Studies in Drosophila help implicate a variant in the human MTSS2/MTSS1L gene in a a syndromic form of intellectual disability

Am J Hum Genet. 2022 Oct 6;109(10):1923-1931. doi: 10.1016/j.ajhg.2022.08.011

The recurrent de novo c.2011C>T missense variant in MTSS2 causes syndromic intellectual disability

Huang Y, Lemire G, Briere LC, Liu F, Wessels MW, Wang X, Osmond M, Kanca O, Lu S, High FA, Walker MA, Rodan LH; Undiagnosed Diseases Network; Care4Rare Canada Consortium, Kernohan KD, Sweetser DA, Boycott KM, Bellen HJ

Abstract:

MTSS2, also known as MTSS1L, binds to plasma membranes and modulates their bending. MTSS2 is highly expressed in the central nervous system (CNS) and appears to be involved in activity-dependent synaptic plasticity. Variants in MTSS2 have not yet been associated with a human phenotype in OMIM. Here we report five individuals with the same heterozygous de novo variant in MTSS2 (GenBank: NM_138383.2: c.2011C>T [p.Arg671Trp]) identified by exome sequencing. The individuals present with global developmental delay, mild intellectual disability, ophthalmological anomalies, microcephaly or relative microcephaly, and shared mild facial dysmorphisms. Immunoblots of fibroblasts from two affected individuals revealed that the variant does not significantly alter MTSS2 levels. We modeled the variant in Drosophila and showed that the fly ortholog missing-in-metastasis (mim) was widely expressed in most neurons and a subset of glia of the CNS. Loss of mim led to a reduction in lifespan, impaired locomotor behavior, and reduced synaptic transmission in adult flies. Expression of the human MTSS2 reference cDNA rescued the mim loss-of-function (LoF) phenotypes, whereas the c.2011C>T variant had decreased rescue ability compared to the reference, suggesting it is a partial LoF allele. However, elevated  expression of the variant, but not the reference MTSS2 cDNA, led to similar defects as observed by mim LoF, suggesting that the variant is toxic and may act as a dominant-negative allele when expressed in flies. In summary, our findings support that mim is important for appropriate neural function, and that the MTSS2 c.2011C>T variant causes a syndromic form of intellectual disability.

DOI: 10.1016/j.ajhg.2022.08.011
PMID: 36067766

Drosophila studies contribute to a study associating variants of PP2A/PPP2R4 with juvenile-onset parkinsonism

Brain. 2022 Sep 8:awac326. doi: 10.1093/brain/awac326 

PTPA variants and impaired PP2A activity in early-onset parkinsonism with
intellectual disability

Fevga C, Tesson C, Mascaro AC, Courtin T, van Coller R, Sakka S, Ferraro F, Farhat N, Bardien S, Damak M, Carr J, Ferrien M, Boumeester V, Hundscheid J, Grillenzoni N, Kessissoglou IA, Kuipers DJS, Quadri M; French and Mediterranean Parkinson disease Genetics Study Group; International Parkinsonism Genetics Network, Corvol JC, Mhiri C, Hassan BA, Breedveld GJ, Lesage S, Mandemakers W, Brice A, Bonifati V

Abstract:

The protein phosphatase 2A complex (PP2A), the major Ser/Thr phosphatase in the brain, is involved in a number of signaling pathways and functions, including the regulation of crucial proteins for neurodegeneration, such as alpha-synuclein, tau, and LRRK2. Here, we report the identification of variants in the PTPA/PPP2R4 gene, encoding a major PP2A activator, in two families with early-onset parkinsonism and intellectual disability. We carried out clinical studies and genetic analyses, including genome-wide linkage analysis, whole-exome sequencing, and Sanger sequencing of candidate variants. We next performed functional studies on the disease-associated variants in cultured cells and knock-down of ptpa in Drosophila melanogaster. We first identified a homozygous PTPA variant, c.893T > G (p.Met298Arg), in patients from a South African family with early-onset parkinsonism and intellectual disability. Screening of a large series of additional families yielded a second homozygous variant, c.512C > A (p.Ala171Asp), in a Libyan family with a similar phenotype. Both variants co-segregate with disease in the respective families. The affected subjects display juvenile-onset parkinsonism and intellectual disability. The motor symptoms were responsive to treatment with levodopa and deep brain stimulation of the subthalamic nucleus. In overexpression studies, both the PTPA p.Ala171Asp and p.Met298Arg variants were associated with decreased PTPA RNA stability and decreased PTPA protein levels; the p.Ala171Asp variant additionally displayed decreased PTPA protein stability. Crucially, expression of both variants was associated with decreased PP2A complex levels and impaired PP2A phosphatase activation. PTPA ortholog knock-down in Drosophila neurons induced a significant impairment of locomotion in the climbing test. This defect was age-dependent and fully reversed by L-DOPA treatment. We conclude that bi-allelic missense PTPA variants associated with impaired activation of the PP2A phosphatase cause autosomal recessive early-onset parkinsonism with intellectual disability. Our findings might also provide new insights for understanding the role of the PP2A complex in the pathogenesis of more common forms of neurodegeneration.

DOI: 10.1093/brain/awac326
PMID: 36073231

Drosophila studies contribute to identification of a novel disease-associated gene, ZMYND8

Genet Med. 2022 Sep;24(9):1952-1966. doi: 10.1016/j.gim.2022.06.001

De Novo ZMYND8 variants result in an autosomal dominant neurodevelopmental
disorder with cardiac malformations

Dias KR, Carlston CM, Blok LER, De Hayr L, Nawaz U, Evans CA, Bayrak-Toydemir P, Htun S, Zhu Y, Ma A, Lynch SA, Moorwood C, Stals K, Ellard S, Bainbridge MN, Friedman J, Pappas JG, Rabin R, Nowak CB, Douglas J, Wilson TE, Guillen Sacoto MJ, Mullegama SV, Palculict TB, Kirk EP, Pinner JR, Edwards M, Montanari F, Graziano C, Pippucci T, Dingmann B, Glass I, Mefford HC, Shimoji T, Suzuki T, Yamakawa K, Streff H, Schaaf CP, Slavotinek AM, Voineagu I, Carey JC, Buckley MF, Schenck A, Harvey RJ, Roscioli T

Abstract:

PURPOSE: ZMYND8 encodes a multidomain protein that serves as a central interactive hub for coordinating critical roles in transcription regulation, chromatin remodeling, regulation of super-enhancers, DNA damage response and tumor suppression. We delineate a novel neurocognitive disorder caused by variants in the ZMYND8 gene. 

METHODS: An international collaboration, exome sequencing, molecular modeling, yeast two-hybrid assays, analysis of available transcriptomic data and a knockdown Drosophila model were used to characterize the ZMYND8 variants. 

RESULTS: ZMYND8 variants were identified in 11 unrelated individuals; 10 occurred de novo and one suspected de novo; 2 were truncating, 9 were missense, of which one was recurrent. The disorder is characterized by intellectual disability with variable cardiovascular, ophthalmologic and minor skeletal anomalies. Missense variants in the PWWP domain of ZMYND8 abolish the interaction with Drebrin and missense variants in the MYND domain disrupt the interaction with GATAD2A. ZMYND8 is broadly expressed across cell types in all brain regions and shows highest expression in the early stages of brain development. Neuronal knockdown of the Drosophila ZMYND8 ortholog results in decreased habituation learning, consistent with a role in cognitive function. 

CONCLUSION: We present genomic and functional evidence for disruption of ZMYND8 as a novel etiology of syndromic intellectual disability.

DOI: 10.1016/j.gim.2022.06.001
PMID: 35916866

Drosophila studies contribute to understanding impact of a variant of MTSS2 associated with intellectual disability

Am J Hum Genet. 2022 Aug 30:S0002-9297(22)00363-9. doi: 10.1016/j.ajhg.2022.08.011.

The recurrent de novo c.2011C>T missense variant in MTSS2 causes syndromic intellectual disability.

Huang Y, Lemire G, Briere LC, Liu F, Wessels MW, Wang X, Osmond M, Kanca O, Lu S, High FA, Walker MA, Rodan LH; Undiagnosed Diseases Network; Care4Rare Canada Consortium, Kernohan KD(, Sweetser DA, Boycott KM, Bellen HJ

Abstract: MTSS2, also known as MTSS1L, binds to plasma membranes and modulates their bending. MTSS2 is highly expressed in the central nervous system (CNS) and appears to be involved in activity-dependent synaptic plasticity. Variants in MTSS2 have not yet been associated with a human phenotype in OMIM. Here we report five individuals with the same heterozygous de novo variant in MTSS2 (GenBank: NM_138383.2: c.2011C>T [p.Arg671Trp]) identified by exome sequencing. The individuals present with global developmental delay, mild intellectual disability, ophthalmological anomalies, microcephaly or relative microcephaly, and shared mild facial dysmorphisms. Immunoblots of fibroblasts from two affected individuals revealed that the variant does not significantly alter MTSS2 levels. We modeled the variant in Drosophila and showed that the fly ortholog missing-in-metastasis (mim) was widely expressed in most neurons and a subset of glia of the CNS. Loss of mim led to a reduction in lifespan, impaired locomotor behavior, and reduced synaptic transmission in adult flies. Expression of the human MTSS2 reference cDNA rescued the mim loss-of-function (LoF) phenotypes, whereas the c.2011C>T variant had decreased rescue ability compared to the reference, suggesting it is a partial LoF allele. However, elevated expression of the variant, but not the reference MTSS2 cDNA, led to similar defects as observed by mim LoF, suggesting that the variant is toxic and may act as a dominant-negative allele when expressed in flies. In summary, our findings support that mim is important for appropriate neural function, and that the MTSS2 c.2011C>T variant causes a syndromic form of intellectual disability.

DOI: 10.1016/j.ajhg.2022.08.011
PMID: 36067766

Fly study sheds light on function of MEGF8, which is associated with Carpenter Syndrome

J Neurosci. 2022 Aug 9:JN-RM-0442-22. doi: 10.1523/JNEUROSCI.0442-22.2022.

Drosophila Homolog of the Human Carpenter Syndrome Linked Gene, MEGF8, is Required for Synapse Development and Function

Chen S, Venkatesan A, Lin YQ, Xie J, Neely G, Banerjee S, Bhat MA

Abstract: Drosophila Multiple Epidermal Growth Factor-like Domains 8 (dMegf8) is a homolog of human MEGF8. MEGF8 encodes a multi-domain transmembrane protein which is highly conserved across species. In humans, MEGF8 mutations cause a rare genetic disorder called Carpenter syndrome, which is frequently associated with abnormal left-right patterning, cardiac defects and learning disabilities. MEGF8 is also associated with psychiatric disorders. Despite its clinical relevance MEGF8 remains poorly characterized, and though it is highly conserved, studies on animal models of Megf8 are also very limited. The presence of intellectual disabilities in Carpenter syndrome patients and association of MEGF8 with psychiatric disorders indicate that mutations in MEGF8 cause underlying defects in synaptic structure and functions. In this study, we investigated the role of Drosophila dMegf8 in glutamatergic synapses of the larval neuromuscular junctions (NMJ) in both males and females. We show that dMegf8 localizes to NMJ synapses and is required for proper synaptic growth. dMegf8 mutant larvae and adults show severe motor coordination deficits. At the NMJ, dMegf8 mutants show altered localization of pre- and post-synaptic proteins, defects in synaptic ultrastructure and neurotransmission. Interestingly, dMegf8 mutants have reduced levels of the type II BMP receptor Wishful thinking (Wit). dMegf8 displays genetic interactions with neurexin-1 (dnrx) and wit, and in association with Dnrx and Wit plays an essential role in synapse organization. Our studies provide insights into human MEGF8 functions and potentially into mechanisms that may underlie intellectual disabilities observed in Carpenter syndrome as well as MEGF8-related synaptic structural and/or functional deficits in psychiatric disorders.

Significance Statement: Carpenter Syndrome, known for over a century now, is a genetic disorder linked to mutations in Multiple Epidermal Growth Factor-like Domains 8 (MEGF8) gene and associated with intellectual disabilities among other symptoms. MEGF8 is also associated with psychiatric disorders. Despite the high genetic conservation and clinical relevance, the functions of MEGF8 remain largely uncharacterized. Patients with intellectual disabilities and psychiatric diseases often have an underlying defect in synaptic structure and function. This work defines the role of the fly homolog of human MEGF8, dMegf8, in glutamatergic synapse growth, organization and function and provide insights into potential functions of MEGF8 in human central synapses and synaptic mechanisms that may underlie psychiatric disorders and intellectual disabilities seen in Carpenter Syndrome.

Copyright © 2022 the authors.

DOI: 10.1523/JNEUROSCI.0442-22.2022
PMID: 35944997

Two new studies exemplify utility of Drosophila for human genetic disease-related studies

 (1)

Am J Hum Genet. 2022 Apr 7;109(4):571-586. doi: 10.1016/j.ajhg.2022.01.020. Epub
2022 Mar 2.

Loss-of-function variants in TIAM1 are associated with developmental delay,
intellectual disability, and seizures.

Lu et al.

TIAM Rac1-associated GEF 1 (TIAM1) regulates RAC1 signaling pathways that affect the control of neuronal morphogenesis and neurite outgrowth by modulating the actin cytoskeletal network. To date, TIAM1 has not been associated with a Mendelian disorder. Here, we describe five individuals with bi-allelic TIAM1 missense variants who have developmental delay, intellectual disability, speech delay, and seizures. Bioinformatic analyses demonstrate that these variants are rare and likely pathogenic. We found that the Drosophila ortholog of TIAM1, still life (sif), is expressed in larval and adult central nervous system (CNS) and is mainly expressed in a subset of neurons, but not in glia. Loss of sif reduces the survival rate, and the surviving adults exhibit climbing defects,are prone to severe seizures, and have a short lifespan. The TIAM1 reference (Ref) cDNA partially rescues the sif loss-of-function (LoF) phenotypes. We also assessed the function associated with three TIAM1 variants carried by two of the probands and compared them to the TIAM1 Ref cDNA function in vivo. TIAM1 p.Arg23Cys has reduced rescue ability when compared to TIAM1 Ref, suggesting that it is a partial LoF variant. In ectopic expression studies, both wild-type sif and TIAM1 Ref are toxic, whereas the three variants (p.Leu862Phe, p.Arg23Cys, and p.Gly328Val) show reduced toxicity, suggesting that they are partial LoF variants. In summary, we provide evidence that sif is important for appropriate neural function and that TIAM1 variants observed in the probands are disruptive, thus implicating loss of TIAM1 in neurological phenotypes in humans.

Copyright © 2022 American Society of Human Genetics. Published by Elsevier Inc.
All rights reserved.

DOI: 10.1016/j.ajhg.2022.01.020
PMID: 35240055 

Conflict of interest statement: Declaration of interests M.J.G.S. is a salaried employee of GeneDx Inc.

(2)

Am J Hum Genet. 2022 Apr 7;109(4):601-617. doi: 10.1016/j.ajhg.2022.03.002.

Germline variants in tumor suppressor FBXW7 lead to impaired ubiquitination and
a neurodevelopmental syndrome.

Stephenson et al.

Neurodevelopmental disorders are highly heterogenous conditions resulting from abnormalities of brain architecture and/or function. FBXW7 (F-box and WD-repeat-domain-containing 7), a recognized developmental regulator and tumor suppressor, has been shown to regulate cell-cycle progression and cell growth and survival by targeting substrates including CYCLIN E1/2 and NOTCH for degradation via the ubiquitin proteasome system. We used a genotype-first approach and global data-sharing platforms to identify 35 individuals harboring de novo and inherited FBXW7 germline monoallelic chromosomal deletions and nonsense, frameshift, splice-site, and missense variants associated with a neurodevelopmental syndrome. The FBXW7 neurodevelopmental syndrome is distinguished by global developmental delay, borderline to severe intellectual disability, hypotonia, and gastrointestinal issues. Brain imaging detailed variable underlying structural abnormalities affecting the cerebellum, corpus collosum, and white matter. A crystal-structure model of FBXW7 predicted that missense variants were clustered at the substrate-binding surface of the WD40 domain and that these might reduce FBXW7 substrate binding affinity. Expression of recombinant FBXW7 missense variants in cultured cells demonstrated impaired CYCLIN E1 and CYCLIN E2 turnover. Pan-neuronal knockdown of the Drosophila ortholog, archipelago, impaired learning and neuronal function. Collectively, the data presented herein provide compelling evidence of an F-Box protein-related, phenotypically variable neurodevelopmental disorder associated with monoallelic variants in FBXW7.

Copyright © 2022 American Society of Human Genetics. Published by Elsevier Inc.
All rights reserved.

DOI: 10.1016/j.ajhg.2022.03.002
PMID: 35395208

Conflict of interest statement: Declaration of interests I.E.S. has served on scientific advisory boards for UCB, Eisai, GlaxoSmithKline, BioMarin, Nutricia, Rogcon, Chiesi, Encoded Therapeutics, Xenon Pharmaceuticals, and Knopp Biosciences; has received speaker honoraria from GlaxoSmithKline, UCB, BioMarin, Biocodex, and Eisai; has received funding for travel from UCB, Biocodex, GlaxoSmithKline, Biomarin and Eisai; has served as an investigator for Zogenix, Zynerba, Ultragenyx, GW Pharma, UCB, Eisai, Anavex Life Sciences, Ovid Therapeutics, Epygenyx, Encoded Therapeutics and Marinus; and has consulted for Zynerba Pharmaceuticals, Atheneum Partners, Ovid Therapeutics, Care Beyond Diagnosis, Epilepsy Consortium and UCB. She may accrue future revenue on pending patent WO2009/086591; her patent for SCN1A testing is held by Bionomics and is licensed to various diagnostic companies; and she has a patent for a molecular diagnostic/therapeutic target for benign familial infantile epilepsy (BFIE) (PRRT2), WO/2013/059884. She receives and/or has received research support from the National Health and Medical Research Council of Australia, Medical Research Future Fund, Health Research Council of New Zealand, CURE, Australian Epilepsy Research Fund, and the National Institute of Neurological Disorders and Stroke of the National Institutes of Health. J.P. is co-chief scientific officer for Global Gene Corp. All other authors declare no competing interests.

Study looks at molecular mechsnisms underlying circadian rhythm disruption in fly model of Fragile X syndrome

Neurosci Bull. 2021 Apr 15. doi: 10.1007/s12264-021-00682-z.

Dysregulated CRMP Mediates Circadian Deficits in a Drosophila Model of Fragile X Syndrome.

Zhao J, Xue J, Zhu T, He H, Kang H, Jiang X, Huang W, Duan R

Abstract:

Fragile X syndrome (FXS) is the leading inherited cause of intellectual disability, resulting from the lack of functional fragile X mental retardation protein (FMRP), an mRNA binding protein mainly serving as a translational regulator. Loss of FMRP leads to dysregulation of target mRNAs. The Drosophila model of FXS show an abnormal circadian rhythm with disruption of the output pathway downstream of the clock network. Yet the FMRP targets involved in circadian regulation have not been identified. Here, we identified collapsing response mediator protein (CRMP) mRNA as a target of FMRP. Knockdown of pan-neuronal CRMP expression ameliorated the circadian defects and abnormal axonal structures of clock neurons (ventral lateral neurons) in dfmr1 mutant flies. Furthermore, specific reduction of CRMP in the downstream output insulin-producing cells attenuated the aberrant circadian behaviors. Molecular analyses revealed that FMRP binds with CRMP mRNA and negatively regulates its translation. Our results indicate that CRMP is an FMRP target and establish an essential role for CRMP in the circadian output in FXS Drosophila.

DOI: 10.1007/s12264-021-00682-z
PMID: 33856646

Cross-species study helps provide insight on the human gene IQSEC1, variants in which are associated with developmental disease

Ansar M, Chung HL, Al-Otaibi A, Elagabani MN, Ravenscroft TA, Paracha SA, Scholz R, Abdel Magid T, Sarwar MT, Shah SF, Qaisar AA, Makrythanasis P, Marcogliese PC, Kamsteeg EJ, Falconnet E, Ranza E, Santoni FA, Aldhalaan H, Al-Asmari A, Faqeih EA, Ahmed J, Kornau HC, Bellen HJ, Antonarakis SE. Bi-allelic Variants in IQSEC1 Cause Intellectual Disability, Developmental Delay, and Short Stature. Am J Hum Genet. 2019 Nov 7;105(5):907-920. PubMed PMID: 31607425; PubMed Central PMCID: PMC6848997.

From the abstract: "We report two consanguineous families with probands that exhibit intellectual disability, developmental delay, short stature, aphasia, and hypotonia in which homozygous non-synonymous variants were identified in IQSEC1 (GenBank: NM_001134382.3). ... IQSEC1-3 encode guanine nucleotide exchange factors for the small GTPase ARF6 and their loss affects a variety of actin-dependent cellular processes, including AMPA receptor trafficking at synapses. The ortholog of IQSECs in the fly is schizo and its loss affects growth cone guidance at the midline in the CNS, also an actin-dependent process. Overexpression of the reference IQSEC1 cDNA in wild-type flies is lethal, but overexpression of the two variant IQSEC1 cDNAs did not affect viability. Loss of schizo caused embryonic lethality that could be rescued to 2nd instar larvae by moderate expression of the human reference cDNA. However, the p.Arg321Gln and p.Thr343Met variants failed to rescue embryonic lethality. These data indicate that the variants behave as loss-of-function mutations. We also show that schizo in photoreceptors is required for phototransduction. Finally, mice with a conditional Iqsec1 deletion in cortical neurons exhibited an increased density of dendritic spines with an immature morphology. The phenotypic similarity of the affecteds and the functional experiments in flies and mice indicate that IQSEC1 variants are the cause of a recessive disease with intellectual disability, developmental delay, and short stature, and that axonal guidance and dendritic projection defects as well as dendritic spine dysgenesis may underlie disease pathogenesis."

Drosophila protein crystal structure proves useful in study of PURA syndrome

Reijnders MRF, Janowski R, Alvi M, Self JE, van Essen TJ, Vreeburg M, Rouhl RPW, Stevens SJC, Stegmann APA, Schieving J, et al. PURA syndrome: clinical delineation and genotype-phenotype study in 32 individuals with review of published literature. J Med Genet. 2018 Feb;55(2):104-113. PubMed PMID: 29097605; PubMed Central PMCID: PMC5800346.

From the abstract: "De novo mutations in PURA have recently been described to cause PURA syndrome, a neurodevelopmental disorder characterised by severe intellectual disability (ID), epilepsy, feeding difficulties and neonatal hypotonia. ... We systematically collected clinical and mutation data on newly ascertained PURA syndrome individuals, evaluated data of previously reported individuals and performed a computational analysis of photographs. We classified mutations based on predicted effect using 3D in silico models of crystal structures of Drosophila-derived Pur-alpha homologues. ... "

New fly model for understanding cognitive deficits associated with disruption of FOXP genes

Castells-Nobau A, Eidhof I, Fenckova M, Brenman-Suttner DB, Scheffer-de Gooyert JM, Christine S, Schellevis RL, van der Laan K, Quentin C, van Ninhuijs L, Hofmann F, Ejsmont R, Fisher SE, Kramer JM, Sigrist SJ, Simon AF, Schenck A. Conserved regulation of neurodevelopmental processes and behavior by FoxP in Drosophila. PLoS One. 2019 Feb 12;14(2):e0211652. PMID: 30753188; PMCID: PMC6372147.

From the abstract: "FOXP proteins form a subfamily of evolutionarily conserved transcription factors ... In humans, mutations in FOXP1 and FOXP2 have been implicated in cognitive deficits including intellectual disability and speech disorders. Drosophila exhibits a single ortholog, called FoxP ... Here we show that the dimerization property required for mammalian FOXP function is conserved in Drosophila. In flies, FoxP is enriched in the adult brain, showing strong expression in ~1000 neurons of cholinergic, glutamatergic and GABAergic nature. ... At the cellular level, ... Drosophila FoxP is required in larvae for synaptic morphogenesis at axonal terminals of the neuromuscular junction and for dendrite development of dorsal multidendritic sensory neurons. In the developing brain, we find that FoxP plays important roles in α-lobe mushroom body formation. Finally, at a behavioral level, we show that Drosophila FoxP is important for locomotion, habituation learning and social space behavior of adult flies. Our work shows that Drosophila FoxP is important for regulating several neurodevelopmental processes and behaviors that are related to human disease or vertebrate disease model phenotypes. This suggests a high degree of functional conservation with vertebrate FOXP orthologues and established flies as a model system for understanding FOXP related pathologies."

Results of studies in human cells, zebrafish and fly suggest that variants in ZBTB11 can result in intellectual disability

Fattahi Z, Sheikh TI, Musante L, Rasheed M, Taskiran II, Harripaul R, Hu H, Kazeminasab S, Alam MR, Hosseini M, Larti F, Ghaderi Z, Celik A, Ayub M, Ansar M, Haddadi M, Wienker TF, Ropers HH, Kahrizi K, Vincent JB, Najmabadi H. Biallelic missense variants in ZBTB11 can cause intellectual disability in humans. Hum Mol Genet. 2018 Sep 15;27(18):3177-3188. PMID: 29893856.

From the abstract: "Exploring genes and pathways underlying intellectual disability (ID) provides insight into brain development and function ... linkage analysis and next-generation sequencing revealed Zinc Finger and BTB Domain Containing 11 (ZBTB11) as a novel candidate ID gene. ZBTB11 encodes a little-studied transcription regulator, and the two identified missense variants in this study are predicted to disrupt canonical Zn2+-binding residues of its C2H2 zinc finger domain, leading to possible altered DNA binding. Using HEK293T cells transfected with wild-type and mutant GFP-ZBTB11 constructs, we found the ZBTB11 mutants being excluded from the nucleolus, where the wild-type recombinant protein is predominantly localized. Pathway analysis applied to ChIP-seq data deposited in the ENCODE database supports the localization of ZBTB11 in nucleoli, highlighting associated pathways such as ribosomal RNA synthesis, ribosomal assembly, RNA modification and stress sensing, and provides a direct link between subcellular ZBTB11 location and its function. Furthermore, given the report of prominent brain and spinal cord degeneration in a zebrafish Zbtb11 mutant, we investigated ZBTB11-ortholog knockdown in Drosophila melanogaster brain by targeting RNAi using the UAS/Gal4 system. The observed approximate reduction to a third of the mushroom body size-possibly through neuronal reduction or degeneration-may affect neuronal circuits in the brain that are required for adaptive behavior, specifying the role of this gene in the nervous system. In conclusion, we report two ID families segregating ZBTB11 biallelic mutations disrupting Zn2+-binding motifs and provide functional evidence linking ZBTB11 dysfunction to this phenotype."

... and another! Fly study helps point to possible genetic cause of an ARID

Kazeminasab S, Taskiran II, Fattahi Z, Bazazzadegan N, Hosseini M, Rahimi M, Oladnabi M, Haddadi M, Celik A, Ropers HH, Najmabadi H, Kahrizi K. CNKSR1 gene defect can cause syndromic autosomal recessive intellectual disability. Am J Med Genet B Neuropsychiatr Genet. 2018 Nov 18. doi: 10.1002/ajmg.b.32648. PMID: 30450701.

From the abstract: "... A novel frameshift mutation in CNKSR1 gene was detected by Next-Generation Sequencing (NGS) in an Iranian family with syndromic autosomal recessive intellectual disability (ARID). CNKSR1 encodes a connector enhancer of kinase suppressor of Ras 1 ... CNKSR1 interacts with proteins which have already been shown to be associated with intellectual disability (ID) in the MAPK signaling pathway and promotes cell migration through RhoA-mediated c-Jun N-terminal kinase (JNK) activation. Lack of CNKSR1 transcripts and protein was observed in lymphoblastoid cells derived from affected patients using qRT-PCR and western blot analysis ...  RNAi-mediated knockdown of cnk, the CNKSR1 orthologue in Drosophila melanogaster brain, led to defects in eye and mushroom body (MB) structures. In conclusion, our findings support the possible role of CNKSR1 in brain development which can lead to cognitive impairment."

Review of DNA repair, disease, and Drosophila research

Cotterill S. Diseases Associated with Mutation of Replication and Repair Proteins. Adv Exp Med Biol. 2018;1076:215-234. PMID: 29951822.

The abstract: "Alterations in proteins that function in DNA replication and repair have been implicated in the development of human diseases including cancer, premature ageing, skeletal disorders, mental retardation, microcephaly, and neurodegeneration. Drosophila has orthologues of most human replication and repair proteins and high conservation of the relevant cellular pathways, thus providing a versatile system in which to study how these pathways are corrupted leading to the diseased state. In this chapter I will briefly review the diseases associated with defects in replication and repair proteins and discuss how past and future studies on the Drosophila orthologues of such proteins can contribute to the dissection of the mechanisms involved in disease development."

Study of a fly model of fragile X-syndrome suggests "a potentially general mechanism for intellectual disability"

Franco LM, Okray Z, Linneweber GA, Hassan BA, Yaksi E. Reduced Lateral Inhibition Impairs Olfactory Computations and Behaviors in a Drosophila Model of Fragile X Syndrome. Curr Biol. 2017 Apr 24;27(8):1111-1123. PMID: 28366741; PMCID: PMC5405172.

From the abstract: "Fragile X syndrome (FXS) patients present neuronal alterations that lead to severe intellectual disability, but the underlying neuronal circuit mechanisms are poorly understood. An emerging hypothesis postulates that reduced GABAergic inhibition of excitatory neurons is a key component in the pathophysiology of FXS. Here, we directly test this idea in a FXS Drosophila model. ... We provide direct evidence that deficient inhibition impairs sensory computations and behavior in an in vivo model of FXS. Together with evidence of impaired inhibition in autism and Rett syndrome, these findings suggest a potentially general mechanism for intellectual disability."

Also appearing recently, this review:

Drozd M, Bardoni B, Capovilla M. Modeling Fragile X Syndrome in Drosophila. Front Mol Neurosci. 2018 Apr 16;11:124. doi: 10.3389/fnmol.2018.00124. PMID: 29713264; PMCID: PMC5911982.

Fly studies help shed light on contribution of KAT2B variants to ADD3-associated disorders

Gonçalves S, Patat J, Guida MC, Lachaussée N, Arrondel C, Helmstädter M, Boyer O, Gribouval O, Gubler MC, Mollet G, Rio M, Charbit M, Bole-Feysot C, Nitschke P, Huber TB, Wheeler PG, Haynes D, Juusola J, Billette de Villemeur T, Nava C, Afenjar A, Keren B, Bodmer R, Antignac C, Simons M. A homozygous KAT2B variant modulates the clinical phenotype of ADD3 deficiency in humans and flies. PLoS Genet. 2018 May 16;14(5):e1007386. PMID: 29768408.

The abstract: "Recent evidence suggests that the presence of more than one pathogenic mutation in a single patient is more common than previously anticipated. One of the challenges hereby is to dissect the contribution of each gene mutation, for which animal models such as Drosophila can provide a valuable aid. Here, we identified three families with mutations in ADD3, encoding for adducin-γ, with intellectual disability, microcephaly, cataracts and skeletal defects. In one of the families with additional cardiomyopathy and steroid-resistant nephrotic syndrome (SRNS), we found a homozygous variant in KAT2B, encoding the lysine acetyltransferase 2B, with impact on KAT2B protein levels in patient fibroblasts, suggesting that this second mutation might contribute to the increased disease spectrum. In order to define the contribution of ADD3 and KAT2B mutations for the patient phenotype, we performed functional experiments in the Drosophila model. We found that both mutations were unable to fully rescue the viability of the respective null mutants of the Drosophila homologs, hts and Gcn5, suggesting that they are indeed pathogenic in flies. While the KAT2B/Gcn5 mutation additionally showed a significantly reduced ability to rescue morphological and functional defects of cardiomyocytes and nephrocytes (podocyte-like cells), this was not the case for the ADD3 mutant rescue. Yet, the simultaneous knockdown of KAT2B and ADD3 synergistically impaired kidney and heart function in flies as well as the adhesion and migration capacity of cultured human podocytes, indicating that mutations in both genes may be required for the full clinical manifestation. Altogether, our studies describe the expansion of the phenotypic spectrum in ADD3 deficiency associated with a homozygous likely pathogenic KAT2B variant and thereby identify KAT2B as a susceptibility gene for kidney and heart disease in ADD3-associated disorders."

Preprint describes contribution of Drosophila double-knockdown assay to understanding 16p11.2 deletion syndrome

Pervasive epistasis in cell proliferation pathways modulates neurodevelopmental defects of autism-associated 16p11.2 deletion

Janani Iyer, Mayanglambam Dhruba Singh, Matthew Jensen, Payal Patel, Lucilla Pizzo, Emily Huber, Haley Koerselman, Alexis T. Weiner, Paola Lepanto, Komal Vadodaria, Alexis Kubina, Qingyu Wang, Abigail Talbert, Sneha Yennawar, Jose Badano, J. Robert Manak, Melissa M. Rolls, Arjun Krishnan, Santhosh Girirajan

https://www.biorxiv.org/content/early/2017/09/20/185355

From the abstract: "We used RNA interference in Drosophila melanogaster to evaluate the phenotype, function, and interactions of conserved 16p11.2 homologs ... Leveraging the Drosophila eye for studying gene interactions, we performed 561 pairwise knockdowns of gene expression, and identified 24 interactions between 16p11.2 homologs ... and 62 interactions with other neurodevelopmental genes ... Overall, these results point towards a new model for pathogenicity of rare CNVs, where CNV genes interact with each other in conserved pathways to modulate expression of the neurodevelopmental phenotype."

"Independent functional evidence in Drosophila" contributes to study related to intellectual disability

Lugtenberg D, Reijnders MR, Fenckova M, Bijlsma EK, Bernier R, van Bon BW, Smeets E, Vulto-van Silfhout AT, Bosch D, Eichler EE, Mefford HC, Carvill GL, Bongers EM, Schuurs-Hoeijmakers JH, Ruivenkamp CA, Santen GW, van den Maagdenberg AM, Peeters-Scholte CM, Kuenen S, Verstreken P, Pfundt R, Yntema HG, de Vries PF, Veltman JA, Hoischen A, Gilissen C, de Vries BB, Schenck A, Kleefstra T, Vissers LE. De novo loss-of-function mutations in WAC cause a recognizable intellectual disability syndrome and learning deficits in Drosophila. Eur J Hum Genet. 2016 Aug;24(8):1145-53. PMID: 26757981; PMCID: PMC4970694.

From the abstract: "Recently WAC was reported as a candidate gene for intellectual disability (ID) based on the identification of a de novo mutation in an individual with severe ID. ... In this study, we report on 10 individuals with de novo WAC mutations which we identified through routine (diagnostic) exome sequencing and targeted resequencing of WAC in 2326 individuals with unexplained ID. All but one mutation was expected to lead to a loss-of-function of WAC. ... To investigate the role of WAC in ID, we studied the importance of the Drosophila WAC orthologue (CG8949) in habituation, a non-associative learning paradigm. Neuronal knockdown of Drosophila CG8949 resulted in impaired learning, suggesting that WAC is required in neurons for normal cognitive performance. In conclusion, we defined a clinically recognizable ID syndrome, caused by de novo loss-of-function mutations in WAC. Independent functional evidence in Drosophila further supported the role of WAC in ID. On the basis of our data WAC can be added to the list of ID genes with a role in transcription regulation through histone modification."

Uncovering cellular mechanisms relevant to Parkinson's Disease

Dodson MW, Leung LK, Lone M, Lizzio MA, Guo M. Novel ethyl methanesulfonate (EMS)-induced null alleles of the Drosophila homolog of LRRK2 reveal a crucial role in endolysosomal functions and autophagy in vivo. Dis Model Mech. 2014 Dec;7(12):1351-63. PMID: 25288684; PMCID: PMC4257004.

Zhou ZD, Xie SP, Sathiyamoorthy S, Saw WT, Sing TY, Ng SH, Chua HP, Tang AM, Shaffra F, Li Z, Wang H, Ho PG, Lai MK, Angeles DC, Lim TM, Tan EK. F-box protein 7 mutations promote protein aggregation in mitochondria and inhibit mitophagy. Hum Mol Genet. 2015 Nov 15;24(22):6314-30. PMID: 26310625.

Kong Y, Liang X, Liu L, Zhang D, Wan C, Gan Z, Yuan L. High Throughput Sequencing Identifies MicroRNAs Mediating α-Synuclein Toxicity by Targeting Neuroactive-Ligand Receptor Interaction Pathway in Early Stage of Drosophila Parkinson's Disease Model. PLoS One. 2015 Sep 11;10(9):e0137432. PMID: 26361355; PMCID: PMC4567341.

Gehrke S, Wu Z, Klinkenberg M, Sun Y, Auburger G, Guo S, Lu B. PINK1 and Parkin control localized translation of respiratory chain component mRNAs on mitochondria outer membrane. Cell Metab. 2015 Jan 6;21(1):95-108. PMID: 25565208; PMCID: PMC4455944.

Shmueli MD, Schnaider L, Herzog G, Gazit E, Segal D. Computational and experimental characterization of dVHL establish a Drosophila model of VHL syndrome. PLoS One. 2014 Oct 13;9(10):e109864. PMID: 25310726; PMCID: PMC4195687.

Dubos A, Castells-Nobau A, Meziane H, Oortveld MA, Houbaert X, Iacono G, Martin C, Mittelhaeuser C, Lalanne V, Kramer JM, Bhukel A, Quentin C, Slabbert J, Verstreken P, Sigrist SJ, Messaddeq N, Birling MC, Selloum M, Stunnenberg HG, Humeau Y, Schenck A, Herault Y. Conditional depletion of intellectual disability and Parkinsonism candidate gene ATP6AP2 in fly and mouse induces cognitive impairment and neurodegeneration. Hum Mol Genet. 2015 Dec 1;24(23):6736-55. PMID: 26376863; PMCID: PMC4634377.

Arsenijevic Y. Cell Cycle Proteins and Retinal Degeneration: Evidences of New Potential Therapeutic Targets. Adv Exp Med Biol. 2016;854:371-7. PMID: 26427434.

Angelova PR, Agrawalla BK, Elustondo PA, Gordon J, Shiba T, Abramov AY, Chang YT, Pavlov EV. In situ investigation of mammalian inorganic polyphosphate localization using novel selective fluorescent probes JC-D7 and JC-D8. ACS Chem Biol. 2014 Sep 19;9(9):2101-10. PMID: 25007079.

van der Merwe C, Jalali Sefid Dashti Z, Christoffels A, Loos B, Bardien S. Evidence for a common biological pathway linking three Parkinson's disease-causing genes: parkin, PINK1 and DJ-1. Eur J Neurosci. 2015 May;41(9):1113-25. PMID: 25761903.

Review discusses fly as model for studying chromatin factors relevant to intellectual disability

Looks like a nice starting point or resource for someone interested to use the fly to study chromatin regulators and neurological diseases.

Taniguchi H, Moore AW. Chromatin regulators in neurodevelopment and disease: Analysis of fly neural circuits provides insights: Networks of chromatin regulators and transcription factors underlie Drosophila neurogenesis and cognitive defects in intellectual disability and neuropsychiatric disorder models. Bioessays. 2014 Sep;36(9):872-83. PMID: 25067789.

From the abstract:  "Disruptions in chromatin regulator genes are frequently the cause of neurodevelopmental and neuropsychiatric disorders. ... Using Drosophila allows targeted manipulation of chromatin regulators in defined neuronal classes, lineages, or circuits, revealing their roles in neuronal precursor self-renewal, dendrite and axon targeting, neuron diversification, and the tuning of developmental signaling pathways. ..."

Review--how fly research has and can continue to contribute to understanding intellectual disability

van der Voet M, Nijhof B, Oortveld MA, Schenck A. Drosophila models of early onset cognitive disorders and their clinical applications. Neurosci Biobehav Rev. 2014 Oct;46 Pt 2:326-42. PMID: 24661984.

From the abstract: "... For the extremely large, genetically and phenotypically heterogeneous group of intellectual disability (ID) disorders, more than 600 causative genes have been identified to date. However, knowledge about the molecular mechanisms and networks disrupted by these genetic aberrations is lagging behind. The fruit fly Drosophila has emerged as a powerful model organism to close this knowledge gap. This review summarizes recent achievements that have been made in this model and envisions its future contribution to our understanding of ID genetics and neuropathology. ... In conclusion, Drosophila provides many opportunities to advance future medical genomics of early onset cognitive disorders."