis of Wagner syndrome.

Congenital glaucoma in Wagner syndrome

Wagner syndrome is a rare inherited vitreoretinopathy. We describe 3 related patients with Wagner syndrome who presented with congenital glaucoma at age 3 months and required multiple surgical interventions to control their intraocular pressure. All experienced visual loss and glaucomatous optic neuropathy.

A family with Wagner syndrome with uveitis and a new versican mutation

PURPOSE

To report the clinical and molecular findings of a kindred with Wagner syndrome (WS) revealed by intraocular inflammatory features.

METHODS

Eight available family members underwent complete ophthalmologic examination, including laser flare cell meter measurements. Collagen, type II, alpha 1, versican (VCAN), frizzled family receptor 4, low density lipoprotein receptor-related protein 5, tetraspanin 12, and Norrie disease (pseudoglioma) genes were screened with direct sequencing.

RESULTS

The index case was initially referred for unexplained severe and chronic postoperative bilateral uveitis following a standard cataract surgery procedure. Clinical examination of the proband revealed an optically empty vitreous with avascular vitreous strands and veils, features highly suggestive of WS. The systematic familial ophthalmologic examination identified three additional unsuspected affected family members who also presented with the WS phenotype, including uveitis for one of them. We identified a novel c.4004-6T>A nucleotide substitution at the acceptor splice site of intron 7 of the VCAN gene that segregated with the disease phenotype.

CONCLUSIONS

We present a family with WS with typical WS features and intraocular inflammatory manifestations associated with a novel splice site VCAN mutation. Beyond the structural role in the retinal-vitreous architecture, versican is also emerging as a pivotal mediator of the inflammatory response, supporting uveitis predisposition as a clinical manifestation of WS.

Novel VCAN mutations and evidence for unbalanced alternative splicing in the pathogenesis of Wagner syndrome

Wagner syndrome (WS) is an autosomal dominant vitreoretinopathy affecting various ocular features and is caused by mutations in the canonical splice sites of the VCAN gene, which encodes the large chondroitin sulfate proteoglycan, versican. We report the identification of novel splice acceptor and donor-site mutations (c.4004-1G>C and c.9265+2T>A) in two large WS families from France and the United Kingdom. To characterize their pathogenic mechanisms we performed qRT-PCR experiments on RNA from patient-derived tissues (venous blood and skin fibroblasts). We also analyzed RNA from the original Swiss family reported by Wagner (who has the previously reported c.9265+1G>A mutation). All three mutations resulted in a quantitative increase of transcript variants lacking exons 7 and/or 8. However, the magnitude of the increase varied between tissues and mutations. We discuss altered balance of VCAN splice variants in combination with reduction in glycosaminoglycan protein modifications as possible pathogenic mechanisms.

Expression of extracellular matrix proteins fibulin-1 and fibulin-2 by human corneal fibroblasts

PURPOSE

The fibulins are a family of extracellular matrix (ECM) molecules that regulate the organ shape along with other growth factors and stromal cells. We report here the in vitro expression of ECM proteins fibulin-1 and fibulin-2 by human corneal fibroblasts. The ability of fibulin-1 to modulate cell motility was investigated.

METHODS

Fibulin-1 and fibulin-2 mRNA and proteins expression were analyzed in primary and immortalized human corneal fibroblasts (CHN) respectively by gene array, RT-PCR, and immunocytochemistry. The motility and adhesion of the cells transfected with fibulin-1 siRNA were analyzed on tissue culture polystyrene coated with Matrigel or ECM secreted by those fibroblasts.

RESULTS

(1) The microarray analysis shows the expression of fibulin-1, fibulin-2, and their binding partners (i.e., fibronectin, nidogen-1, aggrecan, fibrilin-1, endostatin, and laminin alpha-2 chain). Interestingly, a matrix metalloprotease, ADAMTS-1, for which fibulin-1 acts as a cofactor, was also detected in CHN. (2) The synthesis by CHN of fibulin-1 and 2 mRNA and proteins was confirmed respectively by RT-PCR and immunocytochemistry. (3) Transfection of CHN by fibulin-1 siRNA has no effect on cell adhesion but increases cell migration compared with that of the control cells. This observation suggests an important role of fibulin-1 on cell motility.

CONCLUSIONS

The expression of fibulins and that of their binding partners by human corneal fibroblasts indicate the important role of these proteins in the organization of supramolecular ECM structures of cornea. The variation of their expression and the structural changes of fibulins remain to be determined in corneal pathology.

Clinical characterisation and molecular analysis of Wagner syndrome

AIM

To detail the clinical findings in a British family with molecularly characterised Wagner syndrome.

BACKGROUND

Only in the last year has the specific genetic defect in Wagner syndrome been identified, and the background literature of the molecular genetics is outlined. Clinical and laboratory findings in a second case of Wagner syndrome are included to highlight difficulties that can be encountered when identifying pathogenic mutations for disorders arising in complex genes.

METHODS

Mutation screening was performed using PCR and RT-PCR.

RESULTS

A heterozygous mutation was found converting the donor splice site of exon 8 of the chondroitin sulphate proteoglycan 2 (CSPG2). This is the same mutation that has been reported in the original Wagner pedigree. The main clinical features of Wagner syndrome are vitreous syneresis, thickening and incomplete separation of the posterior hyaloid membrane, chorioretinal changes accompanied by subnormal electroretinographic responses, an ectopic fovea and early-onset cataract. A clinical feature present in this family, but previously undescribed, is anterior uveitis without formation of synechiae. Wagner syndrome has a progressive course, resulting in loss of vision even in the absence of retinal detachment.

CONCLUSION

On a background of considerable confusion regarding the distinction between Wagner syndrome and predominantly ocular Stickler syndrome, it is now apparent the that two conditions are both clinically and genetically distinct. This report summarises the clinical findings in Wagner syndrome and extends the phenotypic characteristics.

Collagens and collagen-related matrix components in the human and mouse eye

The three-dimensional structure of the eye plays an important role in providing a correct optical environment for vision. Much of this function is dependent on the unique structural features of ocular connective tissue, especially of the collagen types and their supramolecular structures. For example, the organization of collagen fibrils is largely responsible for transparency and refraction of cornea, lens and vitreous body, and collagens present in the sclera are largely responsible for the structural strength of the eye. Phylogenetically, most of the collagens are highly conserved between different species, which suggests that collagens also share similar functions in mice and men. Despite considerable differences between the mouse and the human eye, particularly in the proportion of the different tissue components, the difficulty of performing systematic histologic and molecular studies on the human eye has made mouse an appealing alternative to studies addressing the role of individual genes and their mutations in ocular diseases. From a genetic standpoint, the mouse has major advantages over other experimental animals as its genome is better known than that of other species and it can be manipulated by the modern techniques of genetic engineering. Furthermore, it is easy, quick and relatively cheap to produce large quantities of mice for systematic studies. Thus, transgenic techniques have made it possible to study consequences of specific mutations in genes coding for structural components of ocular connective tissues in mice. As these changes in mice have been shown to resemble those in human diseases, mouse models are likely to provide efficient tools for pathogenetic studies on human disorders affecting the extracellular matrix. This review is aimed to clarify the role of collagenous components in the mouse and human eye with a closer look at the new findings of the collagens in the cartilage and the eye, the so-called "cartilage collagens".

The Stickler syndrome: genotype/phenotype correlation in 10 families with Stickler syndrome resulting from seven mutations in the type II collagen gene locus COL2A1

PURPOSE

To evaluate a cohort of clinically diagnosed Stickler patients in which the causative mutation has been identified, determine the prevalence of clinical features in this group as a whole and as a function of age, and look for genotype/phenotype correlations.

METHODS

Review of medical records, clinical evaluations, and mutational analyses of clinically diagnosed Stickler patients.

RESULTS

Patients with seven defined mutations had similar phenotypes, though both inter- and intrafamilial variability were apparent and extensive. The prevalence of certain clinical features was a function of age.

CONCLUSION

Although the molecular determination of a mutation can predict the occurrence of Stickler syndrome, the variability observed in the families described here makes it difficult to predict the severity of the phenotype on the basis of genotype.

Variation in the vitreous phenotype of Stickler syndrome can be caused by different amino acid substitutions in the X position of the type II collagen Gly-X-Y triple helix

Stickler syndrome is a dominantly inherited disorder characterized by arthropathy, midline clefting, hearing loss, midfacial hypoplasia, myopia, and retinal detachment. These features are highly variable both between and within families. Mutations causing the disorder have been found in the COL2A1 and COL11A1 genes. Premature termination codons in COL2A1 that result in haploinsufficiency of type II collagen are a common finding. These produce a characteristic congenital "membranous" anomaly of the vitreous of all affected individuals. Experience has shown that vitreous slit-lamp biomicroscopy can distinguish between patients with COL2A1 mutations and those with dominant negative mutations in COL11A1, who produce a different "beaded" vitreous phenotype. Here we characterize novel dominant negative mutations in COL2A1 that result in Stickler syndrome. Both alter amino acids in the X position of the Gly-X-Y triple-helical region. A recurrent R365C mutation occurred in two unrelated sporadic cases and resulted in the membranous vitreous anomaly associated with haploinsufficiency. In a large family with linkage to COL2A1, with a LOD score of 2.8, a unique L467F mutation produced a novel "afibrillar" vitreous gel devoid of all normal lamella structure. These data extend the mutation spectrum of the COL2A1 gene and help explain the basis for the different vitreous phenotypes seen in Stickler syndrome.

Rapid determination of COL2A1 mutations in individuals with Stickler syndrome: analysis of potential premature termination codons

Stickler syndrome is one of the milder phenotypes resulting from mutations in the gene that encodes type-II collagen, COL2A1. All COL2A1 mutations known to cause Stickler syndrome result in the formation of a premature termination codon within the type-II collagen gene. COL2A1 has 10 in-frame CGA codons, which can mutate to TGA STOP codons via a methylation-deamination mechanism. We have analyzed these sites in genomic DNA from a panel of 40 Stickler syndrome patients to test the hypothesis that mutations that cause Stickler syndrome preferentially occur at these bases. Polymerase chain reaction (PCR) amplification of genomic DNA containing each of the in-frame CGA codons was done by one of two methods: either using primers that amplify DNA that includes the CGA codon, or using allele-specific primers that either amplify normal sequence containing a CGA codon or amplify a mutant sequence containing a TGA codon. Analysis of PCR products by restriction endonuclease digestion or sequencing demonstrated the presence of a normal or mutated codon. TGA mutations were identified in eight patients, at five of the 10 in-frame CGA codons. The identification of these mutations in eight of 40 patients demonstrates that these sites are common sites for mutations in individuals with Stickler syndrome and, we propose, should be analyzed as a first step in the search for mutations that result in this disorder.

COL2A1 exon 2 mutations: relevance to the Stickler and Wagner syndromes

AIMS

To compare the clinical and molecular genetic features of two phenotypically distinct subgroups of families with type 1 Stickler syndrome.

BACKGROUND

Stickler syndrome (hereditary arthro-ophthalmopathy, McKusick Nos 108300 and 184840) is a dominantly inherited disorder of collagen connective tissue, resulting in an abnormal vitreous, myopia, and a variable degree of orofacial abnormality, deafness, and arthropathy. Stickler syndrome is the commonest inherited cause of rhegmatogenous retinal detachment in childhood with a risk of giant retinal tear (GRT) which is commonly bilateral and a frequent cause of blindness.

METHOD

Pedigrees were identified from the vitreoretinal service database and subclassified according to vitreoretinal phenotype. Ophthalmic, skeletal, auditory, and orofacial features were assessed. Linkage analysis was carried out with markers for the candidate genes COL2A1, COL11A1, and COL11A2. The COL2A1 gene was amplified as five overlapping PCR products. Direct sequencing of individual exons identified mutations.

RESULTS

Eight families exhibiting the type 1 vitreous phenotype were studied. Seven were consistent for linkage to COL2A1, with lod scores ranging from 2.1 to 0.3. In most instances linkage to COL11A1 and COL11A2 could be excluded. One family was analysed without prior linkage analysis. Three of the families exhibited a predominantly ocular phenotype with minimal or absent systemic involvement and were found to have mutations in exon 2 of COL2A1. Five other pedigrees with an identical ocular phenotype plus orofacial, auditory, and articular involvement had mutations in others regions of the COL2A1 gene. None of the pedigrees exhibited the characteristic lenticular, retinal pigment epithelial, or choroidal changes seen in Wagner syndrome.

CONCLUSIONS

These data confirm that type 1 Stickler syndrome is caused by mutations in the gene encoding type II collagen (COL2A1). In addition, data are submitted showing that mutations involving exon 2 of COL2A1 are characterised by a predominantly ocular variant of this disorder, consistent with the major form of type II procollagen in non-ocular tissues having exon 2 spliced out. Such patients are all at high risk of retinal detachment. This has important implications for counselling patients with regard to the development of systemic complications. It also emphasises the importance and reliability of the ophthalmic examination in the differential diagnosis of this predominantly ocular form of Stickler syndrome from Wagner's vitreoretinopathy.

Clinical and Molecular genetics of Stickler syndrome

Stickler syndrome is an autosomal dominant disorder with characteristic ophthalmological and orofacial features, deafness, and arthritis. Abnormalities of vitreous gel architecture are a pathognomonic feature, usually associated with high myopia which is congenital and non-progressive. There is a substantial risk of retinal detachment. Less common ophthalmological features include paravascular pigmented lattice degeneration and cataracts. Non-ocular features show great variation in expression. Children with Stickler syndrome typically have a flat midface with depressed nasal bridge, short nose, anteverted nares, and micrognathia. These features can become less pronounced with age. Midline clefting, if present, ranges in severity from a cleft of the soft palate to Pierre-Robin sequence. There is joint hypermobility which declines with age. Osteoarthritis develops typically in the third or fourth decade. Mild spondyloepiphyseal dysplasia is often apparent radiologically. Sensorineural deafness with high tone loss may be asymptomatic or mild. Occasional findings include slender extremities and long fingers. Stature and intellect are usually normal. Mitral valve prolapse was reported to be a common finding in one series but not in our experience. The majority of families with Stickler syndrome have mutations in the COL2A1 gene and show the characteristic type 1 vitreous phenotype. The remainder with the type 2 vitreous phenotype have mutations in COL11A1 or other loci yet to be identified. Mutations in COL111A2 can give rise to a syndrome with the systemic features of Stickler syndrome but no ophthalmological abnormality.

Clinical and molecular genetics of Stickler syndrome

Stickler syndrome is an autosomal dominant disorder with characteristic ophthalmological and orofacial features, deafness, and arthritis. Abnormalities of vitreous gel architecture are a pathognomonic feature, usually associated with high myopia which is congenital and non-progressive. There is a substantial risk of retinal detachment. Less common ophthalmological features include paravascular pigmented lattice degeneration and cataracts. Non-ocular features show great variation in expression. Children with Stickler syndrome typically have a flat midface with depressed nasal bridge, short nose, anteverted nares, and micrognathia. These features can become less pronounced with age. Midline clefting, if present, ranges in severity from a cleft of the soft palate to Pierre-Robin sequence. There is joint hypermobility which declines with age. Osteoarthritis develops typically in the third or fourth decade. Mild spondyloepiphyseal dysplasia is often apparent radiologically. Sensorineural deafness with high tone loss may be asymptomatic or mild. Occasional findings include slender extremities and long fingers. Stature and intellect are usually normal. Mitral valve prolapse was reported to be a common finding in one series but not in our experience. The majority of families with Stickler syndrome have mutations in the COL2A1 gene and show the characteristic type 1 vitreous phenotype. The remainder with the type 2 vitreous phenotype have mutations in COL11A1 or other loci yet to be identified. Mutations in COL11A2 can give rise to a syndrome with the systemic features of Stickler syndrome but no ophthalmological abnormality.

Marshall-Stickler phenotype associated with von Willebrand disease

We report on 6 individuals from three different kindreds with Marshall-Stickler (MS) phenotype, with characteristic orofacial abnormalities, arthropathy, deafness, and eye findings, all of whom were discovered to have a mild bleeding diathesis and coagulation-study findings consistent with mild von Willebrand disease (vWD). MS syndrome has been linked in some cases to the type II procollagen gene (COL2A1) on chromosome 12q, and to the collagen XI gene (COL11A2) on chromosome 6. The von Willebrand factor (vWF) is encoded by a 180-Kb gene located on the short arm of chromosome 12. This is the first reported association of these two disorders.

A-2-->G transition at the 3' acceptor splice site of IVS17 characterizes the COL2A1 gene mutation in the original Stickler syndrome kindred

Hereditary progressive arthro-ophthalmopathy, or "Stickler syndrome," is an autosomal dominant osteochondrodysplasia characterized by a variety of ocular and skeletal anomalies which frequently lead to retinal detachment and precocious osteoarthritis. A variety of mutations in the COL2A1 gene have been identified in "Stickler" families; in most cases studied thus far, the consequence of mutation is the premature generation of a stop codon. We report here the characterization of a COL2A1 gene mutation in the original kindred described by Stickler et al. [1965]. Conformational sensitive gel electrophoresis (CSGE) [Ganguly et al., 1993] was used to screen for mutations in the entire COL2A1 gene in an affected member from the kindred. A prominent heteroduplex species was noted in the polymerase chain reaction (PCR) product from a region of the gene including exons 17 to 20. Direct sequencing of PCR-amplified genomic DNA resulted in the identification of a base substitution at the A-2 position of the 3' splice acceptor site of IVS17. Sequencing of DNA from affected and unaffected family members confirmed that the mutation segregated with the disease phenotype. Reverse transcriptase-PCR analysis of poly A+ RNA demonstrated that the mutant allele utilized a cryptic splice site in exon 18 of the gene, eliminating 16 bp at the start of exon 18. This frameshift eventually results in a premature termination codon. These findings are the first report of a splice site mutation in classical Stickler syndrome and they provide a satisfying historical context in which to view COL2A1 mutations in this dysplasia.

Hereditary vitreopathy

Heterogeneity has long been recognised within the spectrum of inherited vitreo-retinal disease but the extent of the variation has been less easy to quantify. This has been compounded by the small size and numbers of pedigrees available for the study, and the phenotypic variation both within and between pedigrees. Formation abnormalities in the vitreous architecture have, in the past, been eclipsed by classifications based on general skeletal and morphological differences. Stickler syndrome is the commonest disorder within the spectrum of hereditary vitreous abnormalities and many of the recent published advances relate to this. Stickler syndrome has been subclassified on the basis of vitreo-retinal phenotype: type 1 families with a characteristic congenital vitreous anomaly show linkage without recombination to markers at the COL2A1 locus; type 2 families with different congenital vitreo-retinal phenotypes are not linked to COL2A1. A recent report identifies the COL11A2 mutation in a Dutch pedigree with systemic features of Stickler syndrome but without ocular involvement. Others have implicated COL11A1 in a type 2 Stickler syndrome pedigree with ocular abnormalities. Both COL11A1 and COL11A2 are expressed in cartilage, but on the basis of studies of bovine vitreous it is likely that only the alpha 1(XI) chain encoded by COL11A1 is present in vitreous. This would be consistent with the hypothesis that mutations in the genes encoding collagen XI can give rise to manifestations of Stickler syndrome, but of these, only mutations in COL11A1 will give the full syndrome including the vitreo-retinal features.

Stickler syndrome: correlation between vitreoretinal phenotypes and linkage to COL 2A1

Stickler syndrome is an autosomal dominantly inherited condition characterised by ocular, articular, facial, auditory and oral features. There is locus heterogeneity with about two thirds of families showing linkage to the gene encoding type II procollagen (COL 2A1). Clinical overlap with Marshall's, Wagner's and other syndromes has caused considerable confusion but the importance of the congenital vitreous anomaly, as first described by Scott, has not previously been emphasised. This study examines the linkage of two vitreo-retinal phenotype subgroups of Stickler syndrome to COL 2A1. A total of 97 affected patients from 24 pedigrees were examined. This is the largest published series of Stickler syndrome patients to date and all have undergone full clinical and ophthalmological examination by a single investigator. A clinical classification is proposed based on vitreoretinal phenotype. All patients demonstrating the congenital vitreous anomaly have been designated Stickler syndrome type 1 and those without the congenital vitreous anomaly as Stickler syndrome type 2 patients. There were 69 affected patients from 20 unrelated type 1 pedigrees and 28 affected patients from 4 unrelated type 2 pedigrees. Using two markers at the COL 2A1 locus, Stickler syndrome type 1 pedigrees showed complete linkage to COL 2A1 with a maximum lod score of 12.33 at zero recombination. Linkage to COL 2A1 was excluded in the two type 2 pedigrees that were informative. From these data it appears that this clinical classification is a useful first step in resolving the genetic heterogeneity in this condition.

Type II collagen mutations in rare and common cartilage diseases

Cartilage diseases include a wide variety of clinical phenotypes from common osteoarthrosis to several different types of chondrodysplasias, i.e. 'disorders of cartilage', of which more than 100 different have been described. Patients frequently suffer from various symptoms affecting their joints and/or the growth of their long bones. The amount of hyaline cartilage at articular surfaces is often diminished and structurally abnormal. The surface of the cartilage may have an irregular appearance with defects extending into the subchondral bone. The major constituents of this hyaline cartilage are collagens and proteoglycans, the most abundant protein being type II collagen. It is a homotrimer of three identical alpha-chains, which are encoded by a single gene on human chromosome 12. The gene for type II collagen therefore became a likely candidate for some forms of chondrodysplasias and cartilage degeneration. Recently, both linkages and exclusions between this gene and various cartilage diseases have been reported and a growing number of mutations within the gene have also been identified.

Molecular basis of hereditary disorders of connective tissue

The molecular basis for several hereditary disorders of connective tissues has been elucidated in recent years. In this chapter, we discuss recent advances in the molecular characterization of a number of these disorders and examine their clinical applications.

The type II collagenopathies: a spectrum of chondrodysplasias

With the application of molecular techniques the aetiopathogenesis of skeletal dysplasias is gradually elucidated. Recent advances show that some bone dysplasias result from defects in the biosynthesis of type II (cartilage) collagen. Clinical entities caused by mutations in the COL2A1 gene coding for type II collagen comprise achondrogenesis II, hypochondrogenesis, spondyloepiphyseal dysplasia congenita, Kniest dysplasia, Stickler arthroophthalmopathy and mild dominant spondyloarthropathy. The mutations are expressed in the heterozygous state, and inheritance of type II collagenopathies is autosomal dominant. The wide range of clinical manifestations is not well understood but characterization of the basic defect may provide clues to establish specific genotype-phenotype correlations.

Kniest dysplasia is caused by dominant collagen II (COL2A1) mutations: parental somatic mosaicism manifesting as Stickler phenotype and mild spondyloepiphyseal dysplasia

We describe two unrelated children with Kniest dysplasia, a severe autosomal dominant form of chondrodysplastic dwarfism associated with cleft palate, progressive arthropathy, myopia and retinal detachment. In the first patient the disorder was caused by a 28 base pair exon 12/intron 12 deletion in the gene coding for type II collagen. Her mother had mild abnormalities of the vertebral bodies and long bones compatible with abnormalities seen in Stickler arthro-ophthalmopathy. The second child had a transition of AG to GG at the 3' splice site of intron 20 of the COL2A1 gene. Her father had premature polvarthrosis interpreted as a sequela of mild spondyloepiphyseal dysplasia. Molecular studies revealed that the mother of the first and the father of the second child each had somatic mosaicism of the same mutation as their children. Heterozygous mutations of the gene coding for type II collagen can cause Kniest dysplasia, and somatic mosaicism for the same mutations can result in the Stickler phenotype or in mild spondyloepiphyseal dysplasia leading to premature polyarthrosis.

An inbred line of transgenic mice expressing an internally deleted gene for type II procollagen (COL2A1). Young mice have a variable phenotype of a chondrodysplasia and older mice have osteoarthritic changes in joints

Studies were carried out on a line of transgenic mice that expressed an internally deleted COL2A1 gene and developed a phenotype resembling human chondrodysplasias (Vandenberg et al. 1991. Proc. Natl. Acad. Sci. USA. 88:7640-7644. Marked differences in phenotype were observed with propagation of the mutated gene in an inbred strain of mice in that approximately 15% of the transgenic mice had a cleft palate and a lethal phenotype, whereas the remaining mice were difficult to distinguish from normal littermates. 1-d- and 3-mo-old transgenic mice that were viable showed microscopic signs of chondrodysplasia with reduced amounts of collagen fibrils in the cartilage matrix, dilatation of the rough surfaced endoplasmic reticulum in the chondrocytes, and decrease of optical path difference in polarized light microscopy. The transgenic mice also showed signs of disturbed growth as evidenced by lower body weight, lower length and weight of the femur, decreased bone collagen, decreased bone mineral, and decreased resistance of bone to breakage. Comparisons of mice ranging in age from 1 d to 15 mo demonstrated that there was decreasing evidence of a chondrodysplasia as the mice grew older. Instead, the most striking feature in the 15-mo-old mice were degenerative changes of articular cartilage similar to osteoarthritis.

Mutation in type II procollagen (COL2A1) that substitutes aspartate for glycine alpha 1-67 and that causes cataracts and retinal detachment: evidence for molecular heterogeneity in the Wagner syndrome and the Stickler syndrome (arthro-ophthalmopathy)

A search for mutations in the gene for type II procollagen (COL2A1) was carried out in affected members of a family with early-onset cataracts, lattice degeneration of the retina, and retinal detachment. They had no symptoms suggestive of involvement of nonocular tissues, as is typically found in the Stickler syndrome. The COL2A1 gene was amplified with PCR, and the products were analyzed by denaturing gradient gel electrophoresis. The results suggested a mutation in one allele for exon 10. Sequencing of the fragment demonstrated a single-base mutation that converted the codon for glycine at position alpha 1-67 to aspartate. The mutation was found in three affected members of the family available for study but not in unaffected members or 100 unrelated individuals. Comparison with previously reported mutations suggested that mutations introducing premature termination codons in the COL2A1 gene are a frequent cause of the Stickler syndrome, but mutations in the COL2A1 gene that replace glycine codons with codons for bulkier amino acid can produce a broad spectrum of disorders that range from lethal chondrodysplasias to a syndrome involving only ocular tissues, similar to the syndrome in the family originally described by Wagner in 1938.

A second mutation in the type II procollagen gene (COL2AI) causing stickler syndrome (arthro-ophthalmopathy) is also a premature termination codon

Genetic linkage analyses suggest that mutations in type II collagen may be responsible for Stickler syndrome, or arthro-ophthalmopathy (AO), in many families. In the present study oligonucleotide primers were developed to amplify and directly sequence eight of the first nine exons of the gene for type II procollagen (COL2A1). Analysis of the eight exons in 10 unrelated probands with AO revealed that one had a single-base mutation in one allele that changed the codon of -CGA- for arginine at amino acid position alpha 1-9 in exon 7 to a premature termination signal for translation. The second mutation found to cause AO was, therefore, similar to the first in that both created premature termination signals in the COL2A1 gene. Since mutations producing premature termination signals have not previously been detected in genes for fibrillar collagens, the results raise the possibility that such mutations in the COL2A1 gene are a common cause of AO.

Genetic and clinical heterogeneity of Stickler syndrome

We have studied 6 multigeneration Stickler syndrome families. Manifestations of the syndrome in the families included myopia, deafness, arthritis, characteristic facial changes with "flat" midface and cleft palate, although not all these were present in all families. COL2A1 has been implicated as a gene which can give rise to Stickler syndrome based on evidence from 2 large families which each showed significant linkage between the disease locus and restriction fragment length polymorphisms for the gene (Francomano CA, Lieberfarb RM, Hirose T, Maumenee IH, Streeten EA, Meyers DA, Pyeritz RE (1987): Genomics 1:293-296; Knowlton RG, Weaver EJ, Struyk AF, Knobloch WH, King RA, Norris K, Shamban A, Uitoo J, Jimenez SA, Prockop DJ (1989): Am J Hum Genet 45:681-688). We have found crossovers between the disease locus and COL2A1 in 2 families with Stickler syndrome. This could be explained by either genetic heterogeneity or the actual mutation being in a closely linked, currently unrecognized gene. We found a weakly positive overall lod score (z = 0.96 at theta = 0.10) suggesting that genetic heterogeneity is a more likely explanation. In one family, with typical findings, a translocation t5;17 (q15:q23) was found to segregate with the disease in 4 affected relatives. In view of the possible heterogeneity, although no crossovers with COL2A1 were seen in this family, either of these breakpoints could be the position of a further disease causing gene.

Expression of a partially deleted gene of human type II procollagen (COL2A1) in transgenic mice produces a chondrodysplasia

A minigene version of the human gene for type II procollagen (COL2A1) was prepared that lacked a large central region containing 12 of the 52 exons and therefore 291 of the 1523 codons of the gene. The construct was modeled after sporadic in-frame deletions of collagen genes that cause synthesis of shortened pro alpha chains that associate with normal pro alpha chains and thereby cause degradation of the shortened and normal pro alpha chains through a process called procollagen suicide. The gene construct was used to prepare five lines of transgenic mice expressing the minigene. A large proportion of the mice expressing the minigene developed a phenotype of a chondrodysplasia with dwarfism, short and thick limbs, a short snout, a cranial bulge, a cleft palate, and delayed mineralization of bone. A number of mice died shortly after birth. Microscopic examination of cartilage revealed decreased density and organization of collagen fibrils. In cultured chondrocytes from the transgenic mice, the minigene was expressed as shortened pro alpha 1(II) chains that were disulfide-linked to normal mouse pro alpha 1(II) chains. Therefore, the phenotype is probably explained by depletion of the endogenous mouse type II procollagen through the phenomenon of procollagen suicide.

Stop codon in the procollagen II gene (COL2A1) in a family with the Stickler syndrome (arthro-ophthalmopathy)

Linkage analysis with restriction fragment length polymorphisms for the gene for type II procollagen (COL2A1) was carried out in a family with the Stickler syndrome, or arthro-ophthalmopathy, an autosomal dominant disorder that affects the eyes, ears, joints, and skeleton. The analysis demonstrated linkage of the disease and COL2A1 with a logarithm-of-odds score of 1.51 at zero recombination. A newly developed procedure for preparing cosmid clones was employed to isolate the allele for type II procollagen that was linked to the disease. Analysis of over 7000 nucleotides of the gene revealed a single base mutation that altered a CG dinucleotide and converted the codon CGA for arginine at amino acid position alpha 1-732 to TGA, a stop codon. From previous work on procollagen biosynthesis, it is apparent that the truncated polypeptide synthesized from an allele with a stop codon at alpha 1-732 cannot participate in the assembly of type II procollagen, and therefore that the mutation would decrease synthesis of type II procollagen. It was not apparent, however, why the mutation produced marked changes in the eye, which contains only small amounts of type II collagen, but relatively mild effects on the many cartilaginous structures of the body that are rich in the same protein.