Non-progressive congenital ataxias

Microstructural Properties of the Cerebellar Peduncles in Children With Developmental Language Disorder

Children with developmental language disorder (DLD) struggle to learn their native language for no apparent reason. While research on the neurobiological underpinnings of the disorder has focused on the role of corticostriatal systems, little is known about the role of the cerebellum in DLD. Corticocerebellar circuits might be involved in the disorder as they contribute to complex sensorimotor skill learning, including the acquisition of spoken language. Here, we used diffusion-weighted imaging data from 77 typically developing and 54 children with DLD and performed probabilistic tractography to identify the cerebellum's white matter tracts: the inferior, middle, and superior cerebellar peduncles. Children with DLD showed lower fractional anisotropy (FA) in the inferior cerebellar peduncles (ICP), fiber tracts that carry motor and sensory input via the inferior olive to the cerebellum. Lower FA in DLD was driven by lower axial diffusivity. Probing this further with more sophisticated modeling of diffusion data, we found higher orientation dispersion but no difference in neurite density in the ICP of children with DLD. Reduced FA is therefore unlikely to be reflecting microstructural differences in myelination, rather the organization of axons in these pathways is disrupted. ICP microstructure was not associated with language or motor coordination performance in our sample. We also found no differences in the middle and superior peduncles, the main pathways connecting the cerebellum with the cortex. To conclude, it is not corticocerebellar but atypical olivocerebellar white matter connections that characterize DLD and suggest the involvement of the olivocerebellar system in speech and language acquisition and development.

Hereditary Ataxias: From Bench to Clinic, Where Do We Stand?

Cerebellar ataxias are a wide heterogeneous group of movement disorders. Within this broad umbrella of diseases, there are both genetics and sporadic forms. The clinical presentation of these conditions can exhibit a diverse range of symptoms across different age groups, spanning from pure cerebellar manifestations to sensory ataxia and multisystemic diseases. Over the last few decades, advancements in our understanding of genetics and molecular pathophysiology related to both dominant and recessive ataxias have propelled the field forward, paving the way for innovative therapeutic strategies aimed at preventing and arresting the progression of these diseases. Nevertheless, the rarity of certain forms of ataxia continues to pose challenges, leading to limited insights into the etiology of the disease and the identification of target pathways. Additionally, the lack of suitable models hampers efforts to comprehensively understand the molecular foundations of disease's pathophysiology and test novel therapeutic interventions. In the following review, we describe the epidemiology, symptomatology, and pathological progression of hereditary ataxia, including both the prevalent and less common forms of these diseases. Furthermore, we illustrate the diverse molecular pathways and therapeutic approaches currently undergoing investigation in both pre-clinical studies and clinical trials. Finally, we address the existing and anticipated challenges within this field, encompassing both basic research and clinical endeavors.

Microstructural Properties of the Cerebellar Peduncles in Children with Developmental Language Disorder

Children with developmental language disorder (DLD) struggle to learn their native language for no apparent reason. While research on the neurobiological underpinnings of the disorder has focused on the role of cortico-striatal systems, little is known about the role of the cerebellum in DLD. Cortico-cerebellar circuits might be involved in the disorder as they contribute to complex sensorimotor skill learning, including the acquisition of spoken language. Here, we used diffusion-weighted imaging data from 77 typically developing and 54 children with DLD and performed probabilistic tractography to identify the cerebellum's white matter tracts: the inferior, middle, and superior cerebellar peduncles. Children with DLD showed lower fractional anisotropy (FA) in the inferior cerebellar peduncles (ICP), fiber tracts that carry motor and sensory input via the inferior olive to the cerebellum. Lower FA in DLD was driven by lower axial diffusivity. Probing this further with more sophisticated modeling of diffusion data, we found higher orientation dispersion but no difference in neurite density in the ICP of DLD. Reduced FA is therefore unlikely to be reflecting microstructural differences in myelination in this tract, rather the organization of axons in these pathways is disrupted. ICP microstructure was not associated with language or motor coordination performance in our sample. We also found no differences in the middle and superior peduncles, the main pathways connecting the cerebellum with the cortex. To conclude, it is not cortico-cerebellar but atypical olivocerebellar white matter connections that characterize DLD and suggest the involvement of the olivocerebellar system in speech acquisition and development.

A Proposed Clinical Classification and a Diagnostic Approach for Congenital Ataxias

Purpose of Review

This review proposes a clinical classification for congenital ataxias based on clinical features, neuroimaging, and course of the disease.

Recent Findings

Congenital ataxias are an unusual group of neurologic disorders, with heterogeneous clinical and genetic presentation. Typical clinical features of congenital ataxias include variable degrees of motor developmental delay, very early onset cerebellar ataxia, cognitive impairment, and hypotonia, frequently mistakenly diagnosed as cerebral palsy. Congenital ataxias are usually nonprogressive. Neuroimaging plays an important role in the characterization of congenital ataxias. Despite the development of genetics with exome sequencing, several congenital ataxias remain undetermined, and medical literature on this topic is scarce.

Summary

A didactic classification based on the clinical and neuroimaging features for congenital ataxias include the following 4 main groups: cerebellar malformation, syndromic congenital ataxias, congenital cerebellar hypoplasia, and pontocerebellar hypoplasia. A diagnostic approach for congenital ataxias is proposed, and its differential diagnosis is also discussed.

The de novo CACNA1A pathogenic variant Y1384C associated with hemiplegic migraine, early onset cerebellar atrophy and developmental delay leads to a loss of Cav2.1 channel function

CACNA1A pathogenic variants have been linked to several neurological disorders including familial hemiplegic migraine and cerebellar conditions. More recently, de novo variants have been associated with severe early onset developmental encephalopathies. CACNA1A is highly expressed in the central nervous system and encodes the pore-forming Ca_Vα₁ subunit of P/Q-type (Cav2.1) calcium channels. We have previously identified a patient with a de novo missense mutation in CACNA1A (p.Y1384C), characterized by hemiplegic migraine, cerebellar atrophy and developmental delay. The mutation is located at the transmembrane S5 segment of the third domain. Functional analysis in two predominant splice variants of the neuronal Cav2.1 channel showed a significant loss of function in current density and changes in gating properties. Moreover, Y1384 variants exhibit differential splice variant-specific effects on recovery from inactivation. Finally, structural analysis revealed structural damage caused by the tyrosine substitution and changes in electrostatic potentials.

Clinical phenotypes of infantile onset CACNA1A-related disorder

BACKGROUND

CACNA1A-related disorders present with persistent progressive and non-progressive cerebellar ataxia and paroxysmal events: epileptic seizures and non-epileptic attacks. These phenotypes overlap and co-exist in the majority of patients.

OBJECTIVE

To describe phenotypes in infantile onset CACNA1A-related disorder and to explore intra-familial variations and genotype-phenotype correlations.

MATERIAL AND METHODS

This study was a multicenter international collaboration. A retrospective chart review of CACNA1A patients was performed. Clinical, radiological, and genetic data were collected and analyzed in 47 patients with infantile-onset disorder.

RESULTS

Paroxysmal non-epileptic events (PNEE) were observed in 68% of infants, with paroxysmal tonic upward gaze (PTU) noticed in 47% of infants. Congenital cerebellar ataxia (CCA) was diagnosed in 51% of patients including four patients with developmental delay and only one neurological sign. PNEEs were found in 63% of patients at follow-up, with episodic ataxia (EA) in 40% of the sample. Cerebellar ataxia was found in 58% of the patients at follow-up. Four patients had epilepsy in infancy and nine in childhood. Seven infants had febrile convulsions, three of which developed epilepsy later; all three patients had CCA. Cognitive difficulties were demonstrated in 70% of the children. Cerebellar atrophy was found in only one infant but was depicted in 64% of MRIs after age two.

CONCLUSIONS

Nearly all of the infants had CCA, PNEE or both. Cognitive difficulties were frequent and appeared to be associated with CCA. Epilepsy was more frequent after age two. Febrile convulsions in association with CCA may indicate risk of epilepsy in later childhood. Brain MRI was normal in infancy. There were no genotype-phenotype correlations found.

Biallelic Variants in the Nuclear Pore Complex Protein NUP93 Are Associated with Non-progressive Congenital Ataxia

Nuclear pore complexes (NPCs) are the gateways of the nuclear envelope mediating transport between cytoplasm and nucleus. They form huge complexes of 125 MDa in vertebrates and consist of about 30 different nucleoporins present in multiple copies in each complex. Here, we describe pathogenic variants in the nucleoporin 93 (NUP93) associated with an autosomal recessive form of congenital ataxia. Two rare compound heterozygous variants of NUP93 were identified by whole exome sequencing in two brothers with isolated cerebellar atrophy: one missense variant (p.R537W) results in a protein which does not localize to NPCs and cannot functionally replace the wild type protein, whereas the variant (p.F699L) apparently supports NPC assembly. In addition to its recently described pathological role in steroid-resistant nephrotic syndrome, our work identifies NUP93 as a candidate gene for non-progressive congenital ataxia.

X-linked ataxias

X-linked cerebellar ataxias (XLCA) are an expanding group of genetically heterogeneous and clinically variable conditions characterized by cerebellar dysgenesis (hypoplasia, atrophy, or dysplasia) caused by gene mutations or genomic imbalances on the X chromosome. The neurologic features of XLCA include hypotonia, developmental delay, intellectual disability, ataxia, and other cerebellar signs. Normal cognitive development has also been reported. Cerebellar defects may be isolated or associated with other brain malformations or extraneurologic involvement. More than 20 genes on the X chromosome, mainly encoding for proteins involved in brain development and synaptic function that have been constantly or occasionally associated with a pathologic cerebellar phenotype, and several families with X-linked inheritance have been reported. Given the excess of males with ataxia, this group of conditions is probably underestimated and families of patients with neuroradiologic and clinical evidence of a cerebellar disorder should be counseled for high risk of X-linked inheritance.

Spinocerebellar ataxia type 29 due to mutations in ITPR1: a case series and review of this emerging congenital ataxia

Background

Spinocerebellar ataxia type 29 (SCA29) is an autosomal dominant, non-progressive cerebellar ataxia characterized by infantile-onset hypotonia, gross motor delay and cognitive impairment. Affected individuals exhibit cerebellar dysfunction and often have cerebellar atrophy on neuroimaging. Recently, missense mutations in ITPR1 were determined to be responsible.

Results

Clinical information on 21 individuals from 15 unrelated families with ITPR1 mutations was retrospectively collected using standardized questionnaires, including 11 previously unreported singletons and 2 new patients from a previously reported family. We describe the genetic, clinical and neuroimaging features of these patients to further characterize the clinical features of this rare condition and assess for any genotype-phenotype correlation for this disorder. Our cohort consisted of 9 males and 12 females, with ages ranging from 28 months to 49 years. Disease course was non-progressive with infantile-onset hypotonia and delays in motor and speech development. Gait ataxia was present in all individuals and 10 (48%) were not ambulating independently between the ages of 3–12 years of age. Mild-to-moderate cognitive impairment was present in 17 individuals (85%). Cerebellar atrophy developed after initial symptom presentation in 13 individuals (72%) and was not associated with disease progression or worsening functional impairment. We identified 12 different mutations including 6 novel mutations; 10 mutations were missense (with 4 present in >1 individual), 1 a splice site mutation leading to an in-frame insertion and 1 an in-frame deletion. No specific genotype-phenotype correlations were observed within our cohort.

Conclusions

Our findings document significant clinical heterogeneity between individuals with SCA29 in a large cohort of molecularly confirmed cases. Based on the retrospective observed clinical features and disease course, we provide recommendations for management. Further research into the natural history of SCA29 through prospective studies is an important next step in better understanding the condition.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-017-0672-7) contains supplementary material, which is available to authorized users.

Missense mutations of CACNA1A are a frequent cause of autosomal dominant nonprogressive congenital ataxia

BACKGROUND

Mutations in the CACNA1A gene, encoding the pore-forming CaV2.1 (P/Q-type) channel α1A subunit, localized at presynaptic terminals of brain and cerebellar neurons, result in clinically variable neurological disorders including hemiplegic migraine (HM) and episodic or progressive adult-onset ataxia (EA2, SCA6). Most recently, CACNA1A mutations have been identified in patients with nonprogressive congenital ataxia (NPCA).

METHODS

We performed targeted resequencing of known genes involved in cerebellar dysfunction, in 48 patients with congenital or early onset ataxia associated with cerebellar and/or vermis atrophy.

RESULTS

De novo missense mutations of CACNA1A were found in four patients (4/48, ∼8.3%). Three of them developed migraine before or after the onset of ataxia. Seizures were present in half of the cases.

CONCLUSION

Our results expand the clinical and mutational spectrum of CACNA1A-related phenotype in childhood and suggest that CACNA1A screening should be implemented in this subgroup of ataxias.

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.

Non-progressive cerebellar ataxia and previous undetermined acute cerebellar injury: a mysterious clinical condition

Cerebellar ataxias represent a wide group of neurological diseases secondary to dysfunctions of cerebellum or its associated pathways, rarely coursing with acute-onset acquired etiologies and chronic non-progressive presentation. We evaluated patients with acquired non-progressive cerebellar ataxia that presented previous acute or subacute onset. Clinical and neuroimaging characterization of adult patients with acquired non-progressive ataxia were performed. Five patients were identified with the phenotype of acquired non-progressive ataxia. Most patients presented with a juvenile to adult-onset acute to subacute appendicular and truncal cerebellar ataxia with mild to moderate cerebellar or olivopontocerebellar atrophy. Establishing the etiology of the acute triggering events of such ataxias is complex. Non-progressive ataxia in adults must be distinguished from hereditary ataxias.

PMPCA mutations cause abnormal mitochondrial protein processing in patients with non-progressive cerebellar ataxia

Non-progressive cerebellar ataxias are a rare group of disorders that comprise approximately 10% of static infantile encephalopathies. We report the identification of mutations in PMPCA in 17 patients from four families affected with cerebellar ataxia, including the large Lebanese family previously described with autosomal recessive cerebellar ataxia and short stature of Norman type and localized to chromosome 9q34 (OMIM #213200). All patients present with non-progressive cerebellar ataxia, and the majority have intellectual disability of variable severity. PMPCA encodes α-MPP, the alpha subunit of mitochondrial processing peptidase, the primary enzyme responsible for the maturation of the vast majority of nuclear-encoded mitochondrial proteins, which is necessary for life at the cellular level. Analysis of lymphoblastoid cells and fibroblasts from patients homozygous for the PMPCA p.Ala377Thr mutation and carriers demonstrate that the mutation impacts both the level of the alpha subunit encoded by PMPCA and the function of mitochondrial processing peptidase. In particular, this mutation impacts the maturation process of frataxin, the protein which is depleted in Friedreich ataxia. This study represents the first time that defects in PMPCA and mitochondrial processing peptidase have been described in association with a disease phenotype in humans.

De novo point mutations in patients diagnosed with ataxic cerebral palsy

Cerebral palsy is commonly attributed to perinatal asphyxia. However, Schnekenberg et al. describe here four individuals with ataxic cerebral palsy likely due to de novo dominant mutations associated with increased paternal age. Therefore, patients with cerebral palsy should be investigated for genetic causes before the disorder is ascribed to asphyxia.

Cerebral palsy is a sporadic disorder with multiple likely aetiologies, but frequently considered to be caused by birth asphyxia. Genetic investigations are rarely performed in patients with cerebral palsy and there is little proven evidence of genetic causes. As part of a large project investigating children with ataxia, we identified four patients in our cohort with a diagnosis of ataxic cerebral palsy. They were investigated using either targeted next generation sequencing or trio-based exome sequencing and were found to have mutations in three different genes, KCNC3, ITPR1 and SPTBN2. All the mutations were de novo and associated with increased paternal age. The mutations were shown to be pathogenic using a combination of bioinformatics analysis and in vitro model systems. This work is the first to report that the ataxic subtype of cerebral palsy can be caused by de novo dominant point mutations, which explains the sporadic nature of these cases. We conclude that at least some subtypes of cerebral palsy may be caused by de novo genetic mutations and patients with a clinical diagnosis of cerebral palsy should be genetically investigated before causation is ascribed to perinatal asphyxia or other aetiologies.

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.

A missense founder mutation in VLDLR is associated with Dysequilibrium Syndrome without quadrupedal locomotion

BACKGROUND

Dysequilibrium syndrome is a genetically heterogeneous condition that combines autosomal recessive, nonprogressive cerebellar ataxia with mental retardation. The condition has been classified into cerebellar ataxia, mental retardation and disequilibrium syndrome types 1 (CAMRQ1), 2 (CAMRQ2) and 3 (CAMRQ3) and attributed to mutations in VLDLR, CA8 and WDR81 genes, respectively. Quadrupedal locomotion in this syndrome has been reported in association with mutations in all three genes.

METHODS

SNP mapping and candidate gene sequencing in one consanguineous Omani family from the United Arab Emirates with cerebellar hypoplasia, moderate mental retardation, delayed ambulation and truncal ataxia was used to identify the mutation. In a second unrelated consanguineous Omani family, massively parallel exonic sequencing was used.

RESULTS

We identified a homozygous missense mutation (c.2117 G > T, p.C706F) in the VLDLR gene in both families on a shared affected haplotype block.This is the first reported homozygous missense mutation in VLDLR and it occurs in a highly conserved residue and predicted to be damaging to protein function.

CONCLUSIONS

We have delineated the phenotype associated with dysequilibrium syndrome in two Omani families and identified the first homozygous missense pathogenic mutation in VLDLR gene with likely founder effect in the southeastern part of the Arabian Peninsula.

Autosomal-recessive congenital cerebellar ataxia is caused by mutations in metabotropic glutamate receptor 1

Autosomal-recessive congenital cerebellar ataxia was identified in Roma patients originating from a small subisolate with a known strong founder effect. Patients presented with global developmental delay, moderate to severe stance and gait ataxia, dysarthria, mild dysdiadochokinesia, dysmetria and tremors, intellectual deficit, and mild pyramidal signs. Brain imaging revealed progressive generalized cerebellar atrophy, and inferior vermian hypoplasia and/or a constitutionally small brain were observed in some patients. Exome sequencing, used for linkage analysis on extracted SNP genotypes and for mutation detection, identified two novel (i.e., not found in any database) variants located 7 bp apart within a unique 6q24 linkage region. Both mutations cosegregated with the disease in five affected families, in which all ten patients were homozygous. The mutated gene, GRM1, encodes metabotropic glutamate receptor mGluR1, which is highly expressed in cerebellar Purkinje cells and plays an important role in cerebellar development and synaptic plasticity. The two mutations affect a gene region critical for alternative splicing and the generation of receptor isoforms; they are a 3 bp exon 8 deletion and an intron 8 splicing mutation (c.2652_2654del and c.2660+2T>G, respectively [RefSeq accession number NM_000838.3]). The functional impact of the deletion is unclear and is overshadowed by the splicing defect. Although ataxia lymphoblastoid cell lines expressed GRM1 at levels comparable to those of control cells, the aberrant transcripts skipped exon 8 or ended in intron 8 and encoded various species of nonfunctional receptors either lacking the transmembrane domain and containing abnormal intracellular tails or completely missing the tail. The study implicates mGluR1 in human hereditary ataxia. It also illustrates the potential of the Roma founder populations for mutation identification by exome sequencing.

Childhood cerebellar ataxia

Childhood presentations of ataxia, an impairment of balance and coordination caused by damage to or dysfunction of the cerebellum, can often be challenging to diagnose. Presentations tend to be clinically heterogeneous, but key considerations may vary based on the child's age at onset, the course of illness, and subtle differences in phenotype. Systematic investigation is recommended for efficient diagnosis. In this review, we outline common etiologies and describe a comprehensive approach to the evaluation of both acquired and genetic cerebellar ataxia in children.

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.

Dominantly inherited nonprogressive cerebellar hypoplasia identified in utero

Cerebellar hypoplasia is the hallmark of a heterogeneous group of disorders that are caused by genetic and metabolic disorders. Prenatal identification of cerebellar hypoplasia and accurate prediction of outcome are challenging. Autosomal dominant nonprogressive cerebellar ataxia is a rare disorder that typically presents with early hypotonia and delayed motor milestones followed by the onset of mild ataxia and occasionally cognitive impairment. We present a case of a mother and her female fetus. Fetal sonography and magnetic resonance imaging (MRI) showed generalized cerebellar hypoplasia. The mother had mild learning difficulties and clinically showed minor features of cerebellar ataxia. Her MRI also demonstrated extreme cerebellar hypoplasia. The diagnosis of autosomal dominant nonprogressive cerebellar ataxia was suggested. This is the first report of prenatal diagnosis of autosomal dominant nonprogressive cerebellar ataxia. We recommend obtaining a family history, examining the parents, and when appropriate obtaining an MRI before counseling parents of a fetus with a brain malformation.

X-linked disorders with cerebellar dysgenesis

X-linked disorders with cerebellar dysgenesis (XLCD) are a genetically heterogeneous and clinically variable group of disorders in which the hallmark is a cerebellar defect (hypoplasia, atrophy or dysplasia) visible on brain imaging, caused by gene mutations or genomic imbalances on the X-chromosome. The neurological features of XLCD include hypotonia, developmental delay, intellectual disability, ataxia and/or other cerebellar signs. Normal cognitive development has also been reported. Cerebellar dysgenesis may be isolated or associated with other brain malformations or multiorgan involvement. There are at least 15 genes on the X-chromosome that have been constantly or occasionally associated with a pathological cerebellar phenotype. 8 XLCD loci have been mapped and several families with X-linked inheritance have been reported. Recently, two recurrent duplication syndromes in Xq28 have been associated with cerebellar hypoplasia. Given the report of several forms of XLCD and the excess of males with ataxia, this group of conditions is probably underestimated and families of patients with neuroradiological and clinical evidence of a cerebellar disorder should be counseled for high risk of X-linked inheritance.

Congenital ataxia, mental retardation, and dyskinesia associated with a novel CACNA1A mutation

The CACNA1A gene encodes the pore forming alpha-1A subunit of neuronal voltage-dependent P/Q-type Ca( 2+) channels. Mutations in this gene result in clinical heterogeneity, and present with either chronic progressive symptoms, paroxysmal events, or both, with clinical overlap among the different phenotypes. The authors describe a seven year-old boy with mental retardation and congenital cerebellar ataxia that developed dyskinesia at the age of a few months, and recurrent episodes of coma following mild head trauma associated with motor and autonomic signs, from the second year of life. An extensive metabolic evaluation, interictal electroencephalography (EEG), and muscle biopsy were normal. Brain magnetic resonance imaging (MRI) during one of these episodes revealed edema of the right hemisphere and cerebellar atrophy. Genetic testing revealed a R1350Q mutation in the CACNA1A gene. This is a novel de novo mutation.Congenital cerebellar ataxia can be a result of CACNA1A mutations, especially when associated with recurrent unexplained coma.

CAMOS, a nonprogressive, autosomal recessive, congenital cerebellar ataxia, is caused by a mutant zinc-finger protein, ZNF592

CAMOS (Cerebellar Ataxia with Mental retardation, Optic atrophy and Skin abnormalities) is a rare autosomal recessive syndrome characterized by a nonprogressive congenital cerebellar ataxia associated with mental retardation, optic atrophy, and skin abnormalities. Using homozygosity mapping in a large inbred Lebanese Druze family, we previously reported the mapping of the disease gene at chromosome 15q24-q26 to a 3.6-cM interval between markers D15S206 and D15S199. Screening of candidate genes lying in this region led to the identification of a homozygous p.Gly1046Arg missense mutation in ZNF592, in all five affected individuals of the family. ZNF592 encodes a 1267-amino-acid zinc-finger (ZnF) protein, and the mutation, located within the eleventh ZnF, is predicted to affect the DNA-binding properties of ZNF592. Although the precise role of ZNF592 remains to be determined, our results suggest that ZNF592 is implicated in a complex developmental pathway, and that the mutation is likely to disturb the highly orchestrated regulation of genes during cerebellar development, by either disrupting interactions with target DNA or with a partner protein.

Novel VLDLR microdeletion identified in two Turkish siblings with pachygyria and pontocerebellar atrophy

Congenital ataxia with cerebellar hypoplasia is a heterogeneous group of disorders that presents with motor disability, hypotonia, incoordination, and impaired motor development. Among these, disequilibrium syndrome describes a constellation of findings including non-progressive cerebellar ataxia, mental retardation, and cerebellar hypoplasia following an autosomal recessive pattern of inheritance and can be caused by mutations in the Very Low Density Lipoprotein Receptor (VLDLR). Interestingly, while the majority of patients with VLDL-associated cerebellar hypoplasia in the literature use bipedal gait, the previously reported patients of Turkish decent have demonstrated similar neurological sequelae, but rely on quadrupedal gait. We present a consanguinous Turkish family with two siblings with cerebellar atrophy, predominantly frontal pachygyria and ataxic bipedal gait, who were found to have a novel homozygous deletion in the VLDLR gene identified by using high-density single nucleotide polymorphism microarrays for homozygosity mapping and identification of CNVs within these regions. Discovery of disease causing homozygous deletions in the present Turkish family capable of maintaining bipedal movement exemplifies the phenotypic heterogeneity of VLDLR-associated cerebellar hypoplasia and ataxia.

X-linked congenital ataxia: a new locus maps to Xq25-q27.1

We report clinical and molecular studies on a large American family of Norwegian descent with X-linked nonprogressive congenital ataxia (XCA) in six affected males over three generations. Neuroimaging showed global cerebellar hypoplasia without evidence of supratentorial anomalies. Linkage analysis resulted in a maximum LOD score Z = 3.44 for marker DXS1192 at Theta = 0.0 with flanking markers DXS1047 and DXS1227 defining a region of 12 cM in Xq25-q27.1. The clinical and neuroradiological findings in the present family are very similar to those described in two reported X-linked families [Illarioshkin et al., 1996; Bertini et al., 2000]; however, the newly identified locus does not overlap with the one defined previously, indicating that there are at least two genes responsible for this rare form of X-linked congenital cerebellar ataxia with normal intelligence.

Mental retardation and epilepsy in patients with isolated cerebellar hypoplasia

Congenital nonprogressive cerebellar ataxia includes a complex group of disorders with heterogeneous phenotypic and etiopathogenetic characteristics. Despite recent advances in the understanding of the role of the cerebellum in cognition and behavior, the opinion that the clinical presentation of congenital cerebellar diseases is principally linked to motor dysfunction is common. This is largely due to the lack of well-organized epidemiologic studies on the prevalence of nonmotor disturbances in cerebellar disease. The association between congenital cerebellar disease and epilepsy has rarely been described. We report clinical, neurophysiologic, neuroimaging, and neuropsychologic features in a group of 14 patients with congenital nonprogressive cerebellar ataxia associated with cerebellar hypoplasia, 5 of whom have familial disease, aiming to further a better knowledge of the prevalence of cognitive and/or emotional impairment and epilepsy. The results confirm that cerebellar hypoplasia predisposes individuals to psychomotor delay (71.4%) and cognitive impairment (85.7%). Moreover, the tendency toward abnormal electroencephalographic (EEG) findings (78.5%), associated in a minor percentage of cases with epilepsy (28.5%), is also evident in our study.

Diagnostic approach to cerebellar disease in children

We reviewed the clinical records of 51 extensively investigated pediatric patients with structural abnormalities of the cerebellum as revealed by magnetic resonance imaging (MRI). Ten had hypoplasia of the vermis, 21 had hypoplasia of the vermis and cerebellar hemispheres, 2 had pontocerebellar hypoplasia, and 18 had progressive cerebellar atrophy. A clear diagnosis was reached in 37 (72.5%). Initial characterization of the cerebellar alterations by MRI separated hypoplastic from atrophic cases and confirmed MRI as an essential preliminary means for distinguishing malformations from metabolic-degenerative conditions. However, the diagnostic possibilities are so numerous that it is not feasible to propose a standardized diagnostic protocol for pediatric patients with an altered cerebellum. Subsequent investigations should be suggested by the neuroradiologic and clinical peculiarities of each case.

Autosomal dominant congenital non-progressive ataxia overlaps with the SCA15 locus

BACKGROUND

Most patients with pure nonprogressive congenital cerebellar ataxia have a sporadic form of unknown heredity and etiology. Several small families have been reported with a dominantly inherited nonprogressive congenital ataxia (NPCA).

METHODS

The authors ascertained and clinically characterized a four-generation pedigree segregating an autosomal dominant type of congenital nonprogressive cerebellar ataxia associated with cognitive impairment. Following the exclusion of several SCA localizations (SCA-1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 17, IOSCA, and DRPLA), a genome-wide linkage study was performed.

RESULTS

Examination of the family showed that all affected members had gait ataxia and cognitive disability with variable features of dysarthria, dysmetria, dysdiadochokinesia, nystagmus, dystonic movements, and cerebellar hypoplasia on imaging. Clinical signs of pyramidal tract dysfunction and sensory changes were absent. A genome-wide search in this family detected linkage to chromosome 3p with a maximum two-point lod score of 4.26 at D3S3630. This localization to the pter is distal to D3S1304, as defined by a recombination event. This overlaps with the SCA15 locus, with the critical overlapping region between the microsatellite markers, D3S1304 and D3S1620 (approximately 8 cM).

CONCLUSION

Autosomal dominant congenital nonprogressive cerebellar ataxia with or without cerebellar hypoplasia overlaps with the SCA15 locus on chromosome 3pter.

Cerebellum-small brain but large confusion: a review of selected cerebellar malformations and disruptions

Defining and classifying congenital disorders of the cerebellum can be difficult and confusing. One reason is that some abnormalities called "malformations" are not truly (primary) developmental malformations. This applies to Chiari I "malformations" as well as to Chiari II "malformations." The latter results mainly from a prenatal cerebrospinal fluid (CSF) leak. Also disruptive cerebellar lesions are not uncommon, examples being the "vanishing cerebellum" in myelomeningocele, cerebellar lesions in very low birth weight prematurely born infants, unilateral cerebellar hypoplasia/aplasia, and probably some instances of cerebellar agenesis (CA). The cerebellar hypoplasias consist of a heterogeneous group of inherited and prenatally acquired conditions. The concept of pontocerebellar hypoplasias will need to be expanded beyond the two main types (PCH-1 and PCH-2), and demonstrate that a classification system of cerebellar malformations cannot be based on neuroimaging criteria only. Additional studies are expected to show that this also applies to the molar tooth sign, which was initially described in Joubert syndrome (JS). The JS is the prototype of midhindbrain malformation, but its delineation is still unsolved. JS may well be an overdiagnosed entity; many cases likely not having JS are on record. Rhombencephalosynapsis (RS) has been increasingly diagnosed with the advent of neuroimaging. No familial cases have been observed. Although many affected individuals have variable impairments, RS can be found in children with normal cognitive function. In this review, some of the cerebellar anomalies are briefly discussed.

Congenital ataxia and mental retardation in three brothers

Nonprogressive congenital ataxia is a complex group of disorders caused by a variety of etiologic factors, both environmental and genetic. Hereditary forms represent a substantial part of congenital ataxias, which are difficult to classify because of their phenotypic and genetic polymorphism. Despite the advances in molecular genetics, for most nonprogressive congenital ataxia the etiology is still unknown. This report describes three sons of nonconsanguineous healthy parents, who manifested a syndrome characterized by nonprogressive ataxia, mental retardation, pyramidal signs, ocular and ocular motor anomalies, associated with severe hypoplasia of the cerebellar vermis and hemispheres on neuroimaging. All the patients have presented psychomotor developmental delay. As differential diagnosis, a comparison is made between the clinical features of these patients and the previously reported cases of nonprogressive congenital ataxia. This report represents a further example of the phenotypic and genetic heterogeneity of the syndromes with congenital ataxia.

Development of a child with Joubert syndrome

The article describes the development of a child with Joubert Syndrome who, since the age of 16 months, has received personalized stimulation therapy at home and in the Early Intervention Unit (EIU) of the Faculty, in each of the five areas considered by the Portage Guide to Early Education: socialization, language, self-help, cognition, and motoricity. Repeated evaluations during the treatment (up to age 40 months) showed show progress in all developmental areas, as well as in general attitude to and capacity for learning. During treatment, greatest progress was made in the areas of cognition and communication.

Developmental instability of the cerebellum and its relevance to Down syndrome

It has been recognized for many years that cerebellar abnormalities are frequently observed in association with Down syndrome (DS). An important question to be asked about these and other findings in DS is whether their occurrence (i) is attributable to specific loci on the triplicated chromosome or chromosomal segment or (ii) derives from exaggerated responses secondary to the genetic imbalance resulting from trisomy (Ts). Recently, similar cerebellar alterations were observed in subjects with DS and in Ts65Dn mice (Baxter et al., 2000), mice segmentally trisomic for a portion of chromosome 16, which is homologous for loci on the long arm of human chromosome 21. It was concluded by these authors that the occurrence of similar cerebellar changes in DS and in the DS mouse model resulted from triplication of these homologous loci in the two trisomic organisms, i.e. cerebellar development is affected similarly by homologous loci in each species. They wrote that their study of Ts65Dn mice "correctly predicts an analagous pathology in humans". . . and that. . . "The candidate region of genes on chromosome 21 affecting cerebellar development in DS is therefore delimited to the subset of genes whose orthologs are at dosage imbalance in Ts65Dn mice, providing the first localization of genes affecting a neuroanatomical phenotype in DS." Findings described in this review suggest otherwise--that cerebellar findings in DS and in the Ts65Dn mouse are a result of exaggerated vulnerability in general of the cerebellum to disturbing events and that liability to expression of response(s) is exacerbated by trisomy. This conclusion is based on the following: (i) the cerebellum has an extended postnatal development; (ii) numerous genetic, environmental, epigenetic and metabolic conditions express cerebellar changes similar to those observed in Down syndrome; (iii) most if not all chromosomal imbalance syndromes express similar cerebellar abnormalities; (iv) the cerebellum is particularly sensitive to diverse toxic agents which may act prenatally, postnatally and/or in the mature organism; and (v) cerebellar abnormalities similar to those found in Ts65Dn mice have been described in Ts19 mice which have no segments homologous to any segment of human chromosome 21. An unavoidable conclusion from the review is that triplication of specific loci on 21q is an unlikely explanation for the cerebellar findings in DS. A simple positive control, in which the effect of triplication of loci other than those in question on a specific phenotype, should be used in experiments comparing human and experimental trisomies. As pointed out many years ago by Lorke and his coworkers (Lorke et al., 1989; Lorke, 1994; Lorke and Albrecht, 1994) similar phenotypic findings in the presence of different trisomies in the same species would suggest that the trisomic state itself rather than the gene content of a particular trisomy is responsible for the genesis of traits at issue.

XY sex reversal and a nonprogressive neurologic disorder: a new syndrome?

We report a patient with a unique combination of clinical findings: XY sex reversal, spastic paraplegia, mental retardation, dysmorphism, and infantile-onset olivopontocerebellar hypoplasia. The phenotype of our patient did not coincide with any of the described forms of XY reversal syndromes, hereditary or sporadic spastic paraplegias, or congenital or infantile-onset cerebellar or olivopontocerebellar atrophies or hypoplasias. The disorder of this patient likely represents a genetic condition with pleiotropic effects on brain development and sex determination and adds further evidence for the heterogeneity of spastic paraplegia/infantile olivopontocerebellar hypoplasia syndromes and sex reversal syndromes.

The neurologically impaired child and alleged malpractice at birth

Controlled studies, improved epidemiologic and statistical techniques, and an increase in biological information on mechanisms of fetal and neonatal brain injury or maldevelopment have led to a better, although still imperfect, understanding of the cause of developmental disabilities. The role of asphyxia during the birth process is smaller than was once believed. Intrauterine exposure to infection, autoimmune and coagulation disorders, and problems specific to multiple pregnancies are risk factors for cerebral palsy. Electronic fetal monitoring and other observations during birth are unsatisfactory management guides, having enormously high rates of false-positive identification. There is no evidence that caesarean section can prevent cerebral palsy in term infants.