A genetic basis for the variable effect of smoking/nicotine on Parkinson's disease.

Prior studies have established an inverse association between cigarette smoking and the risk of developing Parkinson's disease (PD), and currently, the disease-modifying potential of the nicotine patch is being tested in clinical trials. To identify genes that interact with the effect of smoking/nicotine, we conducted genome-wide interaction studies in humans and in Drosophila. We identified SV2C, which encodes a synaptic-vesicle protein in PD-vulnerable substantia nigra (P=1 × 10(-7) for gene-smoking interaction on PD risk), and CG14691, which is predicted to encode a synaptic-vesicle protein in Drosophila (P=2 × 10(-11) for nicotine-paraquat interaction on gene expression). SV2C is biologically plausible because nicotine enhances the release of dopamine through synaptic vesicles, and PD is caused by the depletion of dopamine. Effect of smoking on PD varied by SV2C genotype from protective to neutral to harmful (P=5 × 10(-10)). Taken together, cross-validating evidence from humans and Drosophila suggests SV2C is involved in PD pathogenesis and it might be a useful marker for pharmacogenomics studies involving nicotine.

Frequency of tau gene mutations in familial and sporadic cases of non-Alzheimer dementia.

BACKGROUND: Mutations in the tau gene have been reported in families with frontotemporal dementia (FTD) linked to chromosome 17. It remains uncertain how commonly such mutations are found in patients with FTD or non-Alzheimer dementia with or without a positive family history. OBJECTIVE: To determine the frequency of tau mutations in patients with non-Alzheimer dementia. PATIENTS AND METHODS: One hundred one patients with non-Alzheimer, nonvascular dementia, most thought to have FTD. Of these, 57 had a positive family history of dementia. Neuropathologic findings were available in 32. The tau gene was sequenced for all exons including flanking intronic DNA, portions of the 3' and 5' untranslated regions, and at least 146 base pairs in the intron following exon 10. RESULTS: Overall, the frequency of the tau mutations was low, being 5.9% (6/101) in the entire group. No mutations were found in the 44 sporadic cases. However, 6 (10.5%) of the 57 familial cases and 4 (33%) of the 12 familial cases with tau pathologic findings had mutations in the tau gene. The most common mutation was P301L. CONCLUSIONS: We conclude that tau mutations are uncommon in a neurology referral population with non-Alzheimer dementia, even in those with a clinical diagnosis of FTD. However, a positive family history and/or tau pathologic findings increase the likelihood of a tau mutation. There must be other genetic and nongenetic causes of FTD and non-Alzheimer dementia, similar to the etiologic heterogeneity present in Alzheimer disease.

Genetic anticipation in Parkinson's disease.

We studied age at onset and family history of 137 patients (probands) with the diagnosis of idiopathic Parkinson's disease (PD). Probands (N = 21) who had an affected parent, aunt, or uncle were younger (p = 0.0001) at the onset of PD (47.7 +/- 8.8 years) than were probands (N = 11) who had an affected sib only (60.3 +/- 12.9 years) and probands (N = 105) who had no affected sib, parent, aunt, or uncle (59.2 +/- 11.4 years). Age at onset of affected family members differed significantly between generations (p = 0.0001). Age at onset was earlier, by an average of 17 years, in the proband generation than in the parental generation. The intrafamily variation in the calendar year of onset was too great to suggest a common point of exposure. Our data are most compatible with genetic anticipation, which could suggest involvement of an unstable trinucleotide repeat.

HLA-A2, or a closely linked gene, confers susceptibility to early-onset sporadic Alzheimer's disease in men.

There is a weak association between Alzheimer's disease (AD) and the histocompatibility antigen HLA-A2, suggesting that A2 has either a minor role in AD or a major role in a subtype of it. To test these alternatives, we studied 54 consecutively ascertained AD patients diagnosed by NINCDS-ADRDA criteria. Patients had a higher frequency of A2 than control subjects, primarily due to the elevated frequency of this antigen in men with early onset of dementia (less than or equal to 60 years): 92% of early-onset men had A2 as compared with 44% of controls. This finding suggests that A2, or a closely linked gene, confers susceptibility to early-onset AD in men. Furthermore, A2 appears to be primarily associated with sporadic AD, rather than with the familial subtype.

Increased risk of familial late-onset Alzheimer's disease in women.

The role of gender in the pathogenesis of Alzheimer's disease (AD) is an important issue that remains controversial. We compared men and women in late-onset familial AD kindreds for the risk of developing AD by studying 26 well-characterized familial AD kindreds from the Oregon Alzheimer Disease Center and, for confirmation, an additional 32 kindreds from the National Cell Repository (NCR) at the Indiana University Alzheimer Disease Center. Comparing women to men, the age-adjusted odds ratio estimates were 3.2 (p = 0.0002) for the Oregon data and 2.3 (p = 0.004) for the NCR data. These results suggest that gender is an independent risk factor for familial late-onset AD and may play a role in the pathogenesis of this disease.

HLA-A2 homozygosity but not heterozygosity is associated with Alzheimer disease.

AD is associated with the A2 allele of the human leukocyte antigen (HLA). However, it is not currently known whether there is any difference between A2 homozygotes and A2 heterozygotes. The authors studied 458 patients with AD and found that A2 homozygotes had earlier onset of AD than either A2 heterozygotes (5.4 years, p = 0.002) or those without A2 (5.2 years, p = 0.003). The "recessive" nature of this association suggests that loss of function at the HLA-A locus or a closely linked gene is associated with AD.

No evidence for association of familial Parkinson's disease with CAG repeat expansion.

In some kindreds, familial Parkinson's disease (PD) exhibits genetic anticipation. Thus, we postulated that familial PD in certain kindreds may be associated with a CAG repeat expansion. However, using the repeat expansion detection method, we found no significant increase in the frequency of CAG repeat expansion among 46 unrelated PD probands compared with controls. Nor did we find evidence for CAG repeat expansion between generations in 11 different PD families that exhibit anticipation in age at onset.

Chromosome 17 and hereditary dementia: linkage studies in three non-Alzheimer families and kindreds with late-onset FAD.

Several previous families with differing clinical and pathologic characteristics have demonstrated linkage to the 17q21-22 region. We have performed a linkage analysis with chromosome 17 markers on three families showing autosomal dominant inheritance of non-Alzheimer dementia and 60 kindreds with late-onset familial Alzheimer's disease (FAD). Family A shows unequivocal evidence of linkage with a maximum lod score of 5.0 for marker D17S934 (theta = 0.001). This family has an unusual syndrome of a schizophrenia-like psychosis beginning in the fifth or sixth decade followed by severe dementia with an average disease duration of 13.8 years. Neuropathology from five autopsies in this family has shown marked neurofibrillary tangle formation (NFT), degeneration of the amygdala, and no amyloid plaques. This confirms the presence of a gene associated with dementia on 17q and extends the related phenotype to include schizophrenia-like symptoms and classic NFT pathology. A second family with early aphasia progressing to dementia and cortical-basal ganglion-like degeneration also has suggestive evidence for linkage to 17q. A third family with very early-onset dementia (mean, 31 years) and nonspecific pathology can be excluded from the 17q region and emphasizes additional genetic heterogeneity in non-Alzheimer hereditary dementia. Finally, we also present evidence against linkage to D17S579 in the set of 60 families with late-onset FAD, providing further evidence that the chromosome 17 gene is unlikely to be involved in the pathogenesis of typical AD.

Parkinson's disease, CYP2D6 polymorphism, and age.

OBJECTIVE: PD may be caused by genetic susceptibility to neurotoxins. CYP2D6 is a candidate gene for PD because it regulates drug and toxin metabolism, but association studies have been inconsistent. The aim of this study was to test if the CYP2D6*4 allele (poor metabolizer phenotype) is associated with earlier age at onset. METHODS: Five hundred seventy-six patients with PD and 247 subjects without PD were studied using standard diagnostic, genotyping, and statistical techniques. RESULTS: Surprisingly, mean onset age was significantly later in *4-positive patients. Frequency of *4 was significantly higher in late-onset PD than early-onset PD. When early- and late-onset PD were analyzed separately, *4 had no effect on onset age; hence, the association with delayed onset was likely an artifact of an elevated *4 frequency in late-onset PD. Contrary to a common assumption that CYP2D6 frequencies do not change with age, *4 frequency rose significantly with advancing age, both in patients with PD (from 0.16 at mean age of 56.5 years to 0.21 at mean age of 72) and subjects without PD (from 0.09 at mean age of 45.5 years to 0.21 at mean age of 72). *4 Frequencies in patients with early- and late-onset PD, although different from each other, were in agreement with similarly aged subjects without PD, suggesting the elevated *4 frequency in late-onset PD was likely an age effect, unrelated to PD. CONCLUSION: The CYP2D6*4 allele is not associated with earlier PD onset. *4 May be associated with survival. Inconsistent results from allelic association studies may have been due to an unrecognized age effect.

Evidence for association of HLA-A2 allele with onset age of Alzheimer's disease.

Our earlier studies had suggested a possible association between the HLA-A2 allele and Alzheimer's disease (AD). In the present study we tested the hypothesis that A2 is associated with earlier AD onset. We performed two independent studies: a collaborative study with 111 patients and a confirmatory study with 96 patients. We found similar patterns of reduced age at onset as a function of A2 in both data sets. Overall, A2 was associated with a significant 3-year shift to earlier onset. The effects of A2 and epsilon 4 on age at onset appeared additive. Our results suggest A2, or a closely linked gene, modulates onset age of AD. Association with A2 would suggest an immune/inflammatory response mechanism for AD.

Segregation analysis of Parkinson disease.

Parkinson disease (PD) is a prevalent movement disorder of unknown cause whose incidence rises with increasing age. Nearly 20% of PD is familial, a small subset of which exhibits autosomal dominant transmission. However, in most families, the inheritance is not clear. To determine the most likely mode of inheritance of PD, we performed complex segregation analyses using kindreds of 136 PD patients randomly ascertained from a clinic population. The hypotheses of a nontransmissible environmental factor, no major gene or type (sporadic), and all Mendelian inheritance (dominant, recessive, additive, decreasing) were rejected (P <0.001). Familial clustering of PD in this data set is best explained by a rare familial factor which a) is transmitted in a nonMendelian fashion, and b) influences the age at onset of PD. If confirmed, our results have immediate implications in gene-mapping studies which often search for genes that behave in a Mendelian fashion that affect susceptibility rather than age at onset and long term implications in understanding the pathogenesis of PD.

Expression of alpha-synuclein in the human brain: relation to Lewy body disease.

Alpha-synuclein is mutated in some hereditary cases of Parkinson's disease and the protein precipitates in Lewy bodies, the pathological hallmark of both Parkinson's disease and Lewy body disease. Transgenic mice overexpressing human wild-type alpha-synuclein develop alpha-synuclein-immunoreactive inclusions in brain regions typically affected with Lewy body disease. We used in situ hybridization to characterize alpha-synuclein expression and examine mRNA levels in patients affected with Lewy body disease and controls. Substantia nigra was avoided because of the extensive neuronal loss and cingulate gyrus was chosen as it is one of the diagnostic regions in Lewy body disease where Lewy bodies most frequently are demonstrated. beta-tubulin was used to control for neuronal degeneration. The alpha-synuclein probe showed intense labeling of pyramidal cells in lamina III and V in both patients and controls. We found no difference in alpha-synuclein mRNA levels and beta-tubulin mRNA was not significantly altered (P=0.06) in patient brains. There was no difference in the ratio of alpha-synuclein and beta-tubulin mRNA levels between patients and controls. Further, we found no relationship between alpha-synuclein mRNA levels and Lewy bodies. Great variability in alpha-synuclein mRNA levels among patients indicates that Lewy body disease may be a heterogeneous disorder with regard to alpha-synuclein involvement.

Cognitive markers preceding Alzheimer's dementia in the healthy oldest old.

OBJECTIVE: To look for preclinical markers of Alzheimer's dementia in a sample of healthy, oldest old individuals. DESIGN: Prospective, longitudinal study of individuals examined at yearly intervals with neuropsychological tests selected to be sensitive to the early detection of dementia. PARTICIPANTS: One hundred and thirty-nine community-dwelling, functionally independent, healthy individuals 65 to 106 years of age who met strict criteria for lack of dementia at entry. Incident dementia cases consisted of 16 volunteers all 80 years old or older who developed dementia of the Alzheimer's type and 31 volunteers 80 years old and older showing no evidence of dementia during a mean 2.8-year follow-up interval. MEASUREMENTS: Scores on 10 neuropsychological measures were analyzed for the initial examination when none of the volunteers showed clinical evidence of dementia and for the two subsequent yearly examinations. RESULTS: Individuals who subsequently developed dementia showed evidence of verbal memory impairment at their initial examination, which was a mean of 2.8 years before clinical evidence of dementia. The average yearly incidence rate for dementia in those 80 years of age and older was 12%. Performance of individuals who did not development dementia remained relatively stable during follow-up for up to 5 years. CONCLUSION: Alzheimer's disease has a preclinical stage in which verbal memory decline is the earliest sign. Dementia in the oldest old is distinguishable from age-related cognitive decline.

Predictors of healthy brain aging.

To determine if superior health at old age protects against cognitive impairment (CI) and Alzheimer's disease (AD), we prospectively studied 100 optimally healthy oldest-old (> or =85 years) individuals. Initially, subjects represented the top 3% of the oldest old for health. During 5.6 +/- 0.3 years of follow-up, 34 subjects developed CI, and 23 progressed to AD. By age 100, probability of CI and AD were.65 +/-.09 and.49 +/-.10. Median onset age was 97 years for CI and 100 for AD. Clearly, superior health at old age does not guarantee protection against cognitive decline. Lifetime risks were similar to the general population but onset ages were later, suggesting factors that delay onset are key to improving cognitive health in the elderly. In this population, absence of apolipoprotein E-epsilon4 and male gender were associated with delayed onset, whereas estrogen use and education had no detectable effect on cognitive outcome.

Exclusion of dominant mutations within the FTDP-17 locus on chromosome 17 for Parkinson's disease.

Parkinson's disease (PD) is a prevalent movement disorder, and 10-30% of PD is familial. Several neurodegenerative disorders which are collectively called frontotemporal dementia and parkinsonism have been mapped to chromosome 17q and mutations in tau have been identified. The clinical and pathological overlap suggests that these related conditions may be due to mutations in tau. We examined linkage to the candidate region on chromosome 17 including and surrounding tau in eight familial PD kindreds. We found no evidence for linkage and excluded the 6cM candidate region which suggest that in our families, PD is not caused by dominant mutations within tau.

Apolipoprotein E genotype does not affect the age of onset of dementia in families with defined tau mutations.

We have assessed whether apolipoprotein E (ApoE) genotype influences the age of onset of dementia in a series of families with frontal temporal dementia with defined mutations in the tau gene. In contrast to the situation in Alzheimer's disease (AD), we could find no evidence that the age of onset of disease was influenced by the ApoE genotype.

Genetic epidemiology of Parkinson's disease.

The cause of Parkinson's disease (PD) is unknown. The major risk factors identified to date are family history, age, and elements of rural living. Nearly one-third of all PD cases are familial, a small subset of which appears autosomal dominant; however, the majority exhibit no clear inheritance pattern. Autosomal dominant PD is genetically heterogeneous: two PD genes have been mapped to chromosomes 2 and 4 and there may be additional as yet unidentified genes. The common forms of PD-both familial and sporadic cases-appear to involve a complex interplay of genetic susceptibility and environmental exposure. The observations that rural residence and pesticide exposure increase the risk of developing PD, and that a synthetic drug, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, can cause parkinsonism, suggest that at least a subset of PD may be caused by a toxin. Furthermore, modest but significant associations have been reported between PD susceptibility and genes that regulate metabolism of drugs and neurotoxins. There is also evidence for mitochondrial dysfunction in PD, a finding that was recently traced to anomalies in mitochondrial DNA. At the present time, the genetics of PD appear to be complex, involving multiple nuclear genes and possibly mitochondrial genes as well.

Cognitive performance of GBA mutation carriers with early-onset PD: the CORE-PD study.

OBJECTIVE: To assess the cognitive phenotype of glucocerebrosidase (GBA) mutation carriers with early-onset Parkinson disease (PD). METHODS: We administered a neuropsychological battery and the University of Pennsylvania Smell Identification Test (UPSIT) to participants in the CORE-PD study who were tested for mutations in PARKIN, LRRK2, and GBA. Participants included 33 GBA mutation carriers and 60 noncarriers of any genetic mutation. Primary analyses were performed on 26 GBA heterozygous mutation carriers without additional mutations and 39 age- and PD duration-matched noncarriers. Five cognitive domains, psychomotor speed, attention, memory, visuospatial function, and executive function, were created from transformed z scores of individual neuropsychological tests. Clinical diagnoses (normal, mild cognitive impairment [MCI], dementia) were assigned blind to genotype based on neuropsychological performance and functional impairment as assessed by the Clinical Dementia Rating (CDR) score. The association between GBA mutation status and neuropsychological performance, CDR, and clinical diagnoses was assessed. RESULTS: Demographics, UPSIT, and Unified Parkinson's Disease Rating Scale-III performance did not differ between GBA carriers and noncarriers. GBA mutation carriers performed more poorly than noncarriers on the Mini-Mental State Examination (p = 0.035), and on the memory (p = 0.017) and visuospatial (p = 0.028) domains. The most prominent differences were observed in nonverbal memory performance (p < 0.001). Carriers were more likely to receive scores of 0.5 or higher on the CDR (p < 0.001), and a clinical diagnosis of either MCI or dementia (p = 0.004). CONCLUSION: GBA mutation status may be an independent risk factor for cognitive impairment in patients with PD.

A comprehensive analysis of deletions, multiplications, and copy number variations in PARK2.

OBJECTIVES: To perform a comprehensive population genetic study of PARK2. PARK2 mutations are associated with juvenile parkinsonism, Alzheimer disease, cancer, leprosy, and diabetes mellitus, yet ironically, there has been no comprehensive study of PARK2 in control subjects; and to resolve controversial association of PARK2 heterozygous mutations with Parkinson disease (PD) in a well-powered study. METHODS: We studied 1,686 control subjects (mean age 66.1 ± 13.1 years) and 2,091 patients with PD (mean onset age 58.3 ± 12.1 years). We tested for PARK2 deletions/multiplications/copy number variations (CNV) using semiquantitative PCR and multiplex ligation-dependent probe amplification, and validated the mutations by real-time quantitative PCR. Subjects were tested for point mutations previously. Association with PD was tested as PARK2 main effect, and in combination with known PD risk factors: SNCA, MAPT, APOE, smoking, and coffee intake. RESULTS: A total of 0.95% of control subjects and 0.86% of patients carried a heterozygous CNV mutation. CNV mutations found in 16 control subjects were all in exons 1-4, sparing exons that encode functionally critical protein domains. Thirteen patients had 2 CNV mutations, 5 had 1 CNV and 1 point mutation, and 18 had 1 CNV mutation. Mutations found in patients spanned exons 2-9. In whites, having 1 CNV was not associated with increased risk (odds ratio 1.05, p = 0.89) or earlier onset of PD (64.7 ± 8.6 heterozygous vs 58.5 ± 11.8 normal). CONCLUSIONS: This comprehensive population genetic study in control subjects fills the void for a PARK2 reference dataset. There is no compelling evidence for association of heterozygous PARK2 mutations, by themselves or in combination with known risk factors, with PD.