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

Micro chromosomal deletions at the NYS7 locus and autosomal dominant nystagmus

Nystagmus is an ocular condition characterized by bilateral involuntary ocular oscillation which can severely affect vision. When not associated with other ocular or systemic diseases, it is referred to as idiopathic or congenital motor nystagmus (CMN). Genome-wide linkage studies have previously identified several loci associated with CMN, however the genes responsible for some of these loci have yet to be identified. We have examined a large, five-generation family with autosomal dominant CMN. Our purpose was to characterize the clinical manifestations and reveal the molecular basis of the disease in this family. In addition to full ophthalmic examination and imaging, molecular analysis included copy number variation analysis, linkage studies, and Sanger sequencing. Expression analyses of candidate genes was done by real-time PCR. Of the 68 family members, 27 subjects in five-generations had CMN, in line with an autosomal dominant inheritance pattern. Molecular analysis was performed on 27 members, 15 of them affected by CMN. Copy number variation analysis using array comparative genomic hybridization (aCGH) revealed a novel deletion located on 1q32 (NYS7) among affected individuals. Linkage analysis using polymorphic markers demonstrated full segregation with a heterozygous haplotype in all affected patients, with a LOD score of >5. Sanger sequencing of affected subjects revealed a novel deletion of 732,526 bp in the linkage interval. No protein-coding genes exist within the deleted region; however, the deletion disrupts topologically associated domains encompassing the gene NR5A2 and the non-protein coding MIR181A. Both are strongly associated with other genes expressed in the retina such as PROX1, which in turn is also associated with genes related to nystagmus such as PAX6. We therefore hypothesized that the deletion might affect NR5A2 and MIR181A expression, causing CMN. Expression analysis by real-time PCR showed significantly lower expression of NR5A2, and significantly higher expression of PROX1 among patients compared with controls. To conclude, among a large five-generation family with autosomal dominant CMN, a large deletion in the interval of NYS7 was linked with the disease. No protein-coding genes exist inside the deleted region, and so the exact mechanism in which CMN is caused is uncertain. Based on topological association and expression analyses we suggest a possible mechanism for the pathogenesis.

Recession-Resection of the Vertical Rectus Muscles for Chin-up Vertical Abnormal Head Position Associated With Infantile Nystagmus Syndrome

PURPOSE

To review the correction of chin-up abnormal head position (AHP) due to infantile nystagmus syndrome via surgery on the vertical rectus muscles, typically a combined recession-resection of these muscles.

METHODS

This was a review of 6 patients who underwent surgical correction of chin-up vertical AHP in the context of infantile nystagmus syndrome at an academic institution. The correction of AHP, visual acuity, ductions, and ocular alignment were noted both preoperatively and postoperatively. The need for repeat surgery, induced strabismus, or correction of AHP were also noted.

RESULTS

Six patients underwent surgery for chin-up AHP. A combined recession-resection of the vertical rectus muscles (bilateral inferior rectus muscle recession of 5 to 8 mm; bilateral superior rectus muscle resection of 7 to 8 mm) was performed in 4 of 6 patients, and isolated bilateral recession of the inferior rectus muscles was performed in the remaining 2 patients. Four of 6 patients (67%) achieved complete correction of their AHP at the last follow-up visit, with a mild residual chin-up AHP persisting in the other 2 patients. One patient developed large angle exotropia, one had restrictive hypertropia and horizontal plane null position, and another developed an incomitant horizontal strabismus with exotropia in right gaze. Reoperation was performed in the former 2 patients, with successful correction of the strabismus in each.

CONCLUSIONS

Surgery on the vertical rectus muscles can reduce or eliminate a chin-up head position in patients with infantile nystagmus syndrome. Care should be taken to avoid producing a restriction of depression in abduction if the amount of resection is too large. [J Pediatr Ophthalmol Strabismus. 2022;59(6):410-415.].

Clinical Application of Different Vertical Position Tests for Posterior Canal-Benign Paroxysmal Positional Vertigo-Cupulolithiasis

Background

Posterior canal-benign paroxysmal positional vertigo-cupulolithiasis (PC-BPPV-cu) is a new and controversial type of benign paroxysmal positional vertigo (BPPV). At present, there are few relevant clinical studies as to whether the Half Dix-Hallpike test (Half D-HT) induces more obvious nystagmus than the Dix Hallpike test (D-HT) and straight head hanging test (SHH) in patients with PC-BPPV-cu.

Objectives

To investigate the clinical characteristics of PC-BPPV-cu, and analyze the diagnostic significance of the Dix-Hallpike test (D-HT), Half D-HT, and straight head hanging (SHH) test in these patients.

Methods

A total of 46 patients with PC-BPPV-cu were enrolled, and divided into two groups (N = 23): a group A (induction order: D-HT, Half D-HT, SHH) and a group B (induction order: Half D-HT, D-HT, SHH).

Results

Among 46 patients with PC-BPPV-cu, the bilateral and unilateral abnormality rates of the disease side were 5 cases and 41 cases, respectively. There were significant differences in the proportion of torsional-upbeating nystagmus and upbeating nystagmus among the three headhanging positions in 46 patients with PC-BPPV-cu (P < 0.001). The slow phase velocity (SPV) of induced nystagmus at half D-HT supine position was slower than D-HT supine position (P < 0.05) and SHH supine position (P < 0.05). The nystagmus latency of D-HT supine position was significantly shorter than half D-HT (P < 0.05) and SHH (P < 0.05). PC-BPPV-cu patients were accompanied by 53.5% semicircular canal paresis, 69.6% audiological abnormalities, 76% cervical vestibular evoked myogenic potential (cVEMP), and 75% video head impulse test (vHIT) abnormalities, the concordance rates of the four detection methods were similar (χ2 = 0.243, P = 0.970).

Conclusions

The Half D-HT is simple and feasible, but might have a risk of false-negative diagnoses of the torsional-upbeating nystagmus and upbeating nystagmus. The D-HT is still a classic induction method for PC-BPPV-cu. The two complement each other and may aid in the diagnosis of PC-BPPV-cu patients. Future clinical applications of Half D-HT require extensive research to determine its diagnostic efficacy.

A Family with a High Incidence of Migraine and Vestibular Migraine and a Case of Menière's Disease

Vestibular migraine (VM) and Menière's disease (MD) are common neurotological disorders causing episodic vertigo. Sometimes, VM is accompanied by cochlear symptoms suggestive for MD. Therefore, in those cases, the differential diagnosis between the two disorders can be difficult. Moreover, a comorbidity with migraine in MD patients is widely reported, up to the hypothesis of a possible MD-VM overlapping syndrome. In this brief case report, we consider the clinical history of a family presenting high incidence of subjects fulfilling the diagnostic criteria of VM and single case fulfilling criteria for definite MD. The relationship between VM and MD is still under debate; anyway, it can be speculated that commonly shared genetic mutations could play a role as predisposing factors in both disorders. A congenital nystagmus in the family was present too, but its correlation with the other conditions is still not clear. Future goal of our work will be to assess genetics in this family.

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.

Analysis of anomalous head posturing in patients with infantile nystagmus syndrome

PURPOSE

To investigate anomalous head posturing in patients with INS.

METHODS

This was a prospective, cohort analysis of clinical and anomalous head posture (AHP) data in 34 patients with INS and an AHP. Particular outcome measures included measurement of AHP in three dimensions of pitch (anterior posterior flexion/extension), yaw (lateral rotation), and roll (lateral flexion) during best-corrected binocular acuity testing and during their subjective sense of straight. Patients were also queried as to their subjective sense of head posture in forced straight position and in their preferred AHP. The paired t test was used to determine significance in differences between measures.

RESULTS

A total of 34 patients (19 males [56%]) 9-56 years of age (mean, 16.5 ± 6) were included. Associated systemic or ocular system deficits were present in 30 patients (88%). AHP during best-corrected visual acuity testing averaged 16.5° ± 8.20° (range, 10°-51°), which was significantly different from the mean voluntary "comfortable" position only in the pitch and roll directions (P < 0.001). There was a significant noncongruous response during subjective response to head posturing with most sensing their head as "crooked" (76.5%) when manually straightened (P = 0.001).

CONCLUSIONS

The clinical AHP of patients with INS exists in all three spatial dimensions of pitch, yaw, and roll. Although the visual system may be causally related to the onset, amount, and direction of a compensatory AHP in patients with INS, its persistence over time or after surgical intervention is likely due to a combination of visual system (eg, nystagmus, strabismus) and nonvisual system (egocentric and musculo-skeletal) factors.

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.

TUBB3 M323V Syndrome Presents with Infantile Nystagmus

Variants in the TUBB3 gene, one of the tubulin-encoding genes, are known to cause congenital fibrosis of the extraocular muscles type 3 and/or malformations of cortical development. Herein, we report a case of a 6-month-old infant with c.967A>G:p.(M323V) variant in the TUBB3 gene, who had only infantile nystagmus without other ophthalmological abnormalities. Subsequent brain magnetic resonance imaging (MRI) revealed cortical dysplasia. Neurological examinations did not reveal gross or fine motor delay, which are inconsistent with the clinical characteristics of patients with the M323V syndrome reported so far. A protein modeling showed that the M323V mutation in the TUBB3 gene interferes with αβ heterodimer formation with the TUBA1A gene. This report emphasizes the importance of considering TUBB3 and TUBA1A tubulinopathy in infantile nystagmus. A brain MRI should also be considered for these patients, although in the absence of other neurologic signs or symptoms.

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.

Comparison of Techniques for Correction of Chin-down Vertical Abnormal Head Position Associated with Infantile Nystagmus Syndrome

PURPOSE

We evaluated the relative effectiveness of combined recession-resection of vertical rectus muscles versus superior rectus recession with inferior oblique weakening for patients who underwent surgical correction of chin-down abnormal head position (AHP) associated with infantile nystagmus syndrome (INS).

DESIGN

Retrospective interventional case series.

METHODS

This is a review of 22 patients who underwent surgical correction of chin-down vertical AHP associated with INS at an academic institution. The primary outcome was collapse of AHP. Unfavorable outcomes included repeat surgery and induced strabismus, in addition to failure of collapse of AHP.

RESULTS

Twenty-two patients had chin-down AHP. Recession-resection (bilateral superior rectus recession 6-9 mm; bilateral inferior rectus resection 5-9 mm) was performed in 11 cases; weakening of both elevators (bilateral superior rectus recession 5-8 mm, bilateral inferior oblique recession or myectomy) occurred in 11 cases. Unfavorable outcome rates were 64% (7/11) compared with 18% (2/11), respectively (P = .03). Reoperation was performed for 6 of 22 patients. Five patients were from the recession-resection group, namely 3 for induced V-pattern esotropia, 1 for alternating esotropia, and 1 to correct recurrent AHP. The last of the 6 who required reoperation was in the elevator weakening group, and required correction of a recurrent AHP (P = .06).

CONCLUSIONS

While recession-resection of the vertical recti and weakening of both elevators each produce acceptable collapse of chin-down AHP, the former frequently induces a V-pattern esotropia requiring reoperation.

Long-term Outcomes Following Surgery for Infantile Nystagmus Syndrome With Abnormal Head Positioning

PURPOSE

To evaluate long-term outcomes of surgical treatment for abnormal head positioning (AHP) associated with infantile nystagmus syndrome (INS).

DESIGN

Retrospective observational case series.

METHODS

Review of 150 patients who underwent surgery for AHP associated with nystagmus. Outcomes included head positioning, duction limitations, and strabismus, and were evaluated several times postoperatively. Successful collapse of AHP was defined as being ≤10°.

RESULTS

Thirty-one patients had surgery for AHP in the pitch (chin up/down) position, whereas 119 had surgery for a horizontal AHP. In addition, 54 underwent 50%-60% augmentation, 19 underwent 40% augmentation, 5 underwent less than 40% augmentation. Thirty-eight had surgical dose modified to correct strabismus, and 3 underwent surgery different from standard Kestenbaum procedures. Collapse of AHP: At the 1-3-week follow-up (n = 131), 125 patients (95%) had collapse of AHP. The percentage trended down at the 2-5-month (91%, n = 106) and 2-year follow-ups (83%, n = 57). However, at 5 and 10 years, it was 93% (n = 42) and 93% (n = 14), respectively, due to reoperation in a small minority. Over- and undercorrection: At 1-3 weeks, 5% of patients were overcorrected whereas 0% were undercorrected. Over- and undercorrection rates peaked at 2 years postoperatively. Ten years out, there were no overcorrections and 7% undercorrections. Four percent of patients required reoperation for overcorrection (mean 2.7 years) and 5% did for undercorrection (mean 3.9 years).

CONCLUSION

Surgery for the head positioning associated with INS produces excellent outcomes throughout 10 years postoperatively. Overcorrection presents early and resolves either over time or with additional surgery. Undercorrection develops later and can persist despite reoperation.

Management of Strabismus Associated With Infantile Nystagmus Syndrome: A Novel Classification to Assist in Surgical Planning

PURPOSE

There is no consensus on the surgical management of head position associated with infantile nystagmus syndrome (INS) when strabismus coexists, and few outcome data have been published. We propose classifying strabismus into concordant or discordant based on the relationship between head positioning and strabismus and then modifying surgery accordingly. Our objective is to describe this system and to review surgical outcomes.

DESIGN

Retrospective observational case series.

METHODS

Twenty-eight patients with INS and coexisting horizontal strabismus underwent surgery for horizontal head positioning and had ≥2 months of follow-up from 1995-2018 at the Vanderbilt Eye Institute. Outcome variables included head positioning (minimal, ≤10°; mild, 11-30°; moderate 31-44°; and severe ≥45°), strabismus (range 0-70 prism diopters [PDs]; minimal ≤10 PD), and reoperation rates. Nonparametric Wilcoxon signed rank, Fisher exact, and Mann-Whitney U tests were used for statistical analysis.

RESULTS

Twenty-one cases were concordant and 7 were discordant; the mean follow-up was 4.1 years. Ninety-six percent of patients had moderate to severe head positioning at baseline. Correction rates (to minimal) were 100% at 2-5 months postoperatively and 86% at last follow-up (P < .0001 at both time points compared with preoperatively). The magnitude of strabismus decreased compared with preoperative strabismus (30.8 ± 10.8 PDs; n = 28), strabismus at 2-5 months (9.1 ± 11.9 PDs; P = .0001; n = 26), and last follow-up (12.0 ± 14.1 PDs; P = .0003; n = 28). The overall reoperation rate was 32%.

CONCLUSIONS

Our classification system in patients with INS allows a systematic way to surgically improve head positioning and strabismus in cases of moderate to severe baseline head positioning.

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.

[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.

Exploring the Functional Impact of Childhood Vision Impairment: An e-Delphi Study

The principles of the World Health Organization's International Classification of Function, Disability and Health have been embraced globally as a framework to support people with disability. This framework recognizes the functional needs of a person, as well as their medical diagnosis. However, the challenge of assessing the functional impact of disability to determine a person's needs and eligibility for support remains an issue. One example is that of childhood vision impairment, where a child's eligibility is often gauged from their visual performance in a clinical environment, a setting that is far removed from the child's real-world environment. Such clinical environments fail to reveal those factors that have a functional impact and affect the child's continuous visual function in their everyday situation. To examine this issue a three round modified e-Delphi technique was applied to explore the functional impact of childhood vision impairment. A panel of experienced Australian orthoptists and specialist teachers in vision impairment was convened, and the recently revised vision classifications in the World Health Organization International Statistical Classification of Diseases and Health Related Problems Version 11 were reviewed and modified for their application to children. This paper describes the e-Delphi technique and the major study outcomes including the modifications proposed by the study's participants, and the emerging paradigm that progresses an understanding of the functional impact of childhood vision impairment.

Visual Target Strategies in Infantile Nystagmus Patients With Horizontal Jerk Waveform

The aim of this study was to propose a new pathophysiological hypothesis for involuntary eye oscillation in infantile nystagmus (IN): patients with IN exhibit impaired gaze fixation, horizontal smooth pursuit and optokinetic nystagmus (OKN) and use saccadic eye movements for these underlying impairments. In order to induce saccades, they make enough angle between gaze and target by precedent exponential slow eye movements. IN consists of the alternate appearance of the saccade and the slow eye movements. Unlike most previous theories, IN is therefore considered a necessary strategy allowing for better vision and not an obstacle to clear vision. In five patients with IN, eye movements were analyzed during the smooth pursuit test, saccadic eye movement test, OKN test and vestibulo-ocular reflex (VOR) test. Their gaze fixation, horizontal smooth pursuit, OKN and the last half of the slow phase of VOR were impaired. The lines obtained by connection of the end eye positions of fast phase of nystagmus coincided with the trajectories of targets. The findings indicate that patients followed the target by the fast but not the slow phase of nystagmus, which supports our hypothesis. By setting the direction of slow phase of nystagmus opposite to the direction of the OKN stimulation, enough angle can be effectively made between the gaze and target for the induction of saccade. This is the mechanism of reversed OKN response. In darkness and when eyes are closed, IN weakens because there is no visual target and neither the saccade for catching up the target or slow phase for induction of the saccade is needed.

Characteristics and Long-term Follow-up of Isolated Vertical Nystagmus in Infancy

PURPOSE

To determine the clinical characteristics and long-term outcomes of infants who presented with isolated vertical nystagmus.

METHODS

The medical records of 114 infants who were diagnosed as having nystagmus from 1996 to 2016 were screened. Patients with vertical nystagmus within the first year of life who had unremarkable magnetic resonance imaging of the brain and demonstrated age-appropriate visual behavior were included. The parents of patients in the final study cohort were contacted by telephone to obtain long-term follow-up information.

RESULTS

Eight patients comprised the final cohort. Vertical nystagmus was first observed at a mean age of 1.4 months (range: 1 to 2.5 months) and resolved in 87.5% of patients at a mean age of 3.8 months (range: 2 to 10 months). Vertical nystagmus was intermittent in 62.5%, upbeat in 62.5%, and pendular in 37.5% of patients. One patient's nystagmus did not resolve. Seventy-five percent of patient guardians participated in the telephone questionnaire. The mean age of patients at follow-up was 3.5 years (range: 0.5 to 8.1 years). Isolated iris transillumination was discovered in one patient without other features of albinism. Fifty percent of patients had speech delay requiring intervention. No other developmental delays or general medical conditions were identified.

CONCLUSIONS

Nystagmus resolved in 87.5% of patients, all before the first year of life, and speech delay was later identified in half of the patients. [J Pediatr Ophthalmol Strabismus. 2018;55(3):159-163.].

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.

AhR-deficiency as a cause of demyelinating disease and inflammation

The Aryl hydrocarbon Receptor(AhR) is among the most important receptors which bind pollutants; however it also regulates signaling pathways independently of such exposure. We previously demonstrated that AhR is expressed during development of the central nervous system(CNS) and that its deletion leads to the occurrence of a congenital nystagmus. Objectives of the present study are to decipher the origin of these deficits, and to identify the role of the AhR in the development of the CNS. We show that the AhR-knockout phenotype develops during early infancy together with deficits in visual-information-processing which are associated with an altered optic nerve myelin sheath, which exhibits modifications in its lipid composition and in the expression of myelin-associated-glycoprotein(MAG), a cell adhesion molecule involved in myelin-maintenance and glia-axon interaction. In addition, we show that the expression of pro-inflammatory cytokines is increased in the impaired optic nerve and confirm that inflammation is causally related with an AhR-dependent decreased expression of MAG. Overall, our findings demonstrate the role of the AhR as a physiological regulator of myelination and inflammatory processes in the developing CNS. It identifies a mechanism by which environmental pollutants might influence CNS myelination and suggest AhR as a relevant drug target for demyelinating diseases.