Characterization of DCTN1 genetic variability in neurodegeneration.

OBJECTIVE: Recently, mutations in DCTN1 were found to cause Perry syndrome, a parkinsonian disorder with TDP-43-positive pathology. Previously, mutations in DCTN1 were identified in a family with lower motor neuron disease, in amyotrophic lateral sclerosis (ALS), and in a family with ALS/frontotemporal dementia (FTD), suggesting a central role for DCTN1 in neurodegeneration. METHODS: In this study we sequenced all DCTN1 exons and exon-intron boundaries in 286 samples diagnosed with Parkinson disease (PD), frontotemporal lobar degeneration (FTLD), or ALS. RESULTS: This analysis revealed 36 novel variants (9 missense, 5 silent, and 22 noncoding). Segregation analysis in families and association studies in PD, FTLD, and ALS case-control series did not identify any variants segregating with disease or associated with increased disease risk. CONCLUSIONS: This study suggests that pathogenic mutations in DCTN1 are rare and do not play a common role in the development of Parkinson disease, frontotemporal lobar degeneration, or amyotrophic lateral sclerosis.

A polymorphic variation in the interleukin 1A gene increases brain microglial cell activity in Alzheimer's disease.

OBJECTIVE: To investigate the impact of possession of the -889 C/T polymorphism of the interleukin 1A gene (IL-1A) and the -511 C/T polymorphism of the interleukin 1B gene (IL-1B) on the extent of neuroinflammation in the brain in Alzheimer's disease (AD), as demonstrated by the degree of microglial cell activity associated with each IL-1A and IL-1B genotype. METHOD: Microglial cell activity within the frontal cortex was determined in 68 patients with necropsy confirmed AD by image analysis as the percentage area of tissue occupied by ferritin immunostained material (microglial cell load). IL-1A, IL-1B, and apolipoprotein E (APOE) genotyping were performed by polymerase chain reaction on DNA extracted from frontal cortex or cerebellum. RESULTS: The microglial cell load was 31% greater in patients with IL-1A T allele, 62% greater with IL-1A TT genotype, but 108% greater with IL-1A TT genotype in combination with APOE epsilon4 allele. No effects on microglial cell load occurred with polymorphisms in IL-1B, or APOE alone. CONCLUSIONS: Polymorphisms within IL-1A influence the degree of brain microglial cell activation, especially in bearers of APOE epsilon4 allele, reinforcing the importance of neuroinflammatory processes in the pathogenesis of AD, and supporting the rationale for treating the disease with inflammation modulating drugs.

Assessment of Nurr1 nucleotide variations in familial Parkinson's disease.

Parkinson's disease (PD) is characterised by the death of dopaminergic neurons of the substantia nigra. As Nurr1 seems to regulate the development and maintenance of these neurons, we evaluated its potential role in Parkinson's disease using genetic methods. We genotyped two polymorphisms and screened a case-control sample for the presence/absence of two mutations recently described in exon 1. Our results failed to replicate the association initially observed and none of the mutations were present in our familial Parkinson's disease cases. These observations suggest that this gene is unlikely to play a major effect in French familial Parkinson disease.

[Genetic complexity of Alzheimer's disease]. / Complexité génétique de la maladie d'Alzheimer.

The discovery of pathogenic mutations in the amyloid precursor protein (APP) gene and the presenilin (PS1, PS2) genes, causing familial early-onset AD has lead to the hypothesis of the amyloid cascade. The epsilon4 allele of the apolipoprotein E (APOE) gene, the only recognized genetic risk factor for AD, may be involved in the mechanism. However, to date, search for new genetic determinants has been hampered by methodological limitations. Some loci, for instance on chromosome 12, have been characterized by linkage studies performed in familial cases, but the regions of interest are very large and contain numerous genes. Furthermore, search for polymorphisms implicated in the development of AD, should not be limited to the coding part of the genes, but should also involve the non-translated sequences of the genes, for instance in the regions regulating gene expression. Indeed, these genetic variations may have important impact on key proteins of the pathologic process. Although this task is difficult, the identification of new susceptibility genes should lead to a better understanding of the development of AD.

Association study of Notch 4 polymorphisms with Alzheimer's disease.

BACKGROUND: The NOTCH4 gene is located at 6p21.3, a site shown in several studies to have significant linkage with Alzheimer's disease. OBJECTIVE: To investigate the potential impact of two polymorphisms within this gene on the risk of developing Alzheimer's disease. METHODS: Genotyping of promoter and 5'-UTR polymorphisms was done in Scottish, English, and French populations. The potential functionality of the 5'-UTR polymorphism was assessed by testing its impact on A beta load in Alzheimer brains and also by undertaking electrophoretic mobility shift assays and transfection experiments. RESULTS: No association of the Notch4 polymorphisms alone with the disease was observed in any of the populations. However, an interaction of the 5'-UTR C/T polymorphism with the epsilon 4 allele of the APOE gene was detected in United Kingdom populations but not in the French. No relation between the 5'-UTR polymorphism and A beta loads was detected overall or in the presence or absence of the epsilon 4 allele. No DNA protein specific binding was found with proteins from neuroblastoma, glioma, or astrocytoma cells, and no allele dependent transcriptional activity was detected. CONCLUSIONS: No association between two NOTCH4 polymorphisms alone and Alzheimer's disease was observed in the three populations, but there was evidence of an increased risk associated with the 5'-UTR CC genotype in epsilon 4 bearers in the United Kingdom. As no functionality for this polymorphism could be determined, it is likely that the interaction is spurious or results from a linkage disequilibrium of this 5'-UTR polymorphism with another marker elsewhere in the 6p21.3 locus.

Association of polymorphisms in the Tau and Saitohin genes with Parkinson's disease.

BACKGROUND: The Saitohin gene has recently been identified in intron 9 of the Tau gene. Because an association between Parkinson's disease and Tau has been described, Saitohin represents a candidate gene for Parkinson's disease. OBJECTIVE: To test these two genes for their association with Parkinson's disease in a large community based case-control study. RESULTS: Cases (n = 208) were more often homozygotes for the Tau H1 haplotype than controls (n = 483; odds ratio (OR) = 1.71 (95% confidence interval, 1.20 to 2.43); p = 0.003), and the saitohin Q allele was in complete linkage disequilibrium with the H1 haplotype. This association was stronger among cases with Parkinson's disease onset below 65 years (< or =65 years: OR = 2.52 (1.49 to 4.25); p<0.001) than among those with older onset (>65 years: OR = 1.20 (0.73 to 1.98); p<0.47). CONCLUSIONS: The data suggest that there is a functional polymorphism at this locus involved in Parkinson's disease.

A polymorphism in the angiotensin 1-converting enzyme gene is associated with damage to cerebral cortical white matter in Alzheimer's disease.

The impact of the insertion (I)/deletion (D) (I/D) polymorphism in the angiotensin 1-converting enzyme (ACE) gene on the extent of white matter myelin loss (ML) was investigated in four regions of the cerebral cortex in an autopsy-confirmed series of 93 patients with Alzheimer's disease (AD). The possible influence of APO E epsilon4 allele acting in concert with ACE D allele was assessed. The extent of ML did not differ between D/D, I/D and I/I genotype groups when data from all four brain regions were combined. However, separate analysis showed that the frontal and temporal cortex tended to be affected more severely by ML in patients with D/D genotype compared to those with I/D and I/I genotypes. Stratification according to APO E epsilon4 allele revealed a greater overall ML in patients bearing at least one copy of ACE D allele and one APO E epsilon4 allele, especially in individuals homozygous for both. The APO E epsilon4 allele may therefore act synergistically in patients with AD (and other subjects) bearing ACE D/D genotype to increase the risk of ML, perhaps through transient ischaemic episodes consequent upon poor cardiac output associated with coronary atherosclerosis in patients with the APO E epsilon4 allele.

Association of 3'-UTR polymorphisms of the oxidised LDL receptor 1 (OLR1) gene with Alzheimer's disease.

Although possession of the epsilon 4 allele of the apolipoprotein E gene appears to be an important biological marker for Alzheimer's disease (AD) susceptibility, strong evidence indicates that at least one additional risk gene exists on chromosome 12. Here, we describe an association of the 3'-UTR +1073 C/T polymorphism of the OLR1 (oxidised LDL receptor 1) on chromosome 12 with AD in French sporadic (589 cases and 663 controls) and American familial (230 affected sibs and 143 unaffected sibs) populations. The age and sex adjusted odds ratio between the CC+CT genotypes versus the TT genotypes was 1.56 (p=0.001) in the French sample and 1.92 (p=0.02) in the American sample. Furthermore, we have discovered a new T/A polymorphism two bases upstream of the +1073 C/T polymorphism. This +1071 T/A polymorphism was not associated with the disease, although it may weakly modulate the impact of the +1073 C/T polymorphism. Using 3'-UTR sequence probes, we have observed specific DNA protein binding with nuclear proteins from lymphocyte, astrocytoma, and neuroblastoma cell lines, but not from the microglia cell line. This binding was modified by both the +1071 T/A and +1073 C/T polymorphisms. In addition, a trend was observed between the presence or absence of the +1073 C allele and the level of astrocytic activation in the brain of AD cases. However, Abeta(40), Abeta(42), Abeta total, and Tau loads or the level of microglial cell activation were not modulated by the 3'-UTR OLR1 polymorphisms. Finally, we assessed the impact of these polymorphisms on the level of OLR1 expression in lymphocytes from AD cases compared with controls. The OLR1 expression was significantly lower in AD cases bearing the CC and CT genotypes compared with controls with the same genotypes. In conclusion, our data suggest that genetic variation in the OLR1 gene may modify the risk of AD.

No association of the HLA-A2 allele with Alzheimer's disease.

A possible association of the human leucocyte antigen (HLA)-A2 allele with increased susceptibility to Alzheimer's disease (AD) has been the subject of debate for more than 20 years. We compared the presence of the HLA-A2 allele in a sample from the French population composed of 451 patients and 477 controls. There was no evidence of an association of this allele with increased risk of AD. Moreover, no effect was observed when we stratified the case-control sample on gender, age of onset or presence of an APOE epsilon4 allele. We conclude that HLA-A2 allele is not a major risk factor for sporadic AD.

No association of the -48CT polymorphism of the presenilin 1 gene with Alzheimer disease in a late-onset sporadic population.

Recently, a polymorphism located in the promoter of the presenilin 1 gene was associated with early-onset Alzheimer disease (EOAD). To determine if this polymorphism is also a risk factor for late-onset Alzheimer's disease (LOAD), we analysed its potential impact in a French population of LOAD patients only. Genotype and allelic distributions of the -48CT polymorphism were similar for controls and AD patients. Our result suggests that this polymorphism may not influence the development of LOAD. Other studies need to be undertaken to confirm this association restricting the impact of this polymorphism to EOAD patients.

Contribution of APOE promoter polymorphisms to Alzheimer's disease risk.

OBJECTIVE: To determine whether the effects of APOE promoter polymorphisms on AD are independent of the APOE-epsilon4 allele. BACKGROUND: Recently, the -491 A-->T and -219 G-->T polymorphisms located in the APOE promoter have been suggested to be risk factors for AD. However, the effects of these polymorphisms have not always been reproduced in case-control studies, possibly because of the strong linkage disequilibrium existing at this locus or the characteristics of the populations studied. METHODS: Data collection was performed from six independent samples (1,732 patients with AD and 1,926 control subjects) genotyped for APOE exon 4 and the two APOE promoter polymorphisms. The risks associated with the APOE polymorphisms for developing AD were estimated using logistic regression procedures and calculation of odds ratios with 95% CI adjusted by age, sex, and collection center. Independence of the APOE promoter polymorphisms was tested by stratification for APOE-epsilon4 and tertile design was used for age stratification. RESULTS: The independence of the -491 AA genotype was observed in the whole sample whereas the independence of the -219 TT genotype was observed only in the oldest population. CONCLUSION: The -491 and -219 APOE promoter polymorphisms incur risk for AD in addition to risk associated with the APOE-epsilon4 allele, with age accentuating the effect of the -219 TT genotype. Because these polymorphisms appear to influence apoE levels, these results suggest that APOE expression is an important determinant of AD pathogenesis.

The angiotensin 1-converting enzyme insertion (I)/deletion (D) polymorphism does not influence the extent of amyloid or tau pathology in patients with sporadic Alzheimer's disease.

An insertion (I)/deletion (D) polymorphism in the angiotensin 1-converting enzyme (ACE) gene has, in some studies, been associated with increased risk for Alzheimer's disease (AD), and functionally the enzyme has been implicated in the degradation of amyloid beta protein (Abeta). We have investigated the frequency of the I/D polymorphism in a clinic-based and autopsy-confirmed series of cases of AD, and investigated what impact the I/D polymorphism in ACE gene might have on the extent of Abeta and tau pathology in the frontal cortex in the autopsy-confirmed series. We found no differences in I/D allele or genotype frequencies between the clinic-based and autopsy-confirmed AD cases, or between the pooled clinic-based and autopsy-confirmed AD cases and a series of normal control subjects. Moreover, Abeta (Abeta(40) and Abeta(42)) load, tau load or extent of amyloid angiopathy did not differ between D/D, I/D and I/I genotype groups, though Abeta(42) load tended to be higher in bearers of I/I genotype (compared to D/D genotype). Neither age at onset nor duration of illness differed according to genotype. We conclude therefore that the frequency of ACE I-allele is not increased in AD and, in autopsy-confirmed AD cases, possession of the ACE I allele has no impact upon the pathology of AD, at least in terms of the amount of Abeta or tau deposited in the brain.

Association study of three polymorphisms of TGF-beta1 gene with Alzheimer's disease.

BACKGROUND: There is evidence that inflammatory processes may contribute to the development of Alzheimer's disease through production of cytokines and free radicals that damage neurones. A recent study has shown that transforming growth factor beta1 (TGF-beta1) signalling in astrocytes promotes Abeta production and could play a critical role in the formation of amyloid plaques in the brain. OBJECTIVES: To explore the impact of the -800 and -509 TGF-beta1 promoter polymorphisms and the +25 polymorphism on the risk of occurrence of Alzheimer's disease in a large population of sporadic cases and controls, and on the amyloid beta (Abeta) load in the brains of Alzheimer patients. METHODS: The TGF-beta1 genotypes of the three polymorphisms were determined in 678 sporadic Alzheimer's disease patients and 667 controls. They were also characterised, along with Abeta load, in the brains of 81 necropsy confirmed Alzheimer patients. RESULTS: No significant variations in the distribution of the genotypes and haplotypes were observed between Alzheimer patients and controls, or in the amount of Abeta deposition. CONCLUSIONS: These results do not suggest an influence of genetic variability at the TGF-beta1 gene locus on the occurrence of Alzheimer's disease.

A polymorphism within intron 11 of the tau gene is not increased in frequency in patients with sporadic Alzheimer's disease, nor does it influence the extent of tau pathology in the brain.

There are numerous polymorphisms within the tau gene but these are in complete linkage disequilibrium and exist as two common extended haplotypes H1 and H2. We have investigated the frequency of these haplotypes in 83 cases of sporadic Alzheimer's disease (AD) using the +34 polymorphism in intron 11 of the tau gene as a marker of H1 and H2 haplotypes. The total amount of hyperphosphorylated tau protein (tau load), present as neurofibrillary tangles, neuropil threads or plaque neurites, was quantified in the frontal cortex of these patients and related to tau haplotype. We found no increase in H1H1 haplotype in this autopsy population of cases with AD compared to published control data. Stratification of cases for apolipoprotein E (APO E) genotype showed a slight, but not statistically significant, overrepresentation of epsilon 4 allele amongst bearers of H2 haplotype. There were no overall differences in tau load between haplotype groups though cases within each haplotype group bearing APO E epsilon 4 allele had a significantly higher tau load than those without epsilon 4 allele. Neither age at onset or duration of illness differed according to tau haplotype. We conclude that the frequency of tau gene H1 haplotype is not elevated in AD and possession of this has no impact upon the amount of tau pathology in AD.

Are interleukin-1 gene polymorphisms risk factors or disease modifiers in AD?

Polymorphisms in the interleukin-1 genes, IL-1A and IL-1B, have been associated with AD, but not in all studies. The authors genotyped the IL-1A(-889) and IL-1B(-511) polymorphisms in large independent cohorts of 503 control individuals and 395 patients with AD, and a further 100 with brain Abeta load. No evidence was found of risk for AD with these variants, nor of an effect on age at onset. However, an impact of IL-1B(-511) on Abeta(40) load (p < 0.05) was detected.

No genetic association of the ubiquitin carboxy-terminal hydrolase-L1 gene S18Y polymorphism with familial Parkinson's disease.

Parkinson's disease (PD) is a neurodegenerative disorder for which genetic susceptibility has been documented in sporadic and familial cases. Recently, a polymorphism located in exon 3 at codon 18 (S18Y) of the Ubiquitin Carboxy-terminal Hydrolase-L1 (UCH-L1) gene has been associated with the disease in 2 populations of German origin and also in a Japanese population. We tested the impact of this polymorphism in a French sample of familial PD patients (n = 114) and controls (n = 93). No association was observed, indicating that this polymorphism did not confer susceptibility for familial PD in our population, even among the youngest age of onset group. This observation suggests that the previous positive results obtained may reflect mechanisms restricted to the sporadic form of the disease or to a founder effect of the disease susceptibility.

Effect of the APOE promoter polymorphisms on cerebral amyloid peptide deposition in Alzheimer's disease.

Polymorphisms in the promoter region of the apolipoprotein E gene (APOE) affect the amount of amyloid peptide (Abeta) in the brains of patients with Alzheimer's disease. We measured Abeta load immunohistochemically in regions 8 and 9 of Brodman's area in 74 people with Alzheimer's disease. The amount of Abeta deposition was independent of APOE genotype in our cohort. These findings in patients with confirmed Alzheimer's disease are consistent with the hypothesis that variation in APOE expression directly affects Alzheimer's disease pathology.

The -48 C/T polymorphism in the presenilin 1 promoter is associated with an increased risk of developing Alzheimer's disease and an increased Abeta load in brain.

Mutations in the presenilin 1 gene (PS1) account for the majority of early onset, familial, autosomal dominant forms of Alzheimer's disease (AD), whereas its role in other late onset forms of AD remains unclear. A -48 C/T polymorphism in the PS1 promoter has been associated with an increased genetic risk in early onset complex AD and moreover has been shown to influence the expression of the PS1 gene. This raises the possibility that previous conflicting findings from association studies with homozygosity for the PS1 intron 8 polymorphism might be the result of linkage disequilibrium with the -48 CC genotype. Here we provide further evidence of increased risk of AD associated with homozygosity for the -48 CC genotype (odds ratio=1.6). We also report a phenotypic correlation with Abeta(40), Abeta(42(43)), and total Abeta load in AD brains. The -48 CC genotype was associated with 47% greater total Abeta load (p<0.003) compared to CT + TT genotype bearers. These results suggest that the -48 C/T polymorphism in the PS1 promoter may increase the risk of AD, perhaps by altering PS1 gene expression and thereby influencing Abeta load.

Genetic analysis of synphilin-1 in familial Parkinson's disease.

alpha-Synuclein is present in Lewy bodies of patients with both sporadic and familial Parkinson's disease. However, pathogenic mutations Ala30Pro and Ala53Thr in alpha-synuclein are rare causes of disease. Synphilin-1 has been demonstrated to associate with alpha-synuclein and promote the formation of cytosolic inclusions in vitro. Two-point genetic linkage analysis of a dinucleotide repeat within the synphilin-1 gene initially implicated this locus as a cause of Parkinson's disease in three of nine families. However, subsequent haplotype, sequencing, and association analyses in these three families and an independent case-control series suggest that variability within the locus does not confer susceptibility to Parkinson's disease.