Inspired by a patient
Abstract
Macroautophagy/autophagy is an evolutionarily highly conserved catabolic process that is important for the clearance of cytosolic contents to maintain cellular homeostasis and survival. Recent findings point toward a critical role for autophagy in brain function, not only by preserving neuronal health, but especially by controlling different aspects of neuronal development and functioning. In line with this, mutations in autophagy-related genes are linked to various key characteristics and symptoms of neurodevelopmental disorders (NDDs), including autism, micro-/macrocephaly, and epilepsy. However, the group of NDDs caused by mutations in autophagy-related genes is relatively small. A significant proportion of NDDs are associated with mutations in genes encoding epigenetic regulatory proteins that modulate gene expression, so-called chromatinopathies. Intriguingly, several of the NDD-linked chromatinopathy genes have been shown to regulate autophagy-related genes, albeit in non-neuronal contexts. From these studies it becomes evident that tight transcriptional regulation of autophagy-related genes is crucial to control autophagic activity. This opens the exciting possibility that aberrant autophagic regulation might underly nervous system impairments in NDDs with disturbed epigenetic regulation. We here summarize NDD-related chromatinopathy genes that are known to regulate transcriptional regulation of autophagy-related genes. Thereby, we want to highlight autophagy as a candidate key hub mechanism in NDD-related chromatinopathies.Abbreviations: ADNP: activity dependent neuroprotector homeobox; ASD: autism spectrum disorder; ATG: AutTophaGy related; CpG: cytosine-guanine dinucleotide; DNMT: DNA methyltransferase; EHMT: euchromatic histone lysine methyltransferase; EP300: E1A binding protein p300; EZH2: enhancer of zeste 2 polycomb repressive complex 2 subunit; H3K4me3: histone 3 lysine 4 trimethylation; H3K9me1/2/3: histone 3 lysine 9 mono-, di-, or trimethylation; H3K27me2/3: histone 3 lysine 27 di-, or trimethylation; hiPSCs: human induced pluripotent stem cells; HSP: hereditary spastic paraplegia; ID: intellectual disability; KANSL1: KAT8 regulatory NSL complex subunit 1; KAT8: lysine acetyltransferase 8; KDM1A/LSD1: lysine demethylase 1A; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; MTOR: mechanistic target of rapamycin kinase; MTORC1: mechanistic target of rapamycin complex 1; NDD: neurodevelopmental disorder; PHF8: PHD finger protein 8; PHF8-XLID: PHF8-X linked intellectual disability syndrome; PTM: post-translational modification; SESN2: sestrin 2; YY1: YY1 transcription factor; YY1AP1: YY1 associated protein 1.
Koemans TS, Kleefstra T, Chubak MC, Stone MH, Reijnders MRF, de Munnik S, Willemsen MH, Fenckova M, Stumpel CTRM, Bok LA, Sifuentes Saenz M, Byerly KA, Baughn LB, Stegmann APA, Pfundt R, Zhou H, van Bokhoven H, Schenck A, Kramer JM. Functional convergence of histone methyltransferases EHMT1 and KMT2C involved in intellectual disability and autism spectrum disorder. PLoS Genet. 2017 Oct 25;13(10):e1006864. doi: 10.1371/journal.pgen.1006864. PMID: 29069077; PMCID: PMC5656305.
Abstract
Kleefstra syndrome, caused by haploinsufficiency of euchromatin histone methyltransferase 1 (EHMT1), is characterized by intellectual disability (ID), autism spectrum disorder (ASD), characteristic facial dysmorphisms, and other variable clinical features. In addition to EHMT1 mutations, de novo variants were reported in four additional genes (MBD5, SMARCB1, NR1I3, and KMT2C), in single individuals with clinical characteristics overlapping Kleefstra syndrome. Here, we present a novel cohort of five patients with de novo loss of function mutations affecting the histone methyltransferase KMT2C. Our clinical data delineates the KMT2C phenotypic spectrum and reinforces the phenotypic overlap with Kleefstra syndrome and other related ID disorders. To elucidate the common molecular basis of the neuropathology associated with mutations in KMT2C and EHMT1, we characterized the role of the Drosophila KMT2C ortholog, trithorax related (trr), in the nervous system. Similar to the Drosophila EHMT1 ortholog, G9a, trr is required in the mushroom body for short term memory. Trr ChIP-seq identified 3371 binding sites, mainly in the promoter of genes involved in neuronal processes. Transcriptional profiling of pan-neuronal trr knockdown and G9a null mutant fly heads identified 613 and 1123 misregulated genes, respectively. These gene sets show a significant overlap and are associated with nearly identical gene ontology enrichments. The majority of the observed biological convergence is derived from predicted indirect target genes. However, trr and G9a also have common direct targets, including the Drosophila ortholog of Arc (Arc1), a key regulator of synaptic plasticity. Our data highlight the clinical and molecular convergence between the KMT2 and EHMT protein families, which may contribute to a molecular network underlying a larger group of ID/ASD-related disorders.
Bock I, Németh K, Pentelényi K, Balicza P, Balázs A, Molnár MJ, Román V, Nagy J, Lévay G, Kobolák J, Dinnyés A. Targeted next generation sequencing of a panel of autism-related genes identifies an EHMT1 mutation in a Kleefstra syndrome patient with autism and normal intellectual performance. Gene. 2016 Dec 31;595(2):131-141. doi: 10.1016/j.gene.2016.09.027. Epub 2016 Sep 17. PMID: 27651234.
Abstract
Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder with unknown genetic and environmental causation in most of the affected individuals. On the other hand, there are a growing number of ASD-associated syndromes, where the exact genetic origin can be revealed. Here we report a method, which included the targeted next generation sequencing (NGS) and filtering of 101 ASD associated genes, followed by database search. Next, RNA sequencing was used to study the region of interest at the transcriptional level. Using this workflow, we identified a de novo mutation in the euchromatic histone-lysine N-methyltransferase 1 gene (EHMT1) of an autistic patient with dysmorphisms. Sequencing of EHMT1 transcripts showed that the premature termination codon (Trp1138Ter) created by a single nucleotide change elicited nonsense-mediated mRNA decay, which led to haploinsufficiency already at the transcriptional level. Database and literature search provided evidence that this mutation caused Kleefstra syndrome (KS), which was confirmed by the presence of the disorder-specific phenotype in the patient. We provide a proof of principle that the implemented method is capable to elucidate the genetic etiology of individuals with syndromic autism. The novel mutation detected in the EHMT1 gene is responsible for KS's symptoms. In addition, further genetic factors might be involved in the ASD pathogenesis of the patient including a missense DPP6 mutation (Arg322Cys), which segregated with the autistic phenotype within the family.
Blackburn PR, Tischer A, Zimmermann MT, Kemppainen JL, Sastry S, Knight Johnson AE, Cousin MA, Boczek NJ, Oliver G, Misra VK, Gavrilova RH, Lomberk G, Auton M, Urrutia R, Klee EW. A Novel Kleefstra Syndrome-associated Variant That Affects the Conserved TPLX Motif within the Ankyrin Repeat of EHMT1 Leads to Abnormal Protein Folding. J Biol Chem. 2017 Mar 3;292(9):3866-3876. doi: 10.1074/jbc.M116.770545. Epub 2017 Jan 5. PMID: 28057753; PMCID: PMC5339767.
Abstract
Kleefstra syndrome (KS) (Mendelian Inheritance in Man (MIM) no. 610253), also known as 9q34 deletion syndrome, is an autosomal dominant disorder caused by haploinsufficiency of euchromatic histone methyltransferase-1 (EHMT1). The clinical phenotype of KS includes moderate to severe intellectual disability with absent speech, hypotonia, brachycephaly, congenital heart defects, and dysmorphic facial features with hypertelorism, synophrys, macroglossia, protruding tongue, and prognathism. Only a few cases of de novo missense mutations in EHMT1 giving rise to KS have been described. However, some EHMT1 variants have been described in individuals presenting with autism spectrum disorder or mild intellectual disability, suggesting that the phenotypic spectrum resulting from EHMT1 alterations may be quite broad. In this report, we describe two unrelated patients with complex medical histories consistent with KS in whom next generation sequencing identified the same novel c.2426C>T (p.P809L) missense variant in EHMT1 To examine the functional significance of this novel variant, we performed molecular dynamics simulations of the wild type and p.P809L variant, which predicted that the latter would have a propensity to misfold, leading to abnormal histone mark binding. Recombinant EHMT1 p.P809L was also studied using far UV circular dichroism spectroscopy and intrinsic protein fluorescence. These functional studies confirmed the model-based hypotheses and provided evidence for protein misfolding and aberrant target recognition as the underlying pathogenic mechanism for this novel KS-associated variant. This is the first report to suggest that missense variants in EHMT1 that lead to protein misfolding and disrupted histone mark binding can lead to KS.
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