Pilar Latorre

Cellular and Molecular Pathways Triggering Neurodegeneration in the Spinocerebellar Ataxias

The autosomal dominant spinocerebellar ataxias (SCAs) are a group of progressive neurodegenerative diseases characterised by loss of balance and motor coordination due to the primary dysfunction of the cerebellum. To date, more than 30 genes have been identified triggering the well-described clinical and pathological phenotype, but the underlying cellular and molecular events are still poorly understood. Studies of the functions of the proteins implicated in SCAs and the corresponding altered cellular pathways point to major aetiological roles for defects in transcriptional regulation, protein aggregation and clearance, alterations of calcium homeostasis, and activation of pro-apoptotic routes among others, all leading to synaptic neurotransmission deficits, spinocerebellar dysfunction, and, ultimately, neuronal demise. However, more mechanistic and detailed insights are emerging on these molecular routes. The growing understanding of how dysregulation of these pathways trigger the onset of symptoms and mediate disease progression is leading to the identification of conserved molecular targets influencing the critical pathways in pathogenesis that will serve as effective therapeutic strategies in vivo, which may prove beneficial in the treatment of SCAs. Herein, we review the latest evidence for the proposed cellular and molecular processes to the pathogenesis of dominantly inherited spinocerebellar ataxias and the ongoing therapeutic strategies.

Alzheimer’s disease and the cystatin C gene polymorphism: an association study

Cystatin C is an amyloidogenic protein that colocalizes with beta-amyloid (Abeta) within arteriolar walls in Alzheimer disease (AD) brains. Recently, a coding polymorphism in the cystatin C gene (CST3) has been claimed to confer risk for the development of late-onset AD. In the present work we have tested the frequencies of CST3-A and CST3-G alleles and used chi-square and logistic regression analyses to assess the association among the CST3 polymorphism, apolipoprotein E4 (APOE4), and AD in a series of 159 AD patients and 155 controls. The CST3-A allele was seen to be an accumulation risk factor for early-onset AD. Furthermore, a synergistic association among the CST3-A allele, APOE4 and AD was found in AD patients whose ages were between 60 and 74 years.

Ataxia Rating Scales—Psychometric Profiles, Natural History and Their Application in Clinical Trials

We aimed to perform a comprehensive systematic review of the existing ataxia scales. We described the disorders for which the instruments have been validated and used, the time spent in its application, its validated psychometric properties, and their use in studies of natural history and clinical trials. A search from 1997 onwards was performed in the MEDLINE, LILACS, and Cochrane databases. The web sites ClinicalTrials.gov and Orpha.net were also used to identify the endpoints used in ongoing randomized clinical trials. We identified and described the semiquantitative ataxia scales (ICARS, SARA, MICARS, BARS); semiquantitative ataxia and non-ataxia scales (UMSARS, FARS, NESSCA); a semiquantitative non-ataxia scale (INAS); quantitative ataxia scales (CATSYS 2000, AFCS, CCFS and CCFSw, and SCAFI); and the self-performed ataxia scale (FAIS). SARA and ICARS were the best studied and validated so far, and their reliability sustain their use. Ataxia and non-ataxia scores will probably provide a better view of the overall disability in long-term trials and studies of natural history. Up to now, no clear advantage has been disclosed for any of them; however, we recommend the use of specific measurements of gait since gait ataxia is the first significant manifestation in the majority of ataxia disorders and comment on the best scales to be used in specific ataxia forms. Quantitative ataxia scales will be needed to speed up evidence from phase II clinical trials, from trials focused on the early phase of diseases, and for secondary endpoints in phase III trials. Finally, it is worth remembering that estimation of the actual minimal clinically relevant difference is still lacking; this, together with changes in quality of life, will probably be the main endpoints to measure in future therapeutic studies.

Methionine synthase polymorphism is a risk factor for Alzheimer disease.

&NA; Alzheimer disease (AD) patients show increased plasma levels of homocysteine, whose conversion to methionine is catalyzed by methionine synthase (MS). Although altered MS activity may result from the MS A2756G polymorphism, the latters possible association with AD remains unexplored. To assess whether the MS A2756G polymorphism holds any influence on AD risk, we have analyzed 172 AD patients and 166 controls. We have also investigated whether the MS‐A or MS‐G allele interacts with the APOE4 allele. Our results indicate that association with the MS‐AA genotype is an APOE4 allele‐independent risk factor for AD. These findings provide novel evidence implicating genetic enzymatic alterations of homocysteine metabolic pathways in the pathogenesis of AD.

Age at onset: an essential variable for the definition of genetic risk factors for sporadic Alzheimer's disease.

The aim of our work was to detect minor loci acting as Alzheimers disease (AD) genetic markers. We divided 206 AD patients and 186 individuals as controls into six age at onset/age‐dependent groups. We studied polymorphisms of the genes of apolipoprotein E (APOE) and its promoter, cathepsin D, butyrylcholinesterase, cystatin C, methionine synthase, and cystathionine beta‐synthase. Our results demonstrated that data analysis according to age at onset allows the detection of minor genetic risk factors for AD. Thus, the Th1/E47cs‐G allele was an independent AD risk factor after 80 years, whereas the catD‐T, BChE‐K, CBS‐844ins68, and CBS‐VNTR 19 alleles are independent AD risk factors after 75 years. On the other hand, the CST3‐A allele was an independent AD risk factor before 60 years while the CBS‐VNTR allele 21 was an independent AD risk factor before 64 years. In contrast, the MS‐AA genotype was an AD risk factor unrelated to age at onset. In conclusion, two main tasks remain to be accomplished to facilitate early detection of people at risk of developing AD: (1) the establishment of common criteria to carry out association studies for different genetic markers, including the introduction of AD age at onset as a crucial variable in each study, and (2) the definition of global and population‐specific genetic markers for each age at onset AD subgroup.

Cystathionine Beta Synthase as a Risk Factor for Alzheimer Disease

One of the known risk factors for developing Alzheimer disease (AD) is hyperhomocysteinemia. The latter may result from mutations of the genes coding for three key enzymes involved in homocysteine metabolism (methylenetetrahydrofolate reductase [MTHFR], methionine synthase [MS], and cystathionine beta-synthase [CBS]). Although MTHFR and MS polymorphisms have been shown to be positively associated with AD in some populations, the relationship of the CBS gene with AD remains undefined. In order to evaluate whether AD is associated with CBS gene changes leading to decreased CBS activity and homocysteine accumulation, we genotyped the CBS 844ins68 mutation and VNTR polymorphisms of the CBS gene in 206 AD patients and 186 age-matched controls. A slight increase in both 844ins68 mutation and VNTR allele 19 frequencies was detected in the whole AD patient group, compared with controls. The division of AD patients and controls into three age-at-onset/age dependent subgroups (<65 years, 65-74 years, > 75 years) revealed that the 844ins68 mutation and VNTR allele 19 are independent risk factors for AD development in subjects aged 75 years or more.

Late-onset episodic ataxia type 2 associated with a novel loss-of-function mutation in the CACNA1A gene

We report a patient with typical features of episodic ataxia type 2 (EA2) but with onset in the sixth decade and associated interictal hand dystonia. He was found to bear the novel heterozygous missense mutation p.Gly638Asp (c.1913G>A) in the CACNA1A gene. Functional analysis of the mutation on P/Q channels expressed in HEK 293 cells revealed a reduction of Ca(2+) current densities, a left-shift in the apparent reversal potential, the slowing of inactivation kinetics and the increase in the rate of current recovery from inactivation. These results are consistent with a decrease in Ca(2+) permeability through mutant P/Q channels. To our knowledge, this is just the second patient with late onset EA2 linked to a CACNA1A mutation and the first to carry a loss-of-function missense mutation.

A variable poly‐T sequence modulates α‐synuclein isoform expression and is associated with aging

α‐Synuclein, the main component of proteinaceous inclusions in synucleinopathies, is centrally involved in aggregation processes preceding Lewy body formation. Here we describe a new α‐synuclein gene poly‐T polymorphism that is situated upstream to exon 3 and consists of three different alleles. A correlation between poly‐T length and expression of α‐synuclein 126 mRNA, an isoform lacking exon 3, was detected in the human cerebral cortex. Specifically, when compared with the most frequent 7T/7T genotype, the shortest poly‐T stretch (5T) was associated with the lowest α‐synuclein 126 expression levels, whereas the longest poly‐T stretch (12T) was accompanied by the highest α‐synuclein 126 expression levels. Thus, three different expression‐level‐specific genotypes, with 5T+ genotypes as low α‐synuclein 126 expression genotypes and 12T+ genotypes as high α‐synuclein 126 expression genotypes, could be established. Poly‐T genotype distributions were also analyzed in a healthy control population. Age‐dependent variations in this distribution were observed and showed accumulation of low α‐synuclein 126 expression genotypes at ages under 60 years and high α‐synuclein 126 expression genotypes at ages over 80 years. To determine human specificity of the variable poly‐T strech, the mouse α‐synuclein gene sequence was analyzed. Although α‐synuclein is very well conserved in vertebrates, the poly‐T sequence was found to be absent in mice, and an α‐synuclein 126 mouse homologue could not be detected. In conclusion, this newly identified poly‐T polymorphism is a human‐specific sequence; its length influences α‐synuclein 126 expression levels; and, finally, it seems to exert a specific influence on normal aging.

Alpha- and beta-synuclein expression in Parkinson disease with and without dementia

Parkinson disease (PD) is the most important movement disorder and about 50% of patients develop dementia over the time. PD belongs to the group of Lewy body disorders. Alpha-synuclein (AS) is the main component of Lewy bodies and its aggregation is a key event in the pathogenesis of PD. Beta-synuclein (BS) inhibits AS aggregation in vitro and in vivo and has been shown to interact directly with AS regulating its functionality and preventing its oligomerization. Recently, we have described a molecular subgroup of DLB characterized by the drastic BS reduction in cortical areas. In this study we have analyzed the expression of two BS transcripts and the main AS transcript SNCA140, in frozen samples of three brain areas, temporal cortex, caudate nucleus and pons, from patients with PD and PDD in comparison with controls. Relative mRNA expression was determined by real-time PCR with SybrGreen, neuron-specific-enolase as housekeeping gene and the deltadeltaCt method. The most important difference in BS and AS mRNA expression between PD and PDD was found in the caudate nucleus, where BS mRNA was overexpressed in PD and AS mRNA diminished in PDD. Our findings provide new insights into the pathogenesis of dementia in PD, indicating that differential BS and AS expression in the caudate nucleus may represent one of the molecular mechanisms involved in these complex diseases.

Identification of a protective allele against Alzheimer disease in the APOE gene promoter.

Alzheimer disease (AD) risk is significantly influenced by the APOE2 and APOE4 alleles. In turn, the −491AT and TH1/E47cs polymorphisms alter APOE gene expression levels. To determine whether these two alleles exert any significant effect on AD development we have analysed the genotypes of the APOE promoter −491AT and Th1/E47cs polymorphisms in 163 AD patients and 155 controls divided into three age at onset/age dependent subgroups. Our study has detected a Th1/E47cs-T allele accumulation in healthy individuals over 75 years of age, which suggests it plays a protective role against AD. The Th1/E47cs-T allele may provide greater protection against AD than APOE2, although this awaits proof of Th1/E47cs-T allele overrepresentation in healthy individuals of other populations.