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

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.

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.

Clinical spectrum of orbital and ocular abnormalities on fetal MRI

BACKGROUND

Fetal magnetic resonance imaging (MRI) may reveal sonographically occult ocular abnormalities. When discovered, acquired causes and genetic associations must be sought.

OBJECTIVE

We aim to evaluate a fetal cohort with orbit and/or globe malformations to determine whether there are imaging patterns that suggest the underlying cause.

MATERIALS AND METHODS

We searched all fetal MRI reports performed at an academic children's hospital over 9 consecutive years for orbit and/or globe abnormalities. Each positive exam and all follow-up MRIs were evaluated for interocular distance, globe size, shape and signal, and brain malformations. Genetic and clinical diagnoses were recorded from the medical record.

RESULTS

Seventy-six of 3,085 fetuses (2.5%) were diagnosed with ocular and/or globe abnormalities; 50% had postnatal follow-up MR exams, all confirming the fetal MRI findings. Ninety-two percent (70/76) had concurrent brain malformations. Sixty-seven percent (51/76) were diagnosed with an underlying disorder and 39% of these were genetically proven. The most common diagnoses with ocular globe abnormalities included CHARGE (coloboma of the eye, heart anomaly, choanal atresia, retardation and genital and ear anomalies) syndrome, trisomy 13 syndrome, dystroglycanopathy, holoprosencephaly and diencephalic-mesencephalic junction dysplasia. Genetic diagnoses were more likely with ocular globe abnormalities than isolated orbital abnormalities (P=0.04). Sixty-seven percent of fetuses with ocular calcifications, hemorrhage and/or lens abnormalities had potential maternal risk factors (P=0.03).

CONCLUSION

Malformed ocular globes are associated with brain malformations and genetic abnormalities. Ocular calcifications, hemorrhage and/or lens abnormalities may be associated with maternal risk factors. Genetic work-up should be considered when an ocular globe size or shape abnormality is detected.

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.