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.

Association of cognitive domains with postural instability/gait disturbance in Parkinson's disease.

INTRODUCTION: Research suggests an association between global cognition and postural instability/gait disturbance (PIGD) in Parkinson disease (PD), but the relationship between specific cognitive domains and PIGD symptoms is not clear. This study examined the association of cognition (global and specific cognitive domains) with PIGD symptoms in a large, well-characterized sample of individuals with PD. METHODS: Cognitive function was measured with a detailed neuropsychological assessment, including global cognition, executive function, memory, visuospatial function, and language. PIGD symptoms were measured using the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS) Part III, Motor Examination subscale. Multiple linear regression analyses were performed to assess the relationship between cognition and PIGD symptoms with models adjusting for age, sex, education, enrollment site, disease duration, and motor symptom severity. RESULTS: The analysis included 783 participants, with mean (standard deviation) age of 67.3 (9.7) years and median (interquartile range) MDS-UPDRS Motor Subscale score of 26 (17, 35). Deficits in global cognition, executive function, memory, and phonemic fluency were associated with more severe PIGD symptoms. Deficits in executive function were associated with impairments in gait, freezing, and postural stability, while visuospatial impairments were associated only with more severe freezing, and poorer memory function was associated only with greater postural instability. DISCUSSION: While impairments in global cognition and aspects of executive functioning were associated with more severe PIGD symptoms, specific cognitive domains were differentially related to distinct PIGD components, suggesting the presence of multiple neural pathways contributing to associations between cognition and PIGD symptoms in persons with PD.

Functional variants at CYP2A6: new genotyping methods, population genetics, and relevance to studies of tobacco dependence.

Cytochrome P450CYP2A6 (CYP2A6) is the predominant enzyme responsible for the metabolism of nicotine to cotinine. Two variants have been identified that encode products presumed to have little or no activity. A previous study suggested that carriers of at least one copy of either null variant may be protected against tobacco dependence, while tobacco-dependent carriers smoke fewer cigarettes. However, different laboratories have reported widely disparate CYP2A6 allele frequencies across European populations. These differences prompted us to reexamine the genotyping methods for CYP2A6. We developed an improved genotyping strategy using CYP2A6-specific nested PCR, and differential restriction enzyme digestion to identify variant nucleotides in exon 3. We used sequencing to verify genotype results and to assess the sequence of exon 4, which previous work predicted should correspond to "wild-type" CYP2A6 sequence. In addition, we developed a new nomenclature in which CYP2A6*1 is designated CYP2A6*A1-*B1, CYP2A6*2 is CYP2A6*A2, and CYP2A6*3 is CYP2A6*B2. The frequencies of CYP2A6*A2 and CYP2A6*B2 were then estimated in samples from six populations. Sequencing confirmed CYP2A6*A2 genotypes in all cases. Unexpectedly, sequencing demonstrated exon 4 sequence corresponding to CYP2A7 in samples genotyped as CYP2A6*B2. In the population study, we found consistently low allele frequencies (

Human genetics of plasma dopamine beta-hydroxylase activity: applications to research in psychiatry and neurology.

RATIONALE: Norepinephrine (NE) is a key neurotransmitter in the central and peripheral nervous systems. Dopamine beta-hydroxylase (DbetaH) catalyzes the synthesis of NE from dopamine (DA) and occurs in the plasma as a stable heritable trait. Studies of this trait have been useful in psychiatric and neurological research. OBJECTIVE: To selectively and critically review the literature on plasma DbetaH, and on recent progress understanding the molecular genetic basis for its inheritance. Based on this review, directions for future research in psychiatry and neurology will be suggested. METHODS: We selectively review the literature on the biochemical and molecular genetics of plasma DbetaH activity, as well as research on plasma and cerebrospinal fluid (CSF) DbetaH in psychiatric and neurological disorders. RESULTS: Strong evidence implicates DBH, the structural locus encoding DbetaH enzyme, as the major quantitative trait locus influencing plasma DbetaH activity, with one single nucleotide polymorphism (SNP) accounting for up to 50% of the variance. Mutations at DBH appear to be responsible for the rare syndrome of DbetaH deficiency. Some biochemical and genetic studies suggest associations between low plasma or CSF DbetaH and psychotic symptoms in several psychiatric disorders. Studies combining genotyping at DBH with biochemical measurement of plasma DbetaH have proven useful in studies of schizophrenia, cocaine-induced paranoia (CIP), depression, attention deficit hyperactivity disorder, and alcoholism. Such studies may also elucidate the contribution of noradrenergic dysfunction to a variety of symptoms in Parkinson's disease and other degenerative neurological disorders. CONCLUSIONS: A model is proposed, in which lower levels of DbetaH protein may lead to elevated ratios of DA to NE. This model may explain associations between lower plasma DbetaH activity and vulnerability to psychotic symptoms. Genotype-controlled analysis of plasma DbetaH holds promise for promoting further progress in research on psychiatric and neurological disorders.

[3H]-(+)-pentazocine binding to sigma recognition sites in human cerebellum.

The binding characteristics of the sigma-1 selective benzomorphan [3H]-(+)-pentazocine were determined in human cerebellar membranes. Saturation binding analysis revealed two affinity sites with a KDH of 1.4 +/- 0.7 nM and a KDL of 33.6 +/- 11.9 nM. Kinetic studies performed at 25 degrees C demonstrated reversible binding with association and dissociation rate constants determined for two classes of sites. In saturation binding studies, the addition of (+)-SKF 10,047 occluded binding of [3H]-(+)-pentazocine to high affinity sigma binding sites. The affinity profile of ligands displacing [3H]-(+)-pentazocine was consistent with the labeling of sigma-1 recognition sites with haloperidol > (+)-pentazocine > (+)-SKF 10,047 > (+)-3-PPP > DTG > (-)-pentazocine > (-)-SKF 10,047. The potency of the putative D3 receptor-selective ligand (+)-7-OH-DPAT was close to that measured for (+)-pentazocine in displacement experiments. These data suggest that [3H]-(+)-pentazocine labels sigma-1 sites in human cerebellum under appropriate assay conditions.

Cerebrospinal fluid amyloid ß and tau in LRRK2 mutation carriers.

OBJECTIVE: The goal of the current investigation was to examine a cohort of symptomatic and asymptomatic LRRK2 mutation carriers, in order to address whether the reported alterations in amyloid ß (Aß) and tau species in the CSF of patients with sporadic Parkinson disease (PD) are a part of PD pathogenesis, the aging process, or a comorbid disease in patients with PD, and to explore the possibility of Aß and tau as markers of early or presymptomatic PD. METHODS: CSF Aß42, total tau, and phosphorylated tau were measured with Luminex assays in 26 LRRK2 mutation carriers, who were either asymptomatic (n = 18) or had a phenotype resembling sporadic PD (n = 8). All patients also underwent PET scans with 18F-6-fluoro-l-dopa (FD), 11C-(±)-α-dihydrotetrabenazine (DTBZ), and 11C-d-threo-methylphenidate (MP) to measure dopaminergic function in the striatum. The levels of CSF markers were then compared to each PET measurement. RESULTS: Reduced CSF Aß42 and tau levels correlated with lower striatal dopaminergic function as determined by all 3 PET tracers, with a significant association between Aß42 and FD uptake. When cases were restricted to carriers of the G2019S mutation, the most common LRRK2 variant in our cohort, significant correlations were also observed for tau. CONCLUSIONS: The disposition of Aß and tau is likely important in both LRRK2-related and sporadic PD, even during early phases of the disease. A better understanding of their production, aggregation, and degradation, including changes in their CSF levels, may provide insights into the pathogenesis of PD and the potential utility of these proteins as biomarkers.

Human PON1, a biomarker of risk of disease and exposure.

Human paraoxonase 1 (PON1) is a high-density lipoprotein (HDL)-associated serum enzyme that exhibits a broad substrate specificity. In addition to protecting against exposure to some organophosphorus (OP) pesticides by hydrolyzing their toxic oxon metabolites, PON1 is important in protecting against vascular disease by metabolizing oxidized lipids. Recently, PON1 has also been shown to play a role in inactivating the quorum sensing factor N-(3-oxododecanoyl)-l-homoserine lactone (3OC12-HSL) of Pseudomonas aeruginosa. Native, untagged engineered recombinant human PON1 (rHuPON1) expressed in Escherichia coli and purified by conventional column chromatographic purification is stable, active, and capable of protecting PON1 knockout mice (PON1(-/-)) from exposure to high levels of the OP compound diazoxon. The bacterially derived rHuPON1 can be produced in large quantities and lacks the glycosylation of eukaryotic systems that can produce immunogenic complications when inappropriately glycosylated recombinant proteins are used as therapeutics. Previous studies have shown that the determination of PON1 status, which reveals both PON1(192) functional genotype and serum enzyme activity level, is required for a meaningful evaluation of PON1's role in risk of disease or exposure. We have developed a new two-substrate assay/analysis protocol that provides PON1 status without use of toxic OP substrates, allowing for use of this protocol in non-specialized laboratories. Factors were also determined for inter-converting rates of hydrolysis of different substrates. PON1 status also plays an important role in revealing changes in HDL-associated PON1 activities in male patients with Parkinson disease (PD). Immunolocalization studies of PONs 1, 2 and 3 in nearly all mouse tissues suggest that the functions of PONs 1 and 3 extend beyond the plasma and the HDL particle.

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.

Lrrk2 R1441C parkinsonism is clinically similar to sporadic Parkinson disease.

OBJECTIVE: Leucine-rich repeat kinase 2 (LRRK2) mutations are the most common cause of Parkinson disease (PD). Several dominantly inherited pathogenic substitutions have been identified in different domains of the Lrrk2 protein. Herein, we characterize the clinical and genetic features associated with Lrrk2 p.R1441C. METHODS: We identified 33 affected and 15 unaffected LRRK2 c.4321C>T (p.R1441C) mutation carriers through an international consortium originating from three continents. The age-specific cumulative incidence of PD was calculated by Kaplan-Meier analysis. RESULTS: The clinical presentation of Lrrk2 p.R1441C carriers was similar to sporadic PD and Lrrk2 p.G2019S parkinsonism. The mean age at onset for parkinsonism was 60 years, range 30-79 years; fewer than 20% of the patients had symptoms before the age 50 years, while by 75 years >90% of them had developed symptoms. Haplotype analysis suggests four independent founders for the p.R1441C mutation. CONCLUSIONS: The distribution in age at onset and clinical features in Lrrk2 p.R1441C patients are similar to idiopathic and Lrrk2 p.G2019S parkinsonism. Several independent founders of the p.R1441C substitution suggest this site is prone to recurrent mutagenesis.

Identification and haplotype analysis of LRRK2 G2019S in Japanese patients with Parkinson disease.

LRRK2 G2019S is the most common known cause of Parkinson disease (PD) in patients of European origin, but little is known about its distribution in other populations. The authors identified two of 586 Japanese patients with PD heterozygous for the mutation who shared a haplotype distinct from that observed in Europeans. This suggests that G2019S originated from separate founders in Europe and Japan and is more widely dispersed than previously recognized.

A clinic-based study of the LRRK2 gene in Parkinson disease yields new mutations.

Referral-based studies indicate that a mutation (G2019S) in exon 41 of the LRRK2 gene might be a common cause of Parkinson disease (PD). The authors sequenced leucine-rich repeat kinase 2 (LRRK2) exons 31, 35, and 41 in 371 consecutively recruited patients with PD and found mutations in six (1.6%) subjects, including two heterozygous for new putative pathogenic variants (R1441H, IVS31 + 3A-->G). These data confirm the important contribution of LRRK2 to PD susceptibility in a clinic-based population.

Sigma receptors are associated with cortical limbic areas in the primate brain.

Putative sigma receptors are a current target for antipsychotic drug development. Novel antipsychotic agents which possess selective and high affinity for sigma binding sites may serve as an alternative to the principal neuroleptic drugs currently in clinical use which mediate extrapyramidal side effects and dyskinesias through their blockade of dopamine receptors. We have used in vitro autoradiography to localize putative sigma receptors labelled with (+)-[3H]-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine [(+)-[3H]-3-PPP] in the brain of the rhesus macaque. The binding characteristics of (+)-[3H]-3-PPP in the primate brain were comparable to those previously described in the rodent. Saturation analysis demonstrated a single class of sites in cerebellar and hippocampal membranes with a Kd value of 28 nM. Sigma receptors labeled with (+)-[3H]-3-PPP in the primate brain displayed the appropriate rank order of potency and stereoselectivity in competition binding assays. Haloperidol displaced (+)-[3H]-3-PPP binding in the low nanomolar range, and the (+) isomer of pentazocine was 50-fold more potent than (-) pentazocine. Computerized densitometric analysis of the autoradiograms demonstrated a striking enrichment of sigma binding sites over the paralimbic belt cortices, including the orbitofrontal, cingulate, insular, parahippocampal, and temporopolar gyri. Peak densities of sigma receptors were seen over the medial and central nuclei of the amygdala and were widely distributed within the hippocampal formation. Sigma binding sites densities were elevated over the suprachiasmatic and supraoptic nuclei of the hypothalamus. Moderate sigma receptor densities were observed over the ventromedial sectors of the caudate and the putamen. Sigma receptors were also elevated over autonomic relay nuclei of the brainstem, including the nucleus of the solitary tract and the dorsal motor nucleus of the vagus. The distribution of sigma receptors in the primate brain suggests that the paralimbic belt cortices, amygdala, hippocampus, hypothalamus, and autonomic relay nuclei of the brainstem may be interrelated by a topographic chemical linkage. The autoradiographic visualization of sigma receptor distributions in the primate brain provides further support for a role of sigma receptor mechanisms in the functions of the limbic system.

A quantitative-trait analysis of human plasma-dopamine beta-hydroxylase activity: evidence for a major functional polymorphism at the DBH locus.

Dopamine-beta-hydroxylase (D beta H) catalyzes the conversion of dopamine to norepinephrine and is released from sympathetic neurons into the circulation. Plasma-D beta H activity varies widely between individuals, and a subgroup of the population has very low activity levels. Mounting evidence suggests that the DBH structural gene is itself the major quantitative-trait locus (QTL) for plasma-D beta H activity, and a single unidentified polymorphism may account for a majority of the variation in activity levels. Through use of both sequencing-based mutational analysis of extreme phenotypes and genotype/phenotype correlations in samples from African American, European American (EA), and Japanese populations, we have identified a novel polymorphism (--1021C-->T), in the 5' flanking region of the DBH gene, that accounts for 35%--52% of the variation in plasma-D beta H activity in these populations. In EAs, homozygosity at the T allele predicted the very low D beta H-activity trait, and activity values in heterozygotes formed an intermediate distribution, indicating codominant inheritance. Our findings demonstrate that --1021C-->T is a major genetic marker for plasma-D beta H activity and provide new tools for investigation of the role of both D beta H and the DBH gene in human disease.