NEXMIF encephalopathy

Inspired by a patient

Stamberger H, Hammer TB, Gardella E, Vlaskamp DRM, Bertelsen B, Mandelstam S, de Lange I, Zhang J, Myers CT, Fenger C, Afawi Z, Almanza Fuerte EP, Andrade DM, Balcik Y, Ben Zeev B, Bennett MF, Berkovic SF, Isidor B, Bouman A, Brilstra E, Busk ØL, Cairns A, Caumes R, Chatron N, Dale RC, de Geus C, Edery P, Gill D, Granild-Jensen JB, Gunderson L, Gunning B, Heimer G, Helle JR, Hildebrand MS, Hollingsworth G, Kharytonov V, Klee EW, Koeleman BPC, Koolen DA, Korff C, Küry S, Lesca G, Lev D, Leventer RJ, Mackay MT, Macke EL, McEntagart M, Mohammad SS, Monin P, Montomoli M, Morava E, Moutton S, Muir AM, Parrini E, Procopis P, Ranza E, Reed L, Reif PS, Rosenow F, Rossi M, Sadleir LG, Sadoway T, Schelhaas HJ, Schneider AL, Shah K, Shalev R, Sisodiya SM, Smol T, Stumpel CTRM, Stuurman K, Symonds JD, Mau-Them FT, Verbeek N, Verhoeven JS, Wallace G, Yosovich K, Zarate YA, Zerem A, Zuberi SM, Guerrini R, Mefford HC, Patel C, Zhang YH, Møller RS, Scheffer IE. NEXMIF encephalopathy: an X-linked disorder with male and female phenotypic patterns. Genet Med. 2021 Feb;23(2):363-373. doi: 10.1038/s41436-020-00988-9. Epub 2020 Nov 4. PMID: 33144681.

Abstract

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.

Cioclu MC, Coppola A, Tondelli M, Vaudano AE, Giovannini G, Krithika S, Iacomino M, Zara F, Sisodiya SM, Meletti S. Cortical and Subcortical Network Dysfunction in a Female Patient With NEXMIF Encephalopathy. Front Neurol. 2021 Sep 9;12:722664. doi: 10.3389/fneur.2021.722664. PMID: 34566868; PMCID: PMC8459922.

Abstract

The developmental and epileptic encephalopathies (DEE) are the most severe group of epilepsies. Recently, NEXMIF mutations have been shown to cause a DEE in females, characterized by myoclonic-atonic epilepsy and recurrent nonconvulsive status. Here we used advanced neuroimaging techniques in a patient with a novel NEXMIF de novo mutation presenting with recurrent absence status with eyelid myoclonia, to reveal brain structural and functional changes that can bring the clinical phenotype to alteration within specific brain networks. Indeed, the alterations found in the patient involved the visual pericalcarine cortex and the middle frontal gyrus, regions that have been demonstrated to be a core feature in epilepsy phenotypes with visual sensitivity and eyelid myoclonia with absences.

Panda PK, Sharawat IK, Joshi K, Dawman L, Bolia R. Clinical spectrum of KIAA2022/NEXMIF pathogenic variants in males and females: Report of three patients from Indian kindred with a review of published patients. Brain Dev. 2020 Oct;42(9):646-654. doi: 10.1016/j.braindev.2020.06.005. Epub 2020 Jun 27. PMID: 32600841.

Abstract

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.