Torpedo Maculopathy Associated with NEXMIF Mutation

NEXMIF variants are associated with epilepsy with or without intellectual disability

OBJECTIVES

Variants in NEXMIF had been reported associated with intellectual disability (ID) without epilepsy or developmental epileptic encephalopathy (DEE). It is unkown whether NEXMIF variants are associated with epilepsy without ID. This study aims to explore the phenotypic spectrum of NEXMIF and the genotype-phenotype correlations.

MATERIALS AND METHODS

Trio-based whole-exome sequencing was performed in patients with epilepsy. Previously reported NEXMIF variants were systematically reviewed to analyze the genotype-phenotype correlations.

RESULTS

Six variants were identified in seven unrelated cases with epilepsy, including two de novo null variants and four hemizygous missense variants. The two de novo variants were absent in all populations of gnomAD and four hemizygous missense variants were absent in male controls of gnomAD. The two patients with de novo null variants exhibited severe developmental epileptic encephalopathy. While, the patients with hemizygous missense variants had mild focal epilepsy with favorable outcome. Analysis of previously reported cases revealed that males with missense variants presented significantly higher percentage of normal intellectual development and later onset age of seizure than those with null variants, indicating a genotype-phenotype correlation.

CONCLUSION

This study suggested that NEXMIF variants were potentially associated with pure epilepsy with or without intellectual disability. The spectrum of epileptic phenotypes ranged from the mild epilepsy to severe developmental epileptic encephalopathy, where the epileptic phenotypes variability are potentially associated with patients' gender and variant type.

Heterozygous Nexmif female mice demonstrate mosaic NEXMIF expression, autism-like behaviors, and abnormalities in dendritic arborization and synaptogenesis

Autism spectrum disorder (ASD) is a neurodevelopmental disorder with a strong genetic basis. ASDs are commonly characterized by impairments in language, restrictive and repetitive behaviors, and deficits in social interactions. Although ASD is a highly heterogeneous disease with many different genes implicated in its etiology, many ASD-associated genes converge on common cellular defects, such as aberrant neuronal morphology and synapse dysregulation. Our previous work revealed that, in mice, complete loss of the ASD-associated X-linked gene NEXMIF results in a reduction in dendritic complexity, a decrease in spine and synapse density, altered synaptic transmission, and ASD-like behaviors. Interestingly, human females of NEXMIF haploinsufficiency have recently been reported to demonstrate autistic features; however, the cellular and molecular basis for this haploinsufficiency-caused ASD remains unclear. Here we report that in the brains of Nexmif± female mice, NEXMIF shows a mosaic pattern in its expression in neurons. Heterozygous female mice demonstrate behavioral impairments similar to those of knockout male mice. In the mosaic mixture of neurons from Nexmif± mice, cells that lack NEXMIF have impairments in dendritic arborization and spine development. Remarkably, the NEXMIF-expressing neurons from Nexmif± mice also demonstrate similar defects in dendritic growth and spine formation. These findings establish a novel mouse model of NEXMIF haploinsufficiency and provide new insights into the pathogenesis of NEXMIF-dependent ASD.

Infantile spasms caused by NEXMIF mutation: A case report and literature review

BACKGROUND

Infantile spasms are rare epileptic syndromes associated with neurodevelopment and genes. The NEXMIF gene, identified as KIDLIA, KIAA2022 or Xpn, is a gene of unknown biological identity located on the q13.2 X chromosome.

CASE DESCRIPTION

We presented a 4-month-old infant with a diagnosis of infantile spasms with NEXMIF mutation. Clinical manifestations include psychomotor retardation, loss of consciousness, and seizures. After oral therapy with vigabatrin, sodium valproate, and levetiracetam, the syndrome was alleviated and no recurrence was observed during one month of follow-up.

CONCLUSIONS

A loss-of-function mutation in the NEXMIF gene has been reported. There are few reports on this mutation worldwide. This study provides a new idea for the clinical treatment of infantile spasms.

NEXMIF mutations in intellectual disability and epilepsy: A report of 2 cases and literature review

More than 100 genes located on the X chromosome have been found to be associated with X-linked intellectual disability (XLID) to date, and NEXMIF is a pathogenic gene for XLID. In addition to intellectual disability, patients with NEXMIF gene mutation can also have other neurological symptoms, such as epilepsy, abnormal behavior, and hypotonia, as well as abnormalities of other systems. Two children with intellectual disability and epilepsy caused by NEXMIF gene mutation were treated in the Department of Pediatrics, Xiangya Hospital, Central South University from March 8, 2017 to June 20, 2020. Patient 1, a 7 years and 8 months old girl, visited our department because of the delayed psychomotor development. Physical examination revealed strabismus (right eye), hyperactivity, and loss of concentration. Intelligence test showed a developmental quotient of 43.6. Electroencephalogram showed abnormal discharge, and cranial imaging appeared normal. Whole exome sequencing revealed a de novo heterozygous mutation, c.2189delC (p.S730Lfs*17) in the NEXMIF gene (NM_001008537). During the follow-up period, the patient developed epileptic seizures, mainly manifested as generalized and absent seizures. She took the medicine of levetiracetam and lamotrigine, and the seizures were under control. Patient 2, a 6-months old boy, visited our department due to developmental regression and seizures. He showed poor reactions to light and sound, and was not able to raise head without aid. Hypotonia was also noticed. The electroencephalogram showed intermittent hyperarrhythmia, and spasms were monitored. He was given topiramate and adrenocorticotrophic hormone (ACTH). Whole exome sequencing detected a de novo c.592C>T (Q198X) mutation in NEXMIF gene. During the follow-up period, the seizures were reduced with vigabatrin. He had no obvious progress in the psychomotor development, and presented strabismus. There were 91 cases reported abroad, 1 case reported in China, and 2 patients were included in this study. A total of 85 variants in NEXMIF gene were found, involving 83 variants reported in PubMed and HGMD, and the 2 new variants presented in our patients. The patients with variants in NEXMIF gene all had mild to severe intellectual disability. Behavioral abnormalities, epilepsy, hypotonia, and other neurological symptoms are frequently presented. The phenotype of male partially overlaps with that of female. Male patients often have more severe intellectual disability, impaired language, and autistic features, while female patients often have refractory epilepsy. Most of the variants reported so far were loss-of-function resulted in the reduced protein expression of NEXMIF. The degree of NEXMIF loss appears to correlate with the severity of the phenotype.

Clinical evaluation of torpedo maculopathy in an infant population with additional genetic testing for NEXMIF mutation

PURPOSE

To assess clinical characteristics of torpedo maculopathy (TM) lesions in an infant population with age ≤1.5 years and to investigate the role of NEXMIF mutation in the development of TM.

METHODS

Retrospective analysis of medical records of 17 consecutive infants with the diagnosis of TM between 2016 January and 2019 December were done. Fundus images and a hand-held spectral-domain optical coherence tomography (Envisu 2300, Bioptigen, Morrisville, NC, USA) were used to identify clinical characteristics of TM lesions. Additional molecular testing for mutation screening for NEXMIF gene was also carried out.

RESULTS

Totally 55334 infants were screened during the study period and 17 (0.03%) were identified as having TM. The mean age at the time of diagnosis was 3.94±5.08 months. All TM lesions showed variable degrees of hypopigmentation. Satellite lesion in one infant was nasally located to the main TM lesion. Absence, disruption, loss, degeneration and/or irregularity of the ellipsoid zone were common findings on OCT examination. No pathogenic or likely pathogenic variant of NEXMIF gene was detected.

CONCLUSION

Fundoscopic appearance and OCT findings of lesions show similarities to those already reported previously. Contrary to popular belief, a nasally located satellite lesion was observed in one of our case.

Coexistence of torpedo maculopathy and retinoblastoma: Differentiation the lesions with hand-held optical coherence tomography

Torpedo maculopathy (TM) is a rare congenital defect of the retina pigment epithelium, which always localizes to the temporal fovea. It is most commonly unilateral and often occurs in patients without any relevant disease. Classic finding is a flat, hypopigmented, oval lesion, resembling a 'torpedo,' with a wedge-shaped tail extending outward and directed toward the foveola. Visual acuity is generally unaffected due to the central fovea is not involved and this lesions remain stable. Therefore, when it accompanied with a posterior segment disease, we should make differential diagnosis to avoid unnecessary treatment. Herein, we present a child with coexistence of TM and retinoblastoma, and how to manage the lesions. We aimed to alert the ophthalmologists to this unusual combination for avoiding unnecessary treatment modalities. To the best of our knowledge, this combination that has never before been described.

NEXMIF encephalopathy: an X-linked disorder with male and female phenotypic patterns

PURPOSE

Pathogenic variants in the X-linked gene NEXMIF (previously KIAA2022) are associated with intellectual disability (ID), autism spectrum disorder, and epilepsy. We aimed to delineate the female and male phenotypic spectrum of NEXMIF encephalopathy.

METHODS

Through an international collaboration, we analyzed the phenotypes and genotypes of 87 patients with NEXMIF encephalopathy.

RESULTS

Sixty-three females and 24 males (46 new patients) with NEXMIF encephalopathy were studied, with 30 novel variants. Phenotypic features included developmental delay/ID in 86/87 (99%), seizures in 71/86 (83%) and multiple comorbidities. Generalized seizures predominated including myoclonic seizures and absence seizures (both 46/70, 66%), absence with eyelid myoclonia (17/70, 24%), and atonic seizures (30/70, 43%). Males had more severe developmental impairment; females had epilepsy more frequently, and varied from unaffected to severely affected. All NEXMIF pathogenic variants led to a premature stop codon or were deleterious structural variants. Most arose de novo, although X-linked segregation occurred for both sexes. Somatic mosaicism occurred in two males and a family with suspected parental mosaicism.

CONCLUSION

NEXMIF encephalopathy is an X-linked, generalized developmental and epileptic encephalopathy characterized by myoclonic-atonic epilepsy overlapping with eyelid myoclonia with absence. Some patients have developmental encephalopathy without epilepsy. Males have more severe developmental impairment. NEXMIF encephalopathy arises due to loss-of-function variants.

Clinical spectrum of KIAA2022/NEXMIF pathogenic variants in males and females: Report of three patients from Indian kindred with a review of published patients

BACKGROUND

In the last two decades, with the advent of whole-exome and whole-genome sequencing, supplemented with linkage analysis, more than 150 genes responsible for X-linked intellectual disability have been identified. Some genes like NEXMIF remain an enigmatic entity, as often the carrier females show wide phenotypic diversity ranging from completely asymptomatic to severe intellectual disability and drug-resistant epilepsy.

METHODS

We report three patients with pathogenic NEXMIF variants from an Indian family. All of them had language predominant developmental delay and later progressed to moderate intellectual disability with autistic features. We also reviewed the previously published reports of patients with pathogenic NEXMIF variants.

RESULTS

Together with the presented cases, 45 cases (24 symptomatic females) were identified from 15 relevant research items for analysis. Males have demonstrated a more severe intellectual disability and increasingly delayed walking age, autistic features, central hypotonia, and gastroesophageal reflux. In contrast, females have shown a predominant presentation with drug-resistant epilepsy and mild to moderate intellectual impairment. Notably, the affected females demonstrate a higher incidence of myoclonic, absence, and atonic seizures. The majority of the variants reported are nonsense or frameshift mutations, causing loss of function of the NEXMIF gene, while a considerable proportion possesses chromosomal translocations, microdeletions, and duplications.

CONCLUSIONS

NEXMIF gene mutations should be suspected in all cases of X-linked ID and autism cases in males or even in refractory epilepsy cases in females.

Clonazepam as an Effective Treatment for Epilepsy in a Female Patient with NEXMIF Mutation: Case Report

The NEXMIF (KIAA2022) gene is located in the X chromosome, and hemizygous mutations in NEXMIF cause X-linked intellectual disability in male patients. Female patients with heterozygous mutations in NEXMIF also show similar, but milder, intellectual disability. Most female patients demonstrate intractable epilepsy compared with male patients, and the treatment strategy for epilepsy is still uncertain. Thus far, 24 female patients with NEXMIF mutations have been reported. Of these 24 patients, 20 also have epilepsy. Until now, epilepsy has been controlled in only 2 of these female patients. We report a female patient with a heterozygous de novo mutation, NM_001008537.2:c.1123del (p.Glu375Argfs*21), in NEXMIF. The patient showed mild intellectual disability, facial dysmorphism, obesity, generalized tonic-clonic seizures, and nonconvulsive status epilepticus. Sodium valproate was effective but caused secondary amenorrhea. We successfully treated her epilepsy with clonazepam without side effects, indicating that clonazepam might be a good choice to treat epilepsy in patients with NEXMIF mutations.

NEXMIF/KIDLIA Knock-out Mouse Demonstrates Autism-Like Behaviors, Memory Deficits, and Impairments in Synapse Formation and Function

Autism spectrum disorder (ASD) is a heterogeneous neurodevelopmental disability that demonstrates impaired social interactions, communication deficits, and restrictive and repetitive behaviors. ASD has a strong genetic basis and many ASD-associated genes have been discovered thus far. Our previous work has shown that loss of expression of the X-linked gene NEXMIF/KIDLIA is implicated in patients with autistic features and intellectual disability (ID). To further determine the causal role of the gene in the disorder, and to understand the cellular and molecular mechanisms underlying the pathology, we have generated a NEXMIF knock-out (KO) mouse. We find that male NEXMIF KO mice demonstrate reduced sociability and communication, elevated repetitive grooming behavior, and deficits in learning and memory. Loss of NEXMIF/KIDLIA expression results in a significant decrease in synapse density and synaptic protein expression. Consistently, male KO animals show aberrant synaptic function as measured by excitatory miniatures and postsynaptic currents in the hippocampus. These findings indicate that NEXMIF KO mice recapitulate the phenotypes of the human disorder. The NEXMIF KO mouse model will be a valuable tool for studying the complex mechanisms involved in ASD and for the development of novel therapeutics for this disorder.SIGNIFICANCE STATEMENT Autism spectrum disorder (ASD) is a heterogeneous neurodevelopmental disorder characterized by behavioral phenotypes. Based on our previous work, which indicated the loss of NEXMIF/KIDLIA was associated with ASD, we generated NEXMIF knock-out (KO) mice. The NEXMIF KO mice demonstrate autism-like behaviors including deficits in social interaction, increased repetitive self-grooming, and impairments in communication and in learning and memory. The KO neurons show reduced synapse density and a suppression in synaptic transmission, indicating a role for NEXMIF in regulating synapse development and function. The NEXMIF KO mouse faithfully recapitulates the human disorder, and thus serves as an animal model for future investigation of the NEXMIF-dependent neurodevelopmental disorders.