Abnormal retinal development associated with FRMD7 mutations

Differences of ocular oscillations and neuro-retinal structures in patients with nystagmus caused by GPR143 and FRMD7 gene variants

PURPOSE

Mutations of G protein-coupled receptor 143 (GPR143) and FERM domain containing 7 (FRMD7) may result in congenital nystagmus (CN) in the first 6 months of life. We aimed to compare the differences in ocular oscillations between patients with these two gene mutations as well as the functional and structural changes in their retinas and visual pathways.

METHODS

Medical records were retrospectively reviewed to identify patients of congenital nystagmus with confirmed mutations in either GPR143 or FMRD7 genes from January 2018 to May 2023. The parameters of the ocular oscillations were recorded using Eyelink 1000 Plus. The retinal structure and function were evaluated using optical coherence tomography and multi-focal electroretinography (mERG). The visual pathway and optical nerve projection were evaluated using visual evoked potentials. The next-generation sequencing technique was used to identify the pathogenic variations in the disease-causing genes for CN.

RESULTS

Twenty nystagmus patients of GPR143 and 21 patients of FMRD7 who had been confirmed by molecular testing between January 2018 and May 2023 were included. Foveal hypoplasia was detected only in patients with the GPR143 pathogenic variant. mERG examination showed a flat response topography in the GPR143 group compared to the FRMD7 group. VEP showed that bilateral amplitude inconsistency was detected only in the patients with GPR143 gene mutation. The amplitude and frequency of the ocular oscillations were not found to differ between patients with two different genetic mutations.

CONCLUSIONS

Although the etiology and molecular mechanisms are completely different between CN patients, they may have similar ocular oscillations. A careful clinical examination and electrophysiological test will be helpful in making a differential diagnosis. Our novel identified variants will further expand the spectrum of the GPR143 and FRMD7 variants.

ERG Responses in Albinism, Idiopathic Infantile Nystagmus, and Controls

Purpose

Our primary aim was to compare adult full-field ERG (ffERG) responses in albinism, idiopathic infantile nystagmus (IIN), and controls. A secondary aim was to investigate the effect of within-subject changes in nystagmus eye movements on ffERG responses.

Methods

Dilated Ganzfeld flash ffERG responses were recorded using DTL electrodes under conditions of dark (standard and dim flash) and light adaptation in 68 participants with albinism, 43 with IIN, and 24 controls. For the primary aim, the effect of group and age on ffERG responses was investigated. For the secondary aim, null region characteristics were determined using eye movements recorded prior to ffERG recordings. ffERG responses were recorded near and away from the null regions of 18 participants also measuring the success rate of recordings.

Results

For the primary aim, age-adjusted photopic a- and b-wave amplitudes were consistently smaller in IIN compared with controls (P < 0.0001), with responses in both groups decreasing with age. In contrast, photopic a-wave amplitudes increased with age in albinism (P = 0.0035). For the secondary aim, more intense nystagmus significantly reduced the success rate of measurable responses. Within-subject changes in nystagmus intensity generated small, borderline significant differences in photopic b-wave peak times and a-and b-wave amplitudes under scotopic conditions with standard flash.

Conclusions

Age-adjusted photopic ffERG responses are significantly reduced in IIN adding to the growing body of evidence of retinal abnormalities in IIN. Differences between photopic responses in albinism and controls depend on age. Success at obtaining ffERG responses could be improved by recording responses at the null region.

Visual Field Deficits in Albinism in Comparison to Idiopathic Infantile Nystagmus

Purpose

This is the first systematic comparison of visual field (VF) deficits in people with albinism (PwA) and idiopathic infantile nystagmus (PwIIN) using static perimetry. We also compare best-corrected visual acuity (BCVA) and optical coherence tomography measures of the fovea, parafovea, and circumpapillary retinal nerve fiber layer in PwA.

Methods

VF testing was performed on 62 PwA and 36 PwIIN using a Humphrey Field Analyzer (SITA FAST 24-2). Mean detection thresholds for each eye were calculated, along with quadrants and central measures. Retinal layers were manually segmented in the macular region.

Results

Mean detection thresholds were significantly lower than normative values for PwA (-3.10 ± 1.67 dB, P << 0.0001) and PwIIN (-1.70 ± 1.54 dB, P < 0.0001). Mean detection thresholds were significantly lower in PwA compared to PwIIN (P < 0.0001) and significantly worse for left compared to right eyes in PwA (P = 0.0002) but not in PwIIN (P = 0.37). In PwA, the superior nasal VF was significantly worse than other quadrants (P < 0.05). PwIIN appeared to show a mild relative arcuate scotoma. In PwA, central detection thresholds were correlated with foveal changes in the inner and outer retina. VF was strongly correlated to BCVA in both groups.

Conclusions

Clear peripheral and central VF deficits exist in PwA and PwIIN, and static VF results need to be interpreted with caution clinically. Since PwA exhibit considerably lower detection thresholds compared to PwIIN, VF defects are unlikely to be due to nystagmus in PwA. In addition to horizontal VF asymmetry, PwA exhibit both vertical and interocular asymmetries, which needs further exploration.

Truncated FRMD7 proteins in congenital Nystagmus: novel frameshift mutations and proteasomal pathway implications

Idiopathic congenital nystagmus (ICN) manifests as involuntary and periodic eye movements. To identify the genetic defect associated with X-linked ICN, Whole Exome Sequencing (WES) was conducted in two affected families. We identified two frameshift mutations in FRMD7, c.1492dupT/p.(Y498Lfs*15) and c.1616delG/p.(R539Kfs*2). Plasmids harboring the mutated genes and qPCR analysis revealed mRNA stability, evading degradation via the NMD pathway, and corroborated truncated protein production via Western-blot analysis. Notably, both truncated proteins were degraded through the proteasomal (ubiquitination) pathway, suggesting potential therapeutic avenues targeting this pathway for similar mutations. Moreover, we conducted a comprehensive analysis, summarizing 140 mutations within the FRMD7 gene. Our findings highlight the FERM and FA structural domains as mutation-prone regions. Interestingly, exons 9 and 12 are the most mutated regions, but 90% (28/31) mutations in exon 9 are missense while 84% (21/25) mutations in exon 12 are frameshift. A predominant occurrence of shift code mutations was observed in exons 11 and 12, possibly associated with the localization of premature termination codons (PTCs), leading to the generation of deleterious truncated proteins. Additionally, our conjecture suggests that the loss of FRMD7 protein function might not solely drive pathology; rather, the emergence of aberrant protein function could be pivotal in nystagmus etiology. We propose a dependence of FRMD7 protein normal function primarily on its anterior domain. Future investigations are warranted to validate this hypothesis.

Zebrafish Optokinetic Reflex: Minimal Reporting Guidelines and Recommendations

Optokinetic reflex (OKR) assays in zebrafish models are a valuable tool for studying a diverse range of ophthalmological and neurological conditions. Despite its increasing popularity in recent years, there are no clear reporting guidelines for the assay. Following reporting guidelines in research enhances reproducibility, reduces bias, and mitigates underreporting and poor methodologies in published works. To better understand optimal reporting standards for an OKR assay in zebrafish, we performed a systematic literature review exploring the animal, environmental, and technical factors that should be considered. Using search criteria from three online databases, a total of 109 research papers were selected for review. Multiple crucial factors were identified, including larval characteristics, sample size, fixing method, OKR set-up, distance of stimulus, detailed stimulus parameters, eye recording, and eye movement analysis. The outcome of the literature analysis highlighted the insufficient information provided in past research papers and the lack of a systematic way to present the parameters related to each of the experimental factors. To circumvent any future errors and champion robust transparent research, we have created the zebrafish optokinetic (ZOK) reflex minimal reporting guideline.

Human embryonic and fetal biobanking: Establishing the Dutch Fetal Biobank and a framework for standardization

Recent studies of human embryos and fetuses have advanced our understanding not only of basic biology but also of health and disease, through a combination of detailed three-dimensional (3D) morphology and processes such as gene expression, cellular decision-making and differentiation, and epigenetics during the various phases of human development and growth. Large-scale research initiatives focusing on these topics have been initiated during the last decade, all of which depend on biobanks that provide high-quality images of human embryonic and fetal morphology, as well as on high-quality collections of tissue samples that are obtained and stored appropriately. In this perspective, we describe our experience in establishing the Dutch Fetal Biobank to present the framework and workflow of the biobank, provide a brief discussion of the main legal and ethical aspects involved in establishing a pre-natal tissue bank, and present the preliminary data on the first 329 donated specimens.

Nystagmus Characteristics in Albinism: Unveiling the Link to Foveal Hypoplasia and Visual Acuity

Purpose

The purpose of this study was to describe the association among nystagmus characteristics, foveal hypoplasia, and visual acuity in patients with albinism.

Methods

We studied nystagmus recordings of 50 patients with albinism. The nystagmus waveform was decomposed into two types: dominantly pendular and dominantly jerk. We correlated the nystagmus type, amplitude, frequency, and percentage of low velocity (PLOV) to Snellen visual acuity and foveal hypoplasia grades.

Results

The grade of foveal hypoplasia and visual acuity showed a strong correlation (r = 0.87, P < 0.0001). Nystagmus type and PLOV had the strongest significant (P < 0.0001) correlation with visual acuity (r = 0.70 and r = -0.56, respectively) and with foveal hypoplasia (r = 0.76 and r = -0.60, respectively). Patients with pendular nystagmus type had the lowest PLOV, and the highest grade of foveal hypoplasia (P < 0.0001). Severe foveal hypoplasia (grade 4), was almost invariably associated with pendular nystagmus (86%).

Conclusions

Foveal hypoplasia grade 4 is associated with pendular nystagmus, lower PLOV, and worse visual acuity. Based on these results, nystagmus recordings at a young age may contribute to predicting visual outcomes.

Visual Function and Neuropsychological Profiling of Idiopathic Infantile Nystagmus

Though considered a benign condition, idiopathic infantile nystagmus (IIN) may be associated with decreased visual acuity and oculo-motor abnormalities, resulting in developmental delays and poor academic performance. Nevertheless, the specific visual function profile of IIN and its possible impact on neuropsychological development have been poorly investigated. To fill this gap, we retrospectively collected the clinical data of 60 children presenting with IIN over a 10-year period (43 male; mean age of 7 years, range of 2 months-17 years, 9 months). The majority of the subjects in our cohort presented with reduced visual acuity for far distances and normal visual acuity for near distances, associated with oculo-motor abnormalities. The overall scores of cognitive and visual-cognitive tests were in the normal range, but revealed peculiar cognitive and visual-cognitive profiles, defined by specific frailties in processing speed and visual-motor integration. The same neuropsychological profiles characterize many neurodevelopmental disorders and may express a transnosographic vulnerability of the dorsal stream. As the first study to explore the neuropsychologic competencies in children with IIN, our study unveils the presence of subclinical frailties that need to be addressed to sustain academic and social inclusion.

Case report: A novel pathogenic FRMD7 variant in a Turner syndrome patient with familial idiopathic infantile nystagmus

Infantile idiopathic nystagmus (IIN) is an oculomotor disorder characterized by involuntary bilateral, periodic ocular oscillations, predominantly on the horizontal axis. X-linked IIN (XLIIN) is the most common form of congenital nystagmus, and the FERM domain-containing gene (FRMD7) is the most common cause of pathogenesis, followed by mutations in GPR143. To date, more than 60 pathogenic FRMD7 variants have been identified, and the physiopathological pathways leading to the disease are not yet completely understood. FRMD7-associated nystagmus usually affects male patients, while it shows incomplete penetrance in female patients, who are mostly asymptomatic but sometimes present with mild ocular oscillations or, occasionally, with clear nystagmus. Here we report the first case of a patient with Turner syndrome and INN in an XLIIN pedigree, in which we identified a novel frameshift mutation (c.1492dupT) in the FRMD7 gene: the absence of one X chromosome in the patient unmasked the presence of the familial genetic nystagmus.

X-linked FRMD7 gene mutation in idiopathic congenital nystagmus and its role in eye movement: A case report and literature review

Background

Idiopathic congenital nystagmus (ICN) is an inherited disorder characterized by uncontrollable binocular conjugating oscillation. X-linked idiopathic congenital nystagmus is one of the most prevalent types of ICN. Elucidation of the genetic mechanisms involved in ICN will enhance our understanding of its molecular etiology.

Case presentation

We report a girl with uncontrollable binocular oscillation and anomalous head posture, then presented a novel heterozygous missense variant (c.686G>T) within the mutation-rich region of the FERM domain containing 7 (FRMD7) gene in her family member. The girl received occlusion therapy and surgical operation which balanced her binocular vision and corrected the anomalous head posture.

Conclusions

This is the first report on a mutation (c.686G>T) caused the substitution of Arg (R) with Leu (L) at position 229 (p.R229L) of the FRMD7 protein in a patient with ICN.

FRMD7 Gene Alterations in a Pakistani Family Associated with Congenital Idiopathic Nystagmus

Congenital idiopathic nystagmus (CIN) is an oculomotor disorder characterized by repetitive and rapid involuntary movement of the eye that usually develops in the first six months after birth. Unlike other forms of nystagmus, CIN is widely associated with mutations in the FRMD7 gene. This study involves the molecular genetic analysis of a consanguineous Pakistani family with individuals suffering from CIN to undermine any potential pathogenic mutations. Blood samples were taken from affected and normal individuals of the family. Genomic DNA was extracted using an in-organic method. Whole Exome Sequencing (WES) and analysis were performed to find any mutations in the causative gene. To validate the existence and co-segregation of the FRMD7 gene variant found using WES, sanger sequencing was also carried out using primers that targeted all of the FRMD7 coding exons. Additionally, the pathogenicity of the identified variant was assessed using different bioinformatic tools. The WES results identified a novel nonsense mutation in the FRMD7 (c.443T>A; p. Leu148 *) gene in affected individuals from the Pakistani family, with CIN resulting in a premature termination codon, further resulting in the formation of a destabilized protein structure that was incomplete. Co-segregation analysis revealed that affected males are hemizygous for the mutated allele c.443T>A; p. Leu148 * and the affected mother is heterozygous. Overall, such molecular genetic studies expand our current knowledge of the mutations associated with the FRMD7 gene in Pakistani families with CIN and significantly enhance our understanding of the molecular mechanisms involved in genetic disorders.

Infantile nystagmus without overt eye abnormality: Early features and neuro-ophthalmological diagnosis

AIM

To analyse the neuro-ophthalmological data of children referred for further work-up of infantile nystagmus where ophthalmological evaluation had not achieved a diagnosis.

METHOD

We retrospectively reviewed medical records of patients presenting with infantile nystagmus at our institution between 2007 and 2019. Inclusion criteria were onset before 6 months of age, availability of complete ophthalmic examination, visual electrophysiological tests, and neurological examination. Children with a previous definite ophthalmological diagnosis at onset and those with uncertain nystagmus onset age were not recruited.

RESULTS

Out of 142 infants (mean age at nystagmus onset 3.6 mo, SD 1.7, range 0-6 mo; 56 females, 86 males), 23% had neurological nystagmus, 7% mixed neurological and sensory nystagmus, 48% sensory defect, and 22% idiopathic infantile nystagmus. The neurological diagnoses were inborn errors of metabolism, white matter genetic disorders, and brain malformations. The prevalent diagnosis in the sensory defect subgroup was retinal dystrophy.

INTERPRETATION

Infantile nystagmus without diagnostic ocular findings may be due to neurological, retinal, and optic nerve disorders or be a benign idiopathic condition. In infants with and without neurological abnormalities, the search for a sensory defect should include visual electrophysiology performed early in the diagnostic pathway.

WHAT THIS PAPER ADDS

Infantile nystagmus without diagnostic ophthalmological signs has an underlying neurological cause in 30% of cases. Neurological diagnoses include congenital brain malformations, and metabolic and genetic disorders. Sensory defects are part of systemic neurological disorders in 23% of infants. Electrophysiology is useful when ophthalmological examination is uninformative.

Prospective study of pediatric patients presenting with idiopathic infantile nystagmus-Management and molecular diagnostics

Idiopathic infantile nystagmus (IIN) is an inherited disorder occurring in the first 6 months of life, with no underlying retinal or neurological etiologies and is predominantly caused by mutations in the FRMD7 gene. IIN poses a diagnostic challenge as underlying pre-symptomatic "multisystem" disorders varying from benign to life-threatening should first be ruled out before nystagmus can be labeled as idiopathic. A multidisciplinary approach including multimodal ocular investigations and next-generation sequencing with whole-genome sequencing (WGS) or targeted gene panel testing is required to delineate the exact etiology. We report the clinical and genetic outcomes of 22 patients, from 22 unrelated families of diverse ethnicities, with IIN seen in the ocular genetics service at Moorfields Eye Hospital NHS Foundation Trust between 2016 and 2022. Thirty-six percent (8/22) received a confirmed molecular diagnosis with eight mutations identified in two genes (seven in FRMD7 including one novel variant c.706_707del; p. [Lys236Alafs*66], and one in GPR143). This study expands the mutational spectrum of IIN and highlights the significant role of an integrated care pathway and broader panel testing in excluding underlying pathologies.

Correlations of FRMD7 gene mutations with ocular oscillations

Mutations in the FERM domain containing 7 (FRMD7) gene have been proven to be responsible for infantile nystagmus (IN). The purpose of this study is to investigate FRMD7 gene mutations in patients with IN, and to evaluate the nystagmus intensity among patients with and without FRMD7 mutations. The affected males were subdivided into three groups according to whether or not having FRMD7 mutations and the types of mutations. Fifty-two mutations were detected in FRMD7 in 56 pedigrees and 34 sporadic patients with IN, including 28 novel and 24 previous reported mutations. The novel identified mutations further expand the spectrum of FRMD7 mutations. The parameters of nystagmus intensity and the patients’ best corrected visual acuity were not statistically different among the patients with and without identified FRMD7 mutations, and also not different among patients with different mutant types. The FERM-C domain, whose amino acids are encoded by exons 7, 8 and 9, could be the harbor region for most mutations. Loss-of-function is suggested to be the common molecular mechanism for the X-linked infantile nystagmus.

Noncanonical Splice Site and Deep Intronic FRMD7 Variants Activate Cryptic Exons in X-linked Infantile Nystagmus

Purpose

We aim to report noncoding pathogenic variants in patients with FRMD7-related infantile nystagmus (FIN).

Methods

Genome sequencing (n = 2 families) and reanalysis of targeted panel next generation sequencing (n = 2 families) was performed in genetically unsolved cases of suspected FIN. Previous sequence analysis showed no pathogenic coding variants in genes associated with infantile nystagmus. SpliceAI, SpliceRover, and Alamut consensus programs were used to annotate noncoding variants. Minigene splicing assay was performed to confirm aberrant splicing. In silico analysis of exonic splicing enhancer and silencer was also performed.

Results

FRMD7 intronic variants were identified based on genome sequencing and targeted next-generation sequencing analysis. These included c.285-12A>G (pedigree 1), c.284+63T>A (pedigrees 2 and 3), and c. 383-1368A>G (pedigree 4). All variants were absent in gnomAD, and the both c.285-12A>G and c.284+63T>A variants were predicted to enhance new splicing acceptor gains with SpliceAI, SpliceRover, and Alamut consensus approaches. However, the c.383-1368 A>G variant only had a significant impact score on the SpliceRover program. The c.383-1368A>G variant was predicted to promote pseudoexon inclusion by binding of exonic splicing enhancer. Aberrant exonizations were validated through minigene constructs, and all variants were segregated in the families.

Conclusions

Deep learning–based annotation of noncoding variants facilitates the discovery of hidden genetic variations in patients with FIN. This study provides evidence of effectiveness of combined deep learning–based splicing tools to identify hidden pathogenic variants in previously unsolved patients with infantile nystagmus.

Translational Relevance

These results demonstrate robust analysis using two deep learning splicing predictions and in vitro functional study can lead to finding hidden genetic variations in unsolved patients.

Genotypic and Phenotypic Spectrum of Foveal Hypoplasia: A Multicenter Study

PURPOSE

To characterize the genotypic and phenotypic spectrum of foveal hypoplasia (FH).

DESIGN

Multicenter, observational study.

PARTICIPANTS

A total of 907 patients with a confirmed molecular diagnosis of albinism, PAX6, SLC38A8, FRMD7, AHR, or achromatopsia from 12 centers in 9 countries (n = 523) or extracted from publicly available datasets from previously reported literature (n = 384).

METHODS

Individuals with a confirmed molecular diagnosis and availability of foveal OCT scans were identified from 12 centers or from the literature between January 2011 and March 2021. A genetic diagnosis was confirmed by sequence analysis. Grading of FH was derived from OCT scans.

MAIN OUTCOME MEASURES

Grade of FH, presence or absence of photoreceptor specialization (PRS+ vs. PRS-), molecular diagnosis, and visual acuity (VA).

RESULTS

The most common genetic etiology for typical FH in our cohort was albinism (67.5%), followed by PAX6 (21.8%), SLC38A8 (6.8%), and FRMD7 (3.5%) variants. AHR variants were rare (0.4%). Atypical FH was seen in 67.4% of achromatopsia cases. Atypical FH in achromatopsia had significantly worse VA than typical FH (P < 0.0001). There was a significant difference in the spectrum of FH grades based on the molecular diagnosis (chi-square = 60.4, P < 0.0001). All SLC38A8 cases were PRS- (P = 0.003), whereas all FRMD7 cases were PRS+ (P < 0.0001). Analysis of albinism subtypes revealed a significant difference in the grade of FH (chi-square = 31.4, P < 0.0001) and VA (P = 0.0003) between oculocutaneous albinism (OCA) compared with ocular albinism (OA) and Hermansky-Pudlak syndrome (HPS). Ocular albinism and HPS demonstrated higher grades of FH and worse VA than OCA. There was a significant difference (P < 0.0001) in VA between FRMD7 variants compared with other diagnoses associated with FH.

CONCLUSIONS

We characterized the phenotypic and genotypic spectrum of FH. Atypical FH is associated with a worse prognosis than all other forms of FH. In typical FH, our data suggest that arrested retinal development occurs earlier in SLC38A8, OA, HPS, and AHR variants and later in FRMD7 variants. The defined time period of foveal developmental arrest for OCA and PAX6 variants seems to demonstrate more variability. Our findings provide mechanistic insight into disorders associated with FH and have significant prognostic and diagnostic value.

Abnormal Retinal Vessel Architecture in Albinism and Idiopathic Infantile Nystagmus

Purpose

Infantile nystagmus syndrome (INS) causes altered visual development and can be associated with abnormal retinal structure, to which vascular development of the retina is closely related. Abnormal retinal vasculature has previously been noted in albinism but not idiopathic infantile nystagmus. We compared the number and diameter of retinal vessels in participants with albinism (PWA) and idiopathic infantile nystagmus (PWIIN) with controls.

Methods

Fundus photography data from 24 PWA, 10 PWIIN, and 34 controls was analyzed using Automated Retinal Image Analyzer (ARIA) software on a field of analysis centered on the optic disc, the annulus of which extended between 4.2 mm and 8.4 mm in diameter.

Results

Compared with controls, the mean number of arterial branches was reduced by 24% in PWA (15.5 vs. 20.3, P < 0.001), and venous branches were reduced in both PWA (29%; 12.9 vs. 18.2, P < 0.001) and PWIIN (17%; 15.1 vs. 18.2, P = 0.024). PWA demonstrated 7% thinner "primary" (before branching) arteries (mean diameter: 75.39 µm vs. 80.88 µm, P = 0.043), and 13% thicker (after branching) "secondary" veins (66.72 µm vs. 59.01 µm in controls, P = 0.009).

Conclusions

PWA and PWIIN demonstrated reduced retinal vessel counts and arterial diameters compared with controls. These changes in the superficial retinal vascular network may be secondary to underdevelopment of the neuronal network, which guides vascular development and is also known to be disrupted in INS.

Normal and abnormal foveal development

Normal foveal development begins in utero at midgestation with centrifugal displacement of inner retinal layers (IRLs) from the location of the incipient fovea. The outer retinal changes such as increase in cone cell bodies, cone elongation and packing mainly occur after birth and continue until 13 years of age. The maturity of the fovea can be assessed invivo using optical coherence tomography, which in normal development would show a well-developed foveal pit, extrusion of IRLs, thickened outer nuclear layer and long outer segments. Developmental abnormalities of various degrees can result in foveal hypoplasia (FH). This is a characteristic feature for example in albinism, aniridia, prematurity, foveal hypoplasia with optic nerve decussation defects with or without anterior segment dysgenesis without albinism (FHONDA) and optic nerve hypoplasia. In achromatopsia, there is disruption of the outer retinal layers with atypical FH. Similarly, in retinal dystrophies, there is abnormal lamination of the IRLs sometimes with persistent IRLs. Morphology of FH provides clues to diagnoses, and grading correlates to visual acuity. The outer segment thickness is a surrogate marker for cone density and in foveal hypoplasia this correlates strongly with visual acuity. In preverbal children grading FH can help predict future visual acuity.

Single-Cell RNA-Seq Reveals the Cellular Diversity and Developmental Characteristics of the Retinas of an Infant and a Young Child

The human retina, located in the innermost layer of the eye, plays a decisive role in visual perception. Dissecting the heterogeneity of retinal cells is essential for understanding the mechanism of visual development. Here, we performed single-cell RNA-seq to analyze 194,967 cells from the donors of infants and young children, resulting in 17 distinct clusters representing major cell types in the retina: rod photoreceptors (PRs), cone PRs, bipolar cells (BCs), horizontal cells (HCs), amacrine cells (ACs), retinal ganglion cells (RGCs), Müller glial cells (MGs), microglia, and astrocytes (ASTs). Through reclustering, we identified known subtypes of cone PRs as well as additional unreported subpopulations and corresponding markers in BCs. Additionally, we linked inherited retinal diseases (IRDs) to certain cell subtypes or subpopulations through enrichment analysis. We next constructed extensive intercellular communication networks and identified ligand-receptor interactions that play crucial roles in regulating neural cell development and immune homeostasis in the retina. Intriguingly, we found that the status and functions of PRs changed drastically between the young children and adult retina. Overall, our study offers the first retinal cell atlas in infants and young children dissecting the heterogeneity of the retina and identifying the key molecules in the developmental process, which provides an important resource that will pave the way for research on retinal development mechanisms and advancements in regenerative medicine concerning retinal biology.

Diagnostic yield of targeted next-generation sequencing in infantile nystagmus syndrome

Background: Infantile nystagmus syndrome (INS) is a genetically heterogeneous disorder. Identifying genetic causes of INS would help clinicians to facilitate clinical diagnosis and provide appropriate treatment. The aim of this study was to determine the diagnostic utility of targeted next-generation sequencing (NGS) for INS.Materials and methods: We recruited 37 patients who were referred to the Neuro-ophthalmology clinics for evaluations of INS. NGS was performed using a targeted panel that included 98 candidate genes associated with INS. We identified pathogenic variants according to guidelines of the American College of Medical Genetics and Genomics. We also calculated the sensitivity and specificity of each clinical sign to assess the diagnostic yield of our gene panel.Results: After variant filtering, annotation, and interpretation, the potential pathogenic variants were detected in 13 of the 37 patients, achieving a molecular diagnostic rate of 35%. The identified genes were PAX6 (n = 4), FRMD7 (n = 4), GPR143 (n = 2), CACNA1F (n = 1), CNGA3 (n = 1) and GUCY2D (n = 1). In approximately 30% (n = 4) of the patients, the initial clinical diagnosis was revised after a molecular diagnosis was performed. The presence of a family history had the highest predictive power for a molecular diagnosis (sensitivity = 61.5%, specificity = 91.7%), and the sensitivity increased when the family history was considered together with one of two clinical signs such as pendular nystagmus waveforms or anterior segment dysgenesis.Conclusions: Our study shows that targeted NGS can be useful to determine a molecular diagnosis for patients with INS. Targeted NGS also helps to confirm a clinical diagnosis in atypical phenotypes or unresolved cases.

Biallelic mutations in L-dopachrome tautomerase (DCT) cause infantile nystagmus and oculocutaneous albinism

Infantile nystagmus syndrome (INS) denominates early-onset, involuntary oscillatory eye movements with different etiologies. Nystagmus is also one of the symptoms in oculocutaneus albinism (OCA), a heterogeneous disease mainly caused by defects in melanin synthesis or melanosome biogenesis. Dopachrome tautomerase (DCT, also called TYRP2) together with tyrosinase (TYR) and tyrosin-related protein 1 (TYRP1) is one of the key enzymes in melanin synthesis. Although DCT´s role in pigmentation has been proven in different species, until now only mutations in TYR and TYRP1 have been found in patients with OCA. Detailed ophthalmological and orthoptic investigations identified a consanguineous family with two individuals with isolated infantile nystagmus and one family member with subtle signs of albinism. By whole-exome sequencing and segregation analysis, we identified the missense mutation c.176G > T (p.Gly59Val) in DCT in a homozygous state in all three affected family members. We show that this mutation results in incomplete protein maturation and targeting in vitro compatible with a partial or total loss of function. Subsequent screening of a cohort of patients with OCA (n = 85) and INS (n = 25) revealed two heterozygous truncating mutations, namely c.876C > A (p.Tyr292*) and c.1407G > A (p.Trp469*), in an independent patient with OCA. Taken together, our data suggest that mutations in DCT can cause a phenotypic spectrum ranging from isolated infantile nystagmus to oculocutaneous albinism.

Prospective Study of the Phenotypic and Mutational Spectrum of Ocular Albinism and Oculocutaneous Albinism

Albinism encompasses a group of hereditary disorders characterized by reduced or absent ocular pigment and variable skin and/or hair involvement, with syndromic forms such as Hermansky-Pudlak syndrome and Chédiak-Higashi syndrome. Autosomal recessive oculocutaneous albinism (OCA) is phenotypically and genetically heterogenous (associated with seven genes). X-linked ocular albinism (OA) is associated with only one gene, GPR143. We report the clinical and genetic outcomes of 44 patients, from 40 unrelated families of diverse ethnicities, with query albinism presenting to the ocular genetics service at Moorfields Eye Hospital NHS Foundation Trust between November 2017 and October 2019. Thirty-six were children (≤ 16 years) with a median age of 31 months (range 2-186), and eight adults with a median age of 33 years (range 17-39); 52.3% (n = 23) were male. Genetic testing using whole genome sequencing (WGS, n = 9) or a targeted gene panel (n = 31) gave an overall diagnostic rate of 42.5% (44.4% (4/9) with WGS and 41.9% (13/31) with panel testing). Seventeen families had confirmed mutations in TYR (n = 9), OCA2, (n = 4), HPS1 (n = 1), HPS3 (n = 1), HPS6 (n = 1), and GPR143 (n = 1). Molecular diagnosis of albinism remains challenging due to factors such as missing heritability. Differential diagnoses must include SLC38A8-associated foveal hypoplasia and syndromic forms of albinism.

Genotype-Phenotype Analysis and Mutation Spectrum in a Cohort of Chinese Patients With Congenital Nystagmus

Purpose: Congenital nystagmus (CN) is a genetically and clinically heterogeneous ocular disorder that manifests as involuntary, periodic oscillations of the eyes. To date, only FRMD7 and GPR143 have been reported to be responsible for causing CN. Here, we aimed to identify the disease-causing mutations and describe the clinical features in the affected members in our study.

Methods: All the subjects underwent a detailed ophthalmic examination. Direct sequencing of all coding exons and splice site regions in FRMD7 and GPR143 and a mutation assessment were performed in each patient.

Results: We found 14 mutations in 14/37 (37.8%) probands, including nine mutations in the FRMD7 gene and five mutations in the GPR143 gene, seven of which are novel, including c.284G>A(R95K), c.964C>T(P322S), c.284+10T>G, c.901T>C (Y301H), and c.2014_2023delTCACCCATGG(S672Pfs^*12) in FRMD7, and c.250+1G>C, and c.485G>A (W162^*) in GPR143. The mutation detection rate was 87.5% (7/8) of familial vs. 24.1% (7/29) of sporadic cases. Ten mutations in 24 (41.7%) non-syndromic subjects and 4 mutations in 13(30.8%) syndromic subjects were detected. A total of 77.8% (7/9) of mutations in FRMD7 were concentrated within the FERM and FA domains, while all mutations in GPR143 were located in exons 1, 2, 4 and 6. We observed that visual acuity tended to be worse in the GPR143 group than in the FRMD7 group, and no obvious difference in other clinical manifestations was found through comparisons in different groups of patients.

Conclusions: This study identified 14 mutations (seven novel and seven known) in eight familial and 29 sporadic patients with congenital nystagmus, expanding the mutational spectrum and validating FRMD7 and GPR143 as mutation hotspots. These findings also revealed a significant difference in the screening rate between different groups of participants, providing new insights for the strategy of genetic screening and early clinical diagnosis of CN.

Discordant phenotypes in twins with infantile nystagmus

Infantile nystagmus (IN) may result from aetiologies including albinism and FRMD7 mutations. IN has low prevalence, and twins with IN are rare. Whilst discordant presentation has been previously reported for IN, we present for the first time the comprehensive assessment of diagnostically discordant monozygotic twins. From a cohort of over 2000 patients, we identified twins and triplets discordant for nystagmus. Using next-generation sequencing, high-resolution infra-red pupil tracking and optical coherence tomography, we characterised differences in genotype and phenotype. Monozygotic twins (n = 1), dizygotic twins (n = 3) and triplets (n = 1) were included. The monozygotic twins had concordant TYR variants. No causative variants were identified in the triplets. Dizygotic twins had discordant variants in TYR, OCA2 and FRMD7. One unaffected co-twin demonstrated sub-clinical nystagmus. Foveal hypoplasia (FH) was noted in four of five probands. Both co-twins of the monozygotic pair and triplets displayed FH. In three families, at least one parent had FH without nystagmus. FH alone may be insufficient to develop nystagmus. Whilst arrested optokinetic reflex pathway development is implicated in IN, discordant twins raise questions regarding where differences in development have arisen. In unaffected monozygotes therefore, genetic variants may predispose to oculomotor instability, with variable expressivity possibly responsible for the discordance observed.

p.His16Arg of STXBP1 (MUNC18-1) Associated With Syntaxin 3B Causes Autosomal Dominant Congenital Nystagmus

Congenital nystagmus (CN) is an ocular movement disorder manifested as involuntary conjugated binocular oscillation and usually occurs in early infancy. The pathological mechanism underlying CN is still poorly understood. We mapped a novel genetic locus 9q33.1-q34.2 in a larger Chinese family with autosomal dominant CN and identified a variant (c.47A>G/p.His16Arg) of STXBP1 by exome sequencing, which fully co-segregated with the nystagmus phenotype in this family and was absent in 571 healthy unrelated individuals. The STXBP1 encodes syntaxin binding protein 1 (also known as MUNC18-1), which plays a pivotal role in neurotransmitter release. In unc-18 (nematode homolog of MUNC18-1) null Caenorhabditis elegans, we found that the p.His16Arg exhibits a compromised ability to rescue the locomotion defect and aldicarb sensitivity, indicating a functional defect in neurotransmitter release. In addition, we also found an enhanced binding of the p.His16Arg mutant to syntaxin 3B, which is a homolog of syntaxin 1A and specifically located in retinal ribbon synapses. We hypothesize that the variant p.His16Arg of STXBP1 is likely to affect neurotransmitter release in the retina, which may be the underlying etiology of CN in this family. Our results provide a new perspective on understanding the molecular mechanism of CN.

SLC38A8 mutations result in arrested retinal development with loss of cone photoreceptor specialization

Foveal hypoplasia, optic nerve decussation defects and anterior segment dysgenesis is an autosomal recessive disorder arising from SLC38A8 mutations. SLC38A8 is a putative glutamine transporter with strong expression within the photoreceptor layer in the retina. Previous studies have been limited due to lack of quantitative data on retinal development and nystagmus characteristics. In this multi-centre study, a custom-targeted next generation sequencing (NGS) gene panel was used to identify SLC38A8 mutations from a cohort of 511 nystagmus patients. We report 16 novel SLC38A8 mutations. The sixth transmembrane domain is most frequently disrupted by missense SLC38A8 mutations. Ninety percent of our cases were initially misdiagnosed as PAX6-related phenotype or ocular albinism prior to NGS. We characterized the retinal development in vivo in patients with SLC38A8 mutations using high-resolution optical coherence tomography. All patients had severe grades of arrested retinal development with lack of a foveal pit and no cone photoreceptor outer segment lengthening. Loss of foveal specialization features such as outer segment lengthening implies reduced foveal cone density, which contributes to reduced visual acuity. Unlike other disorders (such as albinism or PAX6 mutations) which exhibit a spectrum of foveal hypoplasia, SLC38A8 mutations have arrest of retinal development at an earlier stage resulting in a more under-developed retina and severe phenotype.

FRMD7 Mutations Disrupt the Interaction with GABRA2 and May Result in Infantile Nystagmus Syndrome

Purpose

To identify the pathogenic gene of infantile nystagmus syndrome (INS) in three Chinese families and explore the potential pathogenic mechanism of FERM domain-containing 7 (FRMD7) mutations.

Methods

Genetic testing was performed via Sanger sequencing. Western blotting was used to analyze protein expression of FRMD7. Glutathione S-transferase pull-down and immunoprecipitation were conducted to investigate the proteins interacting with FRMD7. Rescue assays were performed in Caenorhabditis elegans to explore the potential role of FRMD7 in vivo.

Results

We recruited three Chinese families with X-linked INS and identified a duplication and two missense mutations in FRMD7: c.998dupA/p.His333Glnfs*2, c.580G>A/p.Ala194Thr, and c.973A>G/p.Arg325Gly (one in each family). Expression levels of three mutants were similar to that of wild-type FRMD7 in vitro. Interestingly, the mutant p.His333Glnfs*2 exhibited a predominantly nuclear location, whereas wild-type FRMD7 localized to the cytoplasm. In addition, we found FRMD7 to directly interact with the loop between transmembrane domains 3 and 4 of GABRA2, a type A gamma-aminobutyric acid (GABA) receptor (GABA_ARs) subunit critical for receptor transport and localization, whereas the mutants p.Ala194Thr and p.Arg325Gly exhibited decreased binding to GABRA2. In frm-3 (a nematode homologue of FRMD7) null C.elegans, we found that FRMD7 mutants exhibited a poor rescue effect on the defects of locomotion and fluorescence recovery after photobleaching of GABA_ARs.

Conclusions

Our findings identified three FRMD7 mutants in three Chinese families with X-linked INS and confirmed GABRA2 as a novel binding partner of FRMD7. These findings suggest that FRMD7 plays an important role by targeting GABA_ARs.

Homozygous stop mutation in AHR causes autosomal recessive foveal hypoplasia and infantile nystagmus

Herein we present a consanguineous family with three children affected by foveal hypoplasia with infantile nystagmus, following an autosomal recessive mode of inheritance. The patients showed normal electroretinography responses, no signs of albinism, and no anterior segment or brain abnormalities. Upon whole exome sequencing, we identified a homozygous mutation (c.1861C>T;p.Q621*) in the aryl hydrocarbon receptor (AHR) gene that perfectly co-segregated with the disease in the larger family. AHR is a ligand-activated transcription factor that has been intensively studied in xenobiotic-induced toxicity. Further, it has been shown to play a physiological role under normal cellular conditions, such as in immunity, inflammatory response and neurogenesis. Notably, knockout of the Ahr gene in mouse impairs optic nerve myelin sheath formation and results in oculomotor deficits sharing many features with our patients: the eye movement disorder in Ahr-/- mice appears early in development and presents as conjugate horizontal pendular nystagmus. We therefore propose AHR to be a novel disease gene for a new, recessively inherited disorder in humans, characterized by infantile nystagmus and foveal hypoplasia.

Reading Individual Words Within Sentences in Infantile Nystagmus

Purpose

Normal readers make immediate and precise adjustments in eye movements during sentence reading in response to individual word features, such as lexical difficulty (e.g., common or uncommon words) or word length. Our purpose was to assess the effect of infantile nystagmus (IN) on these adaptive mechanisms.

Methods

Eye movements were recorded from 29 participants with IN (14 albinism, 12 idiopathic, and 3 congenital stationary night blindness) and 15 controls when reading sentences containing either common/uncommon words or long/short target words. Parameters assessed included: duration of first foveation/fixation, number of first-pass and percentage second-pass foveations/fixations, percentage words skipped, gaze duration, acquisition time (gaze + nongaze duration), landing site locations, clinical and experimental reading speeds.

Results

Participants with IN could not modify first foveation durations in contrast to controls who made longer first fixations on uncommon words (P < 0.001). Participants with IN made more first-pass foveations on uncommon and long words (P < 0.001) to increase gaze durations. However, this also increased nongaze durations (P < 0.001) delaying acquisition times. Participants with IN reread shorter words more often (P < 0.005). Similar to controls, participants with IN landed more first foveations between the start and center of long words. Reading speeds during experiments were lower in IN participants compared to controls (P < 0.01).

Conclusions

People with IN make more first-pass foveations on uncommon and long words influencing reading speeds. This demonstrates that the "slow to see" phenomenon occurs during word reading in IN. These deficits are not captured by clinical reading charts.

Arguments for the Adoption of a Nystagmus Care Pathway

Pathological nystagmus is a spontaneous oscillation of the eyes. It is a complex problem with many subtypes and causes ranging from the acute neurological emergency to chronic visual disorders. There is considerable variability in clinical management and patient experience across the UK. The Nystagmus Care Pathway (NCP) is a proposal to provide an evidence-based, consistent minimum standard of care across all eye services for patients with nystagmus. The NCP coordinates expertise from the various team members with a staged approach: 1) pathway entry; 2) nystagmus identification; 3) finding underlying causes/associations; 4) managing causes/associations; 5) managing the nystagmus and its effects; 6) support for patients and families; 7) pathway exit. Orthoptists are ideally placed to coordinate the NCP as they are trained in ocular motility and visual assessment. They are accustomed to providing continuity of care, multidisciplinary working and via the British and Irish Orthoptic Society (BIOS), they can provide consistency of care across the UK. Key performance indicators are proposed.

X-linked inheritances recessive of congenital nystagmus and autosomal dominant inheritances of congenital cataracts coexist in a Chinese family: a case report and literature review

BACKGROUND

Congenital nystagmus (CN) and congenital cataracts are distinct eye diseases and are usually isolated. Cases with CN and congenital cataracts caused by different genes in one family have been rarely reported.

CASE PRESENTATION

A 27-year-old man presented with CN and congenital cataracts and he underwent cataract extraction 2 weeks after birth. Three years later, he had posterior chamber intraocular lens implantation. The proband's mother was only afflicted by bilateral lens opacities. Lensectomy was performed in both eyes at age 15. The proband's daughter had bilateral central cataracts and no nystagmus. She had undergone cataract extraction when she was two months old. In this family, 8 affected individuals were affected by bilateral cataracts, and three of them presented with CN. The genetic analysis was performed using a specific Hereditary Ophthalmological Disease Gene Panel on proband and his parents (one of which was a patient). PCR and Sanger sequencing verified the presence of these variants in all members of the family. The novel mutation, c.498-3C > T, in FRMD7 explains why X-Linked recessive inheritance of CN was found in a subset of patients. A heterozygous mutation of the GJA8 gene (c.139G > C), was identified in all patients and thus explains the autosomal dominant pattern of inheritance of congenital cataracts within the family.

CONCLUSIONS

This is the first time that FRMD7 and GJA8 gene mutations have been linked to the pathogenesis of a family with both CN and congenital cataracts. The phenomenon of two different genetic patterns coexisting in one family is rare.

Genotype and Phenotype Spectrum of FRMD7-Associated Infantile Nystagmus Syndrome

Purpose

We investigate the genotype and phenotype spectrum of FRMD7-associated infantile nystagmus syndrome in Korean probands.

Methods

A total of 37 patients with infantile nystagmus syndrome were recruited prospectively for genetic analysis. We performed polymerase chain reaction (PCR)-based direct sequencing and haplotype analysis for FRMD7. Detailed ophthalmic examinations and eye movement recordings were compared between FRMD7 and non-FRMD7 groups.

Results

In 13 (35%) of 37 patients, five different mutations of FRMD7 were detected: start codon mutation c.1A>G, splice site mutation c.162+6T>C, and three missense mutations (c.575A>C, c.722A>G, and c.875T>C). The latter mutation was identified in seven unrelated patients, and always was accompanied with two single nucleotide polymorphisms of exon 12 (rs6637934, rs5977623). Compared to non-FRMD7 groups, a cup-to-disc ratio was significantly decreased in FRMD7 groups (P < 0.001), and a disc-macula distance to disc diameter ratio markedly increased in the FRMD7 group (P = 0.015). Most patients in the FRMD7 group had at least two types of the nystagmus waveforms, and the most common type was unidirectional jerk nystagmus (75%), such as pure jerk and jerk with extended foveation, followed by pendular (25%), bidirectional jerk (19%), and dual jerk (6%) nystagmus. No significant differences were observed between FRMD7 and non-FRMD7 groups in terms of the nystagmus waveform, presence of periodic alternating nystagmus, and mean foveation time.

Conclusions

We identified five FRMD7 mutations in 35% of our infantile nystagmus syndrome cohort, expanding its mutational spectrum. The missense mutation c.875T>C may be a common mutation arisen from the founder effect in Korea. Optic nerve dysplasia associated with FRMD7 mutations suggests that the abnormal development of afferent visual systems may affect neural circuitry within the oculomotor system.

A novel frameshift mutation in FRMD7 causes X-linked infantile nystagmus in a Chinese family

Background

Infantile nystagmus (IN) is an oculomotor disorder that is characterized by conjugate involuntary, rapid and repetitive movement of the eyes. To date, the pathogenesis of IN remains unclear. Many patients show an X-linked inheritance pattern. In this study, we explored the mutation in the FERM domain-containing 7 (FRMD7) gene in a Chinese family with X-linked infantile nystagmus.

Methods

We conducted comprehensive ocular examinations and collected 5 ml of blood samples from members of a family with X-linked IN and 100 normal controls. Mutations in FRMD7 were identified by sequencing PCR products.

Results

We found a 7-bp deletion(c.823-829delACCCTAC) in the 9th exon of FRMD7 in a Chinese family with IN, which predicted a truncation of the protein.

Conclusions

This study reported a novel mutation of the FRMD7 gene occurred in a Chinese family with IN, thus expanding the spectrum of FRMD7 mutations causing IN, and further confirming that the mutations of FRMD7 are the underlying molecular cause of IN.

Electroretinograms in idiopathic infantile nystagmus, optic nerve hypoplasia and albinism

PURPOSE

To study electroretinograms in infantile nystagmus syndrome associated with idiopathic infantile nystagmus, optic nerve hypoplasia, and albinism.

METHODS

A total of 30 children with idiopathic infantile nystagmus, 18 with optic nerve hypoplasia, and 18 with albinism were studied. Three electroretinogram protocols were applied according to child's age: 58 (mean: 2.0 years) were recorded with skin electrode to Great Ormond Street Hospital protocol, 11 (mean: 5.3 years) with skin electrode to International Society for Clinical Electrophysiology of Vision protocol, and 7 children (mean: 12.2 years) with HK electrode to International Society for Clinical Electrophysiology of Vision protocol. The electroretinograms were compared to those of age-matched controls.

RESULTS

Electroretinogram waveforms in idiopathic infantile nystagmus, optic nerve hypoplasia, and albinism were comparable to controls in all protocols. Electroretinogram amplitudes in idiopathic infantile nystagmus group showed increased white scotopic and photopic electroretinograms in 26 children (skin electrode to Great Ormond Street Hospital protocol), no difference to the controls in 3 children (skin electrode to International Society for Clinical Electrophysiology of Vision protocol), and increased rod electroretinogram in 3 children (HK electrode to International Society for Clinical Electrophysiology of Vision protocol). Optic nerve hypoplasia group showed increased white scotopic, photopic, and blue electroretinograms in 15 children (skin electrode to Great Ormond Street Hospital protocol); increased 30-Hz electroretinogram in 3 children (HK electrode to International Society for Clinical Electrophysiology of Vision protocol); and reduced combined rod-cone, cone, and 30-Hz electroretinograms in 3 children (skin electrode to International Society for Clinical Electrophysiology of Vision protocol). Albinism group showed increased white scotopic, photopic, and 30-Hz electroretinograms in 17 children (skin electrode to Great Ormond Street Hospital protocol), while it showed reduced cone and 30-Hz electroretinograms in 5 children (skin electrode to International Society for Clinical Electrophysiology of Vision protocol). Implicit times were shorter in albinism.

CONCLUSION

Electroretinogram waveforms in idiopathic infantile nystagmus, optic nerve hypoplasia, and albinism were normal with mostly increased electroretinograms, while reduced electroretinograms did not show a specific pattern as in early-onset retinal dystrophies.

[Etiological assessment of a nystagmus in childhood]

Apart from the latent nystagmus, which arises as a consequence of failure to develop binocular vision, every case of childhood nystagmus needs an etiological assessment. Knowledge of the pathogenesis of the various types of nystagmus guides this assessment, particularly considering the morphological characteristics of the nystagmus. The clinical ophthalmologic examination is complemented by OCT and electrophysiologic testing (ERG, VEP). If this testing is normal, an MRI and genetic assessment are required.

Accuracy of Next-Generation Sequencing for Molecular Diagnosis in Patients With Infantile Nystagmus Syndrome

Importance

Infantile nystagmus syndrome (INS) is a group of disorders presenting with genetic and clinical heterogeneities that have challenged the genetic and clinical diagnoses of INS. Precise molecular diagnosis in early infancy may result in more accurate genetic counseling and improved patient management.

Objective

To assess the accuracy of genomic data from next-generation sequencing (NGS) and phenotypic data to enhance the definitive diagnosis of INS.

Design, Setting, and Participants

A single-center retrospective case series was conducted in 48 unrelated, consecutive patients with INS, with or without associated ocular or systemic conditions, who underwent genetic testing between June 1, 2015, and January 31, 2017. Next-generation sequencing analysis was performed using a target panel that included 113 genes associated with INS (n = 47) or a TruSight One sequencing panel that included 4813 genes associated with known human phenotypes (n = 1). Variants were filtered and prioritized by in-depth clinical review, and finally classified according to the American College of Medical Genetics and Genomics guidelines. Patients underwent a detailed ophthalmic examination, including electroretinography and optical coherence tomography, if feasible.

Main Outcomes and Measures

Diagnostic yield of targeted NGS testing.

Results

Among the 48 patients (21 female and 27 male; mean [SD] age at genetic testing, 9.2 [10.3] years), 8 had a family history of nystagmus and 40 were simplex. All patients were of a single ethnicity (Korean). Genetic variants that were highly likely to be causative were identified in 28 of the 48 patients, corresponding to a molecular diagnostic yield of 58.3% (95% CI, 44.4%-72.2%). FRMD7, GPR143, and PAX6 mutations appeared to be the major genetic causes of familial INS. A total of 10 patients (21%) were reclassified to a different diagnosis based on results of NGS testing, enabling accurate clinical management.

Conclusions and Relevance

These findings suggest that NGS is an accurate diagnostic tool to differentiate causes of INS because diagnostic tests, such as electroretinography and optical coherence tomography, are not easily applicable in young infants. Accurate application of NGS using a standardized, stepwise, team-based approach in early childhood not only facilitated early molecular diagnosis but also led to improved personalized management in patients with INS.

The clinical evaluation of infantile nystagmus: What to do first and why

INTRODUCTION

Infantile nystagmus has many causes, some life threatening. We determined the most common diagnoses in order to develop a testing algorithm.

METHODS

Retrospective chart review. Exclusion criteria were no nystagmus, acquired after 6 months, or lack of examination.

DATA COLLECTED

pediatric eye examination findings, ancillary testing, order of testing, referral, and final diagnoses. Final diagnosis was defined as meeting published clinical criteria and/or confirmed by diagnostic testing. Patients with a diagnosis not meeting the definition were "unknown." Patients with incomplete testing were "incomplete." Patients with multiple plausible etiologies were "multifactorial." Patients with negative complete workup were "motor."

RESULTS

A total of 284 charts were identified; 202 met inclusion criteria. The three most common causes were Albinism (19%), Leber Congenital Amaurosis (LCA; 14%), and Non-LCA retinal dystrophy (13%). Anatomic retinal disorders comprised 10%, motor another 10%. The most common first test was MRI (74/202) with a diagnostic yield of 16%. For 28 MRI-first patients, nystagmus alone was the indication; for 46 MRI-first patients other neurologic signs were present. 0/28 nystagmus-only patients had a diagnostic MRI while 14/46 (30%) with neurologic signs did. The yield of ERG as first test was 56%, OCT 55%, and molecular genetic testing 47%. Overall, 90% of patients had an etiology identified.

CONCLUSION

The most common causes of infantile nystagmus were retinal disorders (56%), however the most common first test was brain MRI. For patients without other neurologic stigmata complete pediatric eye examination, ERG, OCT, and molecular genetic testing had a higher yield than MRI scan. If MRI is not diagnostic, a complete ophthalmologic workup should be pursued.

Retinal microstructures are altered in patients with idiopathic infantile nystagmus

PURPOSE

To compare segmented retinal layer thicknesses between patients with idiopathic infantile nystagmus (IIN) and controls.

METHODS

This retrospective case-control study included 66 patients with IIN and 66 age-matched controls. The retinal layers were examined using spectral domain optical coherence tomography with autosegmentation. Central foveal thickness (CFT), outer nuclear layer (ONL), and outer segment length (OSL) thickness were measured at the fovea center. Mean values for retinal nerve fiber layer, ganglion cell inner plexiform layer (GCIPL), inner nuclear layer, outer plexiform-outer nuclear layer (OPNL) thicknesses were calculated at two measurement points (nasal and temporal hump points at the macula area).

RESULTS

There were no significant between-group differences in age, gender, or refraction error. The CFT was thicker in the IIN group compared with the control group (225.0 μm vs. 217.8 μm, P = 0.017) and OSL was shorter in IIN than in controls (40.0 μm vs. 43.7 μm., P < 0.001). The ONL thickness at the central fovea was not statistically different between the two groups. At the nasal and temporal position where the ganglion cell density was thickest, the GCIPL thickness was thinner in the IIN group compared to the controls (99.5 μm vs. 102.8 μm, P = 0.010). The GCIPL thickness was negatively correlated with logMAR visual acuity (Spearman's rho = -0.502, P < 0.001).

CONCLUSIONS

The foveal pit was shallower, OSL was shorter, and the GCIPL thicknesses at macular humps were decreased in the patients with IIN compared with that of controls. The faulty development of the macula may be related to unknown pathophysiologic mechanism during fovea maturation in IIN or continuous eye movement itself interrupt fovea development.

Development and clinical utility of a novel diagnostic nystagmus gene panel using targeted next-generation sequencing

Infantile nystagmus (IN) is a genetically heterogeneous disorder arising from variants of genes expressed within the developing retina and brain. IN presents a diagnostic challenge and patients often undergo numerous investigations. We aimed to develop and assess the utility of a next-generation sequencing (NGS) panel to enhance the diagnosis of IN. We identified 336 genes associated with IN from the literature and OMIM. NimbleGen Human custom array was used to enrich the target genes and sequencing was performed using HiSeq2000. Using reference genome material (NA12878), we show the sensitivity (98.5%) and specificity (99.9%) of the panel. Fifteen patients with familial IN were sequenced using the panel. Two authors were masked to the clinical diagnosis. We identified variants in 12/15 patients in the following genes: FRMD7 (n=3), CACNA1F (n=2), TYR (n=5), CRYBA1 (n=1) and TYRP1 (n=1). In 9/12 patients, the clinical diagnosis was consistent with the genetic diagnosis. In 3/12 patients, the results from the genetic diagnoses (TYR, CRYBA1 and TYRP1 variants) enabled revision of clinical diagnoses. In 3/15 patients, we were unable to determine a genetic diagnosis. In one patient, copy number variation analysis revealed a FRMD7 deletion. This is the first study establishing the clinical utility of a diagnostic NGS panel for IN. We show that the panel has high sensitivity and specificity. The genetic information from the panel will lead to personalised diagnosis and management of IN and enable accurate genetic counselling. This will allow development of a new clinical care pathway for IN.

Infantile nystagmus syndrome: clinical characteristics, current theories of pathogenesis, diagnosis, and management

Infantile nystagmus syndrome (INS) is an important clinical diagnosis because it is a common presenting sign of many ocular, neurologic, and systemic diseases. Although INS has been studied for more than a century, its diagnosis and treatment remains a challenge to clinicians because of its varied manifestations and multiple associations, and its pathogenesis continues to rouse considerable scientific debate. Fueled by these challenges, recent basic research and clinical investigations have provided new insights into INS. New genetic discoveries and technological advances in ocular imaging have refined our understanding of INS subtypes and offer new diagnostic possibilities. Unexpected surgical outcomes have led to new understanding of its pathogenesis based on novel hypothesized pathways of ocular motor control. Comparative studies on nonhuman visual systems have also informed models of the neural substrate of INS in humans. This review brings together the classic profile of this disorder with recent research to provide an update on the clinical features of INS, an overview of the current theories on how and why INS develops, and a practical approach to the diagnosis and management of INS.

Enabling research with human embryonic and fetal tissue resources

Congenital anomalies are a significant burden on human health. Understanding the developmental origins of such anomalies is key to developing potential therapies. The Human Developmental Biology Resource (HDBR), based in London and Newcastle, UK, was established to provide embryonic and fetal material for a variety of human studies ranging from single gene expression analysis to large-scale genomic/transcriptomic studies. Increasingly, HDBR material is enabling the derivation of stem cell lines and contributing towards developments in tissue engineering. Use of the HDBR and other fetal tissue resources discussed here will contribute to the long-term aims of understanding the causation and pathogenesis of congenital anomalies, and developing new methods for their treatment and prevention.

Congenital Nystagmus Gene FRMD7 Is Necessary for Establishing a Neuronal Circuit Asymmetry for Direction Selectivity

Neuronal circuit asymmetries are important components of brain circuits, but the molecular pathways leading to their establishment remain unknown. Here we found that the mutation of FRMD7, a gene that is defective in human congenital nystagmus, leads to the selective loss of the horizontal optokinetic reflex in mice, as it does in humans. This is accompanied by the selective loss of horizontal direction selectivity in retinal ganglion cells and the transition from asymmetric to symmetric inhibitory input to horizontal direction-selective ganglion cells. In wild-type retinas, we found FRMD7 specifically expressed in starburst amacrine cells, the interneuron type that provides asymmetric inhibition to direction-selective retinal ganglion cells. This work identifies FRMD7 as a key regulator in establishing a neuronal circuit asymmetry, and it suggests the involvement of a specific inhibitory neuron type in the pathophysiology of a neurological disease.

Video Abstract

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FRMD7 is required for the horizontal optokinetic reflex in mice as in humans

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Horizontal direction selectivity is lost in the retina of FRMD7 mutant mice

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Asymmetry of inhibitory inputs to horizontal DS cells is lost in FRMD7 mutant mice

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FRMD7 is expressed in ChAT-expressing cells in the retina of mice and primates

A start codon mutation of the FRMD7 gene in two Korean families with idiopathic infantile nystagmus

Idiopathic infantile nystagmus (IIN) is the involuntary oscillation of the eyes with onset in the first few months of life. The most common form of inheritance is X-linked, and mutations in FRMD7 gene are a major cause. To identify the FRMD7 gene mutations associated with X-linked IIN, we performed PCR-based DNA direct sequencing in 4 affected subjects from 2 Korean families. We also assessed structural abnormalities of retina and optic nerve head using optical coherence tomography (OCT). Genetic analysis revealed a A>G transversion at nucleotide c.1, the first base of the start codon. This mutation leads to the loss of the primary start codon ATG for methionine, which is replaced by a triplet GTG for valine. The alternative in-frame start codon is not present around a mutation. OCT revealed the morphological changes within the optic nerve head, including shallow cup depth and small cup-to-disc ratio. In summary, we identified a novel start codon mutation within the FRMD7 gene of 2 Korean families. Our data expands the mutation spectrum of FRMD7 causing IIN. We also demonstrated abnormal developments of afferent system in patients with FRMD7 mutations using OCT, which may help to understand the etiological factor in development of nystagmus.