MEHMO syndrome

Moortgat S, Manfroid I, Pendeville H, Freeman S, Bourdouxhe J, Benoit V, Merhi A, Philippe C, Faivre L, Maystadt I. Broadening the phenotypic spectrum and physiological insights related to EIF2S3 variants. Hum Mutat. 2021 Jul;42(7):827-834. doi: 10.1002/humu.24215. Epub 2021 May 19. PMID: 33942450.

Abstract

Mental deficiency, epilepsy, hypogonadism, microcephaly, and obesity syndrome is a severe X-linked syndrome caused by pathogenic variants in EIF2S3. The gene encodes the γ subunit of the eukaryotic translation initiation factor-2, eIF2, essential for protein translation. A recurrent frameshift variant is described in severely affected patients while missense variants usually cause a moderate phenotype. We identified a novel missense variant (c.433A>G, p.(Met145Val)) in EIF2S3 in a mildly affected patient. Studies on zebrafish confirm the pathogenicity of this novel variant and three previously published missense variants. CRISPR/Cas9 knockout of eif2s3 in zebrafish embryos recapitulate the human microcephaly and show increased neuronal cell death. Abnormal high glucose levels were identified in mutant embryos, caused by beta cell and pancreatic progenitor deficiency, not related to apoptosis. Additional studies in patient-derived fibroblasts did not reveal apoptosis. Our results provide new insights into disease physiopathology, suggesting tissue-dependent mechanisms.

Skopkova M, Hennig F, Shin BS, Turner CE, Stanikova D, Brennerova K, Stanik J, Fischer U, Henden L, Müller U, Steinberger D, Leshinsky-Silver E, Bottani A, Kurdiova T, Ukropec J, Nyitrayova O, Kolnikova M, Klimes I, Borck G, Bahlo M, Haas SA, Kim JR, Lotspeich-Cole LE, Gasperikova D, Dever TE, Kalscheuer VM. EIF2S3 Mutations Associated with Severe X-Linked Intellectual Disability Syndrome MEHMO. Hum Mutat. 2017 Apr;38(4):409-425. doi: 10.1002/humu.23170. Epub 2017 Jan 23. PMID: 28055140; PMCID: PMC6267786.

Abstract

Impairment of translation initiation and its regulation within the integrated stress response (ISR) and related unfolded-protein response has been identified as a cause of several multisystemic syndromes. Here, we link MEHMO syndrome, whose genetic etiology was unknown, to this group of disorders. MEHMO is a rare X-linked syndrome characterized by profound intellectual disability, epilepsy, hypogonadism and hypogenitalism, microcephaly, and obesity. We have identified a C-terminal frameshift mutation (Ile465Serfs) in the EIF2S3 gene in three families with MEHMO syndrome and a novel maternally inherited missense EIF2S3 variant (c.324T>A; p.Ser108Arg) in another male patient with less severe clinical symptoms. The EIF2S3 gene encodes the γ subunit of eukaryotic translation initiation factor 2 (eIF2), crucial for initiation of protein synthesis and regulation of the ISR. Studies in patient fibroblasts confirm increased ISR activation due to the Ile465Serfs mutation and functional assays in yeast demonstrate that the Ile465Serfs mutation impairs eIF2γ function to a greater extent than tested missense mutations, consistent with the more severe clinical phenotype of the Ile465Serfs male mutation carriers. Thus, we propose that more severe EIF2S3 mutations cause the full MEHMO phenotype, while less deleterious mutations cause a milder form of the syndrome with only a subset of the symptoms.

Steinmüller R, Steinberger D, Müller U. MEHMO (mental retardation, epileptic seizures, hypogonadism and -genitalism, microcephaly, obesity), a novel syndrome: assignment of disease locus to xp21.1-p22.13. Eur J Hum Genet. 1998 May-Jun;6(3):201-6. doi: 10.1038/sj.ejhg.5200180. PMID: 9781023.

Abstract

A previously unrecognised X-chromosomal mental retardation syndrome is described. Clinical hallmarks are mental retardation, epileptic seizures, hypogonadism, and -genitalism, microcephaly and obesity. Life expectancy of patients is less than two years. Based on the major clinical symptoms this condition is referred to by the acronym MEHMO. Haplotype and two-point linkage analyses in a large three-generation family assign the disease locus to Xp21.1-p22.13, to a region that is flanked by CYBB and DXS365.

Leshinsky-Silver E, Zinger A, Bibi CN, Barash V, Sadeh M, Lev D, Sagie TL. MEHMO (Mental retardation, Epileptic seizures, Hypogenitalism, Microcephaly, Obesity): a new X-linked mitochondrial disorder. Eur J Hum Genet. 2002 Apr;10(4):226-30. doi: 10.1038/sj.ejhg.5200791. PMID: 12032729.

Abstract

MEHMO (Mental retardation, Epileptic seizures, Hypogenitalism, Microcephaly and Obesity) is an X-linked disorder characterised by mental retardation, epileptic seizures, hypogenitalism, microcephaly and obesity. It was recently assigned to the locus Xp21.1-p22.13. We describe a child with MEHMO and lactic acidosis whose muscle biopsy revealed markedly reduced activities of complexes 1,3 and 4 of the mitochondrial electron transport chain. Histological staining showed mitochondrial proliferation and lipid storage. Electron microscopy revealed abnormal and enlarged mitochondria with concentric cristae and electron dense bodies. This is the first identification of MEHMO as a mitochondrial disorder and one of the very few X-linked mitochondrial syndromes.