Novel truncation mutations in MYRF cause autosomal dominant high hyperopia mapped to 11p12-q13.3

MYRF Variants in Patients With 46,XY Differences/Disorders of Sex Development and Literature Review

46,XY differences/disorders of sex development (DSD) are genetically heterogeneous conditions characterized by atypical development of the reproductive system. MYRF, a gene encoding a transcription factor, has been identified as a potential causative gene for DSD and cardiac urogenital syndrome (CUGS). This study aims to delineate the clinical manifestations of patients with 46,XY DSD and MYRF mutations, encompassing both from our cohort and cases reported in the literature. Patients with 46,XY DSD were recruited from Peking Union Medical College Hospital and identified through a comprehensive review of published literature. Whole-exome sequencing was conducted to elucidate the genetic etiology. Comprehensive clinical data, including physical examination findings, hormonal profiles, and imaging results, were retrospectively gathered from medical records and published sources. Three of our patients with 46,XY DSD were found to harbor heterozygous loss-of-function mutations in the MYRF gene, including the recurrent variant c.789dup and two novel variants c.1915C>T and c.2154del. The patients exhibited underdeveloped testicular tissue, inadequate masculinization, and the persistence of Müllerian ducts. A review of the literature indentified 31 MYRF-linked 46,XY DSD patients and two 46,XX DSD patients. Among these, 11 cases presented with isolated testicular dysgenesis, 20 cases exhibited severe cardiopulmonary issues, and the majority of patients had congenital diaphragmatic hernia. Genetic analysis revealed 26 distinct MYRF variants among these patients, including 10 missense, 8 frameshift, 5 nonsense, and 3 splice site alterations, affecting critical domains of the MYRF gene. Our study broadens the spectrum of MYRF mutations in 46,XY DSD patients and highlighting the gene's indispensable role in gonadal development. However, a clear genotype-phenotype correlation in MYRF-related DSD remain elusive.

Clinical features of patients with mutations in genes for nanophthalmos

BACKGROUND/AIMS

To distinguish the clinical feature of nanophthalmos (NNO) caused by mutations in protease serine 56 (PRSS56), membrane-type frizzled-related protein (MFRP), myelin regulatory factor (MYRF) and transmembrane protein 98 (TMEM98) and to evaluate the association between angle-closure glaucoma (ACG) and NNO.

METHODS

Variants in those four genes were identified through exome sequencing/whole genome sequencing data, and bioinformatic analysis was conducted to identify pathogenic/likely pathogenic (P/LP) variants. This observational study comprehensively summarised ophthalmological data of 67 patients with NNO from 63 families. Ocular parameters from 68 eyes without surgical treatment were subjected to further analysis.

RESULTS

Totally, 67 patients from 63 families harboured 57 P/LP variants in the four genes, including 30 in PRSS56 (47.6%), 23 in MFRP (36.5%), 5 in TMEM98 (7.9%) and 5 in MYRF (7.9%). ACG was present in 79.1% of patients. An analysis of ocular parameters from 68 eyes revealed that shorter axial length (AL), lower vitreous-to-AL ratios and severe foveal hypoplasia were associated with variants in PRSS56 and MFRP. Uveal effusion was more common in patients with PRSS56 variants, while retinitis pigmentosa was frequently observed in patients with MFRP variants. Patients with MYRF variants exhibited the thinnest retinal nerve fibre layer thickness. Patients with TMEM98 variants had an earlier average onset age of glaucoma.

CONCLUSION

Variants in PRSS56 and MFRP are the most common genetic cause of NNO. ACG is a severe complication frequently observed in these patients. Earlier onset of ACG is observed in patients with dominant NNO, while foveal hypoplasia is more common in patients with recessive disease. Recognising these features is helpful in clinical care and genetic counselling.

Nanophthalmos-Associated MYRF gene mutation facilitates intraocular inflammation in mice

PURPOSE

Patients with nanophthalmos might be prone to developing intraocular inflammation following an acute glaucoma attack. Here, we aimed to investigate the role of MYRF in intraocular inflammation by modeling the mutation in mice.

METHODS

Nanophthalmos frameshift mutation of Myrf was introduced into the mouse genome with the CRISPR-Cas9 system. Signaling pathways in eye tissues were delineated using RNA sequencing and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis. Intraocular inflammation was induced by a lipopolysaccharide (LPS) intravitreal injection. Dexamethasone (DEX) was administered systemically and locally a week before the LPS injection. The anterior segment clinical scores of the mice were examined 24 h after the LPS injection. Infiltrating inflammatory cells were evaluated with histopathology and immunofluorescence. The mRNA levels of inflammatory cytokines were quantified with reverse transcription-quantitative PCR (RT-qPCR) and the corresponding protein concentrations using enzyme-linked immunosorbent assay (ELISA).

RESULTS

Many inflammation-associated signaling pathways were enriched in Myrf mut/+ mice ocular tissues. Clinical scores of Myrf mut/+ mice were significantly higher than those of Myrf +/+ mice 24 h after LPS administration. Histological examination demonstrated high inflammatory cell infiltration in the anterior and vitreous chambers in Myrf mut/+ mice, with numerous CD45+ and CD11b+ inflammatory cells. Moreover, enhanced expression of inflammatory cytokines MCP-1, TGF-β, and IL-1β in eyes and aqueous humor of Myrf mut/+ mice was detected. Remarkably, pretreating Myrf mut/+ mice with DEX relieved the intraocular inflammation.

CONCLUSION

Nanophthalmos-associated MYRF mutation renders mouse eyes more susceptible to inflammation. Dexamethasone treatment ameliorates the inflammatory response.

MYRF: A unique transmembrane transcription factor- from proteolytic self-processing to its multifaceted roles in animal development

The Myelin Regulator Factor (MYRF) is a master regulator governing myelin formation and maintenance in the central nervous system. The conservation of MYRF across metazoans and its broad tissue expression suggest it has functions extending beyond the well-established role in myelination. Loss of MYRF results in developmental lethality in both invertebrates and vertebrates, and MYRF haploinsufficiency in humans causes MYRF-related Cardiac Urogenital Syndrome, underscoring its importance in animal development; however, these mechanisms are largely unexplored. MYRF, an unconventional transcription factor, begins embedded in the membrane and undergoes intramolecular chaperone mediated trimerization, which triggers self-cleavage, allowing its N-terminal segment with an Ig-fold DNA-binding domain to enter the nucleus for transcriptional regulation. Recent research suggests developmental regulation of cleavage, yet the mechanisms remain enigmatic. While some parts of MYRF's structure have been elucidated, others remain obscure, leaving questions about how these motifs are linked to its intricate processing and function.

Hypoplastic Left Heart Syndrome: Signaling & Molecular Perspectives, and the Road Ahead

Hypoplastic left heart syndrome (HLHS) is a lethal congenital heart disease (CHD) affecting 8-25 per 100,000 neonates globally. Clinical interventions, primarily surgical, have improved the life expectancy of the affected subjects substantially over the years. However, the etiological basis of HLHS remains fundamentally unclear to this day. Based upon the existing paradigm of studies, HLHS exhibits a multifactorial mode of etiology mediated by a complicated course of genetic and signaling cascade. This review presents a detailed outline of the HLHS phenotype, the prenatal and postnatal risks, and the signaling and molecular mechanisms driving HLHS pathogenesis. The review discusses the potential limitations and future perspectives of studies that can be undertaken to address the existing scientific gap. Mechanistic studies to explain HLHS etiology will potentially elucidate novel druggable targets and empower the development of therapeutic regimens against HLHS in the future.

Design and Outcomes of a Novel Multidisciplinary Ophthalmic Genetics Clinic

The Multidisciplinary Ophthalmic Genetics Clinic (MOGC) at the University of Michigan Kellogg Eye Center aims to provide medical and ophthalmic genetics care to patients with inherited ocular conditions. We have developed a clinical and referral workflow where each patient undergoes coordinated evaluation by our multidisciplinary team followed by discussions on diagnosis, prognosis, and genetic testing. Testing approaches are specific to each patient and can be targeted (single-gene, gene panel), broad (chromosomal microarray, whole-exome sequencing), or a combination. We hypothesize that this clinic model improves patient outcomes and quality of care. A retrospective chart review of patients in the MOGC from July 2020 to October 2022 revealed that the most common referral diagnoses were congenital cataracts, optic neuropathy, and microphthalmia, with 52% syndromic cases. Within this patient cohort, we saw a 76% uptake for genetic testing, among which 33% received a diagnostic test result. Our results support a tailored approach to genetic testing for specific conditions. Through case examples, we highlight the power and impact of our clinic. By integrating ophthalmic care with medical genetics and counseling, the MOGC has not only helped solve individual patient diagnostic challenges but has aided the greater population in novel genetic discoveries and research towards targeted therapeutics.

Truncation mutations in MYRF underlie primary angle closure glaucoma

Mutations in myelin regulatory factor (MYRF), a gene mapped to 11q12-q13.3, are responsible for autosomal dominant high hyperopia and seem to be associated with angle closure glaucoma, which is one of the leading causes of irreversible blindness worldwide. Whether there is a causal link from the MYRF mutations to the pathogenesis of primary angle-closure glaucoma (PACG) remains unclear at this time. Six truncation mutations, including five novel and one previously reported, in MYRF are identified in seven new probands with hyperopia, of whom all six adults have glaucoma, further confirming the association of MYRF mutations with PACG. Immunofluorescence microscopy demonstrates enriched expression of MYRF in the ciliary body and ganglion cell layer in humans and mice. Myrfmut/+ mice have elevated IOP and fewer ganglion cells along with thinner retinal nerve fiber layer with ganglion cell layer than wild-type. Transcriptome sequencing of Myrfmut/+ retinas shows downregulation of Dnmt3a, a gene previously associated with PACG. Co-immunoprecipitation demonstrates a physical association of DNMT3A with MYRF. DNA methylation sequencing identifies several glaucoma-related cell events in Myrfmut/+ retinas. The interaction between MYRF and DNMT3A underlies MYRF-associated PACG and provides clues for pursuing further investigation into the pathogenesis of PACG and therapeutic target.

MYRF: A New Regulator of Cardiac and Early Gonadal Development—Insights from Single Cell RNA Sequencing Analysis

De novo variants in the myelin regulatory factor (MYRF), a transcription factor involved in the differentiation of oligodendrocytes, have been linked recently to the cardiac and urogenital syndrome, while familiar variants are associated with nanophthalmos. Here, we report for the first time on a patient with a de novo stop-gain variant in MYRF (p.Q838*) associated with Scimitar syndrome, 46,XY partial gonadal dysgenesis (GD) and severe hyperopia. Since variants in MYRF have been described in both 46,XX and 46,XY GD, we assumed a role of MYRF in the early development of the bipotential gonad. We used publicly available single cell sequencing data of human testis and ovary from different developmental stages and analysed them for MYRF expression. We identified MYRF expression in the subset of coelomic epithelial cells at stages of gonadal ridge development in 46,XX and 46,XY individuals. Differential gene expression analysis revealed significantly upregulated genes. Within these, we identified CITED2 as a gene containing a MYRF binding site. It has been shown that Cited2^−/− mice have gonadal defects in both testis and ovary differentiation, as well as defects in heart development and establishment of the left–right axis. This makes MYRF a potential candidate as an early regulator of gonadal and heart development via upregulation of the transcriptional cofactor CITED2.

Diverse clinical manifestations and intrafamilial variability due to an inherited recurrent MYRF variant

MYRF monoallelic variants have been described in syndromic forms characterized by cardiac-urogenital syndrome and isolated nanophthalmos with/without minor systemic manifestations. We describe a large family with a paternally inherited pathogenic variant in MYRF that manifested as congenital diaphragmatic hernia (CDH), cardiac and urogenital abnormalities, and/or nanophthalmos with significant intrafamilial variability.

Genetic analysis assists diagnosis of clinical systemic disease in children with excessive hyperopia

BACKGROUND

A thorough examination (especially those including visual functional evaluation) is very important in children's eye-development during clinical practice, when they encountered with unusual excessive hyperopia especially accompanied with other possible complications. Genetic testing would be beneficial for early differential diagnosis as blood sampling is more convenient than all other structural imaging capture tests or functional tests which need children to cooperate well. Thus genetic testing helps us to filter other possible multi-systemic diseases in children patients with eye disorder.

CASE PRESENTATION

A 3-year-old and an 8-year-old boy, both Chinese children clinically manifested as bilateral excessive hyperopia (≥+10.00), severe amblyopia and exotropia, have been genetically diagnosed as Senior-Loken syndrome-5 (SLSN5) and isolated posterior microphthalmos (MCOP6), respectively.

CONCLUSIONS

This report demonstrates the importance of genetic diagnosis before a clinical consult. When children are too young to cooperate with examinations, genetic testing is valuable for predicting other systemic diseases and eye-related development and for implementing early interventions for the disease.

Case Report: De novo variant in myelin regulatory factor in a Chinese child with 46,XY disorder/difference of sex development, cardiac and urogenital anomalies, and short stature

The myelin regulatory factor (MYRF; MIM# 608329) gene was first identified as a critical transcription factor involved in oligodendrocyte differentiation and central nervous system myelination. With the recent development of exome sequencing, pathogenic variants of MYRF had been considered as the cause of cardiac-urogenital syndrome (CUGS), 46,XY and 46,XX disorders/differences of sex development (DSDs), and nanophthalmos. Herein, we described a 4-year-7-month-old "girl" with ventricular septal defect, atrial septal defect, patent ductus arteriosus, severe pulmonary hypertension, moderate-to-severe tricuspid regurgitation, enlarged coronary sinus, left superior vena cava, and right lung hypoplasia at birth. Later, the patient developed short stature and amblyopia. Further examination revealed a karyotype 46,XY and visible uterus, whereas the presence of gonads were not explored. Laparoscopy revealed dysplasia of testicular gonad. Whole-exome sequencing (WES) was performed and a de novo heterozygous mutation in MYRF was identified, known as c.2817G > A/p. W939* (NM_001127392.3). Therefore, this case report presented multiple clinical manifestations with syndromic symptoms of CUGS, 46,XY DSD, and ocular symptoms. These new data expanded the phenotype of the MYRF variant and may benefit to characterize the phenotypes caused by the variants of this gene.

Evaluation of MYRF as a candidate gene for primary angle closure glaucoma

PURPOSE

Primary angle-closure glaucoma (PACG) is a leading cause of blindness. Despite tremendous human effort and financial input, no definitive causative gene has been identified either through genome-wide association or Mendelian family studies. In the current study, novel candidate genes for PACG were investigated by studying the variants of nanophthalmos-associated genes.

METHODS

A case-control study was conducted that included 45 PACG patients and 12 normal controls with short axial length (AL, less than 23.5 mm but more than 20.5 mm). Whole-exome sequencing (WES) was performed to screen the variants in previously identified nanophthalmos-associated genes, as well as other risk genes.

RESULTS

The age range of the 45 PACG patients was 24 to 80 years, with an average AL of 21.87±0.65 mm (range: 20.54-23.45 mm) in the right eye and 21.89±0.64 mm (range 20.60-23.23 mm) in the left eye. Four novel myelin regulatory factor (MYRF) gene missense variants (p.G117S, p.H1057R, p.H230R, and p.R316C) were identified in four out of the 45 enrolled PACG patients, respectively. No MYRF or other nanophthalmos-associated gene variants were detected in the 12 normal controls.

CONCLUSIONS

An appropriate approach was adopted to investigate the genetics of PACG through nanophthalmos-associated genes. A genetic variant, MYRF, was identified in four out of 45 PACG patients, which might be a novel candidate gene for PACG.

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.

Crystal structure of the MyRF ICA domain with its upstream β-helical stalk reveals the molecular mechanisms underlying its trimerization and self-cleavage

Myelin gene regulatory factor (MyRF), a novel membrane transcription factor expressed on the endoplasmic reticulum membrane, functions as a trimer. The trimerization of MyRF is associated with a fragment between the DNA binding domain and transmembrane domain that shares homology with the triple-β-helix and intramolecular chaperone autocleavage (ICA) domain of phage tailspike proteins. The molecular details of these domains in eukaryotes have not been elucidated. Here, we present the crystal structure of the MyRF ICA domain with its upstream β-helical stalk, determined at 2.4Å resolution. The structure showed that its upstream β-helical stalk is different from the triple β-helix reported before. This is the first structure of the mammalian protein with a triple β-helix. Structure analysis demonstrated that the triple α-helical coiled-coil formed at the MyRF ICA domain C-terminal was the main driving force for the trimerization. Additionally, our findings showed that MyRF was cleaved via a highly conserved serine-lysine catalytic dyad mechanism and that cleavage would be activated only if the ICA domains were organized as trimers. In contrast to the viral ICA domain, almost no interaction was found between the MyRF ICA domain and its upstream neighboring β-helix of the stalk; thus, activation of self-cleavage may not be triggered by the upstream region of the ICA domain, contrary to the observations made in phages. These findings provided an important insight into the molecular mechanisms of MyRF trimerization and self-cleavage.

Myelin regulatory factor deficiency is associated with the retinal photoreceptor defects in mice

Previously, we reported the myelin regulatory factor (MYRF) as a candidate gene for nanophthalmos. We have also produced Myrf knockdown (Myrf+/-) mouse strain to investigate the cellular and molecular phenotypes of reduced MYRF expression in the retina. Myrf+/- mouse strain was generated using the CRISPR/Cas9 system. Optomotor response system, electroretinogram (ERG), spectral-domain optical coherence tomography (SD-OCT), histology, and immunohistochemistry were performed to evaluate retinal spatial vision, electrophysiological function, retinal thickness, and pathological changes in cone or rod photoreceptors, respectively. RNA sequencing (RNA-seq) was performed to investigate the underlying molecular mechanism linking Myrf deficiency with photoreceptor defects. The genotype and phenotype of CRISPR/Cas9-induced Myrf+/- mice and their offspring were comprehensively investigated. Photoreceptor defects were detected in the retinas of Myrf+/- mice. Visual acuity and ERG responses were decreased in Myrf+/- mice compared with the control mice (Myrf+/+). The loss of cone and rod neurons was proportional to the decreased outer nuclear layer (ONL) thickness. Moreover, RNA-seq revealed that phototransduction and estrogen signaling pathways played important roles in the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. Myrf+/- mouse strain provides a good model to investigate the function of the MYRF gene. Photoreceptor defects with impaired functions of spatial vision and retinal electrophysiology indicate an important role played by MYRF in retinal development. Alterations in phototransduction and estrogen signaling pathways play important roles in linking Myrf deficiency with retinal photoreceptor defects.

Nanophthalmos-Associated MYRF Gene Mutation Causes Ciliary Zonule Defects in Mice

Purpose

Patients with nanophthalmos who undergo intraocular surgery often present with abnormal ciliary zonules. In a previous study, we reported mutation in MYRF that is implicated in the pathogenesis of nanophthalmos. The aim of this study was to model the mutation in mice to explore the role of MYRF on zonule structure and its major molecular composition, including FBN1 and FBN2.

Methods

Human MYRF nanophthalmos frameshift mutation was generated in mouse using the CRISPR-Cas9 system. PCR and Sanger sequencing were used for genotype analysis of the mice model. Anterior chamber depth (ACD) was measured using hematoxylin and eosin–stained histology samples. Morphologic analysis of ciliary zonules was carried out using silver staining and immunofluorescence. Transcript and protein expression levels of MYRF, FBN1, and FBN2 in ciliary bodies were quantified using quantitative real-time PCR (qRT-PCR) and Western blot.

Results

A nanophthalmos frameshift mutation (c.789delC, p.N264fs) of MYRF in mice showed ocular phenotypes similar to those reported in patients with nanophthalmos. ACD was reduced in MYRF mutant mice (MYRF^mut/+) compared with that in littermate control mice (MYRF^+/+). In addition, the morphology of ciliary zonules showed reduced zonular fiber density and detectable structural dehiscence of zonular fibers. Furthermore, qRT-PCR analysis and Western blot showed a significant decrease in mRNA expression levels of MYRF, FBN1, and FBN2 in MYRF^mut/+ mice.

Conclusions

Changes in the structure and major molecular composition of ciliary zonules accompanied with shallowing anterior chamber were detected in MYRF^mut/+ mice. Therefore, MYRF mutant mice strain is a useful model for exploring pathogenesis of zonulopathy, which is almost elusive for basic researches due to lack of appropriate animal models.

Novel TMEM98, MFRP, PRSS56 variants in a large United States high hyperopia and nanophthalmos cohort

Nanophthalmos is a rare condition defined by a small, structurally normal eye with resultant high hyperopia. While six genes have been implicated in this hereditary condition (MFRP, PRSS56, MYRF, TMEM98, CRB1,VMD2/BEST1), the relative contribution of these to nanophthalmos or to less severe high hyperopia (≥ + 5.50 spherical equivalent) has not been fully elucidated. We collected probands and families (n = 56) with high hyperopia or nanophthalmos (≤ 21.0 mm axial length). Of 53 families that passed quality control, plausible genetic diagnoses were identified in 10/53 (18.8%) by high-throughput panel or pooled exome sequencing. These include 1 TMEM98 family (1.9%), 5 MFRP families (9.4%), and 4 PRSS56 families (7.5%), with 4 additional families having single allelic hits in MFRP or PRSS56 (7.5%). A novel deleterious TMEM98 variant (NM_015544.3, c.602G>C, p.(Arg201Pro)) segregated with disease in 4 affected members of a family. Multiple novel missense and frameshift variants in MFRP and PRSS56 were identified. PRSS56 families were more likely to have choroidal folds than other solved families, while MFRP families were more likely to have retinal degeneration. Together, this study defines the prevalence of nanophthalmos gene variants in high hyperopia and nanophthalmos and indicates that a large fraction of cases remain outside of single gene coding sequences.

Nanophthalmos patient with a THR518MET mutation in MYRF, a case report

Background

Nanophthalmos has a significant genetic background and disease-causing mutations have been recently been reported in the myelin regulatory factor (MYRF) gene. We report clinical features in a patient with nanophthalmos and a Thr518Met MYRF mutation.

Case presentation

A three-year-old male was discovered to have nanophthalmos after first presenting to the emergency department for a frontal headache, eye pain, emesis, and lethargy. Imaging studies (CT and MRI) were negative except for increased posterior fossa cerebrospinal fluid. Subsequent examinations revealed nanophthalmos (short axial eye lengths 18.1 mm OD and 18.3 mm OS), microcornea, and a large crystalline lens. Peripheral chorioretinal pigment abnormalities were also observed. He experienced episodes of marked ocular hypertension (53 mmHg OD and 60 mmHg) likely due to intermittent angle closure precipitated by nanophthalmos. The ocular hypertension was responsive to topical medicines. Genetic analysis of known nanophthalmos genes MFRP and TMEM98 were negative, while a novel mutation, Thr518Met was detected in MYRF. The Thr518Met mutation was absent from 362 matched normal controls and was extremely rare in a large population database, allele frequency of 0.000024. The Thr518Met mutation altered a highly conserved amino acid in the MYRF protein and three of four algorithms suggested that this mutation is likely pathogenic. Finally, molecular modeling showed that the Thr518Met mutation is damaging to MYRF structure. Together these data suggest that the Thr518Met mutation causes nanophthalmos.

Conclusions

Nanophthalmos may present at an early age with features of angle closure glaucoma and a Thr518Met mutation in MYRF was detected in a patient with nanophthalmos. Prevalence data, homology data, mutation analysis data, and protein modeling data suggest that this variant is pathogenic and may expand the phenotypic range of syndromic nanophthalmos caused by MYRF mutations to include central nervous system abnormalities (increased posterior fossa cerebrospinal fluid).

The nanophthalmos protein TMEM98 inhibits MYRF self-cleavage and is required for eye size specification

The precise control of eye size is essential for normal vision. TMEM98 is a highly conserved and widely expressed gene which appears to be involved in eye size regulation. Mutations in human TMEM98 are found in patients with nanophthalmos (very small eyes) and variants near the gene are associated in population studies with myopia and increased eye size. As complete loss of function mutations in mouse Tmem98 result in perinatal lethality, we produced mice deficient for Tmem98 in the retinal pigment epithelium (RPE), where Tmem98 is highly expressed. These mice have greatly enlarged eyes that are very fragile with very thin retinas, compressed choroid and thin sclera. To gain insight into the mechanism of action we used a proximity labelling approach to discover interacting proteins and identified MYRF as an interacting partner. Mutations of MYRF are also associated with nanophthalmos. The protein is an endoplasmic reticulum-tethered transcription factor which undergoes autoproteolytic cleavage to liberate the N-terminal part which then translocates to the nucleus where it acts as a transcription factor. We find that TMEM98 inhibits the self-cleavage of MYRF, in a novel regulatory mechanism. In RPE lacking TMEM98, MYRF is ectopically activated and abnormally localised to the nuclei. Our findings highlight the importance of the interplay between TMEM98 and MYRF in determining the size of the eye.

Mutation screening of 17 candidate genes in a cohort of 67 probands with early-onset high myopia

PURPOSE

To detect variants in 17 known potentially causative genes for non-syndromic myopia in 67 Tujia Chinese patients with early-onset high myopia (eo-HM).

METHODS

DNA from 67 unrelated patients with early onset (<7 years old) high myopia (refraction error ≤ -6.00D or axial length > 26 mm) were subjected to whole-exome sequencing (WES). Variants in 17 candidate genes were analysed by multistep bioinformatics analysis. Subsequently, Sanger sequencing was used to verify identified candidate mutations and to assess available family members for co-segregation with myopia.

RESULTS

A multistep systematic analysis of variants in 17 potentially causative genes for eo-HM revealed four novel pathogenic mutations and three potential pathogenic mutations in 4 of 17 genes in 7 of 67 (10.4%) probands. The pathogenic group included one missense mutation (c.100G > C, p.Asp34His) and one splice donor mutation (c.989 + 1G >A) in ARR3, one missense mutation (c.995C > A, p.Thr332Lys) in NDUFAF7 and one novel frameshift mutation (c.726dupA, p.Arg243fs*140) in SLC39A5. The potential pathogenic group included two missense mutations (c.3266A > G, p.Tyr1089Cys; c.913G > A, p.Glu305Lys) in ZNF644 and one missense mutation (c.960T > A, p.His320Gln) in NDUFAF7. Sequence changes were confirmed by Sanger sequencing; all had an allele frequency <0.01 in the 1000G, EVS, ExAC and gnomAD databases. Additionally, both the pathogenic and potentially pathogenic mutations were predicted to be damaging by SIFT, Polyphen-2, PROVEAN, MutationTaster2, CADD and REVEL except the p.Tyr1089Cys and p.Glu305Lys changes were predicted to be neutral by PROVEAN.

CONCLUSION

Our research provides more evidence to support the hypothesis that mutations in ARR3, SLC39A5 and NDUFAF7 are disease-causing genes for eo-HM and broadens the eo-HM mutation spectrum among different ethnic groups. It also deepens understanding of the contributions of ARR3, SLC39A5, and NDUFAF7 to eo-HM.

Autosomal dominant nanophthalmos and high hyperopia associated with a C-terminal frameshift variant in MYRF

Purpose

Nanophthalmos is a rare subtype of microphthalmia associated with high hyperopia and an increased risk of angle-closure glaucoma. We investigated the genetic cause of nanophthalmos and high hyperopia in an autosomal dominant kindred.

Methods

A proband with short axial length, high hyperopia, and dextrocardia was subjected to exome sequencing. Human and rodent gene expression data sets were used to investigate the expression of relevant genes.

Results

We identified a segregating heterozygous frameshift variant at the 3' end of the penultimate exon of MYRF. Using Myc-MYRF chromatin immunoprecipitation data from rat oligodendrocytes, MYRF was found to bind immediately upstream of the transcriptional start site of Tmem98, a gene that itself has been implicated in autosomal dominant nanophthalmos. MYRF and TMEM98 were found to be expressed in the human retina, with a similar pattern of expression across several dissected human eye tissues.

Conclusions

C-terminal variants in MYRF, which are expected to escape nonsense-mediated decay, represent a rare cause of autosomal dominant nanophthalmos with or without dextrocardia or congenital diaphragmatic hernia.