Neurodevelopmental alterations are key drivers of SPG56.

DRP1 mutations associated with EMPF1 encephalopathy perturb the transcriptional profile and maturation of cortical neurons.

With the advent of exome sequencing, a growing number of children are being identified with de novo loss-of-function mutations in the dynamin 1-like (DNM1L) gene, which encodes the large GTPase essential for mitochondrial fission, dynamin-related protein 1 (DRP1). Mutations in DRP1 result in severe neurodevelopmental phenotypes, such as developmental delay, optic atrophy, and epileptic encephalopathies. Though it is established that mitochondrial fission is an essential precursor to the rapidly changing metabolic needs of the developing cortex, it is not understood how identified mutations in different domains of DRP1 uniquely disrupt cortical development and synaptic maturation. We leveraged the power of human induced pluripotent stem cells (iPSCs) harboring DRP1 mutations in either the GTPase or stalk domains to model early stages of cortical development in vitro. High-resolution time-lapse imaging of transport in neuronal projections revealed mutation-specific changes in mitochondrial motility of severely hyperfused mitochondrial structures. Transcriptional profiling of mutant DRP1 cortical neurons during maturation also implicated mutation-dependent alterations in synaptic development and gene expression of calcium-regulatory genes. Disruptions in calcium dynamics were confirmed using live functional recordings of 65-200 days in vitro (DIV) mutant DRP1 cortical neurons. These findings strongly suggest that altered mitochondrial morphology in DRP1 mutant neurons leads to pathogenic dysregulation of synaptic development and activity.

Cross-species functional analysis of a de novo DCLK1 variant associated with a neurodevelopmental disorder

The findings implicate DCLK1 in a previously unrecognized progressive neurodevelopmental disorder and demonstrate the power of integrative cross-species functional genomics in resolving ultra-rare disease variants.

Unraveling the impact of trip12 on neurodevelopment: insights from a zebrafish model

This study provides substantial evidence for the vital role of trip12 in the early stages of development, as homozygous individuals exhibited early mortality by Day 23 post-fertilization, while a substantial mortality rate was observed by Day 35 in ‘heterozygous’ mutants.

Deciphering the Role of LNX2 as a Potential Contributor to Neurodevelopmental Disorders

The biological plausibility of LNX2 as a candidate gene for neurodevelopmental disorders is supported, highlighting its preferential association with neuronal projection-cell networks, synaptic vesicle trafficking pathways, and neuron-specific regulatory programs.

Further characterization of the BRSK2-associated neurodevelopmental disorder.

Variants in BRSK2, encoding brain specific kinase-2, have recently been associated with an autosomal dominant neurodevelopmental disorder (NDD). We have assembled 52 cases with heterozygous BRSK2 variants and variable neurodevelopmental phenotypes with frequent neuropsychiatric and behavioral symptoms. The variant spectrum included 15 different truncating variants, seven (potential) splice variants, three structural variants, and 12 different missense variants. Of the missense variants, seven were in the kinase domain, and the others in the UBA and the KA1 domain or outside domains. Variants occurred de novo in 19 cases and were inherited in 18. We utilized Drosophila melanogaster as a model and assessed viability and performed climbing and bang sensitivity assays upon knockdown of the fly orthologue sff or upon overexpression of wildtype or mutant human BRSK2. Pan-neuronal knockdown of sff resulted in impaired locomotor behavior and seizure susceptibility. Ubiquitous or pan-neuronal overexpression of human wildtype BRSK2 in Drosophila resulted in lethality or locomotor impairment, respectively, indicating toxicity. Overexpressing mutant BRSK2 did not or incompletely affect viability and locomotor behavior for six of seven tested kinase domain missense variants and one KA1 domain variant, indicating a (partial) loss-of-function effect. Interestingly, overexpressing BRSK2 with the remaining missense variant from the kinase domain and the two most C-terminal missense variants resulted in possible gain of function. Our findings further delineate the clinical and molecular spectrum of BRSK2-associated NDD and provide further insights into the role of BRSK2/sff in nervous system function and dysfunction.

Cross-species analysis of GNB1 I80T encephalopathy: conserved developmental, epileptic and neuronal transcriptome signatures