Progranulin genetic variability contributes to amyotrophic lateral sclerosis.

OBJECTIVES: Null mutations in progranulin (PGRN) cause ubiquitin-positive frontotemporal dementia (FTD) linked to chromosome 17q21 (FTDU-17). Here we examined PGRN genetic variability in amyotrophic lateral sclerosis (ALS), a neurodegenerative motor neuron disease that overlaps with FTD at a clinical, pathologic, and epidemiologic level. METHODS: We sequenced all exons, exon-intron boundaries, and 5' and 3' regulatory regions of PGRN in a Belgian sample of 230 patients with ALS. The frequency of observed genetic variants was determined in 436 healthy control individuals. The contribution of eight frequent polymorphisms to ALS risk, onset age, and survival was assessed in an association study in the Belgian sample and a replication series of 308 Dutch patients with ALS and 345 Dutch controls. RESULTS: In patients with ALS we identified 11 mutations, 5 of which were predicted to affect PGRN protein sequence or levels (four missense mutations and one 5' regulatory variant). Moreover, common variants (rs9897526, rs34424835, and rs850713) and haplotypes were significantly associated with a reduction in age at onset and a shorter survival after onset of ALS in both the Belgian and the Dutch studies. CONCLUSION: PGRN acts as a modifier of the course of disease in patients with amyotrophic lateral sclerosis, through earlier onset and shorter survival.

Prospective Belgian study of neurodegenerative and vascular dementia: APOE genotype effects.

OBJECTIVE: The authors conducted a prospective study of neurodegenerative and vascular dementia in Belgium. Strict diagnostic inclusion criteria were used to include well defined patients and controls. The results of apolipoprotein E (APOE) genotype effect on risk and clinical characteristics are presented. METHODS: APOE genotyping was performed in patients with probable Alzheimer's disease (AD) (n=504), frontotemporal dementia (FTD) (n=47), vascular dementia (VaD) (n=152), mixed dementia (n=132), mild cognitive impairment (MCI) (n=44), Parkinson's disease (PD) (n=30), dementia with Lewy bodies (DLB) (n=17), and multisystem atrophy (MSA)/progressive supranuclear palsy (PSP) (n=12). RESULTS: The APOE allele frequencies of this Belgian control population (epsilon 2: 6.9%; epsilon 3: 76.2%; epsilon 4: 16.9%) did not differ from those reported for other white populations. AD, MCI, and mixed dementia patients had higher APOE epsilon 4 (32.9%, 38.6%, and 28.4% respectively) and lower APOE epsilon 3 (62.2%, 53.4%, and 66.3%) frequencies compared with controls, whereas only AD and mixed dementia patients had lower APOE epsilon 2 frequencies (4.9% and 5.3%). Apart from a borderline significant different distribution of APOE allele frequencies in VaD patients compared with controls, no other differences were detected. The influence of APOE epsilon 4 on clinical features of dementia was limited to lower age at onset in AD patients and a less pronounced negative correlation between age at onset and number of epsilon 4 alleles in MCI and mixed dementia patients. CONCLUSIONS: This study confirmed the risk association between APOE epsilon 4 and AD. The observation that APOE epsilon 4 is associated with mixed dementia reflected the role of AD in the aetiopathogenesis of this condition. Although MCI is an aetiologically heterogeneous syndrome, the increased APOE epsilon 4 frequencies indicated that a large proportion of the MCI patients included in the study might be predisposed to develop AD.

Effect of the APOE-491A/T promoter polymorphism on apolipoprotein E levels and risk of Alzheimer disease: The Rotterdam Study.

The apolipoprotein E (APOE) gene is involved in lipid transport. A common polymorphism in this gene with the APOE*2, APOE*3, and APOE*4 alleles influences plasma levels of apolipoprotein E and cholesterol. Besides its role in lipid transport, the APOE*4 allele is a genetic risk factor for Alzheimer disease (AD). Recently, a polymorphism in the APOE promoter region was found to be involved in plasma apolipoprotein E levels and was found associated with AD. We studied the effect of this -491A/T promoter polymorphism on plasma apolipoprotein E levels and risk for AD in a population-based case-control study. We found that there was a modest but statistically significant effect of the -491A/T polymorphism on plasma apolipoprotein E levels independent of the APOE genotype. The lowest plasma levels were measured for the AA genotype, highest levels for the TT genotype, and intermediate levels for the heterozygotes. There was a small effect of the -491 AA genotype on AD risk that disappeared after adjusting for APOE genotypes. Our data suggest that the -491A/T polymorphism has an APOE genotype-independent effect on plasma apolipoprotein E levels but no APOE-independent effect on AD risk.

Long-term changes in Serengeti-Mara wildebeest and land cover: pastoralism, population, or policies?

Declines in habitat and wildlife in semiarid African savannas are widely reported and commonly attributed to agropastoral population growth, livestock impacts, and subsistence cultivation. However, extreme annual and shorter-term variability of rainfall, primary production, vegetation, and populations of grazers make directional trends and causal chains hard to establish in these ecosystems. Here two decades of changes in land cover and wildebeest in the Serengeti-Mara region of East Africa are analyzed in terms of potential drivers (rainfall, human and livestock population growth, socio-economic trends, land tenure, agricultural policies, and markets). The natural experiment research design controls for confounding variables, and our conceptual model and statistical approach integrate natural and social sciences data. The Kenyan part of the ecosystem shows rapid land-cover change and drastic decline for a wide range of wildlife species, but these changes are absent on the Tanzanian side. Temporal climate trends, human population density and growth rates, uptake of small-holder agriculture, and livestock population trends do not differ between the Kenyan and Tanzanian parts of the ecosystem and cannot account for observed changes. Differences in private versus state/communal land tenure, agricultural policy, and market conditions suggest, and spatial correlations confirm, that the major changes in land cover and dominant grazer species numbers are driven primarily by private landowners responding to market opportunities for mechanized agriculture, less by agropastoral population growth, cattle numbers, or small-holder land use.

Pathogenic APP mutations near the gamma-secretase cleavage site differentially affect Abeta secretion and APP C-terminal fragment stability.

Release of amyloid beta (Abeta) from the amyloid precursor protein (APP) requires cleavages by beta- and gamma-secretases and plays a crucial role in Alzheimer's disease (AD) pathogenesis. Missense mutations in the APP gene causing familial AD are clustered around the beta-, alpha- and particular gamma-secretase cleavage sites. We systematically compare in primary neurons the effect on APP processing of a series of clinical APP mutations (two of which not characterized before) located in close proximity to the gamma-secretase cleavage site. We confirm and extend previous observations showing that all these mutations (T714I, V715M, V715A, I716V, V717I and V717L) affect gamma-secretase cleavage causing an increased relative ratio of Abeta42 to Abeta40. Taking advantage of these extended series of APP mutations we were able to demonstrate an inverse correlation between these ratios and the age at onset of the disease in the different families. In addition, a subset of mutations caused the accumulation of APP C-terminal fragments indicating that these mutations also influence the stability of APP C-terminal fragments. However, it is unlikely that these fragments contribute significantly to the disease process.

APOE epsilon4 and Alzheimer's disease: positive association in a Colombian clinical series and review of the Latin-American studies.

OBJECTIVE: As the strength of the association between the APOE epsilon4 allele and Alzheimer's disease (AD) varies across ethnic groups, we studied if there was such an association in Colombian patients. METHOD: We performed apolipoprotein E (APOE) genotyping in a clinical sample of 83 unrelated AD patients, predominantly late-onset (>65 yrs) including familial ( n =30) and sporadic AD cases (n= 53) diagnosed according to NINCDS-ADRDA criteria and assessed by a multi-disciplinary team. Control subjects (n = 44) had no significant cognitive impairment by medical interview and neuro-psychological testing. RESULTS: We found a high association (OR= 5.1 95%CI 1.9 -13.6) between APOE epsilon4 and AD, in this series with predominantly late-onset cases with familial aggregation in 24 cases (28.9%). A significant negative association was found between epsilon2 and AD (OR= 0.2 95% CI 0.05-0.75). CONCLUSION: Further population-based surveys in Colombia are warranted to precise a possible dose effect of APOE epsilon4.

Variable expression of presenilin 1 is not a major determinant of risk for late-onset Alzheimer's disease.

We have previously reported a significant association between early-onset Alzheimer's disease (EOAD) and an allele in the promoter of presenilin 1 (PSEN1) significantly decreasing PSEN1 expression in vitro. For late-onset Alzheimer's disease (LOAD), numerous studies have reported inconsistent associations with a PSEN1 intronic polymorphism. We therefore hypothesized that linkage disequilibrium between the intronic PSEN1 polymorphism and the functional promoter polymorphism might explain the conflicting reports in LOAD. We analysed both variations in 356 LOAD patients and 230 controls in a population-based case-control study. In addition, we re-analysed all published literature on the PSEN1 intronic polymorphism in a meta-analysis. No significant association was found with the PSEN1 intronic or promoter polymorphism in our case-control sample. In the meta-analysis no major differences between patients and controls were found for the PSEN1 intronic variation. Together, our results do not support a major role for variable expression of PSEN1 in LOAD.

Genetic variability in the regulatory region of presenilin 1 associated with risk for Alzheimer's disease and variable expression.

Mutations in the presenilin 1 ( PSEN1 ) gene have been implicated in 18-50% of autosomal dominant cases with early-onset Alzheimer's disease (EOAD). Also, PSEN1 has been suggested as a potential risk gene in late-onset AD cases. We recently showed genetic association in a population-based study of EOAD, pointing to the 5' regulatory region of PSEN1. In this study we systematically screened 3.5 kb of the PSEN1 upstream region and found four novel polymorphisms. Genetic analysis confirmed association of two polymorphisms with increased risk for EOAD. In addition, we detected two different mutations in EOAD cases at-280 and-2818 relative to the transcription initiation site in exon 1A of PSEN1. Analysis of the mutant and wild-type-280 variants using luciferase reporter gene expression in transiently transfected neuroblastoma cells showed a 30% decrease in transcriptional activity for the mutant-280G PSEN1 promoter variant compared with the wild-type variant-280C. Our data suggest that the increased risk for EOAD associated with PSEN1 may result from genetic variations in the regulatory region leading to altered expression levels of the PSEN1 protein.

Genetic association of the presenilin-1 regulatory region with early-onset Alzheimer's disease in a population-based sample.

Genetic association has been reported between a di-allelic polymorphism in intron 8 of presenilin-1 (PSEN1) and Alzheimer's disease (AD) in some studies but not in others. In a population-based series of 102 patients with early onset AD and 118 community controls we examined whether polymorphisms in linkage disequilibrium with intron8 of PSEN1 may explain the association. In addition to the intron 8 polymorphism (P = 0.05), a promoter polymorphism (P = 0.03) and the simple tandem repeat (STR) polymorphism D14S1028 located upstream of PSEN1 (P = 0.04) were found to be marginally significantly associated to AD. When excluding PSEN1 mutation cases (n = 6), the intron 8 association was explained by linkage disequilibrium to the dominant PSEN1 mutations. In the non-mutation cases, the weak associations between the polymorphisms in the regulatory region remained. Our study suggests that a polymorphism/mutation in the promoter or regulatory region of PSEN1 rather than the polymorphism in intron 8 of PSEN1 is associated with early onset AD.

Mutation screening of the tau gene in patients with early-onset Alzheimer's disease.

Hyperphosphorylated microtubule associated protein tau, present in neurofibrillary tangles, is a prominent pathological feature of Alzheimer's disease (AD). The gene encoding tau (MAPT) was recently found mutated in frontotemporal dementia (FTD) and other tauopathies. We studied MAPT as a candidate gene in the etiology of AD. The study population consisted of 101 early-onset AD patients and 117 controls. Mutation analysis did not detect causal mutations in exons 9 to 13 encoding the microtubule-binding domains involved in FTD, however, two novel polymorphisms were detected in exon 9. Using the Ala169 polymorphism in exon 9 and a previously reported (CA)n-repeat polymorphism in intron 9, an association study was performed. No association with early-onset AD was detected. Together, our data indicate that MAPT does not play a role in early-onset AD.

Estimation of the genetic contribution of presenilin-1 and -2 mutations in a population-based study of presenile Alzheimer disease.

Two closely related genes, the presenilins ( PS ), located at chromosomes 14q24.3 and 1q42.1, have been identified for autosomal dominant Alzheimer disease (AD) with onset age below 65 years (presenile AD). We performed a systematic mutation analysis of all coding and 5'-non-coding exons of PS -1 and PS -2 in a population-based epidemiological series of 101 unrelated familial and sporadic presenile AD cases. The familial cases included 10 patients of autosomal dominant AD families sampled for linkage analysis studies. In all patients mutations in the amyloid precursor protein gene ( APP ) had previously been excluded. Four different PS -1 missense mutations were identified in six familial cases, two of which where autosomal dominant cases. Three mutations resulted in onset ages above 55 years, with one segregating in an autosomal dominant family with mean onset age 64 years (range 50-78 years). One PS -2 mutation was identified in a sporadic case with onset age 62 years. Our mutation data provided estimates for PS -1 and PS -2 mutation frequencies in presenile AD of 6 and 1% respectively. When family history was accounted for mutation frequencies for PS -1 were 9% in familial cases and 18% in autosomal dominant cases. Further, polymorphisms were detected in the promoter and the 5'-non-coding region of PS -1 and in intronic and exonic sequences of PS -2 that will be useful in genetic association studies.