Brain calcifications and PCDH12 variants

Morphogenetic theory of mental and cognitive disorders: the role of neurotrophic and guidance molecules

Mental illness and cognitive disorders represent a serious problem for the modern society. Many studies indicate that mental disorders are polygenic and that impaired brain development may lay the ground for their manifestation. Neural tissue development is a complex and multistage process that involves a large number of distant and contact molecules. In this review, we have considered the key steps of brain morphogenesis, and the major molecule families involved in these process. The review provides many indications of the important contribution of the brain development process and correct functioning of certain genes to human mental health. To our knowledge, this comprehensive review is one of the first in this field. We suppose that this review may be useful to novice researchers and clinicians wishing to navigate the field.

New Evidence Suggests a Much Complex Classification for the Genetic Pattern of Inheritance in Primary Brain Calcification

Primary familial brain calcification (PFBC), often called Fahr's disease, is a condition in which calcium phosphate accumulates in the brain, mainly in the basal ganglia, thalamus, and cerebellum, and without the association of any metabolic or infectious cause. Patients present a variety of neurological and psychiatric disorders, usually during adulthood. The disease is caused by autosomal dominant pathogenic variants in genes such as SLC20A2, PDGFRB, PDGFB, and XPR1. MYORG and JAM2 are the other genes linked to homozygous patterns of inheritance. Here, we briefly discuss the recent cases reported by Ceylan et al. (2022) and Al-Kasbi et al. (2022), which challenge the current association with two previous genes and a clear pattern of inheritance. Ceylan et al. report a new biallelic variant related to a pathogenic variant in the SLC20A2 gene, which is typically associated with a heterozygous mutation pattern. The affected siblings displayed a severe and early onset of the disease, revealing a phenotype similar to that seen in CMV infections, often named as pseudo-TORCH. Furthermore, a study of genes related to intellectual disability conducted by Al-Kasbi et al. demonstrated that the biallelic manifestation of the XPR1 gene was associated with early symptoms, leading to the belief that the homozygous pattern of genes responsible for causing PFBC with an autosomal dominant pattern may also be linked to early-onset manifestations of PFBC. Further studies might explore the variety of clinical presentations linked to PFBC genes, especially if we pay attention to complex patterns of inheritance, reinforcing the need for a more detailed bioinformatic analysis.

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.

Random forest-integrated analysis in AD and LATE brain transcriptome-wide data to identify disease-specific gene expression

Alzheimer's disease (AD) is a complex neurodegenerative disorder that affects thinking, memory, and behavior. Limbic-predominant age-related TDP-43 encephalopathy (LATE) is a recently identified common neurodegenerative disease that mimics the clinical symptoms of AD. The development of drugs to prevent or treat these neurodegenerative diseases has been slow, partly because the genes associated with these diseases are incompletely understood. A notable hindrance from data analysis perspective is that, usually, the clinical samples for patients and controls are highly imbalanced, thus rendering it challenging to apply most existing machine learning algorithms to directly analyze such datasets. Meeting this data analysis challenge is critical, as more specific disease-associated gene identification may enable new insights into underlying disease-driving mechanisms and help find biomarkers and, in turn, improve prospects for effective treatment strategies. In order to detect disease-associated genes based on imbalanced transcriptome-wide data, we proposed an integrated multiple random forests (IMRF) algorithm. IMRF is effective in differentiating putative genes associated with subjects having LATE and/or AD from controls based on transcriptome-wide data, thereby enabling effective discrimination between these samples. Various forms of validations, such as cross-domain verification of our method over other datasets, improved and competitive classification performance by using identified genes, effectiveness of testing data with a classifier that is completely independent from decision trees and random forests, and relationships with prior AD and LATE studies on the genes linked to neurodegeneration, all testify to the effectiveness of IMRF in identifying genes with altered expression in LATE and/or AD. We conclude that IMRF, as an effective feature selection algorithm for imbalanced data, is promising to facilitate the development of new gene biomarkers as well as targets for effective strategies of disease prevention and treatment.

Osteogenic Mechanisms of Basal Ganglia Calcification and its ex vivo Model in the Hypoparathyroid Milieu

CONTEXT

Basal-ganglia calcification (BGC) is common (70%) in patients with chronic hypoparathyroidism. Interestingly, cortical gray matter is spared from calcification. The mechanism of BGC, role of hyperphosphatemia, and modulation of osteogenic molecules by parathyroid hormone (PTH) in its pathogenesis is not clear.

OBJECTIVE

We assessed the expression of a large repertoire of molecules with proosteogenic or antiosteogenic effects, including neuroprogenitor cells in caudate, dentate, and cortical gray matter from normal autopsy tissues. The effect of high phosphate and PTH was assessed in an ex vivo model of BGC using striatum tissue culture of the Sprague-Dawley rat.

METHODS

The messenger RNA and protein expression of 39 molecules involved in multiple osteogenic pathways were assessed in 25 autopsy tissues using reverse-transcriptase polymerase chain reaction, Western blot, and immunofluorescence. The striatal culture was maintained in a hypoparathyroid milieu for 24 days with and without (a) high phosphate (10-mm β-glycerophosphate) and (b) PTH(1-34) (50 ng/mL Dulbecco's modified Eagle's medium-F12 media) for their effect on striatal calcification and osteogenic molecules.

RESULTS

Procalcification molecules (osteonectin, β-catenin, klotho, FZD4, NT5E, LRP5, WNT3A, collagen-1α, and SOX2-positive neuroprogenitor stem cells) had significantly higher expression in the caudate than gray matter. Caudate nuclei also had higher expression of antiosteogenic molecules (osteopontin, carbonic anhydrase-II [CA-II], MGP, sclerostin, ISG15, ENPP1, and USP18). In an ex vivo model, striatum culture showed an increased propensity for calcified nodules with mineral deposition similar to that of bone tissue on Fourier-transformed infrared spectroscopy, alizarin, and von Kossa stain. Mineralization in striatal culture was enhanced by high phosphate and decreased by exogenous PTH through increased expression of CA-II.

CONCLUSION

This study provides a conceptual advance on the molecular mechanisms of BGC and the possibility of PTH therapy to prevent this complication in a hypoparathyroid milieu.

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.

SMAD6 transduces endothelial cell flow responses required for blood vessel homeostasis

Fluid shear stress provided by blood flow instigates a transition from active blood vessel network expansion during development, to vascular homeostasis and quiescence that is important for mature blood vessel function. Here we show that SMAD6 is required for endothelial cell flow-mediated responses leading to maintenance of vascular homeostasis. Concomitant manipulation of the mechanosensor Notch1 pathway and SMAD6 expression levels revealed that SMAD6 functions downstream of ligand-induced Notch signaling and transcription regulation. Mechanistically, full-length SMAD6 protein was needed to rescue Notch loss-induced flow misalignment. Endothelial cells depleted for SMAD6 had defective barrier function accompanied by upregulation of proliferation-associated genes and down regulation of junction-associated genes. The vascular protocadherin PCDH12 was upregulated by SMAD6 and required for proper flow-mediated endothelial cell alignment, placing it downstream of SMAD6. Thus, SMAD6 is a required transducer of flow-mediated signaling inputs downstream of Notch1 and upstream of PCDH12, as vessels transition from an angiogenic phenotype to maintenance of a homeostatic phenotype.

Intracranial calcifications in childhood: Part 2

This article is the second of a two-part series on intracranial calcification in childhood. In Part 1, the authors discussed the main differences between physiological and pathological intracranial calcification. They also outlined histological intracranial calcification characteristics and how these can be detected across different neuroimaging modalities. Part 1 emphasized the importance of age at presentation and intracranial calcification location and proposed a comprehensive neuroimaging approach toward the differential diagnosis of the causes of intracranial calcification. Pathological intracranial calcification can be divided into infectious, congenital, endocrine/metabolic, vascular, and neoplastic. In Part 2, the chief focus is on discussing endocrine/metabolic, vascular, and neoplastic intracranial calcification etiologies of intracranial calcification. Endocrine/metabolic diseases causing intracranial calcification are mainly from parathyroid and thyroid dysfunction and inborn errors of metabolism, such as mitochondrial disorders (MELAS, or mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes; Kearns-Sayre; and Cockayne syndromes), interferonopathies (Aicardi-Goutières syndrome), and lysosomal disorders (Krabbe disease). Specific noninfectious causes of intracranial calcification that mimic TORCH (toxoplasmosis, other [syphilis, varicella-zoster, parvovirus B19], rubella, cytomegalovirus, and herpes) infections are known as pseudo-TORCH. Cavernous malformations, arteriovenous malformations, arteriovenous fistulas, and chronic venous hypertension are also known causes of intracranial calcification. Other vascular-related causes of intracranial calcification include early atherosclerosis presentation (children with risk factors such as hyperhomocysteinemia, familial hypercholesterolemia, and others), healed hematoma, radiotherapy treatment, old infarct, and disorders of the microvasculature such as COL4A1- and COL4A2-related diseases. Intracranial calcification is also seen in several pediatric brain tumors. Clinical and familial information such as age at presentation, maternal exposure to teratogens including viruses, and association with chromosomal abnormalities, pathogenic genes, and postnatal infections facilitates narrowing the differential diagnosis of the multiple causes of intracranial calcification.

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.

Loss of Protocadherin-12 Leads to Diencephalic-Mesencephalic Junction Dysplasia Syndrome

OBJECTIVE

To identify causes of the autosomal-recessive malformation, diencephalic-mesencephalic junction dysplasia (DMJD) syndrome.

METHODS

Eight families with DMJD were studied by whole-exome or targeted sequencing, with detailed clinical and radiological characterization. Patient-derived induced pluripotent stem cells were derived into neural precursor and endothelial cells to study gene expression.

RESULTS

All patients showed biallelic mutations in the nonclustered protocadherin-12 (PCDH12) gene. The characteristic clinical presentation included progressive microcephaly, craniofacial dysmorphism, psychomotor disability, epilepsy, and axial hypotonia with variable appendicular spasticity. Brain imaging showed brainstem malformations and with frequent thinned corpus callosum with punctate brain calcifications, reflecting expression of PCDH12 in neural and endothelial cells. These cells showed lack of PCDH12 expression and impaired neurite outgrowth.

INTERPRETATION

DMJD patients have biallelic mutations in PCDH12 and lack of protein expression. These patients present with characteristic microcephaly and abnormalities of white matter tracts. Such pathogenic variants predict a poor outcome as a result of brainstem malformation and evidence of white matter tract defects, and should be added to the phenotypic spectrum associated with PCDH12-related conditions. Ann Neurol 2018;84:646-655.