A PAK1 Mutational Hotspot Within the Regulatory CRIPaK Domain is Associated With Severe Neurodevelopmental Disorders in Children

PAK3 pathogenic variant associated with sleep-related hypermotor epilepsy in a family with parental mosaicism

Protein-activated kinases mediate spine morphogenesis and synaptic plasticity. PAK3 is part of the p21-activated kinases (PAKs) family of Ras-signaling serine/threonine kinases. Pathogenic variants in the X-linked gene PAK3 have been described in patients with neurodevelopmental syndromes. We analyzed an Italian family with sleep-related hypermotor epilepsy, intellectual disability, psychiatric and behavioral problems, and dysmorphic facial features. A novel PAK3 c.342_344del (p.Lys114del) inframe deletion was detected in the family. Protein structure analysis supported deleterious impact of p.Lys114 deletion through loss or partial loss of autoinhibition of PAK3 protein kinase activity. The male proband had drug-resistant hypermotor seizures and moderate intellectual disability. His brother had drug-responsive hypermotor seizures and mild intellectual disability. Both brothers were hemizygous and had psychiatric and behavioral problems as well as dysmorphic facial features. Their mother had never had seizures but was shown to be mosaic for the PAK3 pathogenic variant. She had normal intellect but did have short stature and dysmorphic facial features similar to her sons. This is the first reported association of a PAK3 pathogenic variant with sleep-related hypermotor epilepsy. PAK3 testing should be considered in families with suspected X-linked sleep-related hypermotor epilepsy and intellectual disability, including for mosaicism in mildly affected females. PLAIN LANGUAGE SUMMARY: We studied an Italian family with sleep-related hypermotor epilepsy, intellectual disability, psychiatric and behavioral problems, and dysmorphic facial features. A novel PAK3 c.342_344del (p.Lys114del) inframe deletion was detected in the family. Protein structure analysis supported deleterious impact of p.Lys114 deletion through loss or partial loss of autoinhibition of PAK3 protein kinase activity. This is the first reported association of a PAK3 pathogenic variant with sleep-related hypermotor epilepsy. PAK3 testing should be considered in families with suspected X-linked sleep-related hypermotor epilepsy and intellectual disability, including for mosaicism in mildly affected females.

Neuroradiologic, Clinical, and Genetic Characterization of Cerebellar Heterotopia: A Pediatric Multicentric Study

BACKGROUND AND PURPOSE

Cerebellar heterotopia (CH) is a neuroradiologic abnormality that is poorly reported and investigated in the literature. It can be observed as an isolated finding, but it has been mainly reported in the context of cerebellar dysgenesis and syndromic conditions. This study aims to provide a comprehensive neuroradiologic, clinical, and genetic characterization of a cohort of pediatric patients with CH.

MATERIALS AND METHODS

Patients with a diagnosis of CH were systematically selected from the neuroimaging databases of the 4 Italian centers participating in this retrospective study. For each patient, information regarding demographic, clinical, genetic, and neuroradiologic data was collected.

RESULTS

Thirty-two pediatric patients were recruited and subdivided into 2 groups: patients with isolated CH and/or cerebellar malformations (n = 18) and patients with CH associated with cerebral malformations (n = 14). Isolated CH consistently showed a peripheral subcortical localization in the inferior portion of cerebellar hemispheres, with either unilateral or bilateral distribution. Ten patients belonging to the second group had a diagnosis of CHARGE syndrome, and their nodules of CH were mainly but not exclusively bilateral, symmetric, located in the peripheral subcortical zone and the inferior portion of the cerebellar hemispheres. The remaining 4 patients of the second group showed either bilateral or unilateral CH, located in both the peripheral cortex and deep white matter and the superior and inferior portions of cerebellum. Patients with isolated CH showed a high prevalence of language development delay; neurodevelopmental disorders were the most represented clinical diagnoses. Recurring features were behavioral problems and motor difficulties. A conclusive genetic diagnosis was found in 18/32 patients.

CONCLUSIONS

We found distinctive neuroradiologic patterns of CH. Genetic results raise the possibility of a correlation between cerebellar morphologic and functional developmental disruption, underscoring the importance of CH detection and reporting to orient the diagnostic path.

Antagonistic actions of PAK1 and NF2/Merlin drive myelin membrane expansion in oligodendrocytes

In the central nervous system, the formation of myelin by oligodendrocytes (OLs) relies on the switch from the polymerization of the actin cytoskeleton to its depolymerization. The molecular mechanisms that trigger this switch have yet to be elucidated. Here, we identified P21-activated kinase 1 (PAK1) as a major regulator of actin depolymerization in OLs. Our results demonstrate that PAK1 accumulates in OLs in a kinase-inhibited form, triggering actin disassembly and, consequently, myelin membrane expansion. Remarkably, proteomic analysis of PAK1 binding partners enabled the identification of NF2/Merlin as its endogenous inhibitor. Our findings indicate that Nf2 knockdown in OLs results in PAK1 activation, actin polymerization, and a reduction in OL myelin membrane expansion. This effect is rescued by treatment with a PAK1 inhibitor. We also provide evidence that the specific Pak1 loss-of-function in oligodendroglia stimulates the thickening of myelin sheaths in vivo. Overall, our data indicate that the antagonistic actions of PAK1 and NF2/Merlin on the actin cytoskeleton of the OLs are critical for proper myelin formation. These findings have broad mechanistic and therapeutic implications in demyelinating diseases and neurodevelopmental disorders.

Cerebellar heterotopia in an 11-year-old child with KDM6B-related neurodevelopmental disorder: A case report and review of the literature

Heterozygous pathogenic variants in KDM6B have recently been associated to a rare neurodevelopmental disorder referred to as "Neurodevelopmental disorder with coarse facies and mild distal skeletal abnormalities" and characterized by non-pathognomonic facial and body dysmorphisms, a wide range of neurodevelopmental and behavioral disorders and nonspecific neuroradiological findings. KDM6B encodes a histone demethylase, expressed in different tissues during development, which regulates gene expression through the modulation of chromatin accessibility by RNA polymerase. We herein describe a 11-year-old male patient carrying a novel de novo pathogenic variant in KDM6B exhibiting facial dysmorphisms, dysgraphia, behavioral traits relatable to oppositional defiant, autism spectrum, and attention deficit hyperactivity disorders, a single seizure episode, and a neuroimaging finding of a single cerebellar heterotopic nodule, never described to date in this genetic condition. These findings expand the phenotypic spectrum of this syndrome, highlighting the potential role for KDM6B in cerebellar development and providing valuable insights for genetic counseling.

Control of OPC proliferation and repopulation by the intellectual disability gene PAK1 under homeostatic and demyelinating conditions

Appropriate proliferation and repopulation of oligodendrocyte progenitor cells (OPCs) determine successful (re)myelination in homeostatic and demyelinating brains. Activating mutations in p21-activated kinase 1 (PAK1) cause intellectual disability, neurodevelopmental abnormality, and white matter anomaly in children. It remains unclear if and how PAK1 regulates oligodendroglial development. Here, we report that PAK1 controls proliferation and regeneration of OPCs. Unlike differentiating oligodendrocytes, OPCs display high PAK1 activity which maintains them in a proliferative state by modulating PDGFRa-mediated mitogenic signaling. PAK1-deficient or kinase-inhibited OPCs reduce their proliferation capacity and population expansion. Mice carrying OPC-specific PAK1 deletion or kinase inhibition are populated with fewer OPCs in the homeostatic and demyelinated CNS than control mice. Together, our findings suggest that kinase-activating PAK1 mutations stall OPCs in a progenitor state, impacting timely oligodendroglial differentiation in the CNS of affected children and that PAK1 is a potential molecular target for replenishing OPCs in demyelinating lesions.