Rubinstein-Taybi syndrome (RSTS) is a rare neurodevelopmental disorder caused by mutations in CREBBP or EP300 genes encoding CBP/p300 lysine acetyltransferases. We investigated the efficacy of the histone deacetylase inhibitor (HDACi) Trichostatin A (TSA) in ameliorating morphological abnormalities of iPSC-derived young neurons from P149 and P34 CREBBP-mutated patients and hypoexcitability of mature neurons from P149. Neural progenitors from both patients’ iPSC lines were cultured one week with TSA 20 nM and, only P149, for 6 weeks with TSA 0.2 nM, in parallel to neural progenitors from controls. Immunofluorescence of MAP2/TUJ1 positive cells using the Skeletonize Image J plugin evidenced that TSA partially rescued reduced nuclear area, and decreased branch length and abnormal end points number of both 45 days patients’ neurons, but did not influence the diminished percentage of their neurons with respect to controls. Patch clamp recordings of TSA-treated post-mitotic P149 neurons showed complete/partial rescue of sodium/potassium currents and significant enhancement of neuron excitability compared to untreated replicas. Correction of abnormalities of P149 young neurons was also affected by valproic acid 1 mM for 72 h, with some variation, with respect to TSA, on the morphological parameter. These findings hold promise for development of an epigenetic therapy to attenuate RSTS patients cognitive impairment.

Rett syndrome caused by MECP2 variants is characterized by a heterogenous clinical spectrum accounted for in 60% of cases by hot-spot variants. Focusing on the most frequent variants, we generated in vitro iPSC-neurons from the blood of RTT girls with p.Arg133Cys and p.Arg255*, associated to mild and severe phenotype, respectively, and of an RTT male harboring the close to p.Arg255*, p.Gly252Argfs*7 variant. Truncated MeCP2 proteins were revealed by Western blot and immunofluorescence analysis. We compared the mutant versus control neurons at 42 days for morphological parameters and at 120 days for electrophysiology recordings, including girls’ isogenic clones. A precocious reduced morphological complexity was evident in neurons with truncating variants, while in p.Arg133Cys neurons any significant differences were observed in comparison with the isogenic wild-type clones. Reduced nuclear size and branch number show up as the most robust biomarkers. Patch clamp recordings on mature neurons allowed the assessment of cell biophysical properties, V-gated currents, and spiking pattern in the mutant and control cells. Immature spiking, altered cell capacitance, and membrane resistance of RTT neurons, were particularly pronounced in the Arg255* and Gly252Argfs*7 mutants. The overall results indicate that the specific markers of in vitro cellular phenotype mirror the clinical severity and may be amenable to drug testing for translational purposes.

Loss‐of‐function CHD2 (chromodomain helicase DNA‐binding protein 2) mutations are associated with a spectrum of neurodevelopmental disorders often including early‐onset generalized seizures, photosensitivity, and epileptic encephalopathies. Patients show psychomotor delay/intellectual disability (ID), autistic features, and behavior disorders, such as aggression and impulsivity. Most reported cases are sporadic with description of germline mosaicism only in two families. We detect the first case of parental gonosomal CHD2 mosaicism disclosed by two brothers showing mild ID, born to healthy parents. The eldest brother has a history of drug‐controlled generalized tonic–clonic seizures and displays sleep disorder and aggressive behavior suggestive of Smith–Magenis syndrome (SMS). Analysis of brothers’ DNAs by next‐generation sequencing (NGS) custom gene panel for pediatric epilepsy and/or ID disclosed in both the same pathogenic CHD2 variant. Additional NGS experiment on genomic DNA from parents’ peripheral blood and from buccal swab raised the suspicion of low‐grade gonosomal mosaicism in the unaffected mother subsequently confirmed by digital polymerase chain reaction (dPCR). This report underlines as worthwhile CHD2 screening in individuals presenting ID/developmental delay, with/without epilepsy, and behavior and sleep disorders suggestive of SMS. Detecting a CHD2 variant should prime testing probands' parents by NGS coupled to dPCR on different tissues to exclude/confirm gonosomal mosaicism and define the recurrence risk.

Angelman Syndrome (AS, MIM #105830) is a rare neurodevelopmental disorder caused by imprinting defects, marked by motor issues, intellectual disability, speech challenges, and seizures. The condition arises due to the loss of function in neurons of the maternally-inherited UBE3A gene, mapping in the imprinted chromosomal region 15q11.2-q13, which is caused by genetic and epigenetic mechanisms. UBE3A encodes an ubiquitin E3 ligase, essential for synaptic plasticity. Most studies on AS have been performed on animal models, while induced pluripotent stem cells (IPSCs), mainly from patients with deletions, are still in a limited number. Here we report on the generation and characterization of human cortical neurons derived from IPSCs of children representative of the main AS genotypes: 3 with 15q11–13 deletion, 4 with UBE3A mutations, 2 with uniparental disomy, and 2 with imprinting defects. During early neuronal differentiation, morphological analyses highlighted a reduced dendritic branching and an increase of thin filopodia, while migration assays revealed a reduction in neurite mobility in AS human neurons with deletion. At a later differentiation timepoint, the study of electrical activity revealed an impairment in neurons from AS patients. Basing of data of literature proving a role of JNK (c-Jun N-terminal kinase) signalling pathway in the filopodia formation and synaptic development, we examined the JNK deregulation in our cellular model. We found increased activation of JNK, and importantly the treatment with a JNK-inhibitor, D-JNKI1, partially corrected the neuronal morphological defects, notably reducing the number of immature protrusions, and defects in electrophysiological properties.