Oto-spondylo-megaepiphyseal dysplasia (OSMED): Clinical description of three patients homozygous for a missense mutation in the COL11A2 gene

Age-dependent genetic regulation of osteoarthritis: independent effects of immune system genes

OBJECTIVES

Osteoarthritis (OA) is a joint disease with a heritable component. Genetic loci identified via genome-wide association studies (GWAS) account for an estimated 26.3% of the disease trait variance in humans. Currently, there is no method for predicting the onset or progression of OA. We describe the first use of the Collaborative Cross (CC), a powerful genetic resource, to investigate knee OA in mice, with follow-up targeted multi-omics analysis of homologous regions of the human genome.

METHODS

We histologically screened 275 mice for knee OA and conducted quantitative trait locus (QTL) mapping in the complete cohort (> 8 months) and the younger onset sub-cohort (8-12 months). Multi-omic analysis of human genetic datasets was conducted to investigate significant loci.

RESULTS

We observed a range of OA phenotypes. QTL mapping identified a genome-wide significant locus on mouse chromosome 19 containing Glis3, the human equivalent of which has been identified as associated with OA in recent GWAS. Mapping the younger onset sub-cohort identified a genome-wide significant locus on chromosome 17. Multi-omic analysis of the homologous region of the human genome (6p21.32) indicated the presence of pleiotropic effects on the expression of the HLA - DPB2 gene and knee OA development risk, potentially mediated through the effects on DNA methylation.

CONCLUSIONS

The significant associations at the 6p21.32 locus in human datasets highlight the value of the CC model of spontaneous OA that we have developed and lend support for an immune role in the disease. Our results in mice also add to the accumulating evidence of a role for Glis3 in OA.

Rare variants found in multiplex families with orofacial clefts: Does expanding the phenotype make a difference?

Whole-exome sequencing (WES) is now a relatively straightforward process to identify causal variants in Mendelian disorders. However, the same is not true for WES in families where the inheritance patterns are less clear, and a complex etiology is suspected. Orofacial clefts (OFCs) are highly heritable birth defects with both Mendelian and complex etiologies. The phenotypic spectrum of OFCs may include overt clefts and several subclinical phenotypes, such as discontinuities in the orbicularis oris muscle (OOM) in the upper lip, velopharyngeal insufficiency (VPI), microform clefts or bifid uvulas. We hypothesize that expanding the OFC phenotype to include these phenotypes can clarify inheritance patterns in multiplex families, making them appear more Mendelian. We performed whole-exome sequencing to find rare, likely causal genetic variants in 31 multiplex OFC families, which included families with multiple individuals with OFCs and individuals with subclinical phenotypes. We identified likely causal variants in COL11A2, IRF6, KLF4, SHROOM3, SMC3, TP63 , and TBX3 in seven families. Although we did not find clear evidence supporting the subclinical phenotype hypothesis, our findings support a role for rare variants in the etiology of OFCs.

Clinical and genetic characterization of autosomal recessive stickler syndrome caused by novel compound heterozygous mutations in the COL9A3 gene

Background

Stickler syndrome (STL) is a clinically variable and genetically heterogeneous collagenopathy characterized by ophthalmic, auditory, skeletal, and orofacial abnormalities. STL is mainly inherited in an autosomal dominant pattern with mutations in the COL2A1, COL11A1, and COL11A2 genes. Autosomal recessive forms are rare. However, 19 patients have been reported to date, with STL caused by homozygous or compound heterozygous mutations in genes that encode for the three chains of type IX collagen: COL9A1, COL9A2, and COL9A3.

Methods

Genetic analysis was performed using the next‐generation sequencing of 166 genes associated with skeletal disorders and sequenced on an Ion Torrent S5 system with a minimum coverage of 100X. The two variants in the COL9A3 gene identified in the proband and the parents were confirmed by Sanger sequencing on an ABI3130xl sequencer.

Results

We describe a novel case of autosomal recessive Stickler syndrome caused by two undescribed mutations in the COL9A3 gene: c.268C>T (p.Arg90Ter) and c.1729C>T (p.Arg577Ter). The clinical features included severe sensorineural hearing loss, high myopia, vitreoretinal degeneration, and early‐onset arthropathy of the lower limbs. Radiography revealed mild spondyloepiphyseal dysplasia.

Conclusion

This case further expands the mutational and phenotypic spectrum of COL9A‐associated STL with a more severe presentation.

Otospondylomegaepiphyseal Dysplasia: A Case Report of Clinical and Radiographic Findings

CASE

We present a long-term follow-up on a woman with otospondylomegaepiphyseal dysplasia (OSMED). At the age of 46 years, she is one of the oldest patients with the syndrome in the literature to date. We focus on the musculoskeletal anatomy and orthopaedic interventions over her lifetime.

CONCLUSION

OSMED is a very rare syndrome. Arthritis and joint pains presented in her early adolescence and progressed to the point of requiring joint replacements by her 20s. Early intervention and monitoring improved the quality of life for this patient.

Clinical, histopathological and genetic characterisation of oculoskeletal dysplasia in the Northern Inuit Dog

Seven Northern Inuit Dogs (NID) were diagnosed by pedigree analysis with an autosomal recessive inherited oculoskeletal dysplasia (OSD). Short-limbed dwarfism, angular limb deformities and a variable combination of macroglobus, cataracts, lens coloboma, microphakia and vitreopathy were present in all seven dogs, while retinal detachment was diagnosed in five dogs. Autosomal recessive OSD caused by COL9A3 and COL9A2 mutations have previously been identified in the Labrador Retriever (dwarfism with retinal dysplasia 1-drd1) and Samoyed dog (dwarfism with retinal dysplasia 2-drd2) respectively; both of those mutations were excluded in all affected NID. Nine candidate genes were screened in whole genome sequence data; only one variant was identified that was homozygous in two affected NID but absent in controls. This variant was a nonsense single nucleotide polymorphism in COL9A3 predicted to result in a premature termination codon and a truncated protein product. This variant was genotyped in a total of 1,232 dogs. All seven affected NID were homozygous for the variant allele (T/T), while 31/116 OSD-unaffected NID were heterozygous for the variant (C/T) and 85/116 were homozygous for the wildtype allele (C/C); indicating a significant association with OSD (p = 1.41x10-11). A subset of 56 NID unrelated at the parent level were analysed to determine an allele frequency of 0.08, estimating carrier and affected rates to be 15% and 0.6% respectively in NID. All 1,109 non-NID were C/C, suggesting the variant is rare or absent in other breeds. Expression of retinal mRNA was similar between an OSD-affected NID and OSD-unaffected non-NID. In conclusion, a nonsense variant in COL9A3 is strongly associated with OSD in NID, and appears to be widespread in this breed.

From Structure to Phenotype: Impact of Collagen Alterations on Human Health

The extracellular matrix (ECM) is a highly dynamic and heterogeneous structure that plays multiple roles in living organisms. Its integrity and homeostasis are crucial for normal tissue development and organ physiology. Loss or alteration of ECM components turns towards a disease outcome. In this review, we provide a general overview of ECM components with a special focus on collagens, the most abundant and diverse ECM molecules. We discuss the different functions of the ECM including its impact on cell proliferation, migration and differentiation by highlighting the relevance of the bidirectional cross-talk between the matrix and surrounding cells. By systematically reviewing all the hereditary disorders associated to altered collagen structure or resulting in excessive collagen degradation, we point to the functional relevance of the collagen and therefore of the ECM elements for human health. Moreover, the large overlapping spectrum of clinical features of the collagen-related disorders makes in some cases the patient clinical diagnosis very difficult. A better understanding of ECM complexity and molecular mechanisms regulating the expression and functions of the various ECM elements will be fundamental to fully recognize the different clinical entities.

Molecular genetics of the COL2A1-related disorders

Type II collagen, comprised of three identical alpha-1(II) chains, is the major collagen synthesized by chondrocytes, and is found in articular cartilage, vitreous humour, inner ear and nucleus pulposus. Mutations in the collagen type II alpha-1 gene (COL2A1) have been reported to be responsible for a series of abnormalities, known as type II collagenopathies. To date, 16 definite disorders, inherited in an autosomal dominant or recessive pattern, have been described to be associated with the COL2A1 mutations, and at least 405 mutations ranging from point mutations to complex rearrangements have been reported, though the underlying pathogenesis remains unclear. Significant clinical heterogeneity has been reported in COL2A1-associated type II collagenopathies. In this review, we highlight current knowledge of known mutations in the COL2A1 gene for these disorders, as well as genetic animal models related to the COL2A1 gene, which may help us understand the nature of complex phenotypes and underlying pathogenesis of these conditions.

Non-ocular Stickler syndrome with a novel mutation in COL11A2 diagnosed by massively parallel sequencing in Japanese hearing loss patients

OBJECTIVES

This study aims to document the clinical features of patients with COL11A2 mutations and to describe the usefulness of massively parallel sequencing.

METHODS

One thousand one hundred twenty (1120) Japanese hearing loss patients from 53 ENT departments nationwide participated in this study. Massively parallel sequencing of 63 genes implicated in hearing loss was performed to identify the genetic causes in the Japanese hearing loss patients.

RESULTS

A novel mutation in COL11A2 (c.3937_3948delCCCCCAGGGCCA) was detected in an affected family, and it was segregated in all hearing loss individuals. The clinical findings of this family were compatible with non-ocular Stickler syndrome. Orofacial features of mid-facial hypoplasia and slowly progressive mild to moderate hearing loss were also presented. Audiological examinations showed favorable auditory performance with hearing aid(s).

CONCLUSION

This is the first case report of the genetic diagnosis of a non-ocular Stickler syndrome family in the Japanese population. We suggest that it is important to take both genetic analysis data and clinical symptoms into consideration to make an accurate diagnosis.

Audiological findings in otospondylomegaepiphyseal dysplasia (OSMED) associated with a novel mutation in COL11A2

The aim of the study was to assess the audiological findings of a 4-year-old child with a homozygous COL11A2 mutation and to point out the role of continuous follow-ups in children with craniofacial syndromes after the newborn hearing screening. A 4-year-old boy with otospondylomegaepiphyseal dysplasia (OSMED) was followed up after birth for hearing loss. Transient Otoacoustic Emissions (TEOAEs), Distortion Product Otoacoustic Emissions (DPOAEs), Automated and Clinical Auditory Brainstem Response (AABR and ABR) measurements, Visual Reinforcement Audiometry, immitansmetric measurements and hearing threshold measurements were performed for audiological evaluation. The patient developed sensorineural hearing loss at 11 months of age while his hearing was normal at birth. Because of auditory-verbal training with hearing aids started at 20 months of age, he now has normal verbal communication with his peers. This study clearly demonstrates that hearing loss develops in infancy in patients with OSMED and underscores the importance of continued hearing screening beyond newborn period for early intervention of hearing impairment and communication problems.

Functional modules, mutational load and human genetic disease

The ability to generate a massive amount of sequencing and genotyping data is transforming the study of human genetic disorders. Driven by such innovation, it is likely that whole exome and whole-genome resequencing will replace regionally focused approaches for gene discovery and clinical testing in the next few years. However, this opportunity brings a significant interpretative challenge to assigning function and phenotypic variance to common and rare alleles. Understanding the effect of individual mutations in the context of the remaining genomic variation represents a major challenge to our interpretation of disease. Here, we discuss the challenges of assigning mutation functionality and, drawing from the examples of ciliopathies as well as cohesinopathies and channelopathies, discuss possibilities for the functional modularization of the human genome. Functional modularization in addition to the development of physiologically relevant assays to test allele functionality will accelerate our understanding of disease architecture and enable the use of genome-wide sequence data for disease diagnosis and phenotypic prediction in individuals.

Genetic and orthopedic aspects of collagen disorders

PURPOSE OF REVIEW

'Collagens' are a family of structurally related proteins that play a wide variety of roles in the extracellular matrix. To date, there are at least 29 known types of collagen. Accordingly, abnormality in the various collagens produces a large category of diseases with heterogeneous symptoms. This review presents genetic and orthopedic aspects of type II, IX, and XI collagen disorders.

RECENT FINDINGS

Although a diverse group of conditions, mutation of collagens affecting the articular cartilage typically produces an epiphyseal skeletal dysplasia phenotype. Often, the ocular or auditory systems or both are also involved. Treatment of these collagenopathies is symptomatic and individualized. Study of tissue from animal models allows examination of mutation effects on the abnormal protein structure and function.

SUMMARY

The collagen superfamily comprises an important structural protein in mammalian connective tissue. Mutation of collagens produces a wide variety of genetic disorders, and those mutations affecting types II, IX, and XI collagens produce an overlapping spectrum of skeletal dysplasias. Findings range from lethal to mild, depending on the mutation of the collagen gene and its subsequent effect on the structure and/or metabolism of the resultant procollagen and/or collagen protein and its function in the body.

Bioinformatics methods for identifying candidate disease genes

With the explosion in genomic and functional genomics information, methods for disease gene identification are rapidly evolving. Databases are now essential to the process of selecting candidate disease genes. Combining positional information with disease characteristics and functional information is the usual strategy by which candidate disease genes are selected. Enrichment for candidate disease genes, however, depends on the skills of the operating researcher. Over the past few years, a number of bioinformatics methods that enrich for the most likely candidate disease genes have been developed. Such in silico prioritisation methods may further improve by completion of datasets, by development of standardised ontologies across databases and species and, ultimately, by the integration of different strategies.

The modular nature of genetic diseases

Evidence from many sources suggests that similar phenotypes are begotten by functionally related genes. This is most obvious in the case of genetically heterogeneous diseases such as Fanconi anemia, Bardet-Biedl or Usher syndrome, where the various genes work together in a single biological module. Such modules can be a multiprotein complex, a pathway, or a single cellular or subcellular organelle. This observation suggests a number of hypotheses about the human phenome that are now beginning to be explored. First, there is now good evidence from bioinformatic analyses that human genetic diseases can be clustered on the basis of their phenotypic similarities and that such a clustering represents true biological relationships of the genes involved. Second, one may use such phenotypic similarity to predict and then test for the contribution of apparently unrelated genes to the same functional module. This concept is now being systematically tested for several diseases. Most recently, a systematic yeast two-hybrid screen of all known genes for inherited ataxias indicated that they all form part of a single extended protein-protein interaction network. Third, one can use bioinformatics to make predictions about new genes for diseases that form part of the same phenotype cluster. This is done by starting from the known disease genes and then searching for genes that share one or more functional attributes such as gene expression pattern, coevolution, or gene ontology. Ultimately, one may expect that a modular view of disease genes should help the rapid identification of additional disease genes for multifactorial diseases once the first few contributing genes (or environmental factors) have been reliably identified.

A new autosomal recessive form of Stickler syndrome is caused by a mutation in the COL9A1 gene

Stickler syndrome is characterized by ophthalmic, articular, orofacial, and auditory manifestations. It has an autosomal dominant inheritance pattern and is caused by mutations in COL2A1, COL11A1, and COL11A2. We describe a family of Moroccan origin that consists of four children with Stickler syndrome, six unaffected children, and two unaffected parents who are distant relatives (fifth degree). All family members were clinically investigated for ear, nose, and throat; ophthalmologic; and radiological abnormalities. Four children showed symptoms characteristic of Stickler syndrome, including moderate-to-severe sensorineural hearing loss, moderate-to-high myopia with vitreoretinopathy, and epiphyseal dysplasia. We considered the COL9A1 gene, located on chromosome 6q13, to be a candidate gene on the basis of the structural association with collagen types II and XI and because of the high expression in the human inner ear indicated by cDNA microarray. Mutation analysis of the coding region of the COL9A1 gene showed a homozygous R295X mutation in the four affected children. The parents and four unaffected children were heterozygous carriers of the R295X mutation. Two unaffected children were homozygous for the wild-type allele. None of the family members except the homozygous R295X carriers had any signs of Stickler syndrome. Therefore, COL9A1 is the fourth identified gene that can cause Stickler syndrome. In contrast to the three previously reported Stickler syndrome-causing genes, this gene causes a form of Stickler syndrome with an autosomal recessive inheritance pattern. This finding will have a major impact on the genetic counseling of patients with Stickler syndrome and on the understanding of the pathophysiology of collagens. Mutation analysis of this gene is recommended in patients with Stickler syndrome with possible autosomal recessive inheritance.

Oto-spondylo-megaepiphyseal dysplasia (OSMED): clinical and radiological findings in sibs homozygous for premature stop codon mutation in the COL11A2 gene

Oto-spondylo-megaepiphyseal dysplasia (OSMED) is a very rare disorder due to mutation of type XI collagen. Less than 30 patients have been reported in the literature so far. It could be either of autosomal dominant (OMIM 154780) or recessive (OMIM 215150) etiology. Two sibs with OSMED are presented. They had disproportionate short stature and short limbs, distinct face with midface hypoplasia, short nose, depressed nasal bridge, long philtrum, and non-progressive sensorineural deafness. Radiological findings showed short long bones and large epiphyses with metaphyseal flaring and mild platyspondyly and coronal clefting. Homozygosity of a single nucleotide deletion in exon 55 causing a premature stop codon in exon 56 of COL11A2 was detected in the affected sibs. Parents were heterozygotes for the same mutation and interestingly, the father had mild unilateral non-progressive sensorineural deafness. This finding adds more weight that the type of mutation and location in COL11A2 are crucial in determining the phenotype. The purpose of this study is to report clinical and radiological findings in two molecularly proven Egyptian sibs with autosomal recessive OSMED.

Characterization of an abundant COL9A1 transcript in the cochlea with a novel 3' UTR: Expression studies and detection of miRNA target sequence

EST N66408 represents one of several large unique clusters expressed in the Morton human fetal cochlear cDNA library. N66408 is 575 bp in size and initial BLAST analysis of this sequence showed no homology to any known genes or expressed sequence tags (ESTs) from other organs or tissues. Sequence of the original cochlear clone from which N66408 was derived revealed that the corresponding cDNA was about 700 bp in size, including 125 bp at its 5' end with homology to the 3' end of COL9A1 in addition to 575 bp of novel sequence. RT-PCR analysis using primers specific to COL9A1 isoforms 1 and 2 detected expression of both isoforms in human fetal cochlea. Tissue in situ hybridization using the novel 3' UTR sequence as probe showed abundant expression in spiral limbus and spiral ligament, and a moderate level of expression in the organ of Corti. dbEST analysis of ESTs specific to the 3' UTR of COL9A1 showed 19 ESTs derived from various tissues; three polyadenylation sites were identified and the majority of these ESTs were derived from overlapping polyadenylation signals at the second site (position 749-758). Comparison of the 3' UTR of human COL9A1 with its orthologs as well as with dbEST uncovered a highly conserved region around the overlapping polyadenylation signals at position 749-758 in mammals. A search of the microRNA database revealed a highly conserved target sequence for miR-9 immediately preceding the overlapping polyadenylation signals in the novel 3' UTR of COL9A1, suggesting its role in posttranscriptional regulation of COL9A1.

A mouse model for Stickler's syndrome: ocular phenotype of mice carrying a targeted heterozygous inactivation of type II (pro)collagen gene (Col2a1)

The influences of targeted heterozygous inactivation of type II (pro)collagen gene (Col2a1) on eye structures in the 15-month-old C57BL/6JOlaHsd mouse was studied. The eyes were collected from C57BL mice heterozygous for a targeted inactivation of one allele of the Col2a1 gene (Col2a1(+/-) mice). The eyes of C57BL mice with normal gene alleles were used as controls (Col2a1(+/+) mice). Ocular histology was analyzed from tissue sections, stained with hematoxylin and eosin, toluidine blue and alcian blue. Type II collagen was localized by immunohistochemistry. Hyaluronan (HA) was stained utilizing the biotinylated complex of the hyaluronan-binding region of aggrecan and link protein (bHABC). The anterior segment of the eye was well-formed in both genotypes, but typical folding of ciliary processes was decreased, while increased stromal extracellular matrix vacuolization was seen in the Col2a1(+/-) mice. In the lens of these mice, subcapsular extracellular matrix changes were observed. Differences in retinal structures or the number of the eyes with retinal detachment were not detected between the genotypes. In Col2a1(+/-) mice, staining for type II collagen was weaker in cornea, ciliary body, iris, lens, vitreous, retina, choroid and sclera than in the control mice. HA staining was detected in the extraocular tissues, ciliary body, iris and the choroid of both genotypes. HA staining was observed only in the vitreous body of the control animals. Heterozygous inactivation of Col2a1 gene causes structural defects in the murine eye. The observed structural changes in the ciliary body, lens and vitreous of the Col2a1(+/-) mice may represent ocular features found in the human Stickler syndrome, where the abnormalities result from COL2A1 gene mutations which lead to functional haploinsufficiency.

An overview of hereditary hearing loss

Understanding the genetic basis of hearing loss is important because almost 50% of profound hearing loss are caused by genetic factors and more than 120 independent genes have been identified. In this review, after a brief explanation of some genetic terms (allele, heterozygosis, homozygosis, polymorphism, genotype and phenotype), classification of genetic hearing loss (syndromic versus nonsyndromic, and recessive dominant, X-linked and mitochondrial) was performed. Some of the most common syndromes (Usher, Pendred, Jervell and Lange-Nielsen, Waardenburg, branchio-oto-renal, Stickler, Treacher Collins and Alport syndromes, biotinidase deficiency and Norrie disease) causing genetic hearing loss were also explained briefly. The genes involved in hearing loss and genetic heterogeneity were presented.

A type II collagen mutation also results in oto-spondylo-megaepiphyseal dysplasia

Oto-spondylo-megaepiphyseal dysplasia (OSMED) is a skeletal dysplasia characterized by severe sensorineural hearing loss, enlarged epiphyses and early onset of osteoarthritis. COL11A2 has been reported as a causative gene for OSMED. We have identified a novel COL2A1 mutation at a splice-acceptor site within intron 10 (c.709-2A>G) in an OSMED patient. This mutation caused the skipping of exon 11, and of exons 11 and 13. These exon-skipping events are presumed to cause an in-frame deletion of the triple helical region of the COL2A1 product. Thus, our findings highlight the genetic heterogeneity of OSMED and extend the phenotypic spectrum of type II collagenopathy, as well as confirming the overlap between type II and type XI collagenopathies.

A novel retinoic acid-response element requires an enhancer element mediator for transcriptional activation

The Col11a2 gene codes for alpha2(XI), a subunit of type XI collagen that is a critical component of the cartilage extracellular matrix. The 5' regulatory region of Col11a2 was subjected to deletional analysis to detect any regulatory element in addition to the two known chondrocyte-specific enhancer elements B/C and D/E. Deletion of the region from -342 to -242 bp reduced transcriptional activity to less than 50% of wild-type, but the sequence showed no independent ability to increase transcription from a minimal promoter. When cloned downstream of the D/E enhancer, however, a subsection of the sequence nearly doubled transcriptional activity and produced an additional 3-fold activation in response to RA (retinoic acid). A 6-bp direct repeat, separated by 4 bp (a DR-4 element) near the 5'-end of this region, was found to be essential for its activity, and was further shown to bind the RA X receptor beta in electrophoretic mobility-shift assays. The present study has revealed a novel RA-response element in Col11a2 that does not interact directly with the promoter, but instead requires the D/E enhancer to mediate transcriptional activation. Proteins bound at the enhancer, therefore, would be expected to affect the transcriptional response to RA. Such a system of regulation, particularly if found to be operating in other cartilage genes, could explain the conflicting responses RA produces in chondrocytes under different experimental conditions.

Stickler syndrome: Clinical characteristics and diagnostic criteria

The purpose of this study was to establish diagnostic criteria for Stickler syndrome. Ninety patients from 38 families had complete evaluations for possible Stickler syndrome. Molecular confirmation of COL2A1 mutation status (type I Stickler syndrome) was available on 25 patients from six families. In the remaining 65 patients, 47 from 25 families were affected with Stickler syndrome and 18 from seven families were unaffected with Stickler syndrome. A diagnostic nosology based on type I Stickler patients with known COL2A1 mutations was applied to clinically affected and unaffected patients. A diagnostic scale of 9 points evaluated molecular data or family history data and characteristic ocular, orofacial, auditory, and musculoskeletal findings. A score of > or =5 was diagnostic of Stickler syndrome. These criteria demonstrate 100% sensitivity when applied to type I Stickler syndrome patients with known COL2A1 mutations, 98% sensitivity when applied to clinically affected Stickler patients, and 86% specificity when applied to patients unaffected based on clinical and/or molecular analysis. We conclude that diagnostic criteria based on type I Stickler patients with molecularly confirmed COL2A1 mutations appear to be sensitive and specific for the diagnosis of this syndrome and should be helpful to clinicians when making the diagnosis.

Spondylo-mega-epiphyseal dysplasia with prominent upper limb mesomelia, punctate calcifications, and deafness

We report on a previously undescribed form of skeletal dysplasia with rhizomelic, acromelic, and prominent mesomelic shortening, distal ulnar epiphyseal and pubic punctate calcifications (stippling), mega-epiphyses, platyspondyly, anterior beaking of the vertebrae, and sensorineural hearing loss. We compare this case to the other reported forms of skeletal dysplasias, particularly the mesomelic, acromesomelic, and mega-epiphyseal disorders.

A type XI collagen mutation leads to increased degradation of type II collagen in articular cartilage

OBJECTIVE

To determine in articular cartilage whether degraded type II collagen is more abundant in Col11a1 mutant cho/+ than in age-matched +/+ mice and whether collagen degradation occurs in a generalized or localized fashion.

DESIGN

Knee joints from cho/+ and +/+ mice at 6, 9, 12 and 15 months of age were dissected, fixed, cryosectioned, and stained with antibody COL2-3/4m against denatured type II collagen using a FITC-conjugated secondary antibody. Sections were viewed and photographed under a fluorescence microscope and areas of staining were quantified.

RESULTS

Before 12 months of age, little degraded collagen staining was detectable in +/+ or cho/+ mice. By 15 months, however, cho/+ mice showed significantly more degraded type II collagen than age-matched controls. Degraded collagen staining was localized at the articular surface, not distributed generally throughout the articular cartilage.

CONCLUSIONS

The results suggest a model in which cumulative biomechanical stresses trigger increased collagen synthesis and degradation in both +/+ and cho/+ mice at around 12 months of age. Cho/+ mice, however, are less able to synthesize and assemble normal replacement collagen fibrils because of the Col11a1 mutation. Degradation is further activated, resulting in the accumulation of degraded type II collagen in the articular cartilage extracellular matrix. Similar mutations that do not overtly affect skeletal development may likewise predispose humans to increased collagen degradation and resultant osteoarthritis.

One gene, two phenotypes: ROR2 mutations in autosomal recessive Robinow syndrome and autosomal dominant brachydactyly type B

Autosomal recessive Robinow syndrome (RRS) is a severe skeletal dysplasia with short stature, generalized limb shortening, segmental defects of the spine, brachydactyly, and a dysmorphic facial appearance. The gene encoding receptor orphan receptor tyrosine kinase 2 (ROR2) is located on chromosome 9q22 and homozygous loss-of-function mutations in this gene are responsible for RRS. Moreover, knocking out the mouse Ror2 gene causes mesomelic dwarfism in the homozygous state, with almost identical features to recessive Robinow syndrome. The protein product of this gene is a cell membrane receptor, containing distinct motifs including an immunoglobulin-like (Ig) domain, a Frizzled-like cysteine-rich domain (FRZ or CRD), and a kringle domain (KD) in the extracellular region; and an intracellular region with tyrosine kinase (TK), serine/threonine-rich, and proline-rich structures. The extracellular motifs of the ROR2 protein are known to be involved in protein-protein interactions. The tyrosine kinase domain is involved in an as yet uncharacterized signaling pathway. Interestingly, heterozygous mutations in ROR2 have recently been shown to give rise to autosomal dominant brachydactyly type B1 (BDB1). This condition is characterized by terminal deficiency of fingers and toes. A variety of mutations have been reported in ROR2. Here, these genetic defects are compiled and possible genotype-phenotype correlations are discussed.

Premature vertebral endplate ossification and mild disc degeneration in mice after inactivation of one allele belonging to the Col2a1 gene for Type II collagen

STUDY DESIGN

Skeletal tissues of mice with an inactivated allele of the Col2a1 gene for Type II collagen ("heterozygous knockout") were studied.

OBJECTIVE

To determine whether a heterozygous inactivation of the Col2a1 gene has a role in the etiology of spine disorders such as disc degeneration.

SUMMARY OF BACKGROUND DATA

Mutations in the COL2A1, COL11A1, COL11A2, and COL9A2 genes have been linked to spine disorders. However, the mechanism by which genetic factors lead to disc degeneration still are largely unknown.

METHODS

Spine tissues were studied using radiograph analyses; conventional, quantitative, and polarized light microscopy; immunohistochemistry for the major extracellular components, and in situ hybridization for procollagens alpha1(I) and alpha1(II). Voluntary running activity also was monitored in half of the mice.

RESULTS

As the findings showed, 1-month-old heterozygous knockout mice had shorter limb bones, skulls, and spines, as well as thicker and more irregular vertebral endplates, which calcified earlier than in the control mice. They also had a lower concentration of glycosaminoglycans in the anulus fibrosus, in the endplates, and in the vertebral bone than the controls. These features in the heterozygous knockout mice were compensated by the age of 15 months. However, the long bones and skulls of the mature heterozygous mice remained shorter than those of the controls. Gene-deficient mice used the running wheel less. However, physical exercise did not induce any marked structural changes in the skeleton.

CONCLUSION

Mice with heterozygous knockout of Col2a1 show subtle early skeletal manifestations that bear some resemblance to those of human spine disorders.

Targeted disruption of Col11a2 produces a mild cartilage phenotype in transgenic mice: comparison with the human disorder otospondylomegaepiphyseal dysplasia (OSMED)

Transgenic mice were prepared by homologous recombination with a Col11a2 targeting gene in which an inverted neomycin-resistant gene was inserted between restriction sites in exons 27 and 28. The targeted allele was transcribed in shortened mRNAs, which could be detected by Northern blotting. However, translation of the full-length Col11a2 chain was unable to occur because of the presence of premature termination codons within the inverted neomycin-resistant gene. Analysis of pepsin-resistant collagen chains from rib cartilage of homozygous mice demonstrated the lack of synthesis of intact alpha2(XI) chains. However, pepsin-resistant collagen chains of either alpha1(XI) or alpha1(V) were still detected on sodium dodecyl sulfate polyacrylamide gel electrophoresis. Therefore, alpha2(XI) chains are not essential for the assembly of some molecular forms of triple-helical type V/XI collagen. The phenotype was milder than in the cho/cho mouse in which, as the result of mutation, translation of the full-length alpha1(XI) chain fails to occur and the mice die at birth (Li et al., 1995). Homozygous mice without expression of an alpha2(XI) chain had a smaller body size, receding snouts, and deafness. Nasal bones in the homozygous transgenic mice were specifically shorter and dimpled on their external surfaces. Chondrocytes in growth plates of all long bones were markedly disorganized and failed to align in columns. Analysis of growth plates from transgenic mice by in situ hybridization showed expression of alpha1(II) and alpha1(XI) but not of alpha1(I) or alpha1(V) which, in contrast, were expressed in the developing bone and in the bone collar. Expression of alpha1(X) specifically in the hypertrophic cartilage was observed in normal and transgenic mice. No obvious osteoarthritis was observed throughout the life of homozygous mice up to 1 year of age, although minor morphologic anomalies in the articular cartilages were discernible. The mild phenotype is consistent with similar mutations in the COL11A2 gene seen in patients with nonocular Stickler syndrome and some patients with otospondylomegaepiphyseal dysplasia (OSMED), as well as in patients with a nonsyndromic form of deafness called DFNA13.

Thoracolumbar spinal abnormalities in Stickler syndrome

STUDY DESIGN

Retrospective review of clinical and radiographic records of patients with Stickler syndrome.

OBJECTIVES

To describe thoracolumbar spinal abnormalities and their correlation with age and back pain among patients with Stickler syndrome.

SUMMARY OF BACKGROUND DATA

Stickler syndrome (hereditary arthro-ophthalmopathy) is an autosomal dominant connective tissue disorder characterized by skeletal, ocular, oral-facial, cardiac, and auditory manifestations. Prevalence is approximately 1 in 10,000 (similar to that of Marfan syndrome). No one has investigated spinal abnormalities in a large series of patients.

METHODS

A single-center evaluation of 53 patients from 24 families with Stickler syndrome (age range, 1-70 years) in a multidisciplinary genetics clinic. Thoracolumbar radiographs were analyzed for spinal abnormalities and correlation with age and back pain.

RESULTS

Thirty-four percent of patients had scoliosis, 74% endplate abnormalities, 64% Schmorl's nodes, 43% platyspondylia, and 43% Scheuermann-like kyphosis. Sixty-seven percent of patients and 85% of adults reported chronic back pain. Endplate abnormalities and Schmorl's nodes were associated with adult age; endplate abnormalities, Schmorl's nodes, and adult age were associated with back pain. Only one adult patient was free of spinal abnormalities.

CONCLUSIONS

Spinal abnormalities are nearly uniformly observed in Stickler syndrome, progress with age, and are associated with back pain. Although common, scoliosis is generally self-limited (only one patient needed surgical treatment). Correct diagnosis of this syndrome facilitates early identification and management of other potentially severe systemic manifestations and genetic counseling for affected families. Moreover, recognition of Stickler syndrome allows accurate prognosis for skeletal abnormalities and anticipation of potential surgical complications.

Structural macromolecules and supramolecular organisation of the vitreous gel

The vitreous gel is a transparent extracellular matrix that fills the cavity behind the lens of the eye and is surrounded by and attached to the retina. This gel liquefies during ageing and in 25-30% of the oppulation the residual gel structure eventually collapses away from the posterior retina in a process called posterior retina in a process called posterior vitreous detachment. This process plays a pivotal role in a number of common blinding conditions including rhegmatogenous retinal detachment, proliferative diabetic retinopathy and macular hole formation. In order to understand the molecular events underlying vitreous liquefaction and posterior vitreous detachment and to develop new therapies it is important to understand the molecular basis of normal vitreous gel structure and how this is altered during ageing. It has previously been established that a dilute dispersion of thin (heterotypic) collagen fibrils is essential to the gel structure and that age-related vitreous liquefaction is intimately related to a process whereby these collagen fibrils aggregate. Collagen fibrils have a natural tendency to aggregate so a key question that has to be addressed is: what normally maintains the spacing of the collagen fibrils? In mammalian vitreous a network of hyaluronan normally fills the spaces between these collagen fibrils. This hyaluronan network can be removed without destroying the gel structure, so the hyaluronan is not essential for maintaining the spacing of the collagen fibrils although it probably does increase the mechanical resilience of the gel. The thin heterotypic collagen fibrils have a coating of non-covalently bound macromolecules which, along with the surface features of the collagen fibrils themselves, probably play a fundamental role in maintaining gel stability. They are likely to both maintain the short-range spacing of vitreous collagen fibrils and to link the fibrils together to form a contiguous network. A collagen fibril-associated macromolecule that may contribute to the maintenance of short-range spacing is opticin, a newly discovered extracellular matrix leucine-rich repeat protein. In addition, surface features of the collagen fibrils such as the chondroitin sulphate glycosaminoglycan chains of type IX collagen proteoglycan may also play an important role in maintaining fibril spacing. Furthering our knowledge of these and other components related to the surface of the heterotypic collagen fibrils will allow us to make important strides in understanding the macromolecular organisation of this unique and fascinating tissue. In addition, it will open up new therapeutic opportunities as it will allow the development of therapeutic reagents that can be used to modulate vitreous gel structure and thus treat a number of common, potentially blinding, ocular conditions.

Hearing loss in the nonocular Stickler syndrome caused by a COL11A2 mutation

OBJECTIVE

Evaluation of hearing impairment as a feature of the nonocular Stickler syndrome (type II) linked to COL11A2.

STUDY DESIGN

Family study.

METHODS

General, orthopaedic, ophthalmologic, and otorhinolaryngologic examinations were performed on 15 affected persons in a Dutch family. Audiograms were obtained and/or retrieved from elsewhere. Cross-sectional and longitudinal analyses were conducted on the hearing threshold (sensorineural component) in relation to the patient's age to evaluate whether hearing impairment was progressive.

RESULTS

Mixed hearing loss, i.e., including a substantial air-bone gap of up to 20 to 60 dB, was present in six cases, concomitantly with a submucous or overt cleft palate in five of them. The audiograms in 14 evaluable cases showed the following types of threshold: U-shaped (n = 3), flat (n = 2), flat or gently (downward) sloping (n = 3), gently sloping (n = 3), or steeply sloping (n = 3). Cross-sectional analysis did not reveal any significant effect of age on sensorineural hearing impairment.

CONCLUSION

In contrast to the classic Stickler syndrome (type I) with high myopia, this nonocular type shows a high prevalence of sensorineural hearing impairment. The mean sensorineural hearing threshold in our patients was about 40 dB HL (95% CI, 15-65 dB) and was liable to increase (presumably by presbycusis) by several tens of decibels at the highest frequencies. Given the tendency for otitis media to develop in many of these patients, appropriate otologic care is of major importance.

Autosomal recessive disorder otospondylomegaepiphyseal dysplasia is associated with loss-of-function mutations in the COL11A2 gene

Otospondylomegaepiphyseal dysplasia (OSMED) is an autosomal recessive skeletal dysplasia accompanied by severe hearing loss. The phenotype overlaps that of the autosomal dominant disorders-Stickler and Marshall syndromes-but can be distinguished by disproportionately short limbs, severe hearing loss, and lack of ocular involvement. In one family with OSMED, a homozygous Gly-->Arg substitution has been described in COL11A2, which codes for the alpha2 chain of type XI collagen. We report seven further families with OSMED. All affected individuals had a remarkably similar phenotype: profound sensorineural hearing loss, skeletal dysplasia with limb shortening and large epiphyses, cleft palate, an extremely flat face, hypoplasia of the mandible, a short nose with anteverted nares, and a flat nasal bridge. We screened affected individuals for mutations in COL11A2 and found different mutations in each family. Individuals from four families, including three with consanguineous parents, were homozygous for mutations. Individuals from three other families, in whom parents were nonconsanguineous, were compound heterozygous. Of the 10 identified mutations, 9 are predicted to cause premature termination of translation, and 1 is predicted to cause an in-frame deletion. We conclude that the OSMED phenotype is highly homogenous and results from homozygosity or compound heterozygosity for COL11A2 mutations, most of which are predicted to cause complete absence of alpha2(XI) chains.

Mutations in COL11A2 cause non-syndromic hearing loss (DFNA13)

We report that mutation of COL11A2 causes deafness previously mapped to the DFNA13 locus on chromosome 6p. We found two families (one American and one Dutch) with autosomal dominant, non-syndromic hearing loss to have mutations in COL11A2 that are predicted to affect the triple-helix domain of the collagen protein. In both families, deafness is non-progressive and predominantly affects middle frequencies. Mice with a targeted disruption of Col11a2 also were shown to have hearing loss. Electron microscopy of the tectorial membrane of these mice revealed loss of organization of the collagen fibrils. Our findings revealed a unique ultrastructural malformation of inner-ear architecture associated with non-syndromic hearing loss, and suggest that tectorial membrane abnormalities may be one aetiology of sensorineural hearing loss primarily affecting the mid-frequencies.

Splicing mutations of 54-bp exons in the COL11A1 gene cause Marshall syndrome, but other mutations cause overlapping Marshall/Stickler phenotypes

Stickler and Marshall syndromes are dominantly inherited chondrodysplasias characterized by midfacial hypoplasia, high myopia, and sensorineural-hearing deficit. Since the characteristics of these syndromes overlap, it has been argued whether they are distinct entities or different manifestations of a single syndrome. Several mutations causing Stickler syndrome have been found in the COL2A1 gene, and one mutation causing Stickler syndrome and one causing Marshall syndrome have been detected in the COL11A1 gene. We characterize here the genomic structure of the COL11A1 gene. Screening of patients with Stickler, Stickler-like, or Marshall syndrome pointed to 23 novel mutations. Genotypic-phenotypic comparison revealed an association between the Marshall syndrome phenotype and splicing mutations of 54-bp exons in the C-terminal region of the COL11A1 gene. Null-allele mutations in the COL2A1 gene led to a typical phenotype of Stickler syndrome. Some patients, however, presented with phenotypes of both Marshall and Stickler syndromes.

The spinal manifestations of Stickler's syndrome

STUDY DESIGN

A review of current knowledge, clinical publications, and recent concepts of the causes of Stickler's syndrome was correlated with a clinical review of the condition at the Children's Hospital of Eastern Ontario, Canada.

OBJECTIVES

To acquaint orthopedic spine surgeons with the natural history, associated anomalies, and high incidence of spinal deformity and scoliosis in children with Stickler's syndrome.

SUMMARY OF BACKGROUND DATA

Stickler's syndrome is a hereditary, progressive arthro-ophthalmopathy with an autosomal dominant inheritance pattern. The estimated incidence is 1 in 10,000 people, which is slightly more common than Marfan syndrome.

METHODS

The experience with Stickler's syndrome was reviewed in seven children, 2-15 years of age, with particular attention to the spinal abnormalities secondary to the connective tissue dysplasia.

RESULTS

Six of the children had kyphosis or scoliosis, and four had wedging or flattening of the vertebrae or platyspondylia. In general, the spinal changes became more prominent in the older children with Stickler's syndrome, with the spinal vertebrae affected by the generalized epiphyseal dysplasia. The treatment of scoliosis and kyphosis is no different in children with Stickler's syndrome. The most difficult aspect is in diagnosing the condition.

CONCLUSIONS

The importance of recognizing the syndrome is to allow for the investigation and treatment of the many other associated connective tissue disorders associated with Stickler's syndrome, such as the high incidence of retinal detachment, mitral valve prolapse, and mandibular hypoplasia that may result in problems with anesthesia should the spine require surgical stabilization.

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.

Heterozygous glycine substitution in the COL11A2 gene in the original patient with the Weissenbacher-Zweymüller syndrome demonstrates its identity with heterozygous OSMED (nonocular Stickler syndrome)

The original patient with the Weissenbacher-Zweymüller syndrome was analyzed for mutations in two candidate genes expressed in cartilage (COL2A1 and COL11A2). No mutations were found in the COL2A1 gene but the COL11A2 gene contained a single-base mutation that converted a codon for an obligate glycine to a codon for glutamate at position alpha 2-955 (G955E). The results here and those published previously indicate that the Weissenbacher-Zweymüller syndrome (heterozygous OSMED), nonocular Stickler syndrome, and homozygous OSMED are all caused by mutations in the COL11A2 gene.