A case of new PCDH12 gene variants presented as dyskinetic cerebral palsy with epilepsy

Genetic Mutations in Cell Junction Proteins Associated with Brain Calcification

Intracerebral calcium deposition, classified into primary familial brain calcification (PFBC) and secondary brain calcification, occurs within the brain parenchyma and vasculature. PFBC manifests with progressive motor decline, dysarthria, and cognitive impairment, with limited treatment options available. Recent research has suggested a link between dysfunction of the blood-brain barrier (BBB) and PFBC, with certain genetic variants potentially affecting neurovascular unit (NVU) function, thereby contributing to BBB integrity disruption and brain calcification. Cell junctions play an indispensable role in maintaining the function of NVUs. The pathogenic mechanisms of PFBC-causative genes, such as PDGFRB, PDGFB, MYORG, and JAM2, involve NVU disruption. Cell junctions, such as tight junctions, gap junctions, adherens junctions, desmosomes, hemidesmosomes, and focal adhesions, are vital for cell-cell and cell-extracellular matrix connections, maintaining barrier function, cell adhesion, and facilitating ion and metabolite exchange. Several recent studies have highlighted the role of mutations in genes encoding cell junction proteins in the onset and progression of brain calcification and its related phenotypes. This emerging body of research offers a unique perspective for investigating the underlying mechanisms driving brain calcification. In this review, we conducted an examination of the literature reporting on genetic variants in cell junction proteins associated with brain calcification to delineate potential molecular pathways and investigate genotype-phenotype correlations. This approach not only reinforces the rationale for molecular subtyping of brain calcification but also lays the groundwork for the discovery of novel causative genes involved in pathogenesis. © 2024 International Parkinson and Movement Disorder Society.

Many Faces of Diencephalic-Mesencephalic Junction Dysplasia Syndrome with GSX2 and PCDH12 Variants

Introduction

Diencephalic-mesencephalic junction dysplasia syndrome is a rare neurogenetic disorder reported to be caused by variants in several genes. Phenotypic presentation is characterized by clinical findings including developmental delay, hypotonia, spasticity, and dyskinetic movements in combination with distinctive imaging features on brain magnetic resonance imaging (MRI).

Methods

Whole exome sequencing was conducted to unveil the molecular etiology of patients presenting with neurological manifestations from two unrelated families.

Results

To the best of our knowledge, here we report the third family affected with diencephalic-mesencephalic junction dysplasia caused by a novel variant in GSX2 and two siblings with a PCDH12 variant exhibiting a less severe phenotype. The siblings with a PCDH12 variant were positioned at the milder end of the phenotypic spectrum. Although both exhibited a clinical phenotype resembling cerebral palsy, one showed partial fusion of the hypothalamus and mesencephalon, whereas MRI was unremarkable in the other. Biallelic GSX2 variants have been implicated in basal ganglia agenesis, and similarly, our patients had basal ganglia hypoplasia along with hypothalamic-mesencephalic fusion.

Conclusion

Identifying variants associated with the syndrome in different genes will contribute to genotype-phenotype correlation.

Genetic pathways in cerebral palsy: a review of the implications for precision diagnosis and understanding disease mechanisms

ABSTRACT

Cerebral palsy is a diagnostic term utilized to describe a group of permanent disorders affecting movement and posture. Patients with cerebral palsy are often only capable of limited activity, resulting from non-progressive disturbances in the fetal or neonatal brain. These disturbances severely impact the child's daily life and impose a substantial economic burden on the family. Although cerebral palsy encompasses various brain injuries leading to similar clinical outcomes, the understanding of its etiological pathways remains incomplete owing to its complexity and heterogeneity. This review aims to summarize the current knowledge on the genetic factors influencing cerebral palsy development. It is now widely acknowledged that genetic mutations and alterations play a pivotal role in cerebral palsy development, which can be further influenced by environmental factors. Despite continuous research endeavors, the underlying factors contributing to cerebral palsy remain are still elusive. However, significant progress has been made in genetic research that has markedly enhanced our comprehension of the genetic factors underlying cerebral palsy development. Moreover, these genetic factors have been categorized based on the identified gene mutations in patients through clinical genotyping, including thrombosis, angiogenesis, mitochondrial and oxidative phosphorylation function, neuronal migration, and cellular autophagy. Furthermore, exploring targeted genotypes holds potential for precision treatment. In conclusion, advancements in genetic research have substantially improved our understanding of the genetic causes underlying cerebral palsy. These breakthroughs have the potential to pave the way for new treatments and therapies, consequently shaping the future of cerebral palsy research and its clinical management. The investigation of cerebral palsy genetics holds the potential to significantly advance treatments and management strategies. By elucidating the underlying cellular mechanisms, we can develop targeted interventions to optimize outcomes. A continued collaboration between researchers and clinicians is imperative to comprehensively unravel the intricate genetic etiology of cerebral palsy.

Clinical Characteristics Suggestive of a Genetic Cause in Cerebral Palsy: A Systematic Review

BACKGROUND

Cerebral palsy (CP) is a clinical diagnosis and was long categorized as an acquired disorder, but more and more genetic etiologies are being identified. This review aims to identify the clinical characteristics that are associated with genetic CP to aid clinicians in selecting candidates for genetic testing.

METHODS

The PubMed database was systematically searched to identify genes associated with CP. The clinical characteristics accompanying these genetic forms of CP were compared with published data of large CP populations resulting in the identification of potential indicators of genetic CP.

RESULLTS

Of 1930 articles retrieved, 134 were included. In these, 55 CP genes (described in two or more cases, n = 272) and 79 candidate genes (described in only one case) were reported. The most frequently CP-associated genes were PLP1 (21 cases), ARG1 (17 cases), and CTNNB1 (13 cases). Dyskinesia and the absence of spasticity were identified as strong potential indicators of genetic CP. Presence of intellectual disability, no preterm birth, and no unilateral distribution of symptoms were classified as moderate genetic indicators.

CONCLUSIONS

Genetic causes of CP are increasingly identified. The clinical characteristics associated with genetic CP can aid clinicians regarding to which individual with CP to offer genetic testing. The identified potential genetic indicators need to be validated in large CP cohorts but can provide the first step toward a diagnostic algorithm for genetic CP.

PCDH12 loss results in premature neuronal differentiation and impeded migration in a cortical organoid model

Protocadherins (PCDHs) are cell adhesion molecules that regulate many essential neurodevelopmental processes related to neuronal maturation, dendritic arbor formation, axon pathfinding, and synaptic plasticity. Biallelic loss-of-function variants in PCDH12 are associated with several neurodevelopmental disorders (NDDs). Despite the highly deleterious outcome resulting from loss of PCDH12, little is known about its role during brain development and disease. Here, we show that PCDH12 loss severely impairs cerebral organoid development, with reduced proliferative areas and disrupted laminar organization. 2D models further show that neural progenitor cells lacking PCDH12 prematurely exit the cell cycle and differentiate earlier when compared with wild type. Furthermore, we show that PCDH12 regulates neuronal migration and suggest that this could be through a mechanism requiring ADAM10-mediated ectodomain shedding and/or membrane recruitment of cytoskeleton regulators. Our results demonstrate a critical involvement of PCDH12 in cortical organoid development, suggesting a potential cause for the pathogenic mechanisms underlying PCDH12-related NDDs.

Impaired migration and premature differentiation underlie the neurological phenotype associated with PCDH12 loss of function

Protocadherins (PCDHs) are cell adhesion molecules that regulate many essential neurodevelopmental processes related to neuronal maturation, dendritic arbor formation, axon pathfinding, and synaptic plasticity. Bi-allelic loss-of-function variants in PCDH12 are associated with several neurodevelopmental disorders (NDDs) such as diencephalic-mesencephalic dysplasia syndrome, cerebral palsy, cerebellar ataxia, and microcephaly. Despite the highly deleterious outcome resulting from loss of PCDH12, little is known about its role during brain development and disease. Here, we show that PCDH12 loss severely impairs cerebral organoid development with reduced proliferative areas and disrupted laminar organization. 2D models further show that neural progenitor cells lacking PCDH12 prematurely exit cell cycle and differentiate earlier when compared to wildtype. Furthermore, we show that PCDH12 regulates neuronal migration through a mechanism requiring ADAM10-mediated ectodomain shedding and membrane recruitment of cytoskeleton regulators. Our data demonstrate a critical and broad involvement of PCDH12 in cortical development, revealing the pathogenic mechanisms underlying PCDH12-related NDDs.

The phenotypic spectrum of PCDH12 associated disorders - Five new cases and review of the literature

PCDH12 is a member of the non-clustered protocadherin family of calcium-dependent cell adhesion proteins, which are involved in the regulation of brain development and endothelial adhesion. To date, only 15 families have been reported with PCDH12 associated disease. The main features previously associated with PCDH12 deficiency are developmental delay, movement disorder, epilepsy, microcephaly, visual impairment, midbrain malformations, and intracranial calcifications. Here, we report novel clinical features such as onset of epilepsy after infancy, episodes of transient developmental regression, and dysplasia of the medulla oblongata associated with three different novel truncating PCDH12 mutations in five cases (three children, two adults) from three unrelated families. Interestingly, our data suggests a clinical overlap with interferonopathies, and we show an elevated interferon score in two pediatric patients. This case series expands the genetic and phenotypic spectrum of PCDH12 associated diseases and highlights the broad clinical variability.

PCDH12 variants are associated with basal ganglia anomalies and exudative vitreoretinopathy

PCDH12 is a member of the non-clustered protocadherins that mediate cell-cell adhesion, playing crucial roles in many biological processes. Among these, PCDH12 promotes cell-cell interactions at inter-endothelial junctions, exerting essential functions in vascular homeostasis and angiogenesis. However, its exact role in eye vascular and brain development is not completely understood. To date, biallelic loss of function variants in PCDH12 have been associated with a neurodevelopmental disorder characterized by the typical neuroradiological findings of diencephalic-mesencephalic junction dysplasia and intracranial calcifications, whereas heterozygous variants have been recently linked to isolated brain calcifications in absence of cognitive impairment or other brain malformations. Recently, the phenotypic spectrum associated with PCDH12 deficiency has been expanded including cerebellar and eye abnormalities. Here, we report two female siblings harboring a novel frameshift homozygous variant (c.2169delT, p.(Val724TyrfsTer8)) in PCDH12. In addition to the typical diencephalic-mesencephalic junction dysplasia, brain MRI showed dysmorphic basal ganglia and thalamus that were reminiscent of a tubulin-like phenotype, mild cerebellar vermis hypoplasia and extensive prominence of perivascular spaces in both siblings. The oldest sister developed profound and progressive monocular visual loss and the eye exam revealed exudative vitreoretinopathy. Similar but milder eye changes were also noted in her younger sister. In summary, our report expands the clinical (brain and ocular) spectrum of PCDH12-related disorders and adds a further line of evidence underscoring the important role of PCDH12 in retinal vascular and brain development.

PCDH12-Related Movement Disorder

Protocadherin 12 (PCDH12) is a member of a nonclustered group of cell surface proteins. Mutations in the PCDH12 gene can cause varied phenotypes ranging from epilepsy and movement disorders to congenital malformations and calcifications in neuroimaging. We discussed here a 14-year-old male patient with a movement disorder that mimicked dyskinetic cerebral palsy in the outpatient department; however, exome sequencing revealed a homozygous premature stop codon in exon 1 of the PCDH12(−) gene. The case highlights the importance of careful clinical examination to look for the features that do not match an assigned neurological syndrome and the need for follow-up neuroimaging to look for any progressive changes in all cases of unexplained movement disorder and intellectual impairment.

Ophthalmic phenotypes associated with biallelic loss-of-function PCDH12 variants

Individuals carrying biallelic loss-of-function mutations in PCDH12 have been reported with three different conditions: the diencephalic-mesencephalic junction dysplasia syndrome 1 (DMJDS1), a disorder characterized by global developmental delay, microcephaly, dystonia, and a midbrain malformation at the diencephalic-mesencephalic junction; cerebral palsy combined with a neurodevelopmental disorder; and cerebellar ataxia with retinopathy. We report an additional patient carrying a homozygous PCDH12 frameshift, whose anamnesis combines the most recurrent DMJDS1 clinical features, that is, global developmental delay, microcephaly, and ataxia, with exudative vitreoretinopathy. This case and previously published DMJDS1 patients presenting with nonspecific visual impairments and ophthalmic disorders suggest that ophthalmic alterations are an integral part of clinical features associated with PCDH12 loss-of-function.

Metabolic and genetic disorders mimicking cerebral palsy

Cerebral palsy is a syndrome that encompasses a large group of childhood movement and posture disorders that result from a lesion occurring in the developing brain. The clinical presentation of many metabolic and genetic conditions, particularly in highly consanguineous populations, can mimic cerebral palsy particularly at early age. The aim of this review article is to identify the clinical features that should alert the physician to the possibility of disorders that resemble cerebral palsy, the clinical and neuroimaging red flags, and highlight some metabolic and genetic conditions which may present with spasticity, ataxia and dyskinesia. In the case of metabolic or genetic disorder, making a precise diagnosis is particularly important for the possibility of treatment, accurate prognosis and genetic counseling.

Genetic mimics of cerebral palsy

The term "cerebral palsy mimic" is used to describe a number of neurogenetic disorders that may present with motor symptoms in early childhood, resulting in a misdiagnosis of cerebral palsy. Cerebral palsy describes a heterogeneous group of neurodevelopmental disorders characterized by onset in infancy or early childhood of motor symptoms (including hypotonia, spasticity, dystonia, and chorea), often accompanied by developmental delay. The primary etiology of a cerebral palsy syndrome should always be identified if possible. This is particularly important in the case of genetic or metabolic disorders that have specific disease-modifying treatment. In this article, we discuss clinical features that should alert the clinician to the possibility of a cerebral palsy mimic, provide a practical framework for selecting and interpreting neuroimaging, biochemical, and genetic investigations, and highlight selected conditions that may present with predominant spasticity, dystonia/chorea, and ataxia. Making a precise diagnosis of a genetic disorder has important implications for treatment, and for advising the family regarding prognosis and genetic counseling. © 2019 International Parkinson and Movement Disorder Society.

Homozygous PCDH12 variants result in phenotype of cerebellar ataxia, dystonia, retinopathy, and dysmorphism

We report on a sib pair of Indian origin born of a consanguineous parentage with a novel phenotype of distinct facial dysmorphism, cerebellar ataxia, dystonia, and exudative retinopathy due to homozygous PCDH12 nonsense variations. cDNA studies showed >90% reduction in transcript levels in both patients, indicating nonsense-mediated decay and loss of function as the probable causative molecular mechanism of the phenotype.