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

Pathobiology of the crystalline lens in Stickler syndrome

PURPOSE

The Stickler syndromes are a group of connective tissue disorders characterised by congenital myopia, giant retinal tear and retinal detachment, cleft palate, hearing loss and premature arthropathy. Patients with Stickler syndrome are also susceptible to abnormalities of the crystalline lens. Since neither type II or type XI collagen (those typically affected in the vast majority of Stickler patients) are highly expressed in the lens, this observational cohort study explores potential alternative mechanisms to explain why patients frequently exhibit such unusual but characteristic types of cataract.

METHODS

Author observations drawn from a cohort of over 1,800 patients with genetically confirmed Stickler syndrome.

RESULTS

3 distinct lens pathologies were identified. Firstly, a congenital quadrantic lamellar opacity. This can be present in both type 1 (COL2A1) and type 2 (COL11A1) Stickler syndrome. Secondly, early onset Pantone 557 C blue-green nuclear cataract. Thirdly, congenital lens coloboma associated with localised zonule deficiency.

CONCLUSIONS

The characteristic quadrantic lamellar lens opacity can be helpful in alerting to the possible diagnosis, particularly in sub-groups with an ocular-only phenotype. Temporal and spatial signalling pathways shared embryologically by both the developing vitreous body and crystalline lens suggest an ancillary role of the fibrillar collagens in cell signalling beyond their basic structural function. A common pathway of TGFb/BMP super-family dysregulation may be shared with allied disorders associated with both retinal detachment and cataract as well as the pathobiology linking retinal detachment and cataract in the population at large. Congenital lens coloboma associated with localised zonule deficiency can increase the difficulty and risks of cataract surgery. Strategies to mitigate such risks are presented.

Natural selection on feralization genes contributed to the invasive spread of wild pigs throughout the United States

Despite a long presence in the contiguous United States (US), the distribution of invasive wild pigs (Sus scrofa × domesticus) has expanded rapidly since the 1980s, suggesting a more recent evolutionary shift towards greater invasiveness. Contemporary populations of wild pigs represent exoferal hybrid descendants of domestic pigs and European wild boar, with such hybridization expected to enrich genetic diversity and increase the adaptive potential of populations. Our objective was to characterize how genetic enrichment through hybridization increases the invasiveness of populations by identifying signals of selection and the ancestral origins of selected loci. Our study focused on invasive wild pigs within Great Smoky Mountains National Park, which represents a hybrid population descendent from the admixture of established populations of feral pigs and an introduction of European wild boar to North America. Accordingly, we genotyped 881 wild pigs with multiple high-density single-nucleotide polymorphism (SNP) arrays. We found 233 markers under putative selection spread over 79 regions across 16 out of 18 autosomes, which contained genes involved in traits affecting feralization. Among these, genes were found to be related to skull formation and neurogenesis, with two genes, TYRP1 and TYR, also encoding for crucial melanogenesis enzymes. The most common haplotypes associated with regions under selection for the Great Smoky Mountains population were also common among other populations throughout the region, indicating a key role of putatively selective variants in the fitness of invasive populations. Interestingly, many of these haplotypes were absent among European wild boar reference genotypes, indicating feralization through genetic adaptation.

Posterior Precortical Vitreous Pocket in Stickler Syndrome: A Report of Two Cases

Stickler syndrome is a genetic disorder characterized by collagen abnormalities leading to various ocular manifestations, such as retinal detachment. We present two cases of siblings clinically diagnosed with Stickler syndrome who exhibited retinal detachment. Case 1, a seven-year-old girl, and case 2, her 14-year-old brother, both displayed severe myopia and other clinical signs consistent with Stickler syndrome. Despite their ages, neither case showed evidence of posterior precortical vitreous pocket (PPVP) on imaging or during surgical intervention. These findings suggest a potential relationship between collagen abnormalities and PPVP dysplasia in Stickler syndrome.

A Novel COL2A1 Gene Pathogenic Variant in a Turkish Family With Ocular Stickler Syndrome

A 6-month-old female infant with megalophthalmos was referred with the suspicion of congenital glaucoma. Refractive measurements obtained with handheld autorefractometry were -7.00 -2.00 × 90° in the right eye and -6.00 -2.00 × 100° in the left eye and ultrasonic axial lengths were 22.50 mm in both eyes. Intraocular pressures and vertical and horizontal corneal diameters of the proband were 11 mm Hg, 11 mm, and 11.50 mm in both eyes, respectively. She was diagnosed as having early-onset high myopia. Her father also had degenerative high myopia (-12.00 diopters) in the right eye, bilateral congenital lens opacities, and retinal detachment in the left eye. Her mother was emmetropic with normal eye examination results. Clinical exome sequencing analysis revealed a novel ENST00000380518.3 c.3528_3530 delins GACCATTAGCA (Chr12:48369813: GCA > TGCTAATGGTC) variant in the collagen type II alpha 1 chain (COL2A1) on chromosome 12q13 (OMIM 108300), consistent with the Stickler syndrome type 1. Subsequent segregation analysis revealed paternal inheritance. Although many pathogenic null variants have been described within the COL2A1 gene, there is currently no documented literature pertaining to this specific variant, making this the inaugural report of its manifestation in scientific discourse. [J Pediatr Ophthalmol Strabismus. 2024;61(3):e23-e27.].

The cochlear matrisome: Importance in hearing and deafness

The extracellular matrix (ECM) consists in a complex meshwork of collagens, glycoproteins, and proteoglycans, which serves a scaffolding function and provides viscoelastic properties to the tissues. ECM acts as a biomechanical support, and actively participates in cell signaling to induce tissular changes in response to environmental forces and soluble cues. Given the remarkable complexity of the inner ear architecture, its exquisite structure-function relationship, and the importance of vibration-induced stimulation of its sensory cells, ECM is instrumental to hearing. Many factors of the matrisome are involved in cochlea development, function and maintenance, as evidenced by the variety of ECM proteins associated with hereditary deafness. This review describes the structural and functional ECM components in the auditory organ and how they are modulated over time and following injury.

Whole-Exome Sequencing Among School-Aged Children With High Myopia

Importance

High myopia (HM) is one of the leading causes of visual impairment worldwide. Genetic factors are known to play an important role in the development of HM.

Objective

To identify risk variants in a large HM cohort and to examine the implications of genetic testing of schoolchildren with HM.

Design, Setting, and Participants

This cohort study retrospectively reviewed whole-exome sequencing (WES) results in 6215 schoolchildren with HM who underwent genetic testing between September 2019 and July 2020 in Wenzhou City, China. HM is defined as a spherical equivalent refraction (SER) of -6.00 diopters (D) or less. The study setting was a genetic testing laboratory and a multicenter school census. Data were analyzed from July 2021 to June 2022.

Main Outcomes and Measures

The frequency and distribution of positive germline variants, the percentage of individuals with HM in both eyes, and subsequent variant yield for common high myopia (CHM; -8.00 D ≤ SER ≤ -6.00 D), ultra myopia (UM; -10.00 D ≤ SER < -8.00 D), and extreme myopia (EM; SER < -10.00 D).

Results

Of the 6215 schoolchildren with HM, 3278 (52.74%) were male. Their mean (SD) age was 14.87 (2.02) years, including 355 students in primary school, 1970 in junior high school, and 3890 in senior high school. The mean (SD) SER was -7.51 (-1.36) D for the right eye and -7.46 (-1.34) D for the left eye. Among schoolchildren with HM, genetic testing yielded 271 potential pathogenic variants in 75 HM candidate genes in 964 diagnoses (15.52%). A total of 36 known variants were found in 490 HM participants (7.88%) and 235 protein-truncating variants (PTVs) in 506 participants (8.14%). Involved variant yield was significantly positively associated with SER (Cochran-Armitage test for trend Z = 2.5492; P = .01), which ranged from 7.66% in the CHM group, 8.70% in the UM group, to 11.90% in the EM group. We also found that primary school students with EM had the highest variant yield of PTVs (8 of 35 students [22.86%]), which was 1.77 and 4.78 times that of the UM and CHM, respectively.

Conclusions and Relevance

In this cohort study of WES for HM, several potential pathogenic variants were identified in a substantial number of schoolchildren with HM. The high variation frequency in younger students with EM can provide clues for genetic screening and clinical examinations of HM to promote long-term follow-up assessment.

The genetics and disease mechanisms of rhegmatogenous retinal detachment

Rhegmatogenous retinal detachment (RRD) is a sight threatening condition that warrants immediate surgical intervention. To date, 29 genes have been associated with monogenic disorders involving RRD. In addition, RRD can occur as a multifactorial disease through a combined effect of multiple genetic variants and non-genetic risk factors. In this review, we provide a comprehensive overview of the spectrum of hereditary disorders involving RRD. We discuss genotype-phenotype correlations of these monogenic disorders, and describe genetic variants associated with RRD through multifactorial inheritance. Furthermore, we evaluate our current understanding of the molecular disease mechanisms of RRD-associated genetic variants on collagen proteins, proteoglycan versican, and the TGF-β pathway. Finally, we review the role of genetics in patient management and prevention of RRD. We provide recommendations for genetic testing and prophylaxis of at-risk patients, and hypothesize on novel therapeutic approaches beyond surgical intervention.

Axial length shortening in myopic children with Stickler syndrome after repeated low-level red-light therapy

AIM

To report the myopia-controlling effect of repeated low-level red-light (RLRL) therapy in patients with Stickler syndrome (STL), an inherited collagenic disease typically presenting with early onset myopia.

METHODS

Three STL children, aged 3, 7, and 11y, received RLRL therapy throughout the follow-up period of 17, 3, and 6mo, respectively after exclusion of fundus anomalies. Data on best-corrected visual acuity (BCVA), intraocular pressure, cycloplegic subjective refraction, ocular biometrics, scanning laser ophthalmoscope, optical coherence tomography, genetic testing, systemic disease history, and family history were recorded.

RESULTS

At the initiation of the RLRL therapy, the spherical equivalent (SE) of 6 eyes from 3 patients ranged from -3.75 to -20.38 D, axial length (AL) were from 23.88 to 30.68 mm, and BCVA were from 0.4 to 1.0 (decimal notation). Myopia progression of all six eyes slowed down after RLRL therapy. AL in five out of the six eyes shortened -0.07 to -0.63 mm. No side effects were observed.

CONCLUSION

Three cases of STL whose progression of myopic shift and AL elongation are successfully reduced and even reversed after RLRL therapy.

Cartilage diversification and modularity drove the evolution of the ancestral vertebrate head skeleton

The vertebrate head skeleton has evolved a myriad of forms since their divergence from invertebrate chordates. The connection between novel gene expression and cell types is therefore of importance in this process. The transformation of the jawed vertebrate (gnathostome) head skeleton from oral cirri to jointed jaw elements required a diversity of cartilages as well as changes in the patterning of these tissues. Although lampreys are a sister clade to gnathostomes, they display skeletal diversity with distinct gene expression and histologies, a useful model for addressing joint evolution. Specifically, the lamprey tissue known as mucocartilage has noted similarities with the jointed elements of the mandibular arch in jawed vertebrates. We thus asked whether the cells in lamprey mucocartilage and gnathostome joint tissue could be considered homologous. To do this, we characterized new genes that are involved in gnathostome joint formation and characterized the histochemical properties of lamprey skeletal types. We find that most of these genes are minimally found in mucocartilage and are likely later innovations, but we do identify new activity for gdf5/6/7b in both hyaline and mucocartilage, supporting its role as a chondrogenic regulator. Contrary to previous works, our histological assays do not find any perichondrial fibroblasts surrounding mucocartilage, suggesting that mucocartilage is non-skeletogenic tissue that is partially chondrified. Interestingly, we also identify new histochemical features of the lamprey otic capsule that diverge from normal hyaline. Paired with our new insights into lamprey mucocartilage, we propose a broader framework for skeletal evolution in which an ancestral soxD/E and gdf5/6/7 network directs mesenchyme along a spectrum of cartilage-like features.

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.

FAMILIAL EXUDATIVE VITREOTINOPATHY-LIKE FEATURES IN STICKLER TYPE IV ASSOCIATED WITH NOVEL VARIANTS IN COL9A1

BACKGROUND/PURPOSE

To report a case of Stickler Type IV with familial exudative vitreoretinopathy phenotype.

METHODS

Retrospective case report.

RESULTS

A 24-year-old woman presented with right eye exotropia and decreased vision. She had no facial or typical retinal features of Stickler syndrome but complained of right-sided hearing loss and right-sided neck pain. Examination of the right eye showed a chronic combined exudative and traction retinal detachment with temporal retinal dragging associated with far temporal retinal exudations and fibrovascular proliferations. The left eye had an attached retina with large areas of peripheral temporal retinal nonperfusion on fluorescein angiography, sharply demarcated by end circulation vascular pruning and mild peripheral vascular leakage, consistent with familial exudative vitreoretinopathy phenotype. Genetic analysis identified two heterozygous c.1052C>A and c.1349A>G variants in COL9A1, but did not disclose any mutation in genes classically associated with familial exudative vitreoretinopathy.

CONCLUSION

Familial exudative vitreoretinopathy-like retinal vascular features can be the presenting sign in patients with Stickler syndrome Type IV.

Progressive degeneration of the retina in Loxl3 mutant mouse model of Stickler syndrome

Stickler syndrome is a multisystem collagenopathy with affected individuals exhibiting a high rate of ocular complications. Lysyl oxidase-like 3 (LOXL3) is a human disease gene candidate with a critical role in catalyzing collagen crosslinking. A homozygous missense variant of LOXL3 was reported in Stickler syndrome with severe myopia. However, the underlying mechanisms of the LOXL3 missense mutation that causes Stickler syndrome are unknown. In this study, a mouse model of Stickler syndrome induced by LOXL3 mutation (c.2027G ​> ​A, p.Cys676Try) was obtained using CRISPR/Cas9 gene editing techniques. The Loxl3 mutant mice exhibited perinatal death, spinal deformity, and cleft palate, and Loxl3 mutation also induced skeletal dysplasia and progressive visual degeneration. Furthermore, we observed the damage of the bruch's membrane (BrM) and an increase in the levels of glial fibrillary acidic protein (GFAP) and Rpe65 in the Loxl3 mutant mice. Thus, we provided the critical in vivo evidence that Loxl3 possibly has a pivotal role in maintaining the eye function.

Novel Exon 7 Deletions in TSPAN12 in a Three-Generation FEVR Family: A Case Report and Literature Review

Familial exudative vitreoretinopathy (FEVR) is a severe clinically and genetically heterogeneous disease that is characterized by vascular disorder. FEVR exhibits strikingly variable clinical phenotypes, ranging from asymptomatic to total blindness. In this case, we present a patient who was first treated as having high myopia and retinopathy but was finally diagnosed with FEVR caused by the heterozygous deletion of exon 7 in TSPAN12 with the aid of whole genome sequencing (WGS). Typical vascular changes, including vascular leakage and an avascular zone in the peripheral retina, were observed in the proband using fundus fluorescein angiography (FFA), and the macular dragging was shown to be progressing in the follow-up visit. Furthermore, the proband showed unreported TSPAN12-related phenotypes of FEVR: ERG (full-field electroretinogram) abnormalities and retinoschisis. Only mild vascular changes were exhibited in the FFA for the other three family members who carried the same deletion of exon 7 in TSPAN12. This case expands our understanding of the phenotype resulting from TSPAN12 mutations and signifies the importance of combining both clinical and molecular analysis approaches to establish a complete diagnosis.

Growth plate extracellular matrix defects and short stature in children

Many etiological factors causing short stature have already been identified in humans. In the last few years, the advent of new techniques for the detection of chromosomal and molecular abnormalities has made it possible to better identify patients with genetic causes of growth failure. Some of these factors directly affect the development and growth of the skeleton, since they damage the epiphyseal growth plate, where linear growth occurs, influencing chondrogenesis. In particular, defects in genes involved in the organization and function of the growth plate are responsible for several well-known conditions with short stature. These genes play a pivotal role in various mechanisms involving the extracellular matrix, intracellular signaling, paracrine signaling, endocrine signaling, and epigenetic regulation. In this review, we will discuss the genes involved in extracellular matrix disorders. The identification of genetic defects in linear growth failure is important for clinicians and researchers in order to improve the care of children affected by growth disorders.

Zebrafish Model of Stickler Syndrome Suggests a Role for Col2a1a in the Neural Crest during Early Eye Development

Most cases of Stickler syndrome are due to autosomal-dominant COL2A1 gene mutations leading to abnormal type II collagen. Ocular findings include axial eye lengthening with vitreal degeneration and early-onset glaucoma, which can result in vision loss. Although COL2A1 is a major player in cartilage and bone formation, its specific role in eye development remains elusive. We investigated the role of Col2a1a in neural crest migration and differentiation during early zebrafish eye development. In situ hybridization, immunofluorescence, live imaging, exogenous treatments [10 μM diethylaminobenzaldehyde (DEAB), 100 nM all-trans retinoic acid (RA) and 1-3% ethanol (ETOH)] and morpholino oligonucleotide (MO) injections were used to analyze wildtype Casper (roy-/-;nacre-/-), TgBAC(col2a1a::EGFP), Tg(sox10::EGFP) and Tg(foxd3::EGFP) embryos. Col2a1a colocalized with Foxd3- and Sox10-positive cells in the anterior segment and neural crest-derived jaw. Col2a1a expression was regulated by RA and inhibited by 3% ETOH. Furthermore, MO knockdown of Col2a1a delayed jaw formation and disrupted the ocular anterior segment neural crest migration of Sox10-positive cells. Interestingly, human COL2A1 protein rescued the MO effects. Altogether, these results suggest that Col2a1a is a downstream target of RA in the cranial neural crest and is required for both craniofacial and eye development.

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.

Autosomal Recessive Stickler Syndrome

Stickler syndrome (SS) is a genetic disorder with manifestations in the eye, ear, joints, face and palate. Usually inherited in a dominant fashion due to heterozygous pathogenic variants in the collagen genes COL2A1 and COL11A1, it can rarely be inherited in a recessive fashion from variants in COL9A1, COL9A2, and COL9A3, COL11A1, as well as the non-collagen genes LRP2, LOXL3 and GZF1. We review the published cases of recessive SS, which comprise 40 patients from 23 families. Both homozygous and compound heterozygous pathogenic variants are found. High myopia is near-universal, and sensorineural hearing loss is very common in patients with variants in genes for type IX or XI collagen, although hearing appears spared in the LRP2 and LOXL3 patients and is variable in GZF1. Cleft palate is associated with type XI collagen variants, as well as the non-collagen genes, but is so far unreported with type IX collagen variants. Retinal detachment has occurred in 18% of all cases, and joint pain in 15%. However, the mean age of this cohort is 11 years old, so the lifetime incidence of both problems may be underestimated. This paper reinforces the importance of screening for SS in congenital sensorineural hearing loss, particularly when associated with myopia, and the need to warn patients and parents of the warning signs of retinal detachment, with regular ophthalmic review.

Comparative Genomics Provides Insights into Adaptive Evolution in Tactile-Foraging Birds

Tactile-foraging birds have evolved an enlarged principal sensory nucleus (PrV) but smaller brain regions related to the visual system, which reflects the difference in sensory dependence. The “trade-off” may exist between different senses in tactile foragers, as well as between corresponding sensory-processing areas in the brain. We explored the mechanism underlying the adaptive evolution of sensory systems in three tactile foragers (kiwi, mallard, and crested ibis). The results showed that olfaction-related genes in kiwi and mallard and hearing-related genes in crested ibis were expanded, indicating they may also have sensitive olfaction or hearing, respectively. However, some genes required for visual development were positively selected or had convergent amino acid substitutions in all three tactile branches, and it seems to show the possibility of visual degradation. In addition, we may provide a new visual-degradation candidate gene PDLIM1 who suffered dense convergent amino acid substitutions within the ZM domain. At last, two genes responsible for regulating the proliferation and differentiation of neuronal progenitor cells may play roles in determining the relative sizes of sensory areas in brain. This exploration offers insight into the relationship between specialized tactile-forging behavior and the evolution of sensory abilities and brain structures.

Glaucoma Syndromes: Insights into Glaucoma Genetics and Pathogenesis from Monogenic Syndromic Disorders

Monogenic syndromic disorders frequently feature ocular manifestations, one of which is glaucoma. In many cases, glaucoma in children may go undetected, especially in those that have other severe systemic conditions that affect other parts of the eye and the body. Similarly, glaucoma may be the first presenting sign of a systemic syndrome. Awareness of syndromes associated with glaucoma is thus critical both for medical geneticists and ophthalmologists. In this review, we highlight six categories of disorders that feature glaucoma and other ocular or systemic manifestations: anterior segment dysgenesis syndromes, aniridia, metabolic disorders, collagen/vascular disorders, immunogenetic disorders, and nanophthalmos. The genetics, ocular and systemic features, and current and future treatment strategies are discussed. Findings from rare diseases also uncover important genes and pathways that may be involved in more common forms of glaucoma, and potential novel therapeutic strategies to target these pathways.

Hiding in plain sight: genetic deaf-blindness is not always Usher syndrome

Hearing loss (HL) is the most common congenital sensory impairment. Usher syndrome (USH) is the leading genetic etiology of congenital deafness combined with progressive vision loss, and individuals presenting with these symptoms are often assumed to have USH. This can be an erroneous assumption, as there are additional genetic causes of deaf-blindness. Our objective is to describe and accurately diagnose non-USH genetic causes of deaf-blindness. We present three children with hearing and vision loss with clinical and genetic findings suggestive of USH. However, ongoing clinical assessment did not completely support an USH diagnosis, and exome analysis was pursued for all three individuals. Updated genetic testing showed pathogenic variants in ALMS1 in the first individual and TUBB4B in the second and third. Although HL in all three was consistent with USH type 2, vision impairment with retinal changes was noted by age 2 yr, which is unusual for USH. In all three the updated genotype more accurately fit the clinical phenotype. Because USH is the most common form of genetic deaf-blindness, individuals with HL, early vision impairment, and retinal dysfunction are often assumed to have USH. However, additional genes associated with HL and retinal impairment include ALMS1, TUBB4B, CEP78, ABHD12, and PRPS1. Accurate genetic diagnosis is critical to these individuals’ understanding of their genetic conditions, prognosis, vision and hearing loss management, and future access to molecular therapies. If clinically or genetically USH seems uncertain, updated genetic testing for non-USH genes is essential.

Familial Short Stature-A Novel Phenotype of Growth Plate Collagenopathies

CONTEXT

Collagens are the most abundant proteins in the human body. In a growth plate, collagen types II, IX, X, and XI are present. Defects in collagen genes cause heterogeneous syndromic disorders frequently associated with short stature. Less is known about oligosymptomatic collagenopathies.

OBJECTIVE

This work aims to evaluate the frequency of collagenopathies in familial short stature (FSS) children and to describe their phenotype, including growth hormone (GH) treatment response.

METHODS

Eighty-seven FSS children (pretreatment height ≤ -2 SD both in the patient and his or her shorter parent) treated with GH were included in the study. Next-generation sequencing was performed to search for variants in the COL2A1, COL9A1, COL9A2, COL9A3, COL10A1, COL11A1, and COL11A2 genes. The results were evaluated using American College of Medical Genetics and Genomics guidelines. The GH treatment response of affected children was retrospectively evaluated.

RESULTS

A likely pathogenic variant in the collagen gene was found in 10 of 87 (11.5%) children. Detailed examination described mild asymmetry with shorter limbs and mild bone dysplasia signs in 2 of 10 and 4 of 10 affected children, respectively. Their growth velocity improved from a median of 5.3 cm/year to 8.7 cm/year after 1 year of treatment. Their height improved from a median of -3.1 SD to -2.6 SD and to -2.2 SD after 1 and 3 years of therapy, respectively. The final height reached by 4 of 10 children differed by -0.67 to +1.0 SD and -0.45 to +0.5 SD compared to their pretreatment height and their affected untreated parent's height, respectively.

CONCLUSION

Oligosymptomatic collagenopathies are a frequent cause of FSS. The short-term response to GH treatment is promising.

Proline metabolism and transport in retinal health and disease

The retina is one of the most energy-demanding tissues in the human body. Photoreceptors in the outer retina rely on nutrient support from the neighboring retinal pigment epithelium (RPE), a monolayer of epithelial cells that separate the retina and choroidal blood supply. RPE dysfunction or cell death can result in photoreceptor degeneration, leading to blindness in retinal degenerative diseases including some inherited retinal degenerations and age-related macular degeneration (AMD). In addition to having ready access to rich nutrients from blood, the RPE is also supplied with lactate from adjacent photoreceptors. Moreover, RPE can phagocytose lipid-rich outer segments for degradation and recycling on a daily basis. Recent studies show RPE cells prefer proline as a major metabolic substrate, and they are highly enriched for the proline transporter, SLC6A20. In contrast, dysfunctional or poorly differentiated RPE fails to utilize proline. RPE uses proline to fuel mitochondrial metabolism, synthesize amino acids, build the extracellular matrix, fight against oxidative stress, and sustain differentiation. Remarkably, the neural retina rarely imports proline directly, but it uptakes and utilizes intermediates and amino acids derived from proline catabolism in the RPE. Mutations of genes in proline metabolism are associated with retinal degenerative diseases, and proline supplementation is reported to improve RPE-initiated vision loss. This review will cover proline metabolism in RPE and highlight the importance of proline transport and utilization in maintaining retinal metabolism and health.

Challenging Diagnosis of Stickler Syndrome in a Patient with Premature Osteoarthritis: A Case Report

CASE

A 53-year-old male patient, subsequently diagnosed with type I Stickler syndrome, presented with severe premature osteoarthritis associated with bilateral hip dysplasia and knee epiphyseal dysplasia. Despite the presence of the typical manifestations of orofacial defects, hearing, ocular, and musculoskeletal abnormalities, the patient had never been diagnosed with the syndrome.

CONCLUSION

Stickler syndrome can present with a wide spectrum of musculoskeletal abnormalities without previous diagnosis. It is often underrecognized if the manifestations of other systems are not appreciated. Stickler syndrome should be considered in the differential diagnosis of patients with unexplained musculoskeletal abnormality particularly in the presence of other system manifestations.

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.

Choroidal and peripapillary changes in high myopic eyes with Stickler syndrome

Background

To compare different clinical and Spectral-Domain Optical Coherence Tomography (SD-OCT) features of high myopic eyes with Stickler syndrome (STL) with matched controls.

Methods

Patients with genetically confirmed STL with axial length ≥ 26 mm and controls matched for axial length were included. The following data were obtained from SD-OCT scans and fundus photography: choroidal and retinal thickness (respectively, CT and RT), peripapillary atrophy area (PAA), presence of posterior staphyloma (PS).

Results

Twenty-six eyes of 17 patients with STL and 25 eyes of 19 controls were evaluated. Compared with controls, patients with STL showed a greater CT subfoveally, at 1000 μm from the fovea at both nasal and temporal location, and at 2000 and 3000 μm from the fovea in nasal location (respectively, 188.7±72.8 vs 126.0±88.7 μm, 172.5±77.7 vs 119.3±80.6 μm, 190.1±71.9 vs 134.9±79.7 μm, 141.3±56.0 vs 98.1±68.5 μm, and 110.9±51.0 vs 67.6±50.7 μm, always P< 0.05). Furthermore, patients with STL showed a lower prevalence of PS (11.5% vs 68%, P< 0.001) and a lower PAA (2.2±2.1 vs 5.4±5.8 mm², P=0.03), compared with controls.

Conclusions

This study shows that high myopic patients with STL show a greater CT, a lower PAA and a lower prevalence of PS, compared with controls matched for axial length. These findings could be relevant for the development and progression of myopic maculopathy in patients with STL.

Autosomal recessive Stickler syndrome associated with homozygous mutations in the COL9A2 gene

Background: Stickler syndrome is a hereditary disorder of collagen tissues causing ocular, auditory, orofacial, and joint manifestations. Ocular findings typically include vitreous degeneration, high myopia, retinal detachment, and cataract. Many subjects demonstrate sensorineural or conductive hearing loss. The inheritance is autosomal dominant with mutations in COL2A1, COL11A1, or COL11A2 or autosomal recessive due to mutations in COL9A1, COL9A2, or COL9A3. We describe a family with Stickler syndrome caused by homozygous loss-of-function mutations in COL9A2.Methods: Two brothers from a consanguineous family were examined with genetic testing, visual acuity, Goldmann perimetry, full-field and multifocal electroretinography (ffERG, mERG), optical coherence tomography (OCT), fundus autofluorescence (FAF), fundus photography, and pure-tone audiograms.Results: Both subjects were homozygous for the mutation c.1332del in COL9A2. Their parents were heterozygous for the same mutation. The boys demonstrated reduced visual acuity, vitreous changes and myopia. The proband was operated for retinal detachment and cataract in one eye. FfERG revealed reduced function of both rods and cones and mERG showed reduced macular function. No morphological macular changes were found by OCT or FAF. Both brothers have severe sensorineural hearing loss with down-sloping audiograms but only subtle midface hypoplasia and no, or mild joint problems.Conclusion: Only a few families with Stickler syndrome caused by COL9A2 mutations have been reported. We confirm previous descriptions with a severe ocular and auditory phenotype but mild orofacial and joint manifestations. Moreover, we demonstrate reduced macular and overall retinal function explaining the reduced visual acuity in patients with Stickler syndrome also without retinal complications.

Complex Phenotypic Presentation of Syndromic Hearing Loss Deciphered as Three Separate Clinical Entities: How Genetic Testing Guides Final Diagnosis

BACKGROUND

Genetically determined prelingual hearing loss (HL) may occur in an isolated or syndromic form.

OBJECTIVE

The aim of the study was to unravel the genetic cause of medical problems in a 21-year-old woman, whose phenotypic presentation extended beyond Stickler syndrome and included enlarged vestibular aqueduct (EVA) and persistent microhematuria.

METHODS AND RESULTS

After sequencing of clinical exome, a known de novo COL2A1 pathogenic variant (c.1833+1G>A, p.?) causative for Stickler syndrome and one paternally inherited pathogenic change in COL4A5 (c.1871G>A, p.Gly624Asp) causative for X-linked Alport syndrome were found. No pathogenic variants, including those within the SLC26A4 5' region (Caucasian EVA haplotype), explaining the development of EVA, were identified.

CONCLUSIONS

The study reveals a multilocus genomic variation in one individual and provides a molecular diagnosis of two HL syndromes that co-occur in the proband independent of each other. For the third entity, EVA, no etiological factor was identified. Our data emphasize the relevance of detailed clinical phenotyping for accurate genotype interpretation. Focus on broadening the phenotypic spectrum of known genetic syndromes may actually obscure patients with multiple molecular diagnoses.

Exon-Trapping Assay Improves Clinical Interpretation of COL11A1 and COL11A2 Intronic Variants in Stickler Syndrome Type 2 and Otospondylomegaepiphyseal Dysplasia

Stickler syndrome (SS) is a hereditary connective tissue disorder affecting bones, eyes, and hearing. Type 2 SS and the SS variant otospondylomegaepiphyseal dysplasia (OSMED) are caused by deleterious variants in COL11A1 and COL11A2, respectively. In both genes, available database information indicates a high rate of potentially deleterious intronic variants, but published evidence of their biological effect is usually insufficient for a definite clinical interpretation. We report four previously unpublished intronic variants in COL11A1 (c.2241 + 5G>T, c.2809 − 2A>G, c.3168 + 5G>C) and COL11A2 (c.4392 + 1G>A) identified in type 2 SS/OSMED individuals. The pathogenic effect of these variants was first predicted in silico and then investigated by an exon-trapping assay. We demonstrated that all variants can induce exon in-frame deletions, which lead to the synthesis of shorter collagen XI α1 or 2 chains. Lacking residues are located in the α-triple helical region, which has a crucial role in regulating collagen fibrillogenesis. In conclusion, this study suggests that these alternative COL11A1 and COL11A2 transcripts might result in aberrant triple helix collagen. Our approach may help to improve the diagnostic molecular pathway of COL11-related disorders.

High Myopia and Strabismus Induced by a Deep Intronic Mutation in COL2A1

Purpose: To characterize a genetic mutation causing Stickler syndrome in a previously undiagnosed family.Methods: Five generations of a single family suspected of having Stickler syndrome were evaluated clinically and genetically.Results: The demographic and clinical data yielded specific clinical phenotypes of Stickler syndrome in 13 family members; 7 had more than one clinical feature. Four family members underwent genetic analysis: the proband (index patient) and his mother, maternal grandfather, and healthy father. No relevant mutation was detected in the proband on whole exome analysis, but subsequent extension of the analysis to intronic areas yielded a deep intronic mutation, NM_001844.5:c.1527 + 135 G > A. Sanger sequencing was used to validate the results in the family members.Conclusions: Stickler syndrome has several subtypes with variable clinical features. Therefore, predicting the genetic locus of the disease based on clinical characteristics is challenging. We present a rarely described intronic mutation in COL2A1. Genetic testing may aid in the early diagnosis of Stickler syndrome, which is important for genetic counselling, proper clinical management, and improved prognosis.

Radiologic Features of Type II and Type XI Collagenopathies

Type II collagen is a major component of the cartilage matrix. Pathogenic variants (ie, disease-causing aberrations) in the type II collagen gene (COL2A1) lead to an abnormal structure of type II collagen, causing a large group of skeletal dysplasias termed type II collagenopathies. Because type II collagen is also located in the vitreous body of the eyes and inner ears, type II collagenopathies are commonly associated with vitreoretinal degeneration and hearing impairment. Type II collagenopathies can be radiologically divided into two major groups: the spondyloepiphyseal dysplasia congenita (SEDC) group and the Kniest-Stickler group. The SEDC group is characterized by delayed ossification of the juxtatruncal bones, including pear-shaped vertebrae. These collagenopathies comprise achondrogenesis type 2, hypochondrogenesis, SEDC, and other uncommon subtypes. The Kniest-Stickler group is characterized by disordered tubular bone growth that leads to "dumbbell" deformities. It comprises Kniest dysplasia and Stickler dysplasia type 1, whose radiographic manifestations overlap with those of type XI collagenopathies (a group of disorders due to abnormal type XI collagen) such as Stickler dysplasia types 2 and 3. This phenotypic overlap is caused by type II and type XI collagen molecules sharing part of the same connective tissues. The authors describe the diagnostic pathways to type II and type XI collagenopathies and the associated differential diagnoses. In addition, they review the clinical features and genetic bases of these conditions, which radiologists should know to participate in multidisciplinary care and translational research. Online supplemental material is available for this article. ^©RSNA, 2020.

Collagen: quantification, biomechanics, and role of minor subtypes in cartilage

Collagen is a ubiquitous biomaterial in vertebrate animals. Although each of its 28 subtypes contributes to the functions of many different tissues in the body, most studies on collagen or collagenous tissues have focussed on only one or two subtypes. With recent developments in analytical chemistry, especially mass spectrometry, significant advances have been made toward quantifying the different collagen subtypes in various tissues; however, high-throughput and low-cost methods for collagen subtype quantification do not yet exist. In this Review, we introduce the roles of collagen subtypes and crosslinks, and describe modern assays that enable a deep understanding of tissue physiology and disease states. Using cartilage as a model tissue, we describe the roles of major and minor collagen subtypes in detail; discuss known and unknown structure-function relationships; and show how tissue engineers may harness the functional characteristics of collagen to engineer robust neotissues.

Stickler Syndrome: A Review of Clinical Manifestations and the Genetics Evaluation

Stickler Syndrome (SS) is a multisystem collagenopathy frequently encountered by ophthalmologists due to the high rate of ocular complications. Affected individuals are at significantly increased risk for retinal detachment and blindness, and early detection and diagnosis are critical in improving visual outcomes for these patients. Systemic findings are also common, with craniofacial, skeletal, and auditory systems often involved. SS is genotypically and phenotypically heterogenous, which can make recognizing and correctly diagnosing individuals difficult. Molecular genetic testing should be considered in all individuals with suspected SS, as diagnosis not only assists in treatment and management of the patient but may also help identify other at-risk family members. Here we review common clinical manifestation of SS and genetic tests frequently ordered as part of the SS evaluation.

Mutation Spectrum and De Novo Mutation Analysis in Stickler Syndrome Patients with High Myopia or Retinal Detachment

Stickler syndrome is a connective tissue disorder that affects multiple systems, including the visual system. Seven genes were reported to cause Stickler syndrome in patients with different phenotypes. In this study, we aimed to evaluate the mutation features of the phenotypes of high myopia and retinal detachment. Forty-two probands diagnosed with Stickler syndrome were included. Comprehensive ocular examinations were performed. A targeted gene panel test or whole exome sequencing was used to detect the mutations, and Sanger sequencing was conducted for verification and segregation analysis. Among the 42 probands, 32 (76%) presented with high myopia and 29 (69%), with retinal detachment. Pathogenic mutations were detected in 35 (83%) probands: 27 (64%) probands had COL2A1 mutations, and eight (19%) probands had COL11A1 mutations. Truncational mutations in COL2A1 were present in 21 (78%) probands. Missense mutations in COL2A1 were present in six probands, five of which presented with retinal detachment. De novo COL2A1 mutations were detected in 10 (37%) probands, with a mean paternal childbearing age of 29.64 ± 4.97 years old. The mutation features of probands with high myopia or retinal detachment showed that the probands had a high prevalence of COL2A1 mutations, truncational mutations, and de novo mutations.

Multiple epiphyseal dysplasia and related disorders: Molecular genetics, disease mechanisms, and therapeutic avenues

For the vast majority of the 6000 known rare disease the pathogenic mechanisms are poorly defined and there is little treatment, leading to poor quality of life and high healthcare costs. Genetic skeletal diseases (skeletal dysplasias) are archetypal examples of rare diseases that are chronically debilitating, often life-threatening and for which no treatments are currently available. There are more than 450 unique phenotypes that, although individually rare, have an overall prevalence of at least 1 per 4000 children. Multiple epiphyseal dysplasia (MED) is a clinically and genetically heterogeneous disorder characterized by disproportionate short stature, joint pain, and early-onset osteoarthritis. MED is caused by mutations in the genes encoding important cartilage extracellular matrix proteins, enzymes, and transporter proteins. Recently, through the use of various cell and mouse models, disease mechanisms underlying this diverse phenotypic spectrum are starting to be elucidated. For example, ER stress induced as a consequence of retained misfolded mutant proteins has emerged as a unifying disease mechanisms for several forms of MED in particular and skeletal dysplasia in general. Moreover, targeting ER stress through drug repurposing has become an attractive therapeutic avenue.

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.

Frequency and Management of Craniofacial Syndromes

BACKGROUND

Craniofacial syndromes occur in approximately 1 in 5600 to 100,000 infants, often resulting in significant morbidity. Due to the heterogeneity of this patient population, no clear consensus consists on optimal treatment modalities and timing. The aim of this study was to analyze the craniofacial syndrome population that were treated at the University Hospital Leuven.

METHODS

A retrospective analysis of patients with a clinical diagnosis of a craniofacial syndrome was performed. Inclusion criteria were patients with a clinical diagnosis of a craniofacial syndrome and that received treatment between "2000-2005" and "2010-2015." Patients with nonsyndromic conditions were excluded. Data regarding patient characteristics, treatment modalities, and treatment outcomes were analyzed.

RESULTS

After matching the inclusion criteria, 98 eligible patients, affected by 40 different syndromes were included. In the period of "2000 to 2005," 48 patients were treated, as compared to 50 patients in the period of "2010 to 2015." A statistically significant decrease over time is seen for cleft surgery and orthodontic treatment (P = 0.0017 and P = 0.0015, respectively). No statistically significant differences were found concerning the age at which treatment was received (P = 0.42). Significant associations between treatment modalities were found for orthognathic surgery and distraction osteogenesis (P < 0.0001), orthognathic surgery and orthodontic treatment (P < 0.0001), and between orthodontic treatment and distraction osteogenesis (P = 0.03311).

CONCLUSION

A decline in cleft reconstruction surgery and orthodontic treatment for patients with craniofacial syndromes was seen over time. A significant association was found between distraction osteogenesis and orthognathic surgery, possibly due to higher reintervention rates for patients treated at a young age.

Therapeutic and diagnostic advances in Stickler syndrome

The Stickler syndromes are the leading cause of inherited retinal detachment and the most common cause of rhegmatogenous retinal detachment in childhood. The clinical and molecular genetic spectrum of this connective tissue disorder is discussed in this article, emphasising the key role the ophthalmologist has to play in the identification, diagnosis and prevention of blindness in the increasingly widely recognised sub-groups with ocular-only (or minimal systemic) involvement. Without diagnosis and prophylaxis in such high-risk subgroups, these patients are at high risk of Giant Retinal Tear detachment and blindness, especially in the paediatric population, where late or second eye involvement is common. Initially considered a monogenic disorder, there are now known to be at least 11 distinct phenotypic subgroups in addition to allied connective tissue disorders that can present to the clinician as part of the differential diagnosis.

Plain language summary

Treatment and diagnostic advances in Stickler syndrome The Stickler syndromes are a group of related connective tissue disorders that are associated with short-sight and a very high risk of blindness from detachment of the retina - the light sensitive film at the back of the eye. Other features include cleft palate, deafness and premature arthritis. It is the most common cause of retinal detachment in children and the most common cause of familial or inherited retinal detachment. In contrast to most other forms of blinding genetic eye disease, blindness from retinal detachment in Stickler syndrome is largely avoidable with accurate diagnosis and prophylactic (preventive) surgery. Recent advances in the understanding of the genetic causes of Stickler syndrome mean that the diagnosis can now be confirmed in over 95% of cases and, most importantly, the patient's individual risk of retinal detachment can be graded. Preventative surgery is hugely effective in reducing the incidence of retinal detachment in those patients shown to be at high risk. NHS England have led the way in the multidisciplinary care for patients with Stickler syndrome by launching a highly specialist service that has been free at point of care to all NHS patients in England since 2011 (https://www.england.nhs.uk/commissioning/spec-services/highly-spec-services, www.vitreoretinalservice.org).

Comprehensive analysis of syndromic hearing loss patients in Japan

More than 400 syndromes associated with hearing loss and other symptoms have been described, corresponding to 30% of cases of hereditary hearing loss. In this study we aimed to clarify the mutation spectrum of syndromic hearing loss patients in Japan by using next-generation sequencing analysis with a multiple syndromic targeted resequencing panel (36 target genes). We analyzed single nucleotide variants, small insertions, deletions and copy number variations in the target genes. We enrolled 140 patients with any of 14 syndromes (BOR syndrome, Waardenburg syndrome, osteogenesis imperfecta, spondyloepiphyseal dysplasia congenita, Stickler syndrome, CHARGE syndrome, Jervell and Lange-Nielsen syndrome, Pendred syndrome, Klippel-Feil syndrome, Alport syndrome, Norrie disease, Treacher-Collins syndrome, Perrault syndrome and auditory neuropathy with optic atrophy) and identified the causative variants in 56% of the patients. This analysis could identify the causative variants in syndromic hearing loss patients in a short time with a high diagnostic rate. In addition, it was useful for the analysis of the cases who only partially fulfilled the diagnostic criteria.

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.

Exome-wide copy number variation analysis identifies a COL9A1 in frame deletion that is associated with hearing loss

Pathogenic variants in COL9A1 are primarily associated with autosomal recessive Stickler syndrome. Patients with COL9A1-associated Stickler syndrome (STL) present hearing loss (HL), ophthalmic manifestations and skeletal abnormalities. However, the clinical spectrum of patients with COL9A1 variants can also include multiple epiphyseal dysplasia, as well as non-syndromic HL that was observed in one previously reported proband. Exome sequencing was performed on the genomic DNA of an Iranian patient and his affected brother who both report non-syndromic HL. A 44.6 kb homozygous in-frame deletion spanning exons 6 to 33 of COL9A1 was detected via exome-based copy number variation analysis. The deleted exons were confirmed by PCR in the patient and his affected brother, who both have non-syndromic HL. Segregation analysis via qPCR confirmed the parents as heterozygous deletion carriers. Breakpoint analysis mapped the homozygous deletion spanning introns 5 to 33 (g.70,948,188_70,997,277del, NM_001851.4(COL9A1):c.697-3754_2112+769del, p.(Phe233_Ser704del), with an additional 67 bp of inserted intronic sequence that may have originated due to a fork stalling and template switching/microhomology-mediated break-induced replication (FoSTeS/MMBIR) mechanism. This mechanism has not been previously implicated in HL or STL. This is also the first reported copy number variation in COL9A1 that was identified through an exome data set in an Iranian family with apparent non-syndromic HL. The present study emphasizes the importance of exome-wide copy number variation analysis in molecular diagnosis and provides supporting evidence to associate COL9A1 with autosomal recessive non-syndromic HL.

Stickler syndrome: exploring prophylaxis for retinal detachment

PURPOSE OF REVIEW

The literature regarding prophylactic treatment of rhegmatogenous retinal detachment in Stickler syndrome remains controversial. We review major published clinical studies and offer a critical analysis of this subject.

SUMMARY

Stickler syndrome is a systemic collagenopathy affecting multiple organ systems including the eye, ear, and skeleton. Stickler syndrome is probably the most common cause of genetically determined pediatric rhegmatogenous retinal detachment. Congenital developmental anomalies constitute over half rhegmatogenous detachments (RRD) in patients less than 10 years. The majority are caused by hereditary vitreoretinopathies associated with Stickler syndrome. Sixty percent of patients with Stickler syndrome develop RRD's over their lifetime with possible severe visual loss and subsequent lifelong morbidity. In view of these complications, some have emphasized the importance of prophylactic laser treatment to the retina of patients with Stickler syndrome to reduce the occurrence of and/or prevent future rhegmatogenous retinal detachment, but there appears to be insufficient data to support the absolute benefit of such prophylactic treatment. Guidelines regarding the age at prophylactic treatment as well as type and frequency of intervention are scarce and would benefit from additional clinical investigations.

Homozygous Type IX collagen variants (COL9A1, COL9A2, and COL9A3) causing recessive Stickler syndrome-Expanding the phenotype

Stickler syndrome (SS) is characterized by ophthalmic, articular, orofacial, and auditory manifestations. SS is usually autosomal dominantly inherited with variants in COL2A1 or COL11A1. Recessive forms are rare but have been described with homozygous variants in COL9A1, COL9A2, and COL9A3 and compound heterozygous COL11A1 variants. This article expands phenotypic descriptions in recessive SS due to variants in genes encoding Type IX collagen. Clinical features were assessed in four families. Genomic DNA samples derived from venous blood were collected from family members. Six affected patients were identified from four pedigrees with variants in COL9A1 (one family, one patient), COL9A2 (two families, three patients), and COL9A3 (one family, two patients). Three variants were novel. All patients were highly myopic with congenital megalophthalmos and abnormal, hypoplastic vitreous gel, and all had sensorineural hearing loss. One patient had severe arthropathy. Congenital megalophthalmos and myopia are common to dominant and recessive forms of SS. Sensorineural hearing loss is more common and severe in recessive SS. We suggest that COL9A1, COL9A2, and COL9A3 be added to genetic screening panels for patients with congenital hearing loss. Although recessive SS is rare, early diagnosis would have a high impact for children with potentially dual sensory impairment, as well as identifying risk to future children.

Genetic regulation of linear growth

Linear growth occurs at the growth plate. Therefore, genetic defects that interfere with the normal function of the growth plate can cause linear growth disorders. Many genetic causes of growth disorders have already been identified in humans. However, recent genome-wide approaches have broadened our knowledge of the mechanisms of linear growth, not only providing novel monogenic causes of growth disorders but also revealing single nucleotide polymorphisms in genes that affect height in the general population. The genes identified as causative of linear growth disorders are heterogeneous, playing a role in various growth-regulating mechanisms including those involving the extracellular matrix, intracellular signaling, paracrine signaling, endocrine signaling, and epigenetic regulation. Understanding the underlying genetic defects in linear growth is important for clinicians and researchers in order to provide proper diagnoses, management, and genetic counseling, as well as to develop better treatment approaches for children with growth disorders.

Genetic Hearing Loss and Gene Therapy

Genetic hearing loss crosses almost all the categories of hearing loss which includes the following: conductive, sensory, and neural; syndromic and nonsyndromic; congenital, progressive, and adult onset; high-frequency, low-frequency, or mixed frequency; mild or profound; and recessive, dominant, or sex-linked. Genes play a role in almost half of all cases of hearing loss but effective treatment options are very limited. Genetic hearing loss is considered to be extremely genetically heterogeneous. The advancements in genomics have been instrumental to the identification of more than 6,000 causative variants in more than 150 genes causing hearing loss. Identification of genes for hearing impairment provides an increased insight into the normal development and function of cells in the auditory system. These defective genes will ultimately be important therapeutic targets. However, the auditory system is extremely complex which requires tremendous advances in gene therapy including gene vectors, routes of administration, and therapeutic approaches. This review summarizes and discusses recent advances in elucidating the genomics of genetic hearing loss and technologies aimed at developing a gene therapy that may become a treatment option for in the near future.

Bone morphogenetic protein 4 (BMP4) loss-of-function variant associated with autosomal dominant Stickler syndrome and renal dysplasia

Stickler syndrome is a genetic disorder that can lead to joint problems, hearing difficulties and retinal detachment. Genes encoding collagen types II, IX and XI are usually responsible, but some families have no causal variant identified. We investigate a variant in the gene encoding growth factor BMP4 in a family with Stickler syndrome with associated renal dysplasia. Next generation sequencing of the coding region of COL2A1, COL11A1 and a panel of genes associated with congenital anomalies of the kidney and urinary tract (CAKUT) was performed. A novel heterozygous BMP4 variant causing a premature stop codon, c. 130G>T, p.(Gly44Ter), which segregated with clinical features of Stickler syndrome in multiple family members, was identified. No variant affecting gene function was detected in COL2A1 or COL11A1. Skin fibroblasts were cultured with and without emetine, and the mRNA extracted and analysed by Sanger sequencing to assess whether the change was causing nonsense-mediated decay. Nonsense-mediated decay was not observed from the extracted BMP4 mRNA. BMP4 is a growth factor known to contribute to eye development in animals, and gene variants in humans have been linked to microphthalmia/anophthalmia as well as CAKUT. The variant identified here further demonstrates the importance of BMP4 in eye development. This is the first report of a BMP4 DNA variant causing Stickler syndrome, and we suggest BMP4 be added to standard diagnostic gene panels for this condition.

Autosomal recessive Stickler syndrome resulting from a COL9A3 mutation

Stickler syndrome is a connective tissue disorder characterized by hearing loss, ocular anomalies, palatal defects, and skeletal abnormalities. The autosomal dominant form is the most common, but autosomal recessive forms have also been described. We report the second case of autosomal recessive Stickler syndrome due to homozygosity for a loss of function mutation in COL9A3, which encodes the α3 chain of type IX procollagen. The clinical features were similar to the previously described COL9A3 Stickler syndrome family, including moderate to severe sensorineural hearing loss, high myopia, and both tibial and femoral bowing at birth. Radiographs demonstrated abnormal capital femoral epiphyses and mild irregularities of the vertebral endplates. This case further establishes the phenotype associated with mutations in this gene. We suggest that loss of the α3 chain of type IX collagen results in a Stickler syndrome phenotype similar to that of the other autosomal recessive forms caused by mutations in genes encoding the α1 and α2 chains of type IX collagen.

Lens-regulated retinoic acid signalling controls expansion of the developing eye

Absence of the developing lens results in severe eye defects, including substantial reductions in eye size. How the lens controls eye expansion and the underlying signalling pathways are very poorly defined. We identified RDH10, a gene crucial for retinoic acid synthesis during embryogenesis, as a key factor downregulated in the peripheral retina (presumptive ciliary body region) of lens-removed embryonic chicken eyes prior to overt reductions in eye size. This is associated with a significant decrease in retinoic acid synthesis by lens-removed eyes. Restoring retinoic acid signalling in lens-removed eyes by implanting beads soaked in retinoic acid or retinal, but not vitamin A, rescued eye size. Conversely, blocking retinoic acid synthesis decreased eye size in lens-containing eyes. Production of collagen II and collagen IX, which are major vitreal proteins, is also regulated by the lens and retinoic acid signalling. These data mechanistically link the known roles of both the lens and retinoic acid in normal eye development, and support a model whereby retinoic acid production by the peripheral retina acts downstream of the lens to support vitreous production and eye expansion.

Targeted next‑generation sequencing identifies two novel COL2A1 gene mutations in Stickler syndrome with bilateral retinal detachment

Stickler syndrome is a group of inherited connective tissue disorders characterized by distinctive facial and ocular abnormalities, hearing loss and early‑onset arthritis. The aim of the present study was to investigate the genetic changes in two Chinese patients with Stickler syndrome, manifested as bilateral retinal detachment and peripheral retinal degeneration. Complete ophthalmic examinations, including best‑corrected visual acuity, slit‑lamp examination and fundus examination, were performed. Genomic DNA was extracted from leukocytes of the peripheral blood collected from the patients, their unaffected family members and 200 unrelated control subjects from the same population. Next‑generation sequencing of established genes associated with ocular disease was performed. A heterozygous collagen type II α1 chain (COL2A1) mutation c.1310G>C (p.R437P) in exon 21 was identified in Family 1 and a heterozygous COL2A1 mutation c.2302‑1G>A in intron 34 was identified in Family 2. The functional effects of the mutations were assessed by polymorphism phenotyping (PolyPhen) and sorting intolerant from tolerant (SIFT) analysis. The c.1310G>C mutation was predicted to damage protein structure and function, and the c.2302‑1G>A mutation was predicted to result in a splicing defect. The findings of the current study expand the established mutation spectrum of COL2A1, and may facilitate genetic counseling and development of therapeutic strategies for patients with Stickler syndrome.