A gene for X-linked idiopathic congenital nystagmus (NYS1) maps to chromosome Xp11.4-p11.3

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.

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.

A new gene mutation in a family with idiopathic infantile nystagmus

Idiopathic infantile nystagmus (IIN) is an inherited disease, which can occur through a number of different inheritance patterns (autosomal dominant, recessive, or X-linked). The most common of these is X-linked inheritance with incomplete penetrance and variable expressivity, and can also be dominant or recessive. To date, only two mutations have been described: the first, affecting the FPR143 gene, which is associated with ocular albinism type I, and located on chromosome Xp22, and the second, affecting the FRMD7 gene located on chromosome X26-q27. To date, a causative gene on locus Xp11.3p11.4 has not yet been identified. The most common cause of IIN is due to mutations in the FRMD7 gene, located on chromosome Xq26. We present a case of a new mutation found in three siblings from a family with FRMD7-related infantile nystagmus, whose parents are consanguineously related in the first degree. A complex mutation has occurred in this family, which, to date, has not been previously reported in the scientific literature. The complex mutation consists of the presence of three consecutive 1 bp deletions in exon 12 (c.1248delT; 1299del C; and 1312delT), causing a secondary deletion (c. 1340–2145 + 214del), and resulting in a truncated protein. We also present a 7-year-old patient from a different family, with periodic alternating nystagmus, having no mutation in the FRMD7 gene, which we assume may be an example of non-FRMD7-related IIN. This patient does not have a family history of nystagmus.

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.

Structural variations in a non-coding region at 1q32.1 are responsible for the NYS7 locus in two large families

Congenital motor nystagmus (CMN) is characterized by early-onset bilateral ocular oscillations without other ocular deficits. To date, mutations in only one gene have been identified to be responsible for CMN, i.e., FRMD7 for X-linked CMN. Four loci for autosomal dominant CMN, including NYS7 (OMIM 614826), have been mapped but the causative genes have yet to be identified. NYS7 was mapped to 1q32.1 based on independent genome-wide linkage scan on two large families with CMN. In this study, mutations in all known protein-coding genes, both intronic sequence with predicted effect and coding sequence, in the linkage interval were excluded by whole-genome sequencing. Then, long-read genome sequencing based on the Nanopore platform was performed with a sample from each of the two families. Two deletions with an overlapping region of 775,699 bp, located in a region without any known protein-coding genes, were identified in the two families in the linkage region. The two deletions as well as their breakpoints were confirmed by Sanger sequencing and co-segregated with CMN in the two families. The 775,699 bp deleted region contains uncharacterized non-protein-coding expressed sequences and pseudogenes but no protein-coding genes. However, Hi-C data predicted that the deletions span two topologically associated domains and probably lead to a change in the 3D genomic architecture. These results provide novel evidence of a strong association between structural variations in non-coding genomic regions and human hereditary diseases like CMN with a potential mechanism involving changes in 3D genome architecture, which provides clues regarding the molecular pathogenicity of CMN.

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.

Clinical and molecular findings of FRMD7 related congenital nystagmus as adifferential diagnosis of ocular albinism

BACKGROUND

Congenital nystagmus is one of the most common neuro-ophthalmological disorders. X chromosome-linked forms are associated with pathogenic variants of the GPR143 and FRMD7 genes.

MATERIALS AND METHODS

Patients' DNA was analyzed using a next-generation sequencing (NGS) panel of genes involved in albinism and related pathologies (TYR, OCA2, TYRP1, SLC45A2, SLC24A5, C10ORF11, GPR143, SLC38A8, HPS 1 to 10, LYST, MITF, FRMD7) Results: We report a 4 generation family with 5 affected members initially referred for molecular diagnosis of ocular albinism. A missense variant of FRMD7 was found in 3 affected cases and one female carrier. We show that the disease in the affected girl is due to skewed inactivation of the X chromosome.

CONCLUSIONS

By compiling all the published cases we discuss the variable penetrance among females due to different types of mutation and to X-inactivation.

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.

Identification and functional characterization of a novel missense mutation in FRMD7 responsible for idiopathic congenital nystagmus

Idiopathic congenital nystagmus (ICN) is a genetically heterogeneous eye movement disorder which seriously reduces childhood visual acuity. X-linked inheritance is the most common pattern, and mutations in FERM domain-containing protein 7 (FRMD7) are the major cause. Here, we recruited a four-generation Chinese family with X-linked ICN for the causative mutational screening of FRMD7. A novel missense variant, c.805 A > C, was identified in the proband. The mutation was confirmed in all the affected individuals but was not detected in unaffected family members or 100 unrelated Chinese male controls. The mutation causes a substitution of lysine to glutamine at position 269 (p.Lys269Gln, K269Q). The FRMD7 mutant inhibits the formation and extension of neurites. Moreover, the mutation disrupts FRMD7 interaction with calcium/calmodulin-dependent serine protein kinase and neurite formation. Together, our data expand the mutation spectrum of FRMD7 causing ICN and provide an insight into the pathogenesis of nystagmus.

Identification of a novel idiopathic congenital nystagmus‑causing missense mutation, p.G296C, in the FRMD7 gene

Exploring the genetic basis for idiopathic congenital nystagmus is critical for improving our understanding of its molecular pathogenesis. In the present study, direct sequencing using gene specific primers was performed in order to identify the causative mutations in two brothers from a Chinese family who had been diagnosed with idiopathic congenital nystagmus. A comprehensive ophthalmological examination, including eye movement recordings, fundus examination, and retinal optical coherence tomography imaging was also conducted, to characterize the disease phenotype. The results revealed that the two brothers exhibited clear signs of nystagmus without any other ocular anomalies. Direct sequencing revealed a G to T transition (c.886G>T) in exon 9 of the four‑point‑one, ezrin, radixin, moesin domain‑containing 7 (FRMD7) gene, which resulted in a conservative substitution of glycine to cysteine at codon 296 (p.G296C), leading to idiopathic congenital nystagmus in the two affected brothers. c.886G>T is a novel idiopathic congenital nystagmus‑inducing mutation in the FRMD7 gene. This finding expands the spectrum of known gene mutations in idiopathic congenital nystagmus, and may be useful for faster gene diagnosis, prenatal testing, the development of potential gene therapies, and for improving the understanding of the molecular pathogenesis of idiopathic congenital nystagmus.

Novel mutations of FRMD7 in Chinese patients with congenital motor nystagmus

The purpose of the current study was to identify novel mutations in the FRMD7 (FERM domain containing 7) gene and to characterize clinical features in Chinese patients with congenital motor nystagmus. For this purpose, 18 patients with congenital motor nystagmus were selected from the ocular genetic diseases bank of the Pediatric and Genetic Clinic of Zhongshan Ophthalmic Center (Guangdong, China). Direct sequencing was used to analyze the exons and adjacent introns of the FRMD7 gene. The heteroduplex-single strand conformation polypeptide method was used to analyze 96 unrelated normal controls and gene-screening positive patients. Slit lamp photography of the anterior segment, fundus photography, optical coherence tomography and electroretinogram were carried out to identify the clinical features of congenital motor nystagmus. The authors noted that in, 18 patients with congenital motor nystagmus, there were 7FRMD7 gene mutations (six new mutations). The screening rate was 38.89%, including c.41_43delAGA (p.13-15delK); c.473T>A (p.I158N); c.605T>A (p.I202N); c.580G>T (p.A194S); c.811T>A (p.C271S); c.1493insA (p.Y498X); c.57+1G>A (slice mutation). There were no such mutations in the 96 normal controls. These results enriched the gene mutation spectrum of FRMD7. The authors systematically investigated the clinical phenotype of congenital motor nystagmus in a Chinese population. The study provides further evidence for clinical diagnosis and differential diagnosis and genetic counseling.

Molecular genetic analysis of patients with sporadic and X-linked infantile nystagmus

OBJECTIVES

Infantile nystagmus (IN) is a genetically heterogeneous condition characterised by involuntary rhythmic oscillations of the eyes accompanied by different degrees of vision impairment. Two genes have been identified as mainly causing IN: FRMD7 and GPR143. The aim of our study was to identify the genetic basis of both sporadic IN and X-linked IN.

DESIGN

Prospective analysis.

PATIENTS

Twenty Chinese patients, including 15 sporadic IN cases and 5 from X-linked IN families, were recruited and underwent molecular genetic analysis. We first performed PCR-based DNA sequencing of the entire coding region and the splice junctions of the FRMD7 and GPR143 genes in participants. Mutational analysis and co-segregation confirmation were then performed.

SETTING

All clinical examinations and genetic experiments were performed in the Eye Hospital of Wenzhou Medical University.

RESULTS

Two mutations in the FRMD7 gene, including one novel nonsense mutation (c.1090C>T, p.Q364X) and one reported missense mutation (c.781C>G, p.R261G), were identified in two of the five (40%) X-linked IN families. However, none of putative mutations were identified in FRMD7 or GPR143 in any of the sporadic cases.

CONCLUSIONS

The results suggest that mutations in FRMD7 appeared to be the major genetic cause of X-linked IN, but not of sporadic IN. Our findings provide further insights into FRMD7 mutations, which could be helpful for future genetic diagnosis and genetic counselling of Chinese patients with nystagmus.

Oculomotor neurocircuitry, a structural connectivity study of infantile nystagmus syndrome

Infantile nystagmus syndrome (INS) is one of the leading causes of significant vision loss in children and affects about 1 in 1000 to 6000 births. In the present study, we are the first to investigate the structural pathways of patients and controls using diffusion tensor imaging (DTI). Specifically, three female INS patients from the same family were scanned, two sisters and a mother. Six regions of interest (ROIs) were created manually to analyze the number of tracks. Additionally, three ROI masks were analyzed using TBSS (Tract-Based Spatial Statistics). The number of fiber tracks was reduced in INS subjects, compared to normal subjects, by 15.9%, 13.9%, 9.2%, 18.6%, 5.3%, and 2.5% for the pons, cerebellum (right and left), brainstem, cerebrum, and thalamus. Furthermore, TBSS results indicated that the fractional anisotropy (FA) values for the patients were lower in the superior ventral aspects of the pons of the brainstem than in those of the controls. We have identified some brain regions that may be actively involved in INS. These novel findings would be beneficial to the neuroimaging clinical and research community as they will give them new direction in further pursuing neurological studies related to oculomotor function and provide a rational approach to studying INS.

A FRMD7 variant in a Japanese family causes congenital nystagmus

Idiopathic congenital nystagmus (ICN) is a genetically heterogeneous eye movement disorder that causes a large proportion of childhood visual impairment. Here we describe a missense variant (p.L292P) within a mutation-rich region of FRMD7 detected in three affected male siblings in a Japanese family with X-linked ICN. Combining sequence analysis and results from structural and functional predictions, we report p.L292P as a variant potentially disrupting FRMD7 function associated with X-linked ICN.

Expression of a novel splice variant of FRMD7 in developing human fetal brains that is upregulated upon the differentiation of NT2 cells

FRMD7 mutations are associated with X-linked idiopathic congenital nystagmus (ICN); however, the underlying mechanisms whereby mutations of FRMD7 lead to ICN remain unclear. In a previous study, the first FRMD7 splice variant (FRMD7-S) was cloned and identified, and FRMD7-S was hypothesized to play a significant role in neuronal differentiation and development. The present study investigated a novel multiple exon-skipping mRNA splice variant of FRMD7, termed FRMD7_SV2, which was detected in NT2 cells using northern blotting. The mRNA expression levels of FRMD7_SV2 in the developing human fetal brain were examined using reverse transcription polymerase chain reaction (PCR), while the expression levels in NT2 cells treated with retinoid acid (RA) or bone morphogenetic protein-2 were investigated using quantitative PCR. The results revealed that the expression of FRMD7_SV2 was spatially and temporally restricted in human fetal brain development, and was upregulated upon RA-induced neuronal differentiation of the NT2 cells. These results indicated that as a novel splice variant of FRMD7, FRMD7_SV2 may play a role in neuronal development.

'Congenital' nystagmus may hide various ophthalmic diagnoses

PURPOSE

To investigate whether patients registered at a low-vision centre with 'nystagmus' had any underlying, but so far unknown, ophthalmic diagnosis.

METHODS

All patients registered at the low-vision centre of Uppsala county with nystagmus as their major diagnosis were identified. Their medical records were studied to exclude those with other general diagnoses that could explain the nystagmus. The remaining group of patients underwent an ophthalmic examination, refraction and optical coherence tomography (OCT). Electroretinogram and genetic analyses were performed when indicated.

RESULTS

Sixty-two patients with nystagmus as their main diagnosis were registered at the low-vision centre, Uppsala, and 43 of them had a major diagnosis other than nystagmus. Nystagmus was the major diagnosis in 19 patients, 15 of whom, aged 6-76 years, participated in the study. Two of the patients had foveal hypoplasia and albinism, four a seemingly isolated foveal hypoplasia, three achromatopsia, one rod-cone dystrophy, one degenerative high myopia, and two could not be evaluated. Only two patients appeared to have 'congenital' nystagmus. Eleven of the patients underwent a comprehensive genetic investigation of the PAX 6 gene. In addition, four of the patients were analysed for mutations in FOXC1 and PITX2 and one in FRMD7. No mutations were found in any of the patients analysed.

CONCLUSION

The study illustrates that many patients in our study group with nystagmus had underlying ophthalmic diagnoses. Early diagnosis is important to facilitate habilitation and to provide genetic counselling and, in the future, possibly also gene therapy.

Identification of three novel mutations in the FRMD7 gene for X-linked idiopathic congenital nystagmus

Idiopathic congenital nystagmus (ICN) consists of involuntary and periodic ocular motility, often with seriously reduced visual acuity. To identify the genetic defects associated with X-linked ICN, we performed PCR-based DNA direct sequencing of two candidate genes, FRMD7 and GPR143, in four families. Mutation analysis led to identification of three novel mutations, p.S260R, p.Q487X, and p.V549Y fsX554, in FRMD7 in three of the recruited families. Results from structural modeling indicated that the p.S260R may potentially disrupt FRMD7 function through loss of a phosphorylation site and/or interference with protein-protein interactions. Both p.Q487X, and p.V549Y fsX554 mutations were predicted to generate nonfunctional truncated proteins. Using a capture next generation sequencing method, we excluded CASK as the responsible gene for the remaining family. Combining sequence analysis and structural modeling, we report three novel mutations in FRMD7 in three independent families with XLICN, and provide molecular insights for future XLICN diagnosis and treatment.

Novel mutation c.980_983delATTA compound with c.986C>A mutation of the FRMD7 gene in a Chinese family with X-linked idiopathic congenital nystagmus

OBJECTIVE

To screen mutations in FERM domain-containing protein 7 (FRMD7) gene in two Chinese families with X-linked idiopathic congenital nystagmus (XLICN).

METHODS

Common ophthalmic data and peripheral blood of two Chinese XLICN families (families A and B) were collected after informed consent. Genomic DNA was prepared from the peripheral blood of members of the two families and from 100 normal controls. Mutations in the FRMD7 gene were determined by directly sequencing polymerase chain reaction (PCR) products.

RESULTS

We identified a novel mutation c.980_983delATTA compound with c.986C>A mutation in the 11th exon of FRMD7 in family B, and a previously reported splicing mutation c.781C>G (p.R261G) [corrected] in family A. The mutations were detected in patients and female carriers, while they were absent in other relatives or in the 100 normal controls.

CONCLUSIONS

Our results expand the spectrum of FRMD7 mutations in association with XLICN, and further confirm that the mutations of FRMD7 are the underlying molecular mechanism for XLICN.

Identifcation of a novel mutation p.I240T in the FRMD7 gene in a family with congenital nystagmus

Congenital Nystagmus (CN) is a genetically heterogeneous ocular disease, which causes a significant proportion of childhood visual impairment. To identify the underlying genetic defect of a CN family, twenty-two members were recruited. Genotype analysis showed that affected individuals shared a common haplotype with markers flanking FRMD7 locus. Sequencing FRMD7 revealed a T > C transition in exon 8, causing a conservative substitution of Isoleucine to Tyrosine at codon 240. By protein structural modeling, we found the mutation may disrupt the hydrophobic core and destabilize the protein structure. We reviewed the literature and found that exons 2, 8, and 9 (11.4% of the sequence of FRMD7 mRNA) represent the majority (55.3%) of the reported FRMD7 mutations. In summary, we identified a novel mutation in FRMD7, showed its molecular consequence, and revealed the mutation-rich exons of the FRMD7 gene. Collectively, this provides molecular insights for future CN clinical genetic diagnosis and treatment.

Autosomal-dominant nystagmus, foveal hypoplasia and presenile cataract associated with a novel PAX6 mutation

Autosomal-dominant idiopathic infantile nystagmus has been linked to 6p12 (OMIM 164100), 7p11.2 (OMIM 608345) and 13q31-q33 (OMIM 193003). PAX6 (11p13, OMIM 607108) mutations can also cause autosomal-dominant nystagmus, typically in association with aniridia or iris hypoplasia. We studied a large multigenerational white British family with autosomal-dominant nystagmus, normal irides and presenile cataracts. An SNP-based genome-wide analysis revealed a linkage to a 13.4-MB region on chromosome 11p13 with a maximum lod score of 2.93. A mutation analysis of the entire coding region and splice junctions of the PAX6 gene revealed a novel heterozygous missense mutation (c.227C>G) that segregated with the phenotype and is predicted to result in the amino-acid substitution of proline by arginine at codon 76 p.(P76R). The amino-acid variation p.(P76R) within the paired box domain is likely to destabilise the protein due to steric hindrance as a result of the introduction of a polar and larger amino acid. Eye movement recordings showed a significant intrafamilial variability of horizontal, vertical and torsional nystagmus. High-resolution in vivo imaging of the retina using optical coherence tomography (OCT) revealed features of foveal hypoplasia, including rudimentary foveal pit, incursion of inner retinal layers, short photoreceptor outer segments and optic nerve hypoplasia. Thus, this study presents a family that segregates a PAX6 mutation with nystagmus and foveal hypoplasia in the absence of iris abnormalities. Moreover, it is the first study showing detailed characteristics using eye movement recordings of autosomal-dominant nystagmus in a multigenerational family with a novel PAX6 mutation.

A novel missense mutation in the FERM domain containing 7 (FRMD7) gene causing X-linked idiopathic congenital nystagmus in a Chinese family

PURPOSE

Idiopathic congenital nystagmus (ICN) is a genetically heterogeneous disease. Thus far, the disease gene has been identified as the FERM domain containing 7 (FRMD7) gene. The purpose of this study was to elucidate the clinical and genetic characteristics of a four- generation Chinese family with ICN.

METHODS

The clinical data and the genomic DNA of a Chinese ICN family were collected following the provision of informed consent. All coding exons of the FRMD7 gene were amplified by PCR and then sequenced. Affinity GST-p21 activated kinase 2 (PAK2) precipitation was used to investigate whether this novel FRMD7 mutant influenced Rac1 signaling activation in the human embryonic kidney 293 T cells (HEK 293T) cells transiently cotransfected with wild-type or mutant FRMD7 and Rac1.

RESULTS

A novel missense mutation (c.635T>C) was identified in all affected members. Obligate female carriers were heterozygous in these mutations and the affected males were homozygous, consistent with X-linked inheritance. This mutation is a substitution of proline for leucine. Function analysis showed that this novel mutant influences Rac1 signaling in human HEK 293T cells.

CONCLUSIONS

This study widens the mutation spectrum of the FRMD7 gene. This mutant was shown to activate GTPase Rac1 signaling in vitro; however, the quantity of activated Rac1 was obviously decreased compared with the wild type (p<0.05). Taken together, our data strongly support the hypothesis that the identified FRMD7 mutant influences GTPase Rac1 signaling, which regulates neurite development. This mutation may be related to the pathogenesis of X-linked ICN.

A novel interaction between FRMD7 and CASK: evidence for a causal role in idiopathic infantile nystagmus

Idiopathic infantile nystagmus (IIN) is a genetically heterogeneous disorder of eye movement that can be caused by mutations in the FRMD7 gene that encodes a FERM domain protein. FRMD7 is expressed in the brain and knock-down studies suggest it plays a role in neurite extension through modulation of the actin cytoskeleton, yet little is known about its precise molecular function and the effects of IIN mutations. Here, we studied four IIN-associated missense mutants and found them to have diverse effects on FRMD7 expression and cytoplasmic localization. The C271Y mutant accumulates in the nucleus, possibly due to disruption of a nuclear export sequence located downstream of the FERM-adjacent domain. While overexpression of wild-type FRMD7 promotes neurite outgrowth, mutants reduce this effect to differing degrees and the nuclear localizing C271Y mutant acts in a dominant-negative manner to inhibit neurite formation. To gain insight into FRMD7 molecular function, we used an IP-MS approach and identified the multi-domain plasma membrane scaffolding protein, CASK, as a FRMD7 interactor. Importantly, CASK promotes FRMD7 co-localization at the plasma membrane, where it enhances CASK-induced neurite length, whereas IIN-associated FRMD7 mutations impair all of these features. Mutations in CASK cause X-linked mental retardation. Patients with C-terminal CASK mutations also present with nystagmus and, strikingly, we show that these mutations specifically disrupt interaction with FRMD7. Together, our data strongly support a model whereby CASK recruits FRMD7 to the plasma membrane to promote neurite outgrowth during development of the oculomotor neural network and that defects in this interaction result in nystagmus.

Infantile and acquired nystagmus in childhood

Nystagmus is an involuntary, periodic eye movement caused by a slow drift of fixation which is followed by a fast refixation saccade (jerk nystagmus) or a slow movement back to fixation (pendular nystagmus). In childhood most cases are benign forms of nystagmus: idiopathic infantile, ocular or latent nystagmus. They arise at the age of 3 months, without oscillopsia and show the absence of the physiologic opto-kinetic nystagmus. A full ophthalmologic evaluation is all that is needed in most cases: albinism, macular or optic nerve hypoplasia and congenital retinal dystrophies are the most common forms of ocular nystagmus. Idiopathic infantile nystagmus can be hereditary, the most common and best analyzed form being a mutation of the FRMD7 gene on chromosome Xq26.2. The mutation shows a mild genotype-phenotype correlation. In all female carriers the opto-kinetic nystagmus is absent and half had mild nystagmus. Latent nystagmus is part of the infantile esotropia syndrome and shows the unique feature of change of direction when the fixing eye changes: it is always beating to the side of the fixing eye. There is no cure for infantile nystagmus but therapeutic options include magnifying visual aids or eye muscle surgery at the age of 6-8 y in patients with head turn. Less than 20% of childhood nystagmus are acquired and need further neurological and imaging work-up. Alarming signs and symptoms are: onset after the age of 4 months, oscillopsia, dissociated (asymmetric) nystagmus, preserved opto-kinetic nystagmus, afferent pupillary defect, papilloedema and neurological symptoms like vertigo and nausea. The most common cause is due to pathology of the anterior optic pathway (e.g. optic nerve gliomas). It shows the same clinical feature of dissociated nystagmus as spasmus nutans but has a higher frequency as in INO. Other forms of acquired nystagmus are due to brainstem, cerebellar or metabolic diseases.

A novel splicing mutation of the FRMD7 gene in a Chinese family with X-linked congenital nystagmus

PURPOSE

To identify a potential pathogenic mutation in a four-generation Chinese family with X-linked congenital nystagmus (XLCN).

METHODS

Routine clinical examination and ophthalmic evaluation were performed on normal controls, two patients and two healthy members of the family. Genomic DNA was prepared from the peripheral blood of members of the family and from 50 normal controls. All coding exons and the intronic boundaries of the four-point-one (4.1), ezrin, radixin, moesin (FERM) domain-containing 7 (FRMD7) gene were amplified using polymerase chain reaction (PCR) followed by direct sequencing.

RESULTS

A previously unreported splicing mutation, c.163-1 G→T transversion (c.163-1 G>T), was detected preceding exon3 of FRMD7 in the patients but not in the unaffected family members and 50 unrelated healthy individuals.

CONCLUSIONS

We identified a novel mutation (c.163-1 G→T) of FRMD7 in this Chinese family with XLCN. Our finding is the first report related to c.163-1 G→T mutation in FRMD7. The result expands the mutation spectrum of FRMD7 in association with congenital nystagmus.

A novel locus for autosomal dominant congenital motor nystagmus mapped to 1q31-q32.2 between D1S2816 and D1S2692

Congenital motor nystagmus (CMN) is characterized by bilateral involuntary ocular oscillation without any other underlying ocular or systemic diseases. An autosomal dominant CMN was identified in a large Chinese family where all patients had nystagmus since infancy. The nystagmus in the family is independent of any known ocular or systemic diseases. After exclusion of known CMN loci, a genome-wide scan was performed by genotyping microsatellite markers at about 10 cM intervals, together with two-point linkage analysis. Exome sequencing was used to screen coding exons of well-annotated genes. Sanger-dideoxy sequencing was used to verify candidate variations inside the linkage interval. Congenital motor nystagmus in this family shows linkage to markers in a 11.39 Mb (12.1 cM) region on chromosome 1q31-q32.2 between D1S2816 and D1S2692. All nine markers in the linkage interval gave positive lod scores, with D1S2655 and D1S2636 yielding lod scores of 5.16 and 5.18, respectively, at θ = 0. No causative mutation in the linkage interval was identified by exome sequencing of gDNA from four patients. A linkage study of additional families and further analysis of candidate genes may ultimately lead to identification of the gene responsible for dominantly inherited CMN.

A novel frame-shift mutation in FRMD7 causes X-linked idiopathic congenital nystagmus in a Chinese family

PURPOSE

To screen mutations in the FERM domain-containing 7 (FRMD7) gene in a Chinese family with X-linked idiopathic congenital nystagmus (ICN).

METHODS

It has been reported that FRMD7 mutations account for approximately 47% of X-linked nystagmus in Chinese patients. We collected 5 ml of blood samples from members of a family with X-linked ICN and 100 normal controls. Mutations in FRMD7 were determined by sequencing PCR products.

RESULTS

We identified a previously unreported 4 bp deletion in FRMD7 (c.1486-1489 del TTTT) in a Chinese family. The mutation co-segregated with the disease phenotype in patients and female carriers, while it was not detected in other relatives or in the 100 normal controls.

CONCLUSIONS

Our results expand the spectrum of FRMD7 mutations causing ICN, and further confirm the role of FRMD7 in the pathogenesis of ICN. Direct sequencing of FRMD7 could be used as a diagnostic testing of idiopathic congenital nystagmus.

The Role of FRMD7 in Idiopathic Infantile Nystagmus

Idiopathic infantile nystagmus (IIN) is an inherited disorder in which the nystagmus arises independently of any other symptoms, leading to the speculation that the disorder represents a primary defect in the area of the brain responsible for ocular motor control. The inheritance patterns are heterogeneous, however the most common form is X-linked. FRMD7 resides at Xq26-27 and approximately 50% of X-linked IIN families map to this region. Currently 45 mutations within FRMD7 have been associated with IIN, confirming the importance of FRMD7 in the pathogenesis of the disease. Although mutations in FRMD7 are known to cause IIN, very little is known about the function of the protein. FRMD7 contains a conserved N-terminal FERM domain suggesting that it may provide a link between the plasma membrane and actin cytoskeleton. Limited studies together with the knowledge of the function of other FERM domain containing proteins, suggest that FRMD7 may play a role in membrane extension during neuronal development through remodeling of the actin cytoskeleton.

A novel GPR143 splicing mutation in a Chinese family with X-linked congenital nystagmus

PURPOSE

The purpose of the current research was to detect the underlying genetic defect in a Chinese family with X-linked congenital nystagmus and perform prenatal genetic diagnosis for their current pregnancy.

METHODS

A common clinical examination and an ophthalmic evaluation were performed on the proband, one carrier, and one unaffected member. Mutation analysis of the G protein-coupled receptor 143 (GPR143) and four-point-one (4.1), ezrin, radixin, moesin (FERM) domain-containing 7 (FRMD7) genes was performed by direct sequencing of PCR-amplified exons in the proband. The detected GPR143 mutation was tested in all available family members and 200 normal controls by direct sequencing.

RESULTS

Congenital nystagmus, obvious fundus hypopigmentation, and foveal hypoplasia were observed in the proband but not in the carriers or the unaffected members. A novel splicing mutation c.658+1 g>t not found in 200 unrelated controls was identified and co-segregated with X-linked ocular albinism (XLOA) in this family. The fetus (V:5) was hemizygous for this mutant allele.

CONCLUSIONS

We identified a novel causative mutation of GPR143 in a five-generation Chinese family with XLOA. This expanded the mutation spectrum of GPR143 and provided data elucidating the diverse and variable effects of GPR143 mutations.

Investigation of the gene mutations in two Chinese families with X-linked infantile nystagmus

PURPOSE

To identify the gene mutations causing X-linked infantile nystagmus in two Chinese families (NYS003 and NYS008), of which the NYS003 family was assigned to the FERM domain-containing 7 (FRMD7) gene linked region in our previous study, and no mutations were found by direct sequencing.

METHODS

Two microsatellites, DXS1047 and DXS1001, were amplified using a PCR reaction for the linkage study in the NYS008 family. FRMD7 was sequenced and mutations were analyzed. Multiplex ligation-dependent probe amplification (MLPA) was used to detect FRMD7 mutations in the NYS003 family.

RESULTS

The NYS008 family yielded a maximum logarithm of odds (LOD) score of 1.91 at θ=0 with DXS1001. FRMD7 sequencing showed a nucleotide change of c. 623A>G in exon7 of the patients' FRMD7 gene, which was predicted to result in an H208R amino acid change. This novel mutation was absent in 100 normal Han Chinese controls. No FRMD7 gene mutations were detected by MLPA in the NYS003 family.

CONCLUSIONS

We identified a novel mutation, c. 623A>G (p. H208R), in a Han Chinese family with infantile nystagmus. This mutation expands the mutation spectrum of FRMD7 and contributes to the research on the molecular pathogenesis of FRMD7.

The clinical and molecular genetic features of idiopathic infantile periodic alternating nystagmus

Periodic alternating nystagmus consists of involuntary oscillations of the eyes with cyclical changes of nystagmus direction. It can occur during infancy (e.g. idiopathic infantile periodic alternating nystagmus) or later in life. Acquired forms are often associated with cerebellar dysfunction arising due to instability of the optokinetic-vestibular systems. Idiopathic infantile periodic alternating nystagmus can be familial or occur in isolation; however, very little is known about the clinical characteristics, genetic aetiology and neural substrates involved. Five loci (NYS1-5) have been identified for idiopathic infantile nystagmus; three are autosomal (NYS2, NYS3 and NYS4) and two are X-chromosomal (NYS1 and NYS5). We previously identified the FRMD7 gene on chromosome Xq26 (NYS1 locus); mutations of FRMD7 are causative of idiopathic infantile nystagmus influencing neuronal outgrowth and development. It is unclear whether the periodic alternating nystagmus phenotype is linked to NYS1, NYS5 (Xp11.4-p11.3) or a separate locus. From a cohort of 31 X-linked families and 14 singletons (70 patients) with idiopathic infantile nystagmus we identified 10 families and one singleton (21 patients) with periodic alternating nystagmus of which we describe clinical phenotype, genetic aetiology and neural substrates involved. Periodic alternating nystagmus was not detected clinically but only on eye movement recordings. The cycle duration varied from 90 to 280 s. Optokinetic reflex was not detectable horizontally. Mutations of the FRMD7 gene were found in all 10 families and the singleton (including three novel mutations). Periodic alternating nystagmus was predominantly associated with missense mutations within the FERM domain. There was significant sibship clustering of the phenotype although in some families not all affected members had periodic alternating nystagmus. In situ hybridization studies during mid-late human embryonic stages in normal tissue showed restricted FRMD7 expression in neuronal tissue with strong hybridization signals within the afferent arms of the vestibulo-ocular reflex consisting of the otic vesicle, cranial nerve VIII and vestibular ganglia. Similarly within the afferent arm of the optokinetic reflex we showed expression in the developing neural retina and ventricular zone of the optic stalk. Strong FRMD7 expression was seen in rhombomeres 1 to 4, which give rise to the cerebellum and the common integrator site for both these reflexes (vestibular nuclei). Based on the expression and phenotypic data, we hypothesize that periodic alternating nystagmus arises from instability of the optokinetic-vestibular systems. This study shows for the first time that mutations in FRMD7 can cause idiopathic infantile periodic alternating nystagmus and may affect neuronal circuits that have been implicated in acquired forms.

Nystagmus and saccadic intrusions

We review current concepts of nystagmus and saccadic oscillations, applying a pathophysiological approach. We begin by discussing how nystagmus may arise when the mechanisms that normally hold gaze steady are impaired. We then describe the clinical and laboratory evaluation of patients with ocular oscillations. Next, we systematically review the features of nystagmus arising from peripheral and central vestibular disorders, nystagmus due to an abnormal gaze-holding mechanism (neural integrator), and nystagmus occurring when vision is compromised. We then discuss forms of nystagmus for which the pathogenesis is not well understood, including acquired pendular nystagmus and congenital forms of nystagmus. We then summarize the spectrum of saccadic disorders that disrupt steady gaze, from intrusions to flutter and opsoclonus. Finally, we review current treatment options for nystagmus and saccadic oscillations, including drugs, surgery, and optical methods. Examples of each type of nystagmus are provided in the form of figures.

Novel intragenic FRMD7 deletion in a pedigree with congenital X-linked nystagmus

OBJECTIVE

To identify the disease-causing mutation in a large 3 generation pedigree of X-linked congenital nystagmus.

METHODS

Twenty-three members of a single pedigree, including 7 affected males, 2 affected females, 5 obligate carriers, and 9 unaffected family members were tested for mutations in the FRMD7 gene using PCR-based DNA sequencing assays and multiplex PCR assays for deletions.

RESULTS

A hemizygous deletion of exons 2, 3, and 4 of FRMD7 was detected in all affected males in the family and was absent from 40 control subjects.

CONCLUSIONS

A range of missense, nonsense, frameshift, and splicing mutations in FRMD7 have been shown to cause X-linked congenital nystagmus. Here we show for the first time that large intragenic deletions of FRMD7 can also cause this form of nystagmus.

The Molecular Genetics of Congenital Idiopathic Nystagmus

Congenital Idiopathic Nystagmus (CIN) is genetically heterogeneous. Autosomal dominant, autosomal recessive and X-linked patterns of inheritance have been reported. Linkage analysis has suggested the existence of at least three distinct loci for both autosomal dominant and x-linked forms, although as yet no disease genes have been identified. The pathophysiological mechanisms underlying nystagmus are poorly understood and it is likely that insights may arise from finding and characterizing disease genes. If linkage experiments are used to find "nystagmus genes," their power will depend heavily on accurate phenotyping to avoid misdiagnosis due to masquerading conditions and phenotypic variations within pedigrees.

A novel GPR143 duplication mutation in a Chinese family with X-linked congenital nystagmus

PURPOSE

To elucidate the molecular genetic defect of X-linked congenital nystagmus in a Chinese family.

METHODS

Genomic DNA was prepared from peripheral blood. We used allele-sharing analysis to identify the possible locus harboring the disease-causing gene. We screened for mutations in the G protein-coupled receptor 143 gene (GPR143) by direct sequencing of the polymerase chain reaction (PCR)-amplified exons.

RESULTS

In analyzing the candidate gene, GPR143, in the linked region, a 19 base pair (bp) duplication mutation in exon 1 was detected after direct DNA sequence analysis, which cosegregated in all patients of this family and was present in obligate female carriers.

CONCLUSIONS

The identified 19 bp duplication in GPR143 induces a frame-shift and a premature stop codon, resulting in a truncated protein of 105 residues. These results suggest that this novel mutation is associated with the congenital nystagmus observed in this Chinese family and further support that GPR143 mutations are the underlying pathogenesis of the molecular mechanism for congenital nystagmus.

A novel frameshift mutation in FRMD7 causing X-linked idiopathic congenital nystagmus

Idiopathic congenital nystagmus (ICN) is a common oculomotor disorder characterized by bilateral involuntary, periodic, and predominantly ocular oscillations. X-linked ICN (XLICN) with incomplete penetrance in females is the most common inheritance form, and FERM domain containing (FRMD7) mutation is the major reason for XLICN families. To date, 39 FRMD7 mutations have been identified, and 50% of the XLICN pedigrees have yielded FRMD7 mutations in the Western population. In this study, we identified a novel frameshift mutation (c.1274-1275delTG) in the FRMD7 gene in six XLICN pedigrees. Incorporated with data reported from other two Chinese groups, approximately 47% XLICN pedigrees were caused by the FRMD7 mutation in China. Therefore, this study showed that mutation analysis of the FRMD7 gene had diagnostic value not only in the Western population but also in one of the biggest Eastern populations, Chinese XLICN families. In addition, the results indicated the type of FRMD7 mutation associated with the penetrance of female carriers of XLICN.

Identification of a novel GPR143 deletion in a Chinese family with X-linked congenital nystagmus

PURPOSE

To map and identify the genetic mutation underlying X-linked congenital nystagmus in a Chinese family.

METHODS

Genomic DNA was prepared from peripheral blood, and linkage analysis was performed using short tandem repeat (STR) polymorphism markers. We used Cyrillic software to manage pedigree and haplotype data and used MLINK to calculate LOD scores. Dye-terminator cycle-sequencing was used to detect the sequence variation of polymerase chain reaction (PCR)-amplified exons.

RESULTS

Linkage analysis mapped the disease-causing gene to Xp22.3 with a significant two-point LOD score (Z) at marker DXS7103 (Z=3.16, recombination fraction [theta]=0). Haplotype analysis in this region supported the result. In analyzing the candidate gene in the linked region, we found a 37-bp deletion in exon 1 of GPR143 in all male patients.

CONCLUSIONS

The revealed 37-bp deletion in GPR143 is frameshift and is predicted to result in a truncated protein of 93 residues. These results indicate that this novel GPR143 mutation is associated with the congenital nystagmus observed in this Chinese family.

A review of the molecular genetics of congenital Idiopathic Nystagmus (CIN)

Congenital Idiopathic Nystagmus (CIN) is genetically heterogeneous. Autosomal dominant, autosomal recessive and X-linked patterns of inheritance have been reported. Linkage analysis has suggested the existence of at least three distinct loci for both autosomal dominant and X-linked forms, although only one disease gene has been identified (FRMD7, Xq26.2). The pathophysiological mechanisms underlying nystagmus are poorly understood but it is anticipated that characterization of the FRMD7 gene and identification of novel nystagmus genes will provide insights into this condition and the functioning and development of the visual pathways in general.

Five novel mutations of the FRMD7 gene in Chinese families with X-linked infantile nystagmus

PURPOSE

Infantile nystagmus (IN) is an inherited disorder characterized by bilateral ocular oscillatory movements. Recently, mutations in FRMD7 were found to be responsible for X-linked idiopathic infantile nystagmus . We investigated the role of the FRMD7 gene mutations in seven Chinese families with infantile nystagmus.

METHODS

Linkage analysis was performed with fluorescently labeled microsatellite markers, DXS1001 and DXS1047. Analysis of FRMD7 gene mutations was performed by direct sequence to the whole coding regions and exon-intron boundaries of FRMD7 gene in all affected members in seven families with IN.

RESULTS

Five novel FRMD7 gene mutations, 70 G>T(p.G24W) in exon 2, c.689-690delAG (p.Ser232del) in exon8, c. 782G>A (p.R260Q) and c. 812G>T (p. C271F) in exon 9, and c. 910C>T (R303X) in exon 10, were identified in five of seven Chinese families with X-linked infantile nystagmus. But we didn't detect the FRMD7 gene mutation in one of seven families, although a positive LOD score of 2.42 (thetamax=0.1) was obtained at DXS1047 . We also found the same mutation, which is c. 782G>A (p.R260Q), occurred in two different families.

CONCLUSIONS

This is first report that five kinds of FRMD7 gene mutation types occurred in Chinese families with IN, which further support that FRMD7 gene mutations are the underlying pathogenesis of the molecular mechanism for infantile nystagmus.

A novel mutation in FRMD7 causing X-linked idiopathic congenital nystagmus in a large family

PURPOSE

To identify the gene responsible for causing an X-linked idiopathic congenital nystagmus (XLICN) in a six-generation Chinese family.

METHODS

Forty-nine members of an XLICN family were recruited and examined after obtaining informed consent. Affected male individuals were genotyped with microsatellite markers around the FRMD7 locus. Mutations were comprehensively screened by direct sequencing using gene specific primers. An X-inactivation pattern was investigated by X chromosome methylation analysis.

RESULTS

The patients showed phenotypes consistent with XLICN. Genotype analysis showed that male affected individuals in the family shared a common haplotype with the selected markers. Sequencing FRMD7 revealed a G>T transversion (c.812G>T) in exon 9, which caused a conservative substitution of Cys to Phe at codon 271 (p.C271F). This mutation co-segregated with all affected individuals and was present in the obligate, non-penetrant female carriers. However, the mutation was not observed in unaffected familial males or 400 control males. Females with the mutant gene could be affected or carrier and they shared the same inactivated X chromosome harboring the mutation in blood cells, which showed there is no clear causal link between X-inactivation pattern and phenotype.

CONCLUSIONS

We identified a novel mutation in FRMD7 and confirmed the role of this mutation in the pathogenesis of X-linked congenital nystagmus.

Identification of a novel GPR143 mutation in a large Chinese family with congenital nystagmus as the most prominent and consistent manifestation

Congenital nystagmus is characterized by involuntary, rhythmical, repeated oscillations of one or both eyes. We studied a large Chinese family with nystagmus as a prominent and consistent manifestation phenotype in nine patients to map and identify a disease-causing gene for nystagmus. X-linked recessive inheritance was observed in the family, and foveal hypoplasia was detected in some of the nine patients. The disease gene was mapped to an approximately 10.6 Mb region flanked by DXS996 and DXS7593 on Xp22 with a significant peak multipoint LOD score. Analysis of 21 candidate genes in the region revealed a novel p.S89F mutation in the second transmembrane domain of GPR143, a G protein-coupled receptor which causes ocular albinism when mutated. All male patients in the family were hemizygous for the mutation; the female carriers were heterozygous for the mutation. The p.S89F mutation was not identified in 100 normal females or 100 normal males. Our results indicate that a mutation in the GPR143 gene can cause a variant form of ocular albinism, with congenital nystagmus as the most prominent and only consistent finding in all patients in this Chinese family. These results expand the spectrum of clinical phenotypes associated with GPR143 mutations.

The NDUFB11 gene is not a modifier in Leber hereditary optic neuropathy

Over 95% of Leber hereditary optic neuropathy (LHON) cases are due to mutations in mitochondrial DNA-encoded subunits of NADH:ubiquinone oxidoreductase (E.C.1.6.5.3., complex I). A recessive X-linked susceptibility gene that acts synergistically with the primary mtDNA mutation to produce visual loss is suggested by the high male-to-female ratio among LHON patients. The ESSS protein is a recently isolated subunit of bovine heart mitochondrial complex I. We revisited the genomic sequence of NDUFB11, the human homolog mapping to chromosome Xp11.23, and identified two mRNA isoforms showing different expression profiles in human tissues. Cultured skin fibroblasts from four LHON patients showed a pattern of expression similar to normal controls. Moreover, NDUFB11 did not seem to influence risk and age at onset of visual loss in a total of 65 individuals from 35 Italian LHON families. Also, the gene was not affected in 11 children with a severe encephalopathy associated with decreased complex I activity in skeletal muscle.

Mutations in FRMD7, a newly identified member of the FERM family, cause X-linked idiopathic congenital nystagmus

Idiopathic congenital nystagmus is characterized by involuntary, periodic, predominantly horizontal oscillations of both eyes. We identified 22 mutations in FRMD7 in 26 families with X-linked idiopathic congenital nystagmus. Screening of 42 singleton cases of idiopathic congenital nystagmus (28 male, 14 females) yielded three mutations (7%). We found restricted expression of FRMD7 in human embryonic brain and developing neural retina, suggesting a specific role in the control of eye movement and gaze stability.

Scanning the ocular albinism 1 (OA1) gene for polymorphisms in congenital nystagmus by DHPLC

BACKGROUND

Nystagmus is common to all types of albinism. Some subjects with nystagmus lack convincing signs of albinism, have no other visual pathway disease, and are classified as possessing congenital idiopathic nystagmus (CN). It has been postulated that CN may be a form of ocular albinism.

METHODS

The presence of nystagmus, iris transillumination, and visual acuity were recorded in 39 CN and albino patients and their families. Physical characteristics were also noted. DNA from buccal swabs was obtained for use in denaturing high performance liquid chromatography (DHPLC) and chemical cleavage of mismatch (CCM) to scan several hotspots for X-linked ocular albinism (OA1) mutations.

RESULTS

Two previously reported polymorphisms were confirmed: neither was found to be a causative mutation.

CONCLUSION

No correlation was identified between nystagmus and OA1.