SysNDD database
To obtain an overview on the clinical and molecular landscape of NDDs and to facilitate diagnostics and research, Christiane Zweier has been involved for many years in establishing and updating a manually curated database with published NDD genes and associated diseases and phenotypes (previously SysID: www.sysid.dbmr.unibe.ch, now SysNDD: https://sysndd.dbmr.unibe.ch). Supported by the European Reference Network (ERN) ITHACA, we are also working on integrating SysID/SysNDD with Orphanet.
RHOBTB2-associated developmental and epileptic encephalopathy
In 2018, we identified de novo missense variants clustering in the BTB domain coding region of atypical RHO GTPase RHOBTB2 to cause a developmental and epileptic encephalopathy. These variants resulted in impaired degradation of RHOBTB2 by the proteasome. In accordance, flies overexpressing the Drosophila orthologue RhoBTB showed seizure susceptibility and severe gross neurological impairment (Straub et al., AJHG, 2018). By assembling data on further individuals with neurodevelopmental disorders and variants in RHOBTB2 we now investigate genotype-phenotype correlations between location of variants and severity of the phenotype. Furthermore, transcriptome data indicated a possible deregulation of ion channels in fly heads with RhoBTB overexpression. We are currently following up the role of ion channel deregulation in RHOBTB2-related epilepsy with a human iPSC based cell model and by genetic interaction studies in Drosophila.
FBXO11-associated Neurodevelopmental Disorder
De novo missense and likely gene-disrupting variants in FBXO11 cause a variable neurodevelopmental disorder (NDD) (Gregor et al., AJHG, 2018). We found that phenotypes for missense and likely gene-disrupting variants strongly overlap and characterized the effects of missense variants in FBXO11 on protein expression and localization in HEK293 and HeLa cells. We found that most reported missense variants alter either expression levels and/or subcellular localization and are therefore likely resulting in a loss of original function. This suggests that haploinsufficiency of FBXO11 may be the common pathomechanism underlying FBXO11-associated NDDs (Gregor et al., HMG, 2021). To better understand the molecular mechanisms resulting from FBXO11 haploinsufficiency, we created a neuronal disease model using human induced pluripotent stem cells and CRISPR/CAS9 technology. Through transcriptome analysis and subsequent functional studies, we are currently further investigating and characterizing the FBXO11-related pathomechanisms.
LHX2-associated Neurodevelopmental Disorder
Recently, we identified de novo missense and truncating variants in transcription factor LHX2 in individuals with variable neurodevelopmental and behavioral phenotypes (manuscript submitted). Anne Gregor recently acquired funding to establish a human brain organoid model for LHX2 deficiency and to perform single-cell RNA sequencing to study the pathomechanisms associated with loss of LHX2.
UPS related Neurodevelopmental Disorders and therapeutic potential of proteasome modifying substances
A growing number of Neurodevelopmental Disorder associated genes/proteins is involved in the ubiquitin proteasome system (UPS). We have started to target phenotypes observed upon knockdown of several UPS-related genes in Drosophila with different substances and found that we can rescue phenotypes involving the wing, dendritic development (multiple dendrite neurons) as well as basic locomotor behavior. We are currently establishing human, cell based models for several of these disorders by using induced pluripotent stem cells and CRISPR/CAS9 to induce knockout of the genes of interest. We are currently also establishing a multi-electrode array (MEA) system to investigate common patterns of neuronal network activity between NDD-UPS-related gene deficiencies and to obtain phenotypes which possibly can by modified by applying substances.
