Strabismus genetics across a spectrum of eye misalignment disorders

Morphometric Analysis of the Eye by Magnetic Resonance Imaging in MGST2-Gene-Deficient Mice

Strabismus, a neuro-ophthalmological condition characterized by misalignment of the eyes, is a common ophthalmic disorder affecting both children and adults. In our previous study, we identified the microsomal glutathione S-transferase 2 (MGST2) gene as one of the potential candidates for comitant strabismus susceptibility in a Japanese population. The MGST2 gene belongs to the membrane-associated protein involved in the generation of pro-inflammatory mediators, and it is also found in the protection against oxidative stress by decreasing the reactivity of oxidized lipids. To look for the roles of the MGST2 gene in the development, eye alignment, and overall morphology of the eye as the possible background of strabismus, MGST2 gene knockout (KO) mice were generated by CRISPR/Cas9-mediated gene editing with guide RNAs targeting the MGST2 exon 2. The ocular morphology of the KO mice was analyzed through high-resolution images obtained by a magnetic resonance imaging (MRI) machine for small animals. The morphometric analyses showed that the height, width, and volume of the eyeballs in MGST2 KO homozygous mice were significantly greater than those of wild-type mice, indicating that the eyes of MGST2 KO homozygous mice were significantly enlarged. There were no significant differences in the axis length and axis angle. These morphological changes may potentially contribute to the development of a subgroup of strabismus.

Halil Pasha's legacy as a Turkish painter: Esotropia or pseudoesotropia in "Yaşlı Halayık"

Introduction: Esotropia is a form of strabismus, a condition characterized by the misalignment of the eyes. Specifically, esotropia refers to inward deviation of one or both eyes. It can manifest at different ages, ranging from infancy to adulthood, and can have varying degrees of severity. The false appearance of esotropia in the alignment of the visual axes is what defines pseudoesotropia. Halil Pasha was a Turkish painter known for his contributions to the art scene during the late 19th and early 20th centuries. His artistic talent, coupled with his influential position as a statesman, allowed him to leave a lasting impact on the cultural landscape of the Ottoman Empire. Methods: In the present study, artistic depictions of esotropia or pseudoesotropia in Halil Pasha's "Yaşlı Halayık" were evaluated. A comprehensive literature review on strabismus in medicine and art was conducted. Results: "Yaşlı Halayık", translated as "Old Servant Woman", is one of the iconic paintings of Turkish art. It reflects the social dynamics and lifestyle of the time, offering a glimpse into the lives of women serving in Ottoman households. When we examine this painting as a physician, the first thing we notice is the old woman's eyes. An eye misalignment in the left eye of the old servant woman is noticed. Discussion: In medical humanities, which are addressed in medical education, medicine and art intersect with different perspectives and understandings. Although the evaluation of medical scenes in artworks seems to have been first observed by an art historian, today physicians and medical students need to examine artworks more carefully and develop their observational skills. Iconodiagnosis is the medical analysis of artworks that looks for clinical signs suggestive of medical disorders and diseases. The application of iconodiagnosis in medical education is an alternative and stimulating way to exercise students' observation skills; not only the physical examination of the patient is important, but also the information obtained from their posture, clothing, general demeanour and even physical aids.

Ophthalmologic diagnoses in youths with autism spectrum disorder: Prevalence and clinical correlates

Autism spectrum disorder (ASD) is associated with a high prevalence of visual dysfunction. This study aimed to investigate the rates of amblyopia, refractive errors, and strabismus, as well as their clinical correlates in ASD. This population-based matched-cohort study used data from the Taiwan National Health Insurance Research Database. A total of 3,551 youths with ASD and 35,510 non-autistic control participants matched by age and sex were included. All the participants were followed-up until they were 18 years old. The prevalence of amblyopia, refractive errors, and strabismus was compared between the ASD and control groups. Effect modifiers, including sex, ASD subgroup, and co-diagnosis of intelligence disability, were examined. Compared to the control group, youths with ASD had a significantly increased risk of amblyopia (adjusted odds ratio [aOR] = 1.75), anisometropia (aOR = 1.66), astigmatism (aOR = 1.51), hypermetropia (aOR = 2.08), exotropia (aOR = 2.86), and esotropia (aOR = 2.63), but a comparable likelihood of myopia according to age. Males with ASD had a significantly lower likelihood of exotropia, but a higher likelihood of myopia than females with ASD. The autism subgroup had a higher OR for hypermetropia, but a lower OR for myopia than the other ASD subgroups. ASD youths with intelligence disabilities demonstrated significantly higher ORs for amblyopia, hypermetropia, and all types of strabismus and lower OR for myopia than those without intelligence disabilities. In conclusion, the rates of amblyopia, refractive errors, and strabismus were higher in youths with ASD. Ocular abnormalities in youths with ASD require a comprehensive assessment and management.

Role of Abelson Helper Integration Site 1, Nebulin, and Paired Box 3 Genes in the Development of Nonsyndromic Strabismus in a Series of Iranian Families: Sequence Analysis and Systematic Review of the Genetics of Nonsyndromic Strabismus

Purpose

To look for causative genetic mutations in a series of Iranian families with strabismus. In addition, we systematically reviewed all the published articles regarding the role of genetic variations in primary and nonsyndromic comitant strabismus.

Methods

Four families with a history of multiple cases of primary and nonsyndromic comitant strabismus were enrolled in this study. Polymerase chain reaction and Sanger sequencing of exons 23, 11, and 3 of the Abelson helper integration site 1 (AHI1), nebulin (NEB), and paired box 3 (PAX3) genes were performed, respectively. One offspring of a consanguineous marriage underwent whole-exome sequencing (WES) to look for possible causative variants. To conduct a systematic review, we thoroughly searched PubMed, Scopus, and ISI Web of Knowledge extracting relevant publications, released by April 2021.

Results

We examined four Iranian strabismus pedigrees with multiple affected offspring in different generations. Among these 17 participants, 10 family members had strabismus and 7 were healthy. Sanger sequencing did not reveal a causative mutation. Therefore, to further investigate, one affected offspring was chosen for WES. The WES study demonstrated two possible variants in MYO5B and DHODH genes. These genetic variants showed high allele frequency in our population and are thought to be polymorphisms in our series of Iranian families.

Conclusions

We demonstrated that mutations in AHI1, NEB, and PAX3 genes were not common in a series of Iranian patients with familial strabismus. Moreover, by performing WES, we revealed that two variants of uncertain significance as possible causative variants for strabismus are not related to this disease in our population.

Comitant strabismus etiology: extraocular muscle integrity and central nervous system involvement-a narrative review

Strabismus is not a condition in itself but the consequence of an underlying problem. Eye misalignment can be caused by disease, injury, and/or abnormalities in any of the structures and processes involved in visual perception and oculomotor control, from the extraocular muscles and their innervations to the oculomotor and visual processing areas in the brain. A small percentage of all strabismus cases are the consequence of well-described genetic syndromes, acquired insult, or disease affecting the extraocular muscles (EOMs) or their innervations. We will refer to them as strabismus of peripheral origin since their etiology lies in the peripheral nervous system. However, in most strabismus cases, that is comitant, non-restrictive, non-paralytic strabismus, the EOMs and their innervations function properly. These cases are not related to specific syndromes and their precise causes remain poorly understood. They are generally believed to be caused by deficits in the central neural pathways involved in visual perception and oculomotor control. Therefore, we will refer to them as central strabismus. The goal of this narrative review is to discuss the possible causes behind this particular type of eye misalignment and to raise awareness among eyecare professionals about the important role the central nervous system plays in strabismus etiology, and the subsequent implications regarding its treatment. A non-systematic search was conducted using PubMed, Medline, Cochrane, and Google Scholar databases with the keywords "origins," "causes," and "etiology" combined with "strabismus." A snowball approach was also used to find relevant references. In the following article, we will first describe EOM integrity in central strabismus; next, we will address numerous reasons that support the idea of central nervous system (CNS) involvement in the origin of the deviation, followed by listing several possible central causes of the ocular misalignment. Finally, we will discuss the implications CNS etiology has on strabismus treatment.

Defects and asymmetries in the visual pathway of non-human primates with natural strabismus and amblyopia

Strabismus and amblyopia are common ophthalmologic developmental diseases caused by abnormal visual experiences. However, the underlying pathogenesis and visual defects are still not fully understood. Most studies have used experimental interference to establish disease-associated animal models, while ignoring the natural pathophysiological mechanisms. This study was designed to investigate whether natural strabismus and amblyopia are associated with abnormal neurological defects. We screened one natural strabismic monkey ( Macaca fascicularis) and one natural amblyopic monkey from hundreds of monkeys, and retrospectively analyzed one human strabismus case. Neuroimaging, behavioral, neurophysiological, neurostructural, and genovariation features were systematically evaluated using magnetic resonance imaging (MRI), behavioral tasks, flash visual evoked potentials (FVEP), electroretinogram (ERG), optical coherence tomography (OCT), and whole-genome sequencing (WGS), respectively. Results showed that the strabismic patient and natural strabismic and amblyopic monkeys exhibited similar abnormal asymmetries in brain structure, i.e., ipsilateral impaired right hemisphere. Visual behavior, visual function, retinal structure, and fundus of the monkeys were impaired. Aberrant asymmetry in binocular visual function and structure between the strabismic and amblyopic monkeys was closely related, with greater impairment of the left visual pathway. Several similar known mutant genes for strabismus and amblyopia were also identified. In conclusion, natural strabismus and amblyopia are accompanied by abnormal asymmetries of the visual system, especially visual neurophysiological and neurostructural defects. Our results suggest that future therapeutic and mechanistic studies should consider defects and asymmetries throughout the entire visual system.

Commonly occurring genetic polymorphisms with a major impact on the risk of nonsyndromic strabismus: replication in a sample from Finland

PURPOSE

To replicate associations between polymorphisms in the WRB and TSPAN10 genes and strabismus in an independent Finnish cohort and to calculate their population attributable risk.

METHODS

Polymorphisms in the WRB (rs2244352) and TSPAN10 (rs6420484) genes were investigated in individuals from the FinnGen study group who had one of three categories of strabismus, with clinical diagnoses of (1) "strabismus-all subtypes" (3,515 cases and 173,384 controls), (2) "convergent concomitant strabismus" (ICD-10 code H50.0; 737 cases and 170,976 controls), and (3) "divergent concomitant strabismus" (ICD-10 code H50.1; 1,059 cases and 170,976 controls).

RESULTS

The WRB polymorphism was associated with "all subtypes" of strabismus (OR = 1.08; P = 0.008) and divergent strabismus (OR = 1.11; P = 0.046) but not with convergent strabismus (P = 0.41). The WRB polymorphism had a population attributable risk of 3.4% for all strabismus subtypes and 4.7% for divergent strabismus. The TSPAN10 polymorphism was associated with all three strabismus phenotypes: "all subtypes" (OR = 1.08; P = 0.002), convergent strabismus (OR = 1.19; P = 0.001) and divergent strabismus (OR = 1.20; P =7.21E-05). The population attributable risk for the TSPAN10 polymorphism was 6.0% for any strabismus, 13.3% for convergent strabismus, and 13.9% for divergent strabismus.

CONCLUSIONS

Genetic association with strabismus was replicated in a Finnish cohort for two common polymorphisms. Under the assumption that these polymorphisms are independent of other risk factors, they are responsible for up to 20% of isolated cases of strabismus in Finland, similar to estimates in other European populations.

Expanding the phenotypic spectrum of mutations in LRP2: a novel candidate gene of non-syndromic familial comitant strabismus

Background

Comitant strabismus (CS) is a heterogeneous disorder that is a major contributing factor to unilateral childhood-onset visual impairment. Studies have confirmed that genetic factors play an important role in the development of CS. The aim of this study was to identify the genetic cause of non-syndromic familial CS.

Methods

Fourteen unrelated CS families were recruited for the study. Twelve affected and 2 unaffected individuals from a large four-generation family (CS08) were selected to perform whole genome-wide linkage analysis. Parallel whole-exome sequencing (WES) was conducted in the same family (9 patients and 1 unaffected member) and 31 additional CS cases from 13 other unrelated families. Sanger sequencing was used to determine whether any of the remaining variants co-segregated with the disease phenotype in the corresponding family.

Results

Based on linkage analysis, CS in family CS08 mapped to a novel region of 34.17 centimorgan (cM) on chromosome 2q22.3-2q32.1 between markers D2S151 and D2S364, with a maximum log odds (LOD) score of 3.54 (theta = 0) at D2S142. Parallel WES identified a heterozygous variant, LRP2 c.335 A > G (p.Q112R), located in such a linkage interval that completely co-segregated with the disease in the family. Furthermore, another novel heterozygous variant (c.7274A > G, p.D2425G) in LRP2 that co-segregated was detected in 2 additional affected individuals from another unrelated family by WES. Both variants are predicted to be damaging by PolyPhen-2, SIFT and MutationTaster, and were absent in 100 ethnically matched normal controls.

Conclusion

LRP2 is a novel candidate genetic cause of non-syndromic familial CS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-03155-z.

Mono-allelic loss of YTHDF3 and neurodevelopmental disorder: clinical features of four individuals with 8q12.3 deletions

The YTH domain family member 3 gene (YTHDF3) encodes a reader of the abundant N6-methyladenosine (m⁶ A) modification of eukaryotic mRNA, which plays an essential role in regulating mRNA stability and is necessary to achieve normal development of the central nervous system in animal models. YTHDF3 has not previously been implicated in Mendelian disease despite a high probability of loss of function intolerance and statistical evidence of enrichment for gene-disruptive de novo variants in large-scale studies of individuals with intellectual disability and/or developmental delay. We report four individuals with deletion of 8q12.3, deletion size 1.38-2.60 Mb, encompassing YTHDF3, three of them were de novo, and in one case, the inheritance was unknown. Common features of the individuals (age range, 4-22 years) were developmental delay and/or intellectual disability. Two individuals underwent squint surgery. We suggest that haploinsufficiency of YTHDF3 causes a neurodevelopmental disorder with developmental delay and intellectual disability of variable degree.

Identification of Possible Risk Variants of Familial Strabismus Using Exome Sequencing Analysis

PURPOSE

To investigate candidate genes associated with familial strabismus and propose a theory of their interaction in familial strabismus associated with early neurodevelopment.

METHODS

Eighteen families, including 53 patients diagnosed with strabismus and 34 unaffected family members, were analyzed. All patients with strabismus and available unaffected family members were evaluated using whole exome sequencing. The primary outcome was to identify rare occurring variants among affected individuals and investigate the evidence of their genetic heterogeneity. These results were compared with exome sequencing analysis to build a comprehensive genetic profile of the study families.

RESULTS

We observed 60 variants from 58 genes in 53 patients diagnosed with strabismus. We prioritized the most credible risk variants, which showed clear segregation in family members affected by strabismus. As a result, we found risk variants in four genes (FAT3, KCNH2, CELSR1, and TTYH1) in five families, suggesting their role in development of familial strabismus. In other families, there were several rare genetic variants in affected cases, but we did not find clear segregation pattern across family members.

CONCLUSION

Genomic sequencing holds great promise in elucidating the genetic causes of strabismus; further research with larger cohorts or other related approaches are warranted.

Linkage analysis identifies an isolated strabismus locus at 14q12 overlapping with FOXG1 syndrome region

Strabismus is a common condition, affecting 1%–4% of individuals. Isolated strabismus has been studied in families with Mendelian inheritance patterns. Despite the identification of multiple loci via linkage analyses, no specific genes have been identified from these studies. The current study is based on a seven-generation family with isolated strabismus inherited in an autosomal dominant manner. A total of 13 individuals from a common ancestor have been included for linkage analysis. Among these, nine are affected and four are unaffected. A single linkage signal has been identified at an 8.5 Mb region of chromosome 14q12 with a multipoint LOD (logarithm of the odds) score of 4.69. Disruption of this locus is known to cause FOXG1 syndrome (or congenital Rett syndrome; OMIM #613454 and *164874), in which 84% of affected individuals present with strabismus. With the incorporation of next-generation sequencing and in-depth bioinformatic analyses, a 4 bp non-coding deletion was prioritised as the top candidate for the observed strabismus phenotype. The deletion is predicted to disrupt regulation of FOXG1, which encodes a transcription factor of the Forkhead family. Suggestive of an autoregulation effect, the disrupted sequence matches the consensus FOXG1 and Forkhead family transcription factor binding site and has been observed in previous ChIP-seq studies to be bound by Foxg1 in early mouse brain development. Future study of this specific deletion may shed light on the regulation of FOXG1 expression and may enhance our understanding of the mechanisms contributing to strabismus and FOXG1 syndrome.

Strabismus in Children With Intellectual Disability: Part of a Broader Motor Control Phenotype?

PURPOSE

Intellectual disability (ID) results from a heterogeneous group of disorders and affects 1% to 2% of children. ID frequently occurs in association with other clinical features such as seizures or malformations. We suspected that strabismus might also be unusually frequent in this population and that it might be associated with ID groups affecting motor control.

METHODS

We reviewed phenotypic descriptors, extracted from medical records, for a heterogeneous series of 222 probands with ID who had been enrolled in a study of clinical application of exome sequencing. We estimated the frequency of strabismus and other common clinical features and explored statistical associations between them. Data from Population Data British Columbia and Online Mendelian Inheritance in Man were also examined for confirmation of our observations.

RESULTS

Strabismus had a higher prevalence among probands with ID than in the general population (odds ratio = 5.46). Moreover, probands with both ID and strabismus were more likely to have problems affecting motor control than those with ID and no strabismus (odds ratio = 2.84). Hypotonia was one of the most common motor control subgroups affecting the ID probands, and a frequent co-occurrence of strabismus and hypotonia was also observed (odds ratio = 2.51) and supported by related gene literature review. There was no evidence for associations between strabismus and other frequent clinical features.

CONCLUSION

Strabismus is a frequent feature in individuals with ID. The frequent co-occurrence of strabismus and motor control phenotypes, in particular hypotonia, suggests that a common cerebellar mechanism or pathway may underlie these phenotypes.

Ultrastructural changes of extraocular muscles in strabismus patients

Strabismus is an ocular disorder characterized by partial or complete inability to keep eye alignment. It represents a very common ocular problem at ophthalmology clinics worldwide. The current study aimed to show the most encountered ultrastructural changes in extraocular muscles (EOMs) collected from patients with different forms of strabismus. Nine specimens of EOMs were collected from five patients during strabismus correction surgery and processed for light and electron microscopy examinations. Histologically, skeletal muscle fibers in normal EOMs appeared tight and normally arranged with clear striations. In strabismic muscles, the fibers appeared disarranged, and atrophied, swollen and disintegrated in some situations. By transmission electron microscopy, normal EOMs were formed of skeletal muscle fibers with intact basal membrane and sarcolemma, tightly aligned myofibrils with well-arranged sarcomeres, Z line and H zone, and normally distributed mitochondria. On the other hand, strabismic EOMs revealed vacuolation and degeneration of myofibrils, accumulation of lipid droplets, subsarcolemmal inclusions and clustering of mitochondria. EOMs obtained from a Down syndrome patient with V-pattern infantile esotropia showed extensive vacuolation and disintegration of myofibrils, and extra- and intracellular deposition of collagen fibers. Interestingly, some skeletal muscle cells exhibited features of autophagic cell death with a trial of engulfing process by neighboring cells. In conclusion, our study traces some characteristic ultrastructural changes in strabismic EOMs, most notably, extensive vacuolation, clustering of mitochondria, degeneration of myofibrils and autophagic changes. These changes might be emphasized as possibly secondary to strabismus.

A commonly occurring genetic variant within the NPLOC4-TSPAN10-PDE6G gene cluster is associated with the risk of strabismus

Strabismus refers to an abnormal alignment of the eyes leading to the loss of central binocular vision. Concomitant strabismus occurs when the angle of deviation is constant in all positions of gaze and often manifests in early childhood when it is considered to be a neurodevelopmental disorder of the visual system. As such, it is inherited as a complex genetic trait, affecting 2-4% of the population. A genome-wide association study (GWAS) for self-reported strabismus (1345 cases and 65,349 controls from UK Biobank) revealed a single genome-wide significant locus on chromosome 17q25. Approximately 20 variants across the NPLOC4-TSPAN10-PDE6G gene cluster and in almost perfect linkage disequilibrium (LD) were most strongly associated (lead variant: rs75078292, OR = 1.26, p = 2.24E-08). A recessive model provided a better fit to the data than an additive model. Association with strabismus was independent of refractive error, and the degree of association with strabismus was minimally attenuated after adjustment for amblyopia. The association with strabismus was replicated in an independent cohort of clinician-diagnosed children aged 7 years old (116 cases and 5084 controls; OR = 1.85, p = 0.009). The associated variants included 2 strong candidate causal variants predicted to have functional effects: rs6420484, which substitutes tyrosine for a conserved cysteine (C177Y) in the TSPAN10 gene, and a 4-bp deletion variant, rs397693108, predicted to cause a frameshift in TSPAN10. The population-attributable risk for the locus was approximately 8.4%, indicating an important role in conferring susceptibility to strabismus.

Curation and bioinformatic analysis of strabismus genes supports functional heterogeneity and proposes candidate genes with connections to RASopathies

Strabismus refers to the misalignment of the eyes and occurs in 2-4% of individuals. The low-resolution label "strabismus" covers a range of heterogeneous defects, which makes it challenging to unravel this condition. Consequently a coherent understanding of the causes is lacking. Here, we attempt to gain a better understanding of the underlying genetics by combining gene curation, diverse bioinformatic analyses (including gene ontology, pathway mapping, expression and network-based methods) and literature review. Through a phenotype-based curation process, we identify high-confidence and permissive sets of 54 and 233 genes potentially involved in strabismus. These genes can be grouped into 10 modules that together span a heterogeneous set of biological and molecular functions, and can be linked to clinical sub-phenotypes. Multiple lines of evidence associate retina and cerebellum biology with the strabismus genes. We further highlight a potential role of the Ras-MAPK pathway. Independently, sets of 11 genes and 15 loci tied to strabismus with definitive genetic basis have been compiled from the literature. We identify strabismus candidate genes for 5 of the 15 reported loci (CHD7; SLC9A6; COL18A1, COL6A2; FRY, BRCA2, SPG20; PARK2). Finally, we synthesize a Strabismus Candidate Gene Collection, which together with our curated gene sets will serve as a resource for future research. The results of this informatics study support the heterogeneity and complexity of strabismus and point to specific biological pathways and brain regions for future focus.

Nonhuman Primate Studies to Advance Vision Science and Prevent Blindness

Most primate behavior is dependent on high acuity vision. Optimal visual performance in primates depends heavily upon frontally placed eyes, retinal specializations, and binocular vision. To see an object clearly its image must be placed on or near the fovea of each eye. The oculomotor system is responsible for maintaining precise eye alignment during fixation and generating eye movements to track moving targets. The visual system of nonhuman primates has a similar anatomical organization and functional capability to that of humans. This allows results obtained in nonhuman primates to be applied to humans. The visual and oculomotor systems of primates are immature at birth and sensitive to the quality of binocular visual and eye movement experience during the first months of life. Disruption of postnatal experience can lead to problems in eye alignment (strabismus), amblyopia, unsteady gaze (nystagmus), and defective eye movements. Recent studies in nonhuman primates have begun to discover the neural mechanisms associated with these conditions. In addition, genetic defects that target the retina can lead to blindness. A variety of approaches including gene therapy, stem cell treatment, neuroprosthetics, and optogenetics are currently being used to restore function associated with retinal diseases. Nonhuman primates often provide the best animal model for advancing fundamental knowledge and developing new treatments and cures for blinding diseases.

A mutation in transcription factor MAFB causes Focal Segmental Glomerulosclerosis with Duane Retraction Syndrome

Focal segmental glomerulosclerosis (FSGS) is a leading cause of end-stage renal disease in children and adults. Genetic factors significantly contribute to early-onset FSGS, but the etiologies of most adult cases remain unknown. Genetic studies of monogenic syndromic FSGS exhibiting extra-renal manifestations have uncovered an unexpected biological role for genes in the development of both podocytes and other cellular lineages. To help define these roles, we studied two unrelated families with FSGS associated with Duane Retraction Syndrome, characterized by impaired horizontal eye movement due to cranial nerve malformation. All four affected individuals developed FSGS and Duane Retraction Syndrome in their first to second decade of life, manifested as restricted abduction together with globe retraction and narrowed palpebral fissure on attempted adduction. Hypoplasia of the abducens nerves and hearing impairment occurred in severely affected individuals. Genetic analyses revealed that affected individuals harbor a rare heterozygous substitution (p.Leu239Pro) in MAFB, a leucine zipper transcription factor. Luciferase assays with cultured monocytes indicated that the substitution significantly reduced transactivation of the F4/80 promoter, the known MAFB recognition element. Additionally, immunohistochemistry indicated reduced MAFB expression in the podocytes of patients. Structural modeling suggested that the p.Leu239Pro substitution in the DNA-binding domain possibly interferes with the stability of the adjacent zinc finger. Lastly, podocytes in neonatal mice with p.Leu239Pro displayed impaired differentiation. Thus, MAFB mutations impair development and/or maintenance of podocytes, abducens neurons and the inner ear. The interactions between MAFB and regulatory elements in these developing organs are likely highly specific based on spatiotemporal requirements.

Involvement of dysregulated coding and long non‑coding RNAs in the pathogenesis of strabismus

Strabismus is a common ocular disorder in children and may result in exterior abnormalities and impaired visual functions. However, the detailed pathogenesis of strabismus unclear. The present study assessed the comprehensive analyses on the roles of RNAs in the development of strabismus. The public datasets of strabismus and the corresponding control tissues were downloaded from the Gene Expression Omnibus (GEO). Reannotations of the dysregulated coding and long non-coding RNAs (lncRNAs) and functional enrichments of the differently expressed genes (DEGs) were conducted. A total of 790 DEGs were screened (648 upregulated and 142 downregulated) in the present study. Among the DEGs, a total of 32 differently expressed lncRNAs were detected (14 upregulated and 18 downregulated). When the Gene Ontology (GO) enrichment was considered, it was identified that a total of 143 GO terms (82 for biological process, 31 for cellular component and 30 for molecular function) were identified. Among all the 57 detected Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, the phagosome pathway, which was labeled as hsa004145, demonstrated the most bioinformatics importance. However, most lncRNAs, except LINC01279 and LOC643733, indicated <3 target mRNAs and were not suitable for advanced bioinformatics analyses. Bioinformatics analyses demonstrated that there was a GO term for each lncRNA (proteinaceous extracellular for LINC01279 and cell surface for LOC643733). In conclusion, a set of coding RNA as well as lncRNAs differentially expressed in strabismus EOM samples were indicated. Notably, the present findings important information for advanced pathogenesis research and biomarkers detection.

Expression of schizophrenia biomarkers in extraocular muscles from patients with strabismus: an explanation for the link between exotropia and schizophrenia?

Recent studies have implicated exotropia as a risk factor for schizophrenia. We determined whether schizophrenia biomarkers have abnormal levels of expression in extraocular muscles from patients with strabismus and explored whether differences in gene expression between medial and lateral rectus muscles may explain the specific association of schizophrenia with exotropia but not esotropia. Samples from horizontal extraocular muscles were obtained during strabismus surgery and compared with age- and muscle type-matched normal muscles from organ donors. We used PCR arrays to identify differences in gene expression among 417 signaling molecules. We then focused on established schizophrenia-related growth factors, cytokines, and regulators of the extracellular matrix. Among 36 genes with significantly altered gene expression in dysfunctional horizontal rectus muscles, over one third were schizophrenia-related: CTGF, CXCR4, IL1B, IL10RA, MIF, MMP2, NPY1R, NRG1, NTRK2, SERPINA3, TIMP1, TIMP2, and TNF (adjusted p value ≤ 0.016667). By PCR array, expression of three of these genes was significantly different in medial rectus muscles, while eleven were significantly altered in lateral rectus muscles. Comparing baseline levels between muscle types, three schizophrenia-related genes (NPY1R, NTRK2, TIMP2) had lower levels of expression in medial rectus muscles. Despite the surprisingly large number of schizophrenia-related genes with altered gene expression levels in dysfunctional muscles, the lack of specificity for medial rectus muscles undermines a model of shared, region-specific gene expression abnormalities between exotropia and schizophrenia, but rather suggests consideration of the alternative model: that exotropia-induced aberrant early visual experiences may enable and/or contribute as a causative factor to the development of schizophrenia.

MGST2 and WNT2 are candidate genes for comitant strabismus susceptibility in Japanese patients

BACKGROUND/AIM

Strabismus is a common condition with misalignment between two eyes that may lead to decrease of visual acuity, lack of binocularity, and diplopia. It is caused by heterogeneous environmental and genetic risk factors. Our previous research has identified new chromosomal susceptibility loci in 4q28.3 and 7q31.2 regions for comitant strabismus in Japanese families. We conducted a verification study by linkage analysis to narrow the chromosomal loci down to a single gene.

METHODS

From Japanese and U.S. databases, 24 rsSNPs and 233 rsSNPs were chosen from the 4q28.3 and 7q31.2 region, respectively, and were typed in 108 affected subjects and 96 unaffected subjects of 58 families with primary and non-syndromic comitant strabismus. Three major analytical methods were used: transmission disequilibrium test (TDT), TDT allowing for errors (TDTae), and linkage analysis under dominant and recessive inheritance.

RESULTS

The SNPs with significant P values in TDT and TDTae were located solely at the gene, microsomal glutathione S-transferase 2 (MGST2), on chromosome 4q28.3 locus. In contrast, significant SNPs were dispersed in a few genes, containing wingless-type MMTV integration site family member 2 (WNT2), on chromosome 7q31.2 locus. The distribution of significant SNPs on the 7q31.2 locus showed that only the ST7 to WNT2 region in the same big haplotype block contained significant SNPs for all three methods of linkage analysis.

CONCLUSIONS

This study suggests that MGST2 and WNT2 are potential candidates for comitant strabismus in Japanese population.

Clinical characteristics of sibling patients with comitant strabismus

AIM

To investigate the clinical characteristics of sibling patients with comitant strabismus.

METHODS

Sibling patients who were diagnosed with comitant strabismus from January 2005 to December 2014 were retrospectively reviewed. Factors including age, sex, types of strabismus, refractive errors, angle of deviation, and coexistence of other strabismus were analyzed.

RESULTS

A total of 62 patients (31 pairs of siblings) were included. Of these, 26 pairs had intermittent exotropia, 3 had accommodative esotropia, and 2 had infantile esotropia. There were no pairs with different subtypes of strabismus. The age at first visit was 3.7±2.6y and the mean follow-up period was 30.5±24.1mo. In siblings with intermittent exotropia, there was no difference in age of onset, age at operation, or refractive errors between the first and second-born children. The 20 (77%) pairs of siblings with exotropia showed more than 80% concordance of maximum angle of deviation during follow-up. In the 9 pairs in which both siblings had an operation, the final angle of deviation after the operation was 8.2±8.1 prism diopters (PD) in first-born children and 8.6±6.5 PD in second-born children.

CONCLUSION

The subtypes of strabismus are the same in all pairs of siblings and clinical characteristics of strabismus are similar between the first and second-born children. This similarity could be an indicator for the diagnosis of second-born children. Further prospective study including a larger number of sibling patients is needed.

Altered Protein Composition and Gene Expression in Strabismic Human Extraocular Muscles and Tendons

Purpose

To determine whether structural protein composition and expression of key regulatory genes are altered in strabismic human extraocular muscles.

Methods

Samples from strabismic horizontal extraocular muscles were obtained during strabismus surgery and compared with normal muscles from organ donors. We used proteomics, standard and customized PCR arrays, and microarrays to identify changes in major structural proteins and changes in gene expression. We focused on muscle and connective tissue and its control by enzymes, growth factors, and cytokines.

Results

Strabismic muscles showed downregulation of myosins, tropomyosins, troponins, and titin. Expression of collagens and regulators of collagen synthesis and degradation, the collagenase matrix metalloproteinase (MMP)2 and its inhibitors, tissue inhibitor of metalloproteinase (TIMP)1 and TIMP2, was upregulated, along with tumor necrosis factor (TNF), TNF receptors, and connective tissue growth factor (CTGF), as well as proteoglycans. Growth factors controlling extracellular matrix (ECM) were also upregulated. Among 410 signaling genes examined by PCR arrays, molecules with downregulation in the strabismic phenotype included GDNF, NRG1, and PAX7; CTGF, CXCR4, NPY1R, TNF, NTRK1, and NTRK2 were upregulated. Signaling molecules known to control extraocular muscle plasticity were predominantly expressed in the tendon rather than the muscle component. The two horizontal muscles, medial and lateral rectus, displayed similar changes in protein and gene expression, and no obvious effect of age.

Conclusions

Quantification of proteins and gene expression showed significant differences in the composition of extraocular muscles of strabismic patients with respect to important motor proteins, elements of the ECM, and connective tissue. Therefore, our study supports the emerging view that the molecular composition of strabismic muscles is substantially altered.

Role of Genetic Factors in the Pathogenesis of Radial Deficiencies in Humans

Radial deficiencies (RDs), defined as under/abnormal development or absence of any of the structures of the forearm, radial carpal bones and thumb, occur with a live birth incidence ranging from 1 out of 30,000 to 1 out 6,000 newborns and represent about one third/one fourth of all the congenital upper limb anomalies. About half of radial disorders have a mendelian cause and pattern of inheritance, whereas the remaining half appears sporadic with no known gene involved. In sporadic forms certain anomalies, such as thumb or radial hypoplasia, may occur either alone or in association with systemic conditions, like vertebral abnormalities or renal defects. All the cases with a mendelian inheritance are syndromic forms, which include cardiac defects (in Holt-Oram syndrome), bone marrow failure (in Fanconi anemia), platelet deficiency (in thrombocytopenia-absent-radius syndrome), ocular motility impairment (in Okihiro syndrome). The genetics of radial deficiencies is complex, characterized by genetic heterogeneity and high inter- and intra-familial clinical variability: this review will analyze the etiopathogenesis and the genotype/phenotype correlations of the main radial deficiency disorders in humans.

Strabismus at Age 2 Years in Children Born Before 28 Weeks' Gestation: Antecedents and Correlates

Children born very preterm are at greater risk of ophthalmic morbidities, including strabismus, than children born at term. We evaluated perinatal factors associated with strabismus at age 2 years in a large population of infants delivered before 28 weeks' gestation. A total of 996 infants in the multicenter ELGAN (Extremely Low Gestational Age Newborn) study who had a retinal exam in infancy and a developmental assessment at 2 years corrected age are included. Their mothers were interviewed about the pregnancy, and both mother and newborn charts were reviewed. Certified examiners administered the Bayley Scales of Infant Development-II and performed an examination of ocular alignment. Time-oriented logistic regression risk models were created to evaluate the associations of characteristics and exposures with the development of strabismus. Overall, 14% (n = 141) of the children had strabismus at 2 years, and 80% of strabismic children had esotropia. Characteristics associated with strabismus were birth before 26 weeks' gestation, severe fetal growth restriction, and maternal history of aspirin ingestion. Associated postnatal factors included a SNAP-II (Score for Neonatal Acute Physiology) illness severity value ≥ 30, brain ventriculomegaly, type I retinopathy of prematurity, and ventilator-dependent severe bronchopulmonary dysplasia. Strabismus in very preterm populations is associated with a number of antenatal and postnatal antecedents as well as clinical and imaging correlates indicative of brain damage in these children. Routine ophthalmologic assessments in the early years can allow appropriate and timely interventions.