X-linked disorders with cerebellar dysgenesis

Rare X-linked variants carry predominantly male risk in autism, Tourette syndrome, and ADHD

Autism spectrum disorder (ASD), Tourette syndrome (TS), and attention-deficit/hyperactivity disorder (ADHD) display strong male sex bias, due to a combination of genetic and biological factors, as well as selective ascertainment. While the hemizygous nature of chromosome X (Chr X) in males has long been postulated as a key point of "male vulnerability", rare genetic variation on this chromosome has not been systematically characterized in large-scale whole exome sequencing studies of "idiopathic" ASD, TS, and ADHD. Here, we take advantage of informative recombinations in simplex ASD families to pinpoint risk-enriched regions on Chr X, within which rare maternally-inherited damaging variants carry substantial risk in males with ASD. We then apply a modified transmission disequilibrium test to 13,052 ASD probands and identify a novel high confidence ASD risk gene at exome-wide significance (MAGEC3). Finally, we observe that rare damaging variants within these risk regions carry similar effect sizes in males with TS or ADHD, further clarifying genetic mechanisms underlying male vulnerability in multiple neurodevelopmental disorders that can be exploited for systematic gene discovery.

Microglial Pruning: Relevance for Synaptic Dysfunction in Multiple Sclerosis and Related Experimental Models

Microglia, besides being able to react rapidly to a wide range of environmental changes, are also involved in shaping neuronal wiring. Indeed, they actively participate in the modulation of neuronal function by regulating the elimination (or “pruning”) of weaker synapses in both physiologic and pathologic processes. Mounting evidence supports their crucial role in early synaptic loss, which is emerging as a hallmark of several neurodegenerative diseases, including multiple sclerosis (MS) and its preclinical models. MS is an inflammatory, immune-mediated pathology of the white matter in which demyelinating lesions may cause secondary neuronal death. Nevertheless, primitive grey matter (GM) damage is emerging as an important contributor to patients’ long-term disability, since it has been associated with early and progressive cognitive decline (CD), which seriously worsens the quality of life of MS patients. Widespread synapse loss even in the absence of demyelination, axon degeneration and neuronal death has been demonstrated in different GM structures, thus raising the possibility that synaptic dysfunction could be an early and possibly independent event in the neurodegenerative process associated with MS. This review provides an overview of microglial-dependent synapse elimination in the neuroinflammatory process that underlies MS and its experimental models.

Crosstalk among Calcium ATPases: PMCA, SERCA and SPCA in Mental Diseases

Calcium in mammalian neurons is essential for developmental processes, neurotransmitter release, apoptosis, and signal transduction. Incorrectly processed Ca²⁺ signal is well-known to trigger a cascade of events leading to altered response to variety of stimuli and persistent accumulation of pathological changes at the molecular level. To counterbalance potentially detrimental consequences of Ca²⁺, neurons are equipped with sophisticated mechanisms that function to keep its concentration in a tightly regulated range. Calcium pumps belonging to the P-type family of ATPases: plasma membrane Ca²⁺-ATPase (PMCA), sarco/endoplasmic Ca²⁺-ATPase (SERCA) and secretory pathway Ca²⁺-ATPase (SPCA) are considered efficient line of defense against abnormal Ca²⁺ rises. However, their role is not limited only to Ca²⁺ transport, as they present tissue-specific functionality and unique sensitive to the regulation by the main calcium signal decoding protein—calmodulin (CaM). Based on the available literature, in this review we analyze the contribution of these three types of Ca²⁺-ATPases to neuropathology, with a special emphasis on mental diseases.

An Affordable Method for Evaluation of Ataxic Disorders Based on Electrooculography

Ataxias are a group of neurodegenerative disorders characterized by cerebellar dysfunction that cause irregularities in the rate, rhythm, amplitude, and force of voluntary movements. The electrooculogram (EOG) may provide clues about ataxic disorders because most of these patients have difficulty with visual tracking and fixing their gaze. Using electrodes, EOG records the biopotentials generated by eye movements. In this paper, three surface electrodes are placed around the eye socket, and the biopotentials generated by eye movements are acquired using a commercial bioamplifier device. Next, the signals are sent to the computer to be digitally processed to extract the rate of saccades as well as the delay and deviation of the gaze in response to a stimulus. These features are analysed in a novel software application designed to help physicians in evaluating ataxia. After applying several tests to both healthy and ataxia-affected patients, differences in EOG results were found. The evaluation of the reliability of the designed software application is made according to three metrics: sensitivity, specificity, and accuracy. The results indicate the proposed system's viability as an affordable method for evaluation of ataxic disorders.

Management of hydrocephalus in infants with severe hemophilia A: report of 2 cases

The authors report on the clinical course of two infants with severe hemophilia A (HA) and concomitant progressive hydrocephalus that required management with a ventriculoperitoneal shunt. The first child, with known HA, presented with a spontaneous intracranial hemorrhage and acquired hydrocephalus. He underwent cerebrospinal fluid diversion with a temporary external ventricular drain, followed by placement of a ventriculoperitoneal shunt. The second child had hydrocephalus secondary to a Dandy-Walker malformation and was diagnosed with severe HA during preoperative evaluation. He underwent placement of a ventriculoperitoneal shunt after progression of the hydrocephalus. The authors also review the treatment of hydrocephalus in patients with HA and describe the perioperative protocols used in their two cases. Treatment of hydrocephalus in infants with HA requires unique perioperative management to avoid complications.

Prenatal diagnosis of posterior fossa anomalies: Additional value of chromosomal microarray analysis in fetuses with cerebellar hypoplasia

OBJECTIVE

To elucidate the relationship between copy number variations (CNVs) detected by high-resolution chromosomal microarray analysis (CMA) and the type of prenatal posterior fossa anomalies (PFAs), especially cerebellar hypoplasia (CH).

METHODS

This study involved 77 pregnancies with PFAs who underwent CMA.

RESULTS

Chromosomal aberrations including pathogenic CNVs and variants of unknown significance were detected in 31.2% (24/77) of all cases by CMA and in 18.5% (12/65) in fetuses with normal karyotypes. The high detection rate of clinically significant CNVs was evident in fetuses with cerebellar hypoplasia (54.6%, 6/11), vermis hypoplasia (33.3%, 1/3), and Dandy-Walker malformation (25.0%, 3/12). Compare with fetuses without other anomalies, cases with CH and additional malformations had the higher CMA detection rate (33.3% vs 88.9%). Three cases of isolated unilateral CH with intact vermis and normal CMA result had normal outcomes. The deletion of 5p15, 6q terminal deletion, and X chromosome aberrations were the most frequent genetic defects associated with cerebellar hypoplasia.

CONCLUSION

Among fetuses with PFA, those with cerebellar hypoplasia, vermis hypoplasia, or Dandy-Walker malformation are at the highest risk of clinically significant CNVs. Chromosomal microarray analysis revealed the most frequent chromosomal aberrations associated with CH.

Genetics of Hereditary Ataxia in Scottish Terriers

BACKGROUND

Scottish Terriers have a high incidence of juvenile onset hereditary ataxia primarily affecting the Purkinje neuron of the cerebellar cortex and causing slowly progressive cerebellar dysfunction.

OBJECTIVE

To identify chromosomal regions associated with hereditary ataxia in Scottish Terriers.

ANIMALS

One hundred and fifty-three Scottish Terriers were recruited through the Scottish Terrier Club of America.

MATERIALS AND METHODS

Prospective study. Dogs were classified as affected if they had slowly progressive cerebellar signs. When possible, magnetic resonance imaging and histopathological evaluation of the brain were completed as diagnostic aids. To identify genomic regions connected with the disease, genome-wide mapping was performed using both linkage- and association-based approaches. Pedigree evaluation and homozygosity mapping were also performed to examine mode of inheritance and to investigate the region of interest, respectively.

RESULTS

Linkage and genome-wide association studies in a cohort of Scottish Terriers both identified a region on CFA X strongly associated with the disease trait. Homozygosity mapping revealed a 4 Mb region of interest. Pedigree evaluation failed to identify the possible mode of inheritance due to the lack of complete litter information.

CONCLUSION AND CLINICAL IMPORTANCE

This finding suggests that further genetic investigation of the potential region of interest on CFA X should be considered in order to identify the causal mutation as well as develop a genetic test to eliminate the disease from this breed.

Current concepts in the treatment of hereditary ataxias

Hereditary ataxias (HA) represents an extensive group of clinically and genetically heterogeneous neurodegenerative diseases, characterized by progressive ataxia combined with extra-cerebellar and multi-systemic involvements, including peripheral neuropathy, pyramidal signs, movement disorders, seizures, and cognitive dysfunction. There is no effective treatment for HA, and management remains supportive and symptomatic. In this review, we will focus on the symptomatic treatment of the main autosomal recessive ataxias, autosomal dominant ataxias, X-linked cerebellar ataxias and mitochondrial ataxias. We describe management for different clinical symptoms, mechanism-based approaches, rehabilitation therapy, disease modifying therapy, future clinical trials and perspectives, genetic counseling and preimplantation genetic diagnosis.

T-Cells Underlie Some but Not All of the Cerebellar Pathology in a Neonatal Rat Model of Congenital Lymphocytic Choriomeningitis Virus Infection

Lymphocytic choriomeningitis virus (LCMV) infection during pregnancy injures the human fetal brain. Neonatal rats inoculated with LCMV are an excellent model of congenital LCMV infection because they develop cerebellar injuries similar to those in humans. To evaluate the role of T-lymphocytes in LCMV-induced cerebellar pathology, congenitally athymic rats, deficient in T-lymphocytes were compared with euthymic rats. Peak viral titers and cellular targets of infection were similar, but viral clearance from astrocytes was impaired in the athymic rats. Cytokines and chemokines rose to higher levels and for a greater duration in the euthymic rats than in their athymic counterparts. The euthymic rats developed an intense lymphocytic infiltration, accompanied by destructive lesions of the cerebellum and a neuronal migration defect because of T-cell-mediated alteration of Bergmann glia. These pathologic changes were absent in the athymic rats but were restored by adoptive transfer of lymphocytes. Athymic rats were not free of pathologic effects, however, as the virus induced cerebellar hypoplasia. Thus, T-lymphocytes play key roles in LCMV clearance, cytokine/chemokine responses, and pathogenesis of destructive lesions and neuronal migration disturbances but not all pathology is T-lymphocyte-dependent. Cerebellar hypoplasia from LCMV occurs even in the absence of T-lymphocytes and is likely due to the viral infection itself.

Mutations in the IRBIT domain of ITPR1 are a frequent cause of autosomal dominant nonprogressive congenital ataxia

Congenital ataxias are nonprogressive neurological disorders characterized by neonatal hypotonia, developmental delay and ataxia, variably associated with intellectual disability and other neurological or extraneurological features. We performed trio-based whole-exome sequencing of 12 families with congenital cerebellar and/or vermis atrophy in parallel with targeted next-generation sequencing of known ataxia genes (CACNA1A, ITPR1, KCNC3, ATP2B3 and GRM1) in 12 additional patients with a similar phenotype. Novel pathological mutations of ITPR1 (inositol 1,4,5-trisphosphate receptor, type 1) were found in seven patients from four families (4/24, ∼16.8%) all localized in the IRBIT (inositol triphosphate receptor binding protein) domain which plays an essential role in the regulation of neuronal plasticity and development. Our study expands the mutational spectrum of ITPR1-related congenital ataxia and indicates that ITPR1 gene screening should be implemented in this subgroup of ataxias.

A novel mouse model for ataxia-telangiectasia with a N-terminal mutation displays a behavioral defect and a low incidence of lymphoma but no increased oxidative burden

Ataxia-telangiectasia (A-T) is a rare multi-system disorder caused by mutations in the ATM gene. Significant heterogeneity exists in the underlying genetic mutations and clinical phenotypes. A number of mouse models have been generated that harbor mutations in the distal region of the gene, and a recent study suggests the presence of residual ATM protein in the brain of one such model. These mice recapitulate many of the characteristics of A-T seen in humans, with the notable exception of neurodegeneration. In order to study how an N-terminal mutation affects the disease phenotype, we generated an inducible Atm mutant mouse model (Atm(tm1Mmpl/tm1Mmpl), referred to as A-T [M]) predicted to express only the first 62 amino acids of Atm. Cells derived from A-T [M] mutant mice exhibited reduced cellular proliferation and an altered DNA damage response, but surprisingly, showed no evidence of an oxidative imbalance. Examination of the A-T [M] animals revealed an altered immunophenotype consistent with A-T. In contrast to mice harboring C-terminal Atm mutations that disproportionately develop thymic lymphomas, A-T [M] mice developed lymphoma at a similar rate as human A-T patients. Morphological analyses of A-T [M] cerebella revealed no substantial cellular defects, similar to other models of A-T, although mice display behavioral defects consistent with cerebellar dysfunction. Overall, these results suggest that loss of Atm is not necessarily associated with an oxidized phenotype as has been previously proposed and that loss of ATM protein is not sufficient to induce cerebellar degeneration in mice.

A de novo X;8 translocation creates a PTK2-THOC2 gene fusion with THOC2 expression knockdown in a patient with psychomotor retardation and congenital cerebellar hypoplasia

BACKGROUND AND AIM

We identified a balanced de novo translocation involving chromosomes Xq25 and 8q24 in an eight year-old girl with a non-progressive form of congenital ataxia, cognitive impairment and cerebellar hypoplasia.

METHODS AND RESULTS

Breakpoint definition showed that the promoter of the Protein Tyrosine Kinase 2 (PTK2, also known as Focal Adhesion Kinase, FAK) gene on chromosome 8q24.3 is translocated 2 kb upstream of the THO complex subunit 2 (THOC2) gene on chromosome Xq25. PTK2 is a well-known non-receptor tyrosine kinase whereas THOC2 encodes a component of the evolutionarily conserved multiprotein THO complex, involved in mRNA export from nucleus. The translocation generated a sterile fusion transcript under the control of the PTK2 promoter, affecting expression of both PTK2 and THOC2 genes. PTK2 is involved in cell adhesion and, in neurons, plays a role in axonal guidance, and neurite growth and attraction. However, PTK2 haploinsufficiency alone is unlikely to be associated with human disease. Therefore, we studied the role of THOC2 in the CNS using three models: 1) THOC2 ortholog knockout in C.elegans which produced functional defects in specific sensory neurons; 2) Thoc2 knockdown in primary rat hippocampal neurons which increased neurite extension; 3) Thoc2 knockdown in neuronal stem cells (LC1) which increased their in vitro growth rate without modifying apoptosis levels.

CONCLUSION

We suggest that THOC2 can play specific roles in neuronal cells and, possibly in combination with PTK2 reduction, may affect normal neural network formation, leading to cognitive impairment and cerebellar congenital hypoplasia.

Inherited cerebellar ataxia in childhood: a pattern-recognition approach using brain MRI

Ataxia is the principal symptom of many common neurologic diseases in childhood. Ataxias caused by dysfunction of the cerebellum occur in acute, intermittent, and progressive disorders. Most of the chronic progressive processes are secondary to degenerative and metabolic diseases. In addition, congenital malformation of the midbrain and hindbrain can also be present, with posterior fossa symptoms related to ataxia. Brain MR imaging is the most accurate imaging technique to investigate these patients, and imaging abnormalities include size, shape, and/or signal of the brain stem and/or cerebellum. Supratentorial and cord lesions are also common. This review will discuss a pattern-recognition approach to inherited cerebellar ataxia in childhood. The purpose is to provide a comprehensive discussion that ultimately could help neuroradiologists better manage this important topic in pediatric neurology.

Mean Expression of the X-Chromosome is Associated with Neuronal Density

Background: Neurodegenerative diseases are characterized by key features such as loss of neurons, astrocytosis, and microglial activation/proliferation. These changes cause differences in the density of cell types between control and disease subjects, confounding results from gene expression studies. Chromosome X (ChrX) is known to be specifically important in the brain. We hypothesized the existence of a chromosomal signature of gene expression associated with the X-chromosome for neurological conditions not normally associated with that chromosome. The hypothesis was investigated using publicly available microarray datasets from studies on Parkinson’s disease, Alzheimer’s disease, and Huntington’s disease. Data were analyzed using Chromowave, an analytical tool for detecting spatially extended expression changes along chromosomes. To examine associations with neuronal density and astrocytosis, the expression of cell specific reporter genes was extracted. The association between these genes and the expression patterns extracted by Chromowave was then analyzed. Further analyses of the X:Autosome ratios for laser dissected neurons, microglia cultures and whole tissue were performed to detect cell specific differences. Results: We observed an extended pattern of low expression of ChrX consistent in all the neurodegenerative disease brain datasets. There was a strong correlation between mean ChrX expression and the pattern extracted from the autosomal genes representing neurons, but not with mean autosomal expression. No chromosomal patterns associated with the neuron specific genes were found on other chromosomes. The chromosomal expression pattern was not present in datasets from blood cells. The X:Autosome expression ratio was also higher in neuronal cells than in tissues with a mix of cell types. Conclusions: The results suggest that neurological disorders show as a reduction in mean expression of many genes along ChrX. The most likely explanation for this finding relates to the documented general up-regulation of ChrX in brain tissue which, this work suggests, occurs primarily in neurons. If validated, this cell specific ChrX expression warrants further research as understanding the biological reasons and mechanisms for this expression, may help to elucidate a connection with the development of neurodegenerative disorders.

Mutation of plasma membrane Ca2+ ATPase isoform 3 in a family with X-linked congenital cerebellar ataxia impairs Ca2+ homeostasis

Ca(2+) in neurons is vital to processes such as neurotransmission, neurotoxicity, synaptic development, and gene expression. Disruption of Ca(2+) homeostasis occurs in brain aging and in neurodegenerative disorders. Membrane transporters, among them the calmodulin (CaM)-activated plasma membrane Ca(2+) ATPases (PMCAs) that extrude Ca(2+) from the cell, play a key role in neuronal Ca(2+) homeostasis. Using X-exome sequencing we have identified a missense mutation (G1107D) in the CaM-binding domain of isoform 3 of the PMCAs in a family with X-linked congenital cerebellar ataxia. PMCA3 is highly expressed in the cerebellum, particularly in the presynaptic terminals of parallel fibers-Purkinje neurons. To study the effects of the mutation on Ca(2+) extrusion by the pump, model cells (HeLa) were cotransfected with expression plasmids encoding its mutant or wild-type (wt) variants and with the Ca(2+)-sensing probe aequorin. The mutation reduced the ability of the PMCA3 pump to control the cellular homeostasis of Ca(2+). It significantly slowed the return to baseline of the Ca(2+) transient induced by an inositol-trisphosphate (InsP(3))-linked plasma membrane agonist. It also compromised the ability of the pump to oppose the influx of Ca(2+) through the plasma membrane capacitative channels.