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PubMed2005

[Predictive testing: presymptomatic diagnosis in neurogenetic disorders].

Presymptomatic testing is available since 15 years for Huntington disease and it is now possible for a number of other neurogenetic disorders, mostly neurodegenerative disorders. The possibility of determining the genetic status of an at-risk person for the disorder which run in his family raises questions because of the absence of preventive and curative treatments in most instances. In addition, being carrier does not tell you when the disease will start and how it will evolve, impairing the possibilities of planning the future. A pluridisciplinary approach to predictive testing with care before, during and after the test taking into account the medical, social and psychological aspects of the disease is good practice. At the present time, only a minority of at-risk individuals request presymptomatic testing and almost 50 % do not pursue until the results. The consequences of the test may be harmful, more frequently after an unfavorable than after a favorable result. Although the motivations and the outcome in terms of request for prenatal testing after a carrier result are different in Huntington's disease and spinocerebellar ataxias, our experience underlines the benefit of pluridisciplinary care and of time for decision taking. For other disorders like familial Alzheimer's disease, or familial Creutzfeldt-Jakob disease, the experience in presymptomatic testing is still limited but the situation seems similar to Huntington's disease because of the presence of dementia. It will be interesting to study the motivations and the outcome of the tests in disorders like autosomal dominant spastic paraplegias which usually do not reduce the life expectancy. Nevertheless, the overall situation might change greatly when efficient treatments will become available in these disorders.

Adult↗
PubMed2002

Ethical issues in clinical practice: cases and analyses.

Given the severity and complexity of the neurologic disorders that can affect infants and children, pediatric neurologists frequently encounter complex and challenging ethical issues. This discussion uses five cases to illustrate common ethical issues and dilemmas that are confronted by pediatric neurologists. These cases involve the provision of artificial nutrition and hydration to patients in vegetative or minimally conscious states, the use of mechanical ventilation for patients with spinal muscular atrophy, controversial therapies for autistic spectrum disorders, the use of medical information obtained over the Internet, and genetic testing in children with suspected Huntington's disease. The ethical concepts discussed in these cases include autonomy, confidentiality, futility, surrogate decision-making, the best-interest principle, and the withholding and withdrawal of treatment.

Brain Damage, Chronic↗
PubMed2000

Involvement of polyglutamine endolysis followed by pyroglutamate formation in the pathogenesis of triplet repeat/polyglutamine-expansion diseases.

The mechanism by which polyglutamine expansions in several proteins lead to neurodegenerative disorders remains largely unknown. The biochemical properties of polyglutamine repeats suggest one possible explanation; endolytic cleavage at a glutaminyl-glutaminyl bond followed by pyroglutamate formation may contribute to the pathogenesis through augmenting the catabolic stability, hydrophobicity, amyloidogenicity, and neurotoxicity of the polyglutaminyl proteins. The hypothesis points out novel therapeutic strategies to delay disease onset in genetically diagnosed presymptomatic patients.

Heredodegenerative Disorders, Nervous System↗
PubMed2000

Alexander disease--classification revisited and isolation of a neonatal form.

Alexander disease is usually classified according to the age of onset, e.g. an infantile form with onset during the first two years of life, a juvenile form with onset in childhood, mainly school age. It has been recognized, however, that the clinical course can be very variable within these groups. Thus, this clinical classification is not a useful predictor of severity and progression of the disease. This is demonstrated here on the basis of the history of seven own patients and a literature review. Only an onset in very early infancy, during the neonatal period, seemed to be associated with a rather uniform pattern of disease course, often leading to early death. This neonatal form showed very stereotyped symptoms, in part different from later onset: Early, often intractable, generalized seizures; hydrocephalus with raised intracranial pressure due to aqueductal stenosis because of pathological astroglia proliferation; lack of developmental progression but without prominent spasticity or ataxia; elevated CSF protein content. This was associated with the well-established neuroradiological findings, e.g. severe white matter affection with fronto-temporal predominance, involvement of basal ganglia and periventricular enhancement as an obligatory symptom. The identification of this early onset form is especially important as seizures and signs of raised intracranial pressure may mislead the diagnosis.

Adolescent↗
PubMed2000

A case of leukoencephalopathy with vanishing white matter.

A 6-year old Turkish boy with a recently defined entity: "leukoencephalopathy with vanishing white matter" is described. He was born to consanguinous parents. His psychomotor development was normal till he first presented with fever and generalized tonic-clonic seizures at the age of 2.5, followed by rapid motor and mental deterioration. Decerebrate posture and marked spasticity subsequently developed. The initial MRI examination showed diffuse involvement of white matter, including subcortical U-fibers, with signal intensity parallel to CSF on all sequences. The white matter appeared swollen. The ventricles were slightly enlarged and there was cavum septi pellucidi et vergae. The posterior crus of the internal capsule, external and extreme capsules were affected. Cerebellar hemispheres and vermis showed atrophy. The involvement pattern of brainstem was noteworthy in that pontine tegmentum and cruri cerebri were affected. Follow-up MRI obtained after three years did not show any interval change. Brain biopsy showed thinned cortex with relatively preserved cortical layering and neuronal structure. There was rarefaction of the white matter with cystic degeneration. Fibrillary gliosis and increased number of oligodendroglial cells were observed within the cerebral white matter.

Biopsy↗
PubMed2006

wasted away, a Drosophila mutation in triosephosphate isomerase, causes paralysis, neurodegeneration, and early death.

To identify genes required for maintaining neuronal viability, we screened our collection of Drosophila temperature-sensitive paralytic mutants for those exhibiting shortened lifespan and neurodegeneration. Here, we describe the characterization of wasted away (wstd), a recessive, hypomorphic mutation that causes progressive motor impairment, vacuolar neuropathology, and severely reduced lifespan. We demonstrate that the affected gene encodes the glycolytic enzyme, triosephosphate isomerase (Tpi). Mutations causing Tpi deficiency in humans are also characterized by progressive neurological dysfunction, neurodegeneration, and early death. In Tpi-deficient flies and humans, a decrease in ATP levels did not appear to cause the observed phenotypes because ATP levels remained normal. We also found no genetic evidence that the mutant Drosophila Tpi was misfolded or involved in aberrant protein-protein associations. Instead, we favor the hypothesis that mutations in Tpi lead to an accumulation of methylglyoxal and the consequent enhanced production of advanced glycation end products, which are ultimately responsible for the death and dysfunction of Tpi-deficient neurons. Our results highlight an essential protective role of Tpi and support the idea that advanced glycation end products may also contribute to pathogenesis of other neurological disorders.

Animals↗
PubMed2002

Live-cell imaging reveals divergent intracellular dynamics of polyglutamine disease proteins and supports a sequestration model of pathogenesis.

Protein misfolding and aggregation are central features of the polyglutamine neurodegenerative disorders, but the dynamic properties of expanded polyglutamine proteins are poorly understood. Here, we use fluorescence recovery after photobleaching (FRAP) and fluorescence loss in photobleaching (FLIP) with green fluorescent protein fusion proteins to study polyglutamine protein kinetics in living cells. Our results reveal markedly divergent mobility states for an expanded polyglutamine protein, ataxin-3, and establish that nuclear inclusions formed by this protein are aggregates. Additional studies of green fluorescent protein-tagged cAMP response element binding protein coexpressed with either of two mutant polyglutamine proteins, ataxin-3 and huntingtin, support a model of disease in which coaggregation of transcriptional components contributes to pathogenesis. Finally, studies of a third polyglutamine disease protein, ataxin-1, reveal unexpected heterogeneity in the dynamics of inclusions formed by different disease proteins, a finding which may help explain disease-specific elements of pathogenesis in these neurodegenerative disorders.

Animals↗
PubMed2005

Saitohin, which is nested in the tau locus and confers allele-specific susceptibility to several neurodegenerative diseases, interacts with peroxiredoxin 6.

Saitohin is a gene unique to humans and their closest relatives, the function of which is not yet known. Saitohin contains a single polymorphism (Q7R), and its Q and R alleles belong to the H1 and H2 tau haplotype, respectively. The Saitohin Q allele confers susceptibility to several neurodegenerative diseases. To get a handle on Saitohin function, we used it as a bait in a yeast two-hybrid screen. By this assay and subsequent co-immunoprecipitation and glutathione S-transferase pull-down assays, we discovered and confirmed that Saitohin interacts with peroxiredoxin 6, a unique member of that family that is bifunctional and the levels of which increase in Pick disease. The strength of the interaction appeared to be allele-specific, giving the first distinction between the two forms of Saitohin.

Alleles↗
PubMedDate not supplied

Quantitative analysis of microglial cells in the degenerating cerebellum of the staggerer (RORA(sg/sg)) mutant mouse.

Elevated levels of pro-inflammatory cytokines, such as IL-1ss and IL-6, have been detected in the cerebellum of Rora(sg/sg) mice during the first postnatal month of neurodegenerative process. This suggests the existence of a microglial reaction in the context of an inflammatory process that would be triggered by the massive neuronal loss. To test this hypothesis, we qualitatively and quantitatively studied the microglial cell population using lectin and nucleosidic diphosphatase labeling of the cerebellum of 30-day-old mice. The massive neuronal loss induces a 11.7-fold smaller size of the Rora(sg/sg) cerebellum compared to wild-types. We showed that the Rora(sg/sg) microglia population is exclusively composed of cells displaying the characteristic morphology of activated cells, with enlarged, heavily stained cell bodies and few thick processes, in contrast to microglial cells in the wild-type. The density of microglia is 2.7-fold higher in Rora(sg/sg) than wild-type mice (22444+/-5011 cells/mm(3) versus 8158+/-1584 cells/mm(3)), although the absolute number is 4-fold smaller. These results show that neurodegeneration in the Rora(sg/sg) cerebellum leads to persistance of microglial activation while in wild-type it disappears around P10.

Acid Anhydride Hydrolases↗
PubMed2005

Possible involvement of the RNAi pathway in trinucleotide repeat expansion diseases.

A new molecular mechanism of trinucleotide expansion diseases is suggested. The mechanism involves the formation of double-helical RNA hairpins by transcripts carrying (CNG)(n) sequences, which are processed via the RNAi pathway with subsequent RNA silencing of genes containing (CNG)(n) sequences. Depletion of proteins encoded by these genes leads to the specific disease phenotype. The available data on human myotonic dystrophy 1, which results from the (CTG)(n) expansion, support the hypothesis.

Base Sequence↗
PubMed2002

Microtubule-associated protein 1B: a neuronal binding partner for gigaxonin.

Giant axonal neuropathy (GAN), an autosomal recessive disorder caused by mutations in GAN, is characterized cytopathologically by cytoskeletal abnormality. Based on its sequence, gigaxonin contains an NH2-terminal BTB domain followed by six kelch repeats, which are believed to be important for protein-protein interactions (Adams, J., R. Kelso, and L. Cooley. 2000. Trends Cell Biol. 10:17-24.). Here, we report the identification of a neuronal binding partner of gigaxonin. Results obtained from yeast two-hybrid screening, cotransfections, and coimmunoprecipitations demonstrate that gigaxonin binds directly to microtubule-associated protein (MAP)1B light chain (LC; MAP1B-LC), a protein involved in maintaining the integrity of cytoskeletal structures and promoting neuronal stability. Studies using double immunofluorescent microscopy and ultrastructural analysis revealed physiological colocalization of gigaxonin with MAP1B in neurons. Furthermore, in transfected cells the specific interaction of gigaxonin with MAP1B is shown to enhance the microtubule stability required for axonal transport over long distance. At least two different mutations identified in GAN patients (Bomont, P., L. Cavalier, F. Blondeau, C. Ben Hamida, S. Belal, M. Tazir, E. Demir, H. Topaloglu, R. Korinthenberg, B. Tuysuz, et al. 2000. Nat. Genet. 26:370-374.) lead to loss of gigaxonin-MAP1B-LC interaction. The devastating axonal degeneration and neuronal death found in GAN patients point to the importance of gigaxonin for neuronal survival. Our findings may provide important insights into the pathogenesis of neurodegenerative disorders related to cytoskeletal abnormalities.

Animals↗
PubMed2006

A motor neuron disease-associated mutation in p150Glued perturbs dynactin function and induces protein aggregation.

The microtubule motor cytoplasmic dynein and its activator dynactin drive vesicular transport and mitotic spindle organization. Dynactin is ubiquitously expressed in eukaryotes, but a G59S mutation in the p150Glued subunit of dynactin results in the specific degeneration of motor neurons. This mutation in the conserved cytoskeleton-associated protein, glycine-rich (CAP-Gly) domain lowers the affinity of p150Glued for microtubules and EB1. Cell lines from patients are morphologically normal but show delayed recovery after nocodazole treatment, consistent with a subtle disruption of dynein/dynactin function. The G59S mutation disrupts the folding of the CAP-Gly domain, resulting in aggregation of the p150Glued protein both in vitro and in vivo, which is accompanied by an increase in cell death in a motor neuron cell line. Overexpression of the chaperone Hsp70 inhibits aggregate formation and prevents cell death. These data support a model in which a point mutation in p150Glued causes both loss of dynein/dynactin function and gain of toxic function, which together lead to motor neuron cell death.

Animals↗
PubMed2000

Localization of the gene for a novel autosomal recessive neurodegenerative Huntington-like disorder to 4p15.3.

A consanguineous family affected by an autosomal recessive, progressive neurodegenerative Huntington-like disorder, was tested to rule out juvenile-onset Huntington disease (JHD). The disease manifests at approximately 3-4 years and is characterized by both pyramidal and extrapyramidal abnormalities, including chorea, dystonia, ataxia, gait instability, spasticity, seizures, mutism, and intellectual impairment. Brain magnetic resonance imaging (MRI) findings include progressive frontal cortical atrophy and bilateral caudate atrophy. Huntington CAG trinucleotide-repeat analyses ruled out JHD, since all affected individuals had repeat numbers within the normal range. The presence of only four recombinant events (straight theta=.2) between the disease and the Huntington locus in 20 informative meioses suggested that the disease localized to chromosome 4. Linkage was initially achieved with marker D4S2366 at 4p15.3 (LOD 3.03). High-density mapping at the linked locus resulted in homozygosity for markers D4S431 and D4S394, which span a 3-cM region. A maximum LOD score of 4.71 in the homozygous interval was obtained. Heterozygosity at the distal D4S2366 and proximal D4S2983 markers defines the maximum localization interval (7 cM). Multiple brain-related expressed sequence tags (ESTs) with no known disease association exist in the linkage interval. Among the three known genes residing in the linked interval (ACOX3, DRD5, QDPR), the most likely candidate, DRD5, encoding the dopamine receptor D5, was excluded, since all five affected family members were heterozygous for an intragenic dinucleotide repeat. The inheritance pattern and unique localization to 4p15.3 are consistent with the identification of a novel, autosomal recessive, neurodegenerative Huntington-like disorder.

Adolescent↗
PubMed2004

Mutations in the X-linked cyclin-dependent kinase-like 5 (CDKL5/STK9) gene are associated with severe neurodevelopmental retardation.

Recently, we showed that truncation of the X-linked cyclin-dependent kinase-like 5 (CDKL5/STK9) gene caused mental retardation and severe neurological symptoms in two female patients. Here, we report that de novo missense mutations in CDKL5 are associated with a severe phenotype of early-onset infantile spasms and clinical features that overlap those of other neurodevelopmental disorders, such as Rett syndrome and Angelman syndrome. The mutations are located within the protein kinase domain and affect highly conserved amino acids; this strongly suggests that impaired CDKL5 catalytic activity plays an important role in the pathogenesis of this neurodevelopmental disorder. In view of the overlapping phenotypic spectrum of CDKL5 and MECP2 mutations, it is tempting to speculate that these two genes play a role in a common pathogenic process.

Amino Acid Sequence↗
PubMed2004

Mutations of CDKL5 cause a severe neurodevelopmental disorder with infantile spasms and mental retardation.

Rett syndrome (RTT) is a severe neurodevelopmental disorder caused, in most classic cases, by mutations in the X-linked methyl-CpG-binding protein 2 gene (MECP2). A large degree of phenotypic variation has been observed in patients with RTT, both those with and without MECP2 mutations. We describe a family consisting of a proband with a phenotype that showed considerable overlap with that of RTT, her identical twin sister with autistic disorder and mild-to-moderate intellectual disability, and a brother with profound intellectual disability and seizures. No pathogenic MECP2 mutations were found in this family, and the Xq28 region that contains the MECP2 gene was not shared by the affected siblings. Three other candidate regions were identified by microsatellite mapping, including 10.3 Mb at Xp22.31-pter between Xpter and DXS1135, 19.7 Mb at Xp22.12-p22.11 between DXS1135 and DXS1214, and 16.4 Mb at Xq21.33 between DXS1196 and DXS1191. The ARX and CDKL5 genes, both of which are located within the Xp22 region, were sequenced in the affected family members, and a deletion of nucleotide 183 of the coding sequence (c.183delT) was identified in CDKL5 in the affected family members. In a screen of 44 RTT cases, a single splice-site mutation, IVS13-1G-->A, was identified in a girl with a severe phenotype overlapping RTT. In the mouse brain, Cdkl5 expression overlaps--but is not identical to--that of Mecp2, and its expression is unaffected by the loss of Mecp2. These findings confirm CDKL5 as another locus associated with epilepsy and X-linked mental retardation. These results also suggest that mutations in CDKL5 can lead to a clinical phenotype that overlaps RTT. However, it remains to be determined whether CDKL5 mutations are more prevalent in specific clinical subgroups of RTT or in other clinical presentations.

Amino Acid Sequence↗
PubMed2006

Phenotypic spectrum associated with mutations of the mitochondrial polymerase gamma gene.

Mutations in the gene coding for the catalytic subunit of the mitochondrial DNA (mtDNA) polymerase gamma (POLG1) have recently been described in patients with diverse clinical presentations, revealing a complex relationship between genotype and phenotype in patients and their families. POLG1 was sequenced in patients from different European diagnostic and research centres to define the phenotypic spectrum and advance understanding of the recurrence risks. Mutations were identified in 38 cases, with the majority being sporadic compound heterozygotes. Eighty-nine DNA sequence changes were identified, including 2 predicted to alter a splice site, 1 predicted to cause a premature stop codon and 13 predicted to cause novel amino acid substitutions. The majority of children had a mutation in the linker region, often 1399G-->A (A467T), and a mutation affecting the polymerase domain. Others had mutations throughout the gene, and 11 had 3 or more substitutions. The clinical presentation ranged from the neonatal period to late adult life, with an overlapping phenotypic spectrum from severe encephalopathy and liver failure to late-onset external ophthalmoplegia, ataxia, myopathy and isolated muscle pain or epilepsy. There was a strong gender bias in children, with evidence of an environmental interaction with sodium valproate. POLG1 mutations cause an overlapping clinical spectrum of disease with both dominant and recessive modes of inheritance. 1399G-->A (A467T) is common in children, but complete POLG1 sequencing is required to identify multiple mutations that can have complex implications for genetic counselling.

Adolescent↗
PubMed2006

The spectrum of clinical disease caused by the A467T and W748S POLG mutations: a study of 26 cases.

We studied 26 patients belonging to 20 families with a disorder caused by mutations in the POLG gene. The patients were homozygous for 1399 G/A or 2243 G/C (giving the amino acid changes A467T and W748S, respectively) or compound heterozygotes for these two mutations. Irrespective of genotype, the patients exhibited a progressive neurological disorder usually starting in their teens and characterized by epilepsy, headache, ataxia, neuropathy, myoclonus and late onset ophthalmoplegia. However, major differences in survival were seen depending on genotype, with compound heterozygotes having a significantly shorter survival time than patients homozygous either for the A467T or W748S (P = 0.006). Epilepsy occurred in 22 of the 26 patients and in the majority of these there was an occipital EEG focus. Episodes of both generalized and focal motor status epilepticus were common and highly resistant to treatment, even with generalized anaesthesia. Status epilepticus was the recorded cause of death in 9 of 11 patients. Liver failure was the sole cause of death in two patients and evolved terminally in six others, all but one of whom were being treated with sodium valproate. Two patients underwent liver transplantation, but only one survived. Delayed psychomotor development and subsequent cognitive decline also occurs. This study demonstrates the clinical spectrum of a disorder that combines features of Alpers' syndrome and a later onset mitochondrial spinocerebellar ataxia with epilepsy and headache. Patients with this disorder are at high risk of death from status epilepticus and from liver failure, if exposed to sodium valproate. Each mutation appears capable of producing a disorder that is recessively inherited, although we also find evidence in one patient suggesting that heterozygotes may manifest. Compound heterozygotes have a significantly more severe phenotype raising the possibility of a dominant negative effect.

Adolescent↗