Heterogeneous phenotype in a family with the FERM domain-containing 7 gene R335X mutation

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.

Next-generation sequencing identifies a novel frameshift variant in FRMD7 in a Chinese family with idiopathic infantile nystagmus

Background

Idiopathic infantile nystagmus (IIN) is a high genetically heterogeneous ophthalmic disease and is often associated with pathogenic mutations in FRMD7 and GPR143, respectively. Idiopathic infantile nystagmus manifests as involuntary periodic rhythmic oscillation of the eyes in the very early life, which decreases visual acuity and affects the quality of life.

Objective and Methods

The aim of our study was to reveal a possible pathogenic variant through the investigation of a Chinese Han family with IIN with an implementation of a next‐generation sequencing method. Isolated DNA analysis was followed by Sanger sequencing validation. We also performed the detailed ophthalmological examination of family members.

Results

We identified a novel frameshift variant in FRMD7 (NM_194277.2: c.1419_1422dup, p.Tyr475fs), which leads to a frameshift mutation since tyrosine (Tyr) at 475 codon of FRMD7 protein (p.Tyr475fs) and co‐segregates with IIN phenotype in this family.

Conclusions

We found a novel frameshift FRMD7 variant in a Chinese Han family, which may be causative variant for IIN and can further enrich the mutation spectrum and uncover the etiology of IIN.

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 Disease-Causing FRMD7 Variant in a Chinese Family with Infantile Nystagmus

In this report, we described a large Han-Chinese family which presents with various phenotypes from unaffected to manifested nystagmus in females. Infantile nystagmus (IN) is characterized by bilateral, involuntary, and periodic eyeball oscillation, occurring at birth or within the first 6 months. The most common inheritance pattern of IN is an X-linked form with incomplete penetrance among females, and the FERM domain containing 7 gene (FRMD7) is a main disease-causing gene. A combination of exome sequencing and Sanger sequencing, as well as detailed clinical examinations were performed on the Chinese IN family. An FRMD7 c.47T>C (p.Phe16Ser) variant was proposed as the disease-causing variant. Incomplete penetrance was found in females with the FRMD7 c.47T>C variant, and hemizygous male affected subjects presented more severe manifestations compared to heterozygous female affected subjects. These findings could enhance genetic counseling and antenatal diagnosis of IN.

Identification of a GNE homozygous mutation in a Han-Chinese family with GNE myopathy

GNE myopathy is a rare, recessively inherited, early adult‐onset myopathy, characterized by distal and proximal muscle degeneration which often spares the quadriceps. It is caused by mutations in the UDP‐N‐acetylglucosamine 2‐epimerase/N‐acetylmannosamine kinase gene (GNE). This study aimed to identify the disease‐causing mutation in a three‐generation Han‐Chinese family with members who have been diagnosed with myopathy. A homozygous missense mutation, c.1627G>A (p.V543M) in the GNE gene co‐segregates with the myopathy present in this family. A GNE myopathy diagnosis is evidenced by characteristic clinical manifestations, rimmed vacuoles in muscle biopsies and the presence of biallelic GNE mutations. This finding broadens the GNE gene mutation spectrum and extends the GNE myopathy phenotype spectrum.

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

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