Ocular complications and prophylactic strategies in Stickler syndrome: a systematic literature review

BACKGROUND

Stickler syndrome is a collagenopathy caused by mutations in the genes COL2A1 (STL1) or COL11A1 (STL2). Affected patients manifest ocular, auditory, articular, and craniofacial manifestations in varying degrees. Ocular symptoms include myopia, retinal detachment, cataract, and glaucoma. The aim of this systematic review was to evaluate the prevalence of ocular manifestations and the outcome of prophylactic treatment on reducing the risk of retinal detachment.

METHOD

A systematic literature search was performed in the PubMed database. Information on the cross-study prevalence of myopia, retinal detachment, cataract, glaucoma, visual impairment, severity and age of onset of myopia and retinal detachments. Studies that reported on the outcome of prophylactic treatment against a control group were explored.

RESULTS

37 articles with 2324 individual patients were included. Myopia was found in 83% of patients, mostly of a moderate to severe degree. Retinal detachments occurred in 45% of patients. Generally, the first detachment occurred in the second decade of life in STL1 patients and later in STL2. Cataracts were more common in STL2 patients, 59% versus 36% in STL1. Glaucoma (10%) and visual impairment (blind: 6%; vision loss in one eye: 10%) were rare. Three studies reported on the effect of prophylactic treatment being protective.

CONCLUSION

Ocular manifestations are common in Stickler patients, but the comparison between studies was difficult because of inconsistencies in diagnostic and inclusion criteria by different studies. Sight-threatening complications such as retinal detachments are common but although prophylactic therapy is reported to be effective in retrospective studies, evidence from randomized trials is missing.

Stickler syndrome, ocular-only variants and a key diagnostic role for the ophthalmologist

The entity described by Gunnar Stickler, which included hereditary arthro-ophthalmopathy associated with retinal detachment, has recently been recognised to consist of a number of subgroups, which might now more correctly be referred to as the Stickler syndromes. They are the most common clinical manifestation of the type II/XI collagenopathies and are the most common cause of inherited rhegmatogenous retinal detachment. This review article is intended to provide the ophthalmologist with an update on current research, subgroups, and their diagnosis together with a brief overview of allied conditions to be considered in the clinical differential diagnosis. We highlight the recently identified subgroups with a high risk of retinal detachment but with minimal or absent systemic involvement--a particularly important group for the ophthalmologist to identify.

Disturbed synthesis of type II collagen interferes with rate of bone formation and growth and increases bone resorption in transgenic mice

Transgenic mice carrying an internally deleted human type II collagen gene (COL2A1) were used to study bone growth and development. This mutation has previously been shown to disturb the development of collagen fibrils in articular cartilage, causing chondrodysplasia and osteoarthritis. Type II collagen expression in bones was investigated with immunohistochemistry. The development and mineralization of the skeleton and anthropometric measurements on bones were evaluated using X-rays and dynamic histomorphometry. Type II collagen was expressed in the cartilage of developing bones. The bones of transgenic mice were smaller compared with the controls. The bone mass remained almost unchanged in transgenic mice after 1 month of age, leading to differences of 47% in trabecular bone volume (P = 0.012) and 40% in trabecular thickness (P < 0.01) at the age of 3 months compared with controls. At the age of 3 months the eroded surface per bone volume was 31% greater in transgenic mice compared with controls (P < 0.05). Trabecular thickness correlated positively with body weight (R = 0.71, P < 0.001). Interestingly, body weight correlated with bone volume in control mice (R = 0.27, P < 0.01), but no correlation was observed in transgenic mice. The disturbed synthesis of cartilage-specific type II collagen in growing transgenic mice retarded bone development, increased bone resorption, and altered tissue properties. This led to a negative net bone balance and small bone size. The results support the idea that an altered synthesis of cartilage-specific molecule(s) can disturb postnatal bone development and growth.

Clinical aspects of hereditary hearing loss

Hearing loss is an etiologically diverse condition with many disease-related complications and major clinical, social, and quality of life implications. As the rate of acquired hearing loss secondary to environmental causes decreases and improvements in the diagnosis of abnormalities occur, the significance of genetic factors that lead to deafness increases. Advancements in molecular biology have led to improved detection and earlier intervention in patients with hearing loss. Subsequently, earlier implementation of educational services and cochlear implant technology in patients with profound hearing loss now results in superior communication skills and enhanced language development. The aim of this review is to provide a comprehensive framework underlying the causes of hearing impairment and to detail the clinical management for patients with hereditary hearing loss.

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.

Lymphocyte enhancer-binding factor 1 (Lef1) inhibits terminal differentiation of osteoblasts

Lef1 is a transcriptional regulator of the Wnt/beta-catenin signaling cascade. Wnts directly augment bone formation and osteoblast differentiation from mesenchymal stem cells by receptor-mediated pathways involving Lrp5 and Frizzled. We previously reported that Lef1 represses Runx2-dependent activation of the late osteoblast differentiation gene, osteocalcin. Lef1 is expressed in preosteoblasts but is undetectable in fully differentiated osteoblasts. To determine if downregulation of Lef1 is necessary for osteoblast maturation, we constitutively overexpressed Lef1 in MC3T3-E1 preosteoblasts. Lef1-overexpressing cells produced alkaline phosphatase (ALP) and osteocalcin later, and at lower levels than control cells. Moreover, the extracellular matrices of Lef1-overexpressing cell cultures never mineralized. To further examine the role of Lef1 in osteoblasts, we suppressed Lef1 expression in MC3T3-E1 cells by RNA interference. Transient expression of a Lef1 shRNA efficiently reduced murine Lef1 levels and transcriptional activity. Stable suppression of Lef1 in MC3T3 preosteoblasts did not affect proliferation or Runx2 levels; however, ALP production and matrix mineralization were accelerated by 3-4 days. Gene chip analyses identified 14 genes that are differentially regulated in Lef1-suppressed cells. These data outline a role for Lef1 in delaying osteoblast maturation and suggest that Lef1 controls the expression of multiple genes in osteoblasts.

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.

Skeletal dysplasias and the osteoarthritic phenotype

In contrast to late-onset osteoarthritis (OA), the appearance of precocious OA has historically been recognized as a particularly aggressive form of the disorder that is frequently inherited as a Mendelian trait. In general, precocious OA appears as a consequence of many skeletal dysplasias, which, although individually rare, comprise a sizable population of patients when viewed in toto. In these patients the disease is often rapidly progressive and includes features of articular and extra-articular involvement that are not typical of classic OA. The molecular pathology of the chondro-osseous disorders has been the focus of intense study in recent years, with the promise of providing insight into skeletal development and homeostasis, as well as the aetiology and pathogenesis of degenerative joint disease.

Snowflake vitreoretinal degeneration

PURPOSE

The ocular findings, systemic features, and genetic loci distinguishing known genetic causes of vitreoretinal degenerations were studied in the original Snowflake family.

DESIGN

Prospective, comparative study and molecular genetic investigation.

PARTICIPANTS

Members of the original snowflake vitreoretinal degeneration family.

METHODS

Clinical data were collected on 26 family members by history and examination. Thirteen of the 26 total family members underwent prospective examination. Linkage to known vitreoretinal degeneration loci (COL2A1, COL11A1, and the Wagner disease locus) was evaluated with short tandem repeat markers.

MAIN OUTCOME MEASURES

Ocular and systemic features of known vitreoretinal degenerations.

RESULTS

Six of the 13 prospectively examined subjects had snowflake vitreoretinal degeneration. Corneal guttae (4/5; 80%), early onset cataract (5/6; 83%), fibrillar vitreous degeneration (6/6; 100%), and peripheral retinal abnormalities (5/6; 83%), including minute crystallinelike deposits called snowflakes (4/6; 67%), were common. Retinal detachment was seen in 1 of 6 of these prospectively examined subjects (17%). A total of 14 affected subjects were identified within the family, and in 3 (21%), retinal detachment developed. Orofacial features, early-onset hearing loss, and arthritis typical of Stickler syndrome were absent. Linkage to known vitreoretinal degeneration loci was excluded.

CONCLUSIONS

The absence of vitreous gel in the retrolental space and presence of fibrillar vitreous degeneration were consistent with the vitreous structure reported for collagen 11A1 (COL11A1) but not collagen 2A1 (COL2A1) mutations. The absence of systemic features was characteristic of the vitreoretinopathies linked to chromosome 5q13 (Wagner disease and erosive vitreoretinopathy) and mutations in exon 2 of the COL2A1 gene. Snowflakes in the peripheral retina and the absence of nyctalopia, posterior chorioretinal atrophy, and tractional retinal detachment were inconsistent with the chromosome 5q13 vitreoretinopathies. The association of Fuchs' corneal endothelial dystrophy found in this family has not been reported previously in other vitreoretinal degenerations. These findings and the exclusion of known genetic loci suggest snowflake is a distinct vitreoretinal degeneration.

Identification, characterization and expression analysis of a new fibrillar collagen gene, COL27A1

The fibrillar collagens provide structural scaffolding and strength to the extracellular matrices of connective tissues. We identified a partial sequence of a new fibrillar collagen gene in the NCBI databases and completed the sequence with bioinformatic approaches and 5' RACE. This gene, designated COL27A1, is approximately 156 kbp long and has 61 exons located on chromosome 9q32-33. The homologous mouse gene is located on chromosome 4. The gene encodes amino- and carboxyl-terminal propeptides similar to those in the 'minor' fibrillar collagens. The triple-helical domain is, however, shorter and contains 994 amino acids with two imperfections of the Gly-Xaa-Yaa repeat pattern. There were three sites of alternative RNA splicing, only one of which led to the intact mRNA that encodes this full-length collagen proalpha chain. Phylogenetic analyses indicated that COL27A1 forms a clade with COL24A1 that is distinct from the two known lineages of fibrillar collagens. Expression analyses of the mouse col27a1 gene demonstrated high expression in cartilage, the eye and ear, but also in lung and colon. It is likely that the major protein product of COL27A1, proalpha1(XXVII), is a component of the extracellular matrices of cartilage and these other tissues. Study of this collagen should yield insights into normal chondrogenesis, and provide clues to the pathogenesis of some chondrodysplasias and disorders of other tissues in which this gene is expressed.

Clinical variability of Stickler syndrome: role of exon 2 of the collagen COL2A1 gene

Stickler syndrome (progressive arthro-ophthalmopathy) is a genetically heterogeneous disorder resulting from mutations in at least three collagen genes. The most common disease-causing gene is COL2A1, a 54-exon-containing gene coding for type II collagen. At least 17 different mutations causing Stickler syndrome have been reported in this gene. Phenotypically, it is also a variably expressed disorder in which most patients present with a wide range of eye and extraocular manifestations including auditory, skeletal, and orofacial manifestations. Some patients, however, present without clinically apparent systemic findings. This observation has led to difficulty distinguishing this Stickler phenotype from other hereditary vitreoretinal degenerations, such as Wagner syndrome and Snowflake vitreoretinal degeneration. In this regard, review of the literature indicates type II collagen exists in two forms resulting from alternative splicing of exon 2 of the COL2A1 gene. One form, designated as type IIB (short form), is preferentially expressed in adult cartilage tissue. The other form, designated as type IIA (long form), is preferentially expressed in the vitreous body of the eye. Because of this selective tissue expression, mutations in exon 2 of the COL2A1 gene have been hypothesized to produce this Stickler syndrome phenotype with minimal or absent extraocular findings. We review the evidence for families with exon 2 mutations of the collagen COL2A1 gene presenting in a distinct manner from families with mutations in the remaining 53 exons, as well as other hereditary vitreoretinal degenerations without significant systemic manifestations.

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.

Molecular genetics of rhegmatogenous retinal detachment

Rhegmatogenous retinal detachment (RRD) most commonly occurs as a spontaneous event resulting from posterior vitreous detachment, typically between the ages of 40-70 yrs. It is also a feature in some inherited disorders, most commonly Stickler syndrome. The relationship between these inherited disorders and the spontaneous cases is unclear. Here in particular we review Stickler syndrome, and discuss the differential diagnosis of Stickler, Wagner and Marshall syndromes. Other rare inherited disorders associated with RRD are also briefly reviewed.

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.

Clinical features of hereditary progressive arthro-ophthalmopathy (Stickler syndrome): a survey

PURPOSE

To define variations in the clinical manifestations of Stickler syndrome.

METHODS

A questionnaire was sent to 612 persons.

RESULTS

Of the 316 usable replies, 95% of persons had eye problems (retinal detachment occurred in 60% of patients, myopia in 90%, and blindness in 4%); 84% had problems with facial structures such as a flat face, small mandible, or cleft palate; 70%, hearing loss; and 90%, joint problems, primarily early joint pain from degenerative joint disease. Treatment included cryotherapy and laser therapy for retinal detachment, repair of cleft palate, use of hearing and mobility aids, and joint replacements.

CONCLUSIONS

There are wide variations of symptoms and signs among affected persons, even within the same family. There are delays in diagnosis, lack of understanding among family members, denial about the risk of serious eye problems, and joint disease.

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.

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.

Identification in vitreous and molecular cloning of opticin, a novel member of the family of leucine-rich repeat proteins of the extracellular matrix

A prominent 45-kDa component was identified by protein staining following SDS-polyacrylamide gel electrophoresis of a 4 M guanidine hydrochloride extract from bovine vitreous collagen fibrils. Peptide sequences obtained from this component were used as a basis for the cloning (from human retinal cDNA) and sequencing of a novel member of the leucine-rich repeat extracellular matrix protein family that we have named opticin. Opticin mRNA was found by reverse transcription polymerase chain reaction in ligament and skin as well as in retina. An open reading frame containing 332 amino acids was identified, the first 19 amino acids representing a signal peptide. The deduced amino acid sequence of the mature protein encodes a 35-kDa protein with a calculated isoelectric point of 5.4. The central domain of this protein consists of six B-type leucine-rich repeats. This domain is flanked by cysteine clusters including a C-terminal two-cysteine cluster containing an additional leucine-rich repeat. The N-terminal region contains a cluster of potential O-glycosylation sites, and analysis of bovine vitreous opticin demonstrated the presence of sialylated O-linked oligosaccharides substituting the core protein. Opticin shows highest protein sequence identity to epiphycan (42%) and osteoglycin (35%) and belongs to Class III of the leucine-rich repeat extracellular matrix protein family.

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.