Dominant Stickler Syndrome

Unraveling the genetic collagen connection: clinical and therapeutic insights on genetic connective tissue disorders

Hereditary connective tissue disorders include more than 200 conditions affecting different organs and tissues, compromising the biological role of the extracellular matrix through interference in the synthesis, development, or secretion of collagen and/or its associated proteins. The clinical phenotype includes multiple signs and symptoms, usually nonspecific but of interest to rheumatologists because of musculoskeletal involvement. The patient´s journey to diagnosis is long, and physicians should include these disorders in their differential diagnoses of diseases with systemic involvement. In this review, insights for the diagnosis and treatment of osteogenesis imperfecta, hypermobility spectrum disorder/Ehlers-Danlos syndrome, Marfan, Loeys-Dietz, and Stickler syndromes are presented.

Ophthalmic manifestations of Czech dysplasia

Czech dysplasia is an autosomal dominant type 2 collagenopathy that is caused by heterozygosity for the recurrent p.(Arg275Cys) COL2A1 variant. Affected individuals usually present with skeletal abnormalities such as metatarsal hypoplasia of the third and fourth toes and early-onset arthropathy, as well as hearing loss. To date, no ophthalmic findings have been reported in patients with Czech dysplasia even though COL2A1 has been implicated in other ocular conditions such as type 1 Stickler syndrome. For the first time, we report the ocular findings in four families with Czech dysplasia, including type 1 vitreous anomaly, hypoplastic vitreous, retinal tears, and significant refractive error. These novel ocular findings expand the phenotype associated with Czech dysplasia and may aid clinicians as an additional diagnostic feature. Patients with congenital abnormalities of vitreous gel architecture have an increased risk of retinal detachment, and as such, patients may benefit from prophylaxis. Considering that many of the patients did not report any ocular symptoms, vitreous phenotyping is of key importance in identifying the need for counseling with regard to prophylaxis.

Glycosylation Modulates the Structure and Functions of Collagen: A Review

Collagens are fundamental constituents of the extracellular matrix and are the most abundant proteins in mammals. Collagens belong to the family of fibrous or fiber-forming proteins that self-assemble into fibrils that define their mechanical properties and biological functions. Up to now, 28 members of the collagen superfamily have been recognized. Collagen biosynthesis occurs in the endoplasmic reticulum, where specific post-translational modification-glycosylation-is also carried out. The glycosylation of collagens is very specific and adds β-d-galactopyranose and β-d-Glcp-(1→2)-d-Galp disaccharide through β-O-linkage to hydroxylysine. Several glycosyltransferases, namely COLGALT1, COLGALT2, LH3, and PGGHG glucosidase, were associated the with glycosylation of collagens, and recently, the crystal structure of LH3 has been solved. Although not fully understood, it is clear that the glycosylation of collagens influences collagen secretion and the alignment of collagen fibrils. A growing body of evidence also associates the glycosylation of collagen with its functions and various human diseases. Recent progress in understanding collagen glycosylation allows for the exploitation of its therapeutic potential and the discovery of new agents. This review will discuss the relevant contributions to understanding the glycosylation of collagens. Then, glycosyltransferases involved in collagen glycosylation, their structure, and catalytic mechanism will be surveyed. Furthermore, the involvement of glycosylation in collagen functions and collagen glycosylation-related diseases will be discussed.

Microphthalmia and congenital cataract in two patients with Stickler syndrome type II: a case report

BACKGROUND

Stickler syndrome (STL) is a collagenopathy caused by pathogenic variants in collagen-coding genes, mainly COL2A1 or COL11A1 associated with Stickler syndrome type 1 (STL1) or type 2 (STL2), respectively. Affected individuals manifest ocular, auditory, articular, and craniofacial findings in varying degrees. Previous literature and case reports describe high variability in clinical findings for patients with STL. With this case report, we broaden the clinical spectrum of the phenotype.

MATERIALS AND METHODS

Case report on two members of a family (mother and son) including clinical examination and genetic testing using targeted trio whole exome sequencing (trio-WES).

RESULTS

A boy and his mother presented with microphthalmia, congenital cataract, ptosis, and moderate-to-severe sensorineural hearing loss. Trio-WES found a novel heterozygote missense variant, c.4526A>G; p(Gln1509Arg) in COL11A1 in both affected individuals.

CONCLUSIONS

We report a previously undescribed phenotype associated with a COL11A1-variant in a mother and son, expanding the spectrum for phenotype-genotype correlation in STL2, presenting with microphthalmia, congenital cataract, and ptosis not normally associated with Stickler syndrome.

Case report: Autosomal recessive type 3 Stickler syndrome caused by compound heterozygous mutations in COL11A2

Background: Stickler syndrome (SS) is a group of hereditary collagenopathies caused by a variety of collagen and non-collagen genes. Affected patients have characteristic manifestations involving ophthalmic, articular, craniofacial and auditory disorders. SS is classified into several subtypes according to clinical and molecular features. Type 3 SS is an ultra-rare disease, known as non-ocular SS or otospondylomegaepiphyseal dysplasia (OSMED) with only a few pathogenic COL11A2 variants reported to date. Case presentation: A 29-year-old Chinese male was referred to our hospital for hearing loss and multiple joint pain. He presented a phenotype highly suggestive of OSMED, including progressive sensorineural deafness, spondyloepiphyseal dysplasia with large epiphyses, platyspondyly, degenerative osteoarthritis, and sunken nasal bridge. We detected compound heterozygous mutations in COL11A2, both of which were predicted to be splicing mutations. One is synonymous mutation c.3774C>T (p.Gly1258Gly) supposed to be a splice site mutation, the other is a novel intron mutation c.4750 + 5 G>A, which is a highly conservative site across several species. We also present a review of the current known pathogenic mutation spectrum of COL11A2 in patients with type 3 SS. Conclusion: Both synonymous extonic and intronic variants are easily overlooked by whole-exome sequencing. For patients with clinical manifestations suspected of SS syndrome, next-generation whole-genome sequencing is necessary for precision diagnosis and genetic counseling.

Characteristics of a Three-Generation Family with Stickler Syndrome Type I Carrying Two Different COL2A1 Mutations

Stickler Syndrome is typically characterized by ophthalmic manifestations including vitreous degeneration and axial lengthening that predispose to retinal detachment. Systemic findings consist of micrognathia, cleft palate, sensorineural hearing loss, and joint abnormalities. COL2A1 mutations are the most common, however, there is a lack of genotype-phenotype correlations. Retrospective, single-center case series of a three-generation family. Clinical features, surgical requirements, systemic manifestations, and genetic evaluations were collected. Eight individuals clinically displayed Stickler Syndrome, seven of whom had genetic confirmation, and two different COL2A1 mutations (c.3641delC and c.3853G>T) were identified. Both mutations affect exon 51, but display distinct phenotypes. The c.3641delC frameshift mutation resulted in high myopia and associated vitreous and retinal findings. Individuals with the c.3853G>T missense mutation exhibited joint abnormalities, but mild ocular manifestations. One individual in the third generation was biallelic heterozygous for both COL2A1 mutations and showed ocular and joint findings in addition to autism and severe developmental delay. These COL2A1 mutations exhibited distinct eye vs. joint manifestations. The molecular basis for these phenotypic differences remains unknown and demonstrates the need for deep phenotyping in patients with Stickler syndrome to correlate COL2A1 gene function and expression with ocular and systemic findings.

The Genetic Confirmation and Clinical Characterization of LOXL3-Associated MYP28: A Common Type of Recessive Extreme High Myopia

Purpose

In previous studies, biallelic LOXL3 variants have been shown to cause autosomal recessive Stickler syndrome in one Saudi Arabian family or autosomal recessive early-onset high myopia (eoHM, MYP28) in two Chinese families. The current study aims to elucidate the clinical and genetic features of LOXL3-associated MYP28 in seven new families and two previously published families.

Methods

LOXL3 variants were detected based on the exome sequencing data of 8389 unrelated probands with various ocular conditions. Biallelic variants were identified through multiple online bioinformatic tools, comparative analysis, and co-segregation analysis. The available clinical data were summarized.

Results

Biallelic LOXL3 variants were exclusively identified in nine of 1226 families with eoHM but in none of the 7163 families without eoHM (P = 2.97 × 10-8, Fisher's exact test), including seven new and two previously reported families. Seven pathogenic variants were detected, including one nonsense (c.1765C>T/p.Arg589*), three frameshift (c.39dupG/p.Leu14Alafs*21; c.544delC/p.Leu182Cysfs*3, c.594delG/p.Gln199Lysfs*35), and three missense (c.371G>A/p.Cys124Tyr; c.1051G>A/p.Gly351Arg; c.1669G>A/p.Glu557Lys) variants. Clinical data of nine patients from nine unrelated families revealed myopia at the first visit at about 5 years of age, showing slow progression with age. Visual acuity at the last visit ranged from 0.04 to 0.9 (median age at last visit = 5 years, range 3.5-15 years). High myopic fundus changes, observed in all nine patients, were classified as tessellated fundus (C1) in five patients and diffuse choroidal atrophy (C2) in four patients. Electroretinograms showed mildly reduced cone responses and normal rod responses. Except for high myopia, no other specific features were shared by these patients.

Conclusions

Biallelic LOXL3 variants exclusively presenting in nine unrelated patients with eoHM provide firm evidence implicating MYP28, with an estimated prevalence of 7.3 × 10-3 in eoHM and of about 7.3 × 10-5 in the general population for LOXL3-associated eoHM. So far, MYP28 represents a common type of autosomal recessive extreme eoHM, with a frequency comparable to LRPAP1-associated MYP23.

LASER PROPHYLAXIS IN STICKLER SYNDROME: The Manchester Protocol

PURPOSE

Patients with Stickler syndrome are at high risk of giant retinal tears (GRTs) and detachments. Vitreoretinal interventions can reduce this risk, but there is presently no consensus about the optimal prophylactic approach. The aim of our study was to determine whether 360° laser prophylaxis is a safe and effective procedure to prevent GRT detachments in patients with Stickler syndrome.

METHODS

Study subjects were recruited retrospectively through the databases of the vitreoretinal and ophthalmic genetic tertiary services in Manchester, United Kingdom. Clinical data were collected including on prophylactic intervention, the occurrence of retinal detachment, and the presence/type of retinal breaks.

RESULTS

One hundred thirteen eyes from 63 patients with Stickler syndrome were studied; 72.6% (82/113) of these eyes received 360° laser prophylaxis. Of these, 9% had a retinal detachment, but no GRTs occurred. Among the 27.4% (31/113) of eyes that had no prophylactic treatment, 23% suffered a retinal detachment and 42.9% of these were associated with a GRT.

CONCLUSION

Patients who underwent laser prophylaxis had fewer retinal detachments and no GRTs during an average of 6.1 years of follow-up (median 5 years), suggesting that this is a safe and effective approach for individuals with Stickler syndrome.

Hearing Loss in Stickler Syndrome: An Update

Stickler syndrome is a connective tissue disorder characterized by ocular, skeletal, orofacial and auditory manifestations. Its main symptoms are high myopia, retinal detachment, joint hypermobility, early osteoarthritis, cleft palate, midfacial hypoplasia, micrognathia and hearing loss. Large phenotypical variability is apparent and partly explained by the underlying genetic heterogeneity, including collagen genes (COL2A1, COL11A1, COL11A2, COL9A1, COL9A2, COL9A3) and non-collagen genes (BMP4, LRP2, LOXL3). The most frequent type of Stickler syndrome (COL2A1) is characterized by a rather mild high-frequency sensorineural hearing loss in about half of the patients. COL11A1- and COL11A2-related Stickler syndrome results in more frequent hearing loss, being moderate and involving all frequencies. Hearing loss in the rarer types of Stickler syndrome depends on the gene expression in the cochlea, with moderate to severe downsloping hearing loss for Stickler syndrome caused by biallelic type IX collagen gene mutations and none or mild hearing loss for the non-collagen genes. Inherent to the orofacial manifestations, middle ear problems and temporary conductive hearing loss, especially at young age, are also prevalent. Consequently, hearing loss should be actively sought for and adequately treated in Stickler syndrome patients given its high prevalence and the concomitant visual impairment in most patients.