Clinical variations of epileptic syndrome associated with PACS2 variant

Understanding PACS2 syndrome's pathomechanism by studying E209K and E211K mutations

Phosphofurin acidic cluster sorting protein 2 (PACS2) plays a vital role in maintaining cellular homeostasis by regulating protein trafficking between cellular membranes. This function impacts crucial processes like apoptosis, mitochondria-endoplasmic reticulum interaction, and subsequently Ca2+ flux, lipid biosynthesis, and autophagy. Missense mutations, particularly E209K and E211K, are linked to developmental and epileptic encephalopathy-66 (DEE66), known as PACS2 syndrome. Individuals with this syndrome exhibit neurodevelopmental delay, seizures, facial dysmorphism, hypotonia, and delayed motor skills.Understanding the impact of these missense mutations on molecular processes is crucial. Studies suggest that E209K mutation decreases phosphorylation, increases the survival time of protein, and modifies protein-protein interaction, consequently leading to disruption of calcium flux and lower resistance to apoptosis induction. Unfortunately, to date, only a limited number of research groups have investigated the effects of mutations in the PACS2 gene. Current research on PACS2 syndrome is hampered by the lack of suitable models. While in vitro models using transfected cell lines offer insights, they cannot fully capture the disease's complexity.To address this, utilizing cells from individuals with PACS2 syndrome, specifically induced pluripotent stem cells (iPSCs), holds promise for understanding phenotypic diversity and developing personalized therapies. However, iPSC models may not fully capture tissue-specific effects of the E209K/E211K mutation. In vivo studies using animal models, particularly mice, could overcome these limitations.This review summarizes current knowledge about PACS2 structure and functions, explores the cellular consequences of E209K and E211K mutations, and highlights the potential of iPSC and mouse models in advancing our understanding of PACS2 syndrome.

PACS2 pathogenic variant associated with malformation of cortical development and epilepsy

PACS2 pathogenic variants are associated with an autosomal dominant syndrome (OMIM DEE66), associating developmental and epileptic encephalopathy, facial dysmorphism, and cerebellar dysgenesis. However, no malformation of cortical development has been reported yet. We report here a seven-year-old child with a history of infantile epileptic spasm syndrome and a right insular polymicrogyria and pachygyria due to de novo PACS2 recurrent mutation c.625G>A (p.Glu209Lys). Our observation raises the question of the role of PACS2 in the cortical development. It also reminds the importance of cerebellar anomalies in the recognition of PACS-related DEE.

Characteristics of Developmental and Epileptic Encephalopathy Associated with PACS2 p.Glu209Lys Pathogenic Variant-Our Experience and Systematic Review of the Literature

BACKGROUND

Developmental and epileptic encephalopathies (DEE) encompass a group of rare diseases with hereditary and genetic causes as well as acquired causes such as brain injuries or metabolic abnormalities. The phosphofurin acidic cluster sorting protein 2 (PACS2) is a multifunctional protein with nuclear gene expression. The first cases of the recurrent c.625G>A pathogenic variant of PACS2 gene were reported in 2018 by Olson et al. Since then, several case reports and case series have been published.

METHODS

We performed a systematic review of the PUBMED and SCOPUS databases using Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines. Our search parameters included DEE66 with a pathogenic PACS2 gene p.Glu209Lys mutation published cases to which we added our own clinical experience regarding this pathology.

RESULTS

A total of 11 articles and 29 patients were included in this review, to which we added our own experience for a total of 30 patients. There was not a significant difference between sexes regarding the incidence of this pathology (M/F: 16/14). The most common neurological and psychiatric symptoms presented by the patients were: early onset epileptic seizures, delayed global development (including motor and speech delays), behavioral disturbances, limited intellectual capacity, nystagmus, hypotonia, and a wide-based gait. Facial dysmorphism and other organs' involvement were also frequently reported. Brain MRIs evidenced anomalies of the posterior cerebellar fossa, foliar distortion of the cerebellum, vermis hypoplasia, white matter reduction, and lateral ventricles enlargement. Genetic testing is more frequent in children. Only 4 cases have been reported in adults to date.

CONCLUSIONS

It is important to maintain a high suspicion of new pathogenic gene variants in adult patients presenting with a characteristic clinical picture correlated with radiologic changes. The neurologist must gradually recognize the distinct evolving phenotype of DEE66 in adult patients, and genetic testing must become a scenario with which the neurologist attending adult patients should be familiar. Accurate diagnosis is required for adequate treatment, genetic counseling, and an improved long-term prognosis.

PACS gene family-related neurological diseases: limited genotypes and diverse phenotypes

BACKGROUND

The PACS gene family has been demonstrated to be related to intracellular vesicular trafficking. The phenotypic manifestations caused by the pathogenic variants of PACS include epilepsy, intellectual disability/developmental delay, and malformations, such as facial abnormalities.

METHODS

We identified seven new cases with pathogenic or likely pathogenic PACS variants using next-generation sequencing. Detailed information obtained from these patients was analyzed along with that obtained from previously reported patients.

RESULTS

With the inclusion of the newly diagnosed cases in this study, 103 cases with PACS gene family-related neurological diseases were reported, of which 43 were PACS2-related cases and the remaining were PACS1-related cases. Most patients had seizures, which have been reported to be effectively controlled by several types of anti-seizure medications (ASMs). The most efficacious and frequently prescribed ASMs included sodium valproate (43.3%, 13/30), oxcarbazepine/carbamazepine (26.7%, 8/30), and levetiracetam (20%, 6/30). Almost all patients had intellectual disability/developmental delay. The most common pathogenic missense variants were PACS1 p. Arg203Trp and PACS2 p.Glu209Lys. In addition, we report a patient carrying a likely pathogenic copy number variation (CNV) (de novo heterozygous deletion of chr14:105821380-106107443, 286 kilobase, destroyed part of the furin-binding region domain and the protein structure after it) with more severe and refractory late-onset epilepsy.

CONCLUSIONS

The clinical phenotypes of the different PACS heterozygous missense variants were similar. The pathogenic variant sites of PACS1 and PACS2 were quite limited but located in different regions. A CNV destroying part of the PACS2 gene might also be pathogenic. These findings may provide an important clue for further functional studies on the pathogenic mechanism of neurological disorders related to the PACS gene family. Video Abstract (MP4 65767 kb).

Long-Term Outcome of Neonatal Seizure with PACS2 Mutation: Case Series and Literature Review

Phosphofurin Acidic Cluster Sorting Protein 2 (PACS2)-related early infantile developmental and epileptic encephalopathy (EIDEE) is a rare neurodevelopmental disorder. EIDEE is characterized by seizures that begin during the first three months of life and are accompanied by developmental impairment over time. In this article, we present three patients with EIDEE who experienced neonatal-onset seizures that developed into intractable seizures during infancy. Whole exome sequencing revealed a de novo heterozygous missense variant in all three patients in the p.Glu209Lys variant of the PACS2 gene. We conducted a literature review and found 29 cases to characterize the seizure patterns, neuroimaging features, the usage of anticonvulsants, and the clinical neurodevelopmental outcomes of PACS2-related EIDEE. The seizures were characterized by brief, recurring tonic seizures in the upper limbs, sometimes accompanied by autonomic features. Neuroimaging abnormalities were observed in the posterior fossa region, including mega cisterna magna, cerebellar dysplasia, and vermian hypoplasia. The long-term prognosis ranges from low–average intelligence to severe developmental retardation, emphasizing the importance of early recognition and accurate diagnosis by pediatric neurologists to provide personalized patient management.

The Phosphofurin Acidic Cluster Sorting Protein 2 (PACS-2) E209K Mutation Responsible for PACS-2 Syndrome Increases Susceptibility to Apoptosis

Phosphofurin acidic cluster sorting protein 2 (PACS-2) is a multifunctional cytosolic membrane trafficking protein with distinct roles in maintaining cellular homeostasis. Recent clinical reports have described 28 individuals possessing a de novo PACS-2 E209K mutation that present with epileptic seizures and cerebellar dysgenesis. As the PACS-2 E209K missense mutation has become a marker for neurodevelopmental disorders, we sought to characterize its biochemical properties. Accordingly, we observed that the PACS-2 E209K protein exhibited a slower turnover rate relative to PACS-2 wild type (WT) upon cycloheximide treatment in 293T cells. The longer half-life of PACS-2 E209K suggests a disruption in its proteostasis, with the potential for altered protein-protein interactions. Indeed, a regulatory protein in neurodevelopment known as 14-3-3ε was identified as having an increased association with PACS-2 E209K. Subsequently, when comparing the effect of PACS-2 WT and E209K expression on the staurosporine-induced apoptosis response, we found that PACS-2 E209K increased susceptibility to staurosporine-induced apoptosis in HCT 116 cells. Overall, our findings suggest PACS-2 E209K alters PACS-2 proteostasis and favors complex formation with 14-3-3ε, leading to increased cell death in the presence of environmental stressors.

Vein of Galen aneurysm, dilated cardiomyopathy, and slender habitus in a patient with a recurrent pathogenic variant in PACS2

The PACS2 gene encodes a multifunctional sorting protein involved in nuclear gene expression and pathway traffic regulation that has been shown to be highly expressed during human prenatal brain development. Pathogenic variants in PACS2 have been recently shown to be implicated in a phenotype with global developmental delay/intellectual disability, seizures, autistic traits, facial dysmorphic features, and cerebellar dysgenesis. Here, we report a 25-year-old male with intellectual disability, epileptic encephalopathy, cerebellar dysgenesis, facial dysmorphism, and a previously reported pathogenic variant in PACS2. To our knowledge, this is the oldest patient reported who, in addition to the known phenotype described in PACS2 patients, presented with a vein of Galen malformation and dilated cardiomyopathy as previously unreported findings.