Mutant debrisoquine hydroxylation genes in Parkinson's disease

Cytochrome P450 2D6 and Parkinson's Disease: Polymorphism, Metabolic Role, Risk and Protection

Cytochrome P450 (CYP) 2D6 is one of the most highly active, oxidative and polymorphic enzymes known to metabolize Parkinsonian toxins and clinically established anti-Parkinson's disease (PD) drugs. Albeit CYP2D6 gene is not present in rodents, its orthologs perform almost the similar function with imprecise substrate and inhibitor specificity. CYP2D6 expression and catalytic activity are found to be regulated at every stage of the central dogma except replication as well as at the epigenetic level. CYP2D6 gene codes for a set of alternate splice variants that give rise to a range of enzymes possessing variable catalytic activity. Case-control studies, meta-analysis and systemic reviews covering CYP2D6 polymorphism and PD risk have demonstrated that poor metabolizer phenotype possesses a considerable genetic susceptibility. Besides, ultra-rapid metabolizer offers protection against the risk in some populations while lack of positive or inverse association is also reported in other inhabitants. CYP2D6 polymorphisms resulting into deviant protein products with differing catalytic activity could lead to inter-individual variations, which could be explained to certain extent on the basis of sample size, life style factors, food habits, ethnicity and tools used for statistical analysis across various studies. Current article describes the role played by polymorphic CYP2D6 in the metabolism of anti-PD drugs/Parkinsonian toxins and how polymorphisms determine PD risk or protection. Moreover, CYP2D6 orthologs and their roles in rodent models of Parkinsonism have also been mentioned. Finally, a perspective on inconsistency in the findings and futuristic relevance of CYP2D6 polymorphisms in disease diagnosis and treatment has also been highlighted.

Impact of CYP2D6 and CYP3A4 genetic polymorphism on combined cholinesterase inhibitors and memantine treatment in mild to moderate Alzheimer's disease

AIM

The impact of CYP2D6 and CYP3A4 polymorphism on the steady-state plasma concentrations and therapeutic outcome of donepezil monotherapy and combination therapy in Alzheimer's disease (AD) patients.

METHODS

A total of 38 patients for donepezil and 17 patients for donepezil and memantine therapy, aged ≥ 55 years, were recruited meeting inclusion and exclusion criteria. Polymerase chain reaction-restriction fragment length polymorphism was performed. The liquid chromatography-tandem mass spectrometry method was used for estimation of drug levels of donepezil and memantine.

RESULTS

Significant allele frequency was observed for CYP2D6*3 polymorphism in patients on donepezil monotherapy and combination therapy. Significant allele frequency for CYP2D6*4 was observed in the patients on donepezil monotherapy.

CONCLUSION

CYP2D6 polymorphism, though not significant, might partially be involved in the plasma concentration of AD drug.

CYP2D6*4 allele polymorphism increases the risk of Parkinson's disease: evidence from meta-analysis

Background

Many epidemiological studies have been conducted to explore the association between a single CYP2D6 gene polymorphism and Parkinson’s disease (PD) susceptibility. However, the results remain controversial.

Objectives

To clarify the effects of a single CYP2D6 gene polymorphism on the risk of PD, a meta-analysis of all available studies relating to CYP2D6*4 polymorphism and the risk of PD was conducted.

Methods

A comprehensive literature search of PubMed, EMBASE, and the China National Knowledge Infrastructure (CNKI) up to September 1, 2013 was conducted. Data were extracted by two independent authors and pooled odds ratio (OR) with 95% confidence interval (CI) were calculated. Meta-regression, Galbraith plots, subgroup analysis, sensitivity analysis, and publication bias analysis were also performed.

Results

Twenty-two separate comparisons consisting of 2,629 patients and 3,601 controls were included in our meta-analysis. The pooled analyses showed a significant association between CYP2D6*4G/A polymorphism and PD risk in all of the comparisons (A vs. G allele: OR = 1.28, 95% CI = 1.14–1.43, P = 0.001; AA vs. GG: OR = 1.43, 95% CI = 1.06–1.93, P = 0.018; AG vs. GG: OR = 1.22, 95% CI = 1.06–1.40, P = 0.006; AG+AA vs. GG: OR = 1.26, 95% CI = 1.10–1.44, P = 0.001; AA vs. AG+GG: OR = 1.37, 95% CI = 1.02–1.83, P = 0.036). In subgroup analysis stratified by ethnicity, significant associations were also demonstrated in Caucasians but not in Asians. No significant association was found in subgroup analysis stratified by age of onset or disease form.

Conclusions

We concluded that the CYP2D6*4G/A polymorphism denotes an increased genetic susceptibility to PD in the overall population, especially in Caucasians. Further large and well-designed studies are needed to confirm this association.

MPP(+) and glutamate in the degeneration of nigral dopaminergic neurons

Glutamate neurotoxicity can be an experimental oxidative stress, and we investigated glutamate toxicity against cultured rat mesencephalic neurons. Although glutamate showed similar toxicity against dopaminergic and nondopaminergic neurons, nitric oxide (NO) showed neurotoxicity restricted exclusively in nondopaminergic neurons. An inhibitor of NO synthase had no significant effect on the glutamate toxicity against dopaminergic neurons, however, it had a significant antagonistic effect on that against nondopaminergic neurons. These findings indicate the presence of two mechanisms of glutamate neurotoxicity, one being not mediated by NO, found in dopaminergic neurons, and the other being mediated via NO, found in nondopaminergic neurons. In contrast to NO, peroxynitrite (ONOO(-)), an active metabolite of NO, caused significant cytotoxicity against dopaminergic and nondopaminergic neurons, suggesting that conversion of NO to ONOO(-) is suppressed in dopaminergic neurons. After pretreatment with small doses of methyl-4-phenylpyridium ion (MPP(+)), NO caused significant cytotoxicity against dopaminergic neurons, and glutamate toxicity was enhanced only against dopaminergic neurons. Therefore, sublethal dose of MPP(+) enhances glutamate toxicity against dopaminergic neurons, probably by the facilitation of suppressed NO conversion to ONOO(-) in dopaminergic neurons. Finally, to provide basic data for neuroprotective therapy in Parkinson's disease, we investigated neuroprotection against glutamate toxicity by dopamine agonists. Preincubation with the D2 type dopamine agonists provides neuroprotection against glutamate neurotoxicity and the protective effects blocked by a D2 antagonist, indicating that D2 agonists provide protection mediated not only by the inhibition of dopamine turnover, but also via D2 type dopamine receptor.

Gene-environment interactions in Parkinson's disease: specific evidence in humans and mammalian models

Interactions between genetic factors and environmental exposures are thought to be major contributors to the etiology of Parkinson's disease. While such interactions are poorly defined and incompletely understood, recent epidemiological studies have identified specific interactions of potential importance to human PD. In this review, the most current data on gene-environment interactions in PD from human studies are critically discussed. Animal models have also highlighted the importance of genetic susceptibility to toxicant exposure and data of potential relevance to human PD are discussed. Goals and needs for the future of the field are proposed.

Parkinson's disease: genetics and beyond

Parkinson's disease (PD) is characterized clinically by resting tremor, rigidity, bradykinesia and postural instability due to progressive and selective loss of dopamine neurons in the ventral substantia nigra, with the presence of ubiquitinated protein deposits called Lewy bodies in the neurons. The pathoetiology of cell death in PD is incompletely understood and evidence implicates impaired mitochondrial complex I function, altered intracellular redox state, activation of proapoptotic factors and dysfunction of ubiquitinproteasome pathway. Now it is believed that genetic aberration, an environmental toxin or combination of both leads to a cascade of events culminating in the destruction of myelinated brainstem catecholaminergic neurons. Also the role of production of significant levels of abnormal proteins, which may misfold, aggregate and interfere with intracellular processes causing cytotoxicity has recently been hypothesized. In this article, the diverse pieces of evidence that have linked the various factors responsible for the pathophysiology of PD are reviewed with special emphasis to various candidate genes and proteins. Furthermore, the present therapeutic strategies and futuristic approaches for the pharmacotherapy of PD are critically discussed.

Polymorphisms in the genes of citohrom oxidase P450 2D6 (CYP2D6), paraoxonase 1 (PON1) and apolipoproteine E (APOE) as risk factors for Parkinson's disease

Background/Aim. The presence of Parkinson's disease (PD) among the members of a family is a clear indication of the significance of genetics in its development. In spite of that, the majority of patients with PD shows a sporadic form of the disease induced as a result of interaction of both environmental and genetic factors. The aim of this study was to examine the effects of polymorphisms in the genes of cytohrome P450 2D6(CYP2D6), paraoxonase 1 (PON 1) and apolipoprotein E (APOE), as risk factors for PD. Methods. We examined 106 patients with PD (65 men and 41 women) and 75 ethnically matched control subjects. The mean age at onset of PD in the patients was 46.9?9.4 years (ranging from 30 to 70 years). Genotyping was performed using standard PCR amplification and restriction endonuclease digestion protocols described for known polymorphism in the candidate genes under study. Results. The genotype A/A polymorphisms 2D6* gene of CYP2D6 and genotype M/M polymorphisms L54M gene of PON1 were significantly more frequent in the patients with PD than in the control group. The patients with genotypes A/A and M/M had 3.4 and 3.2 higher risk of PD, respectively than the control group (p = 0.01). The relation between genotypes A/A gene of CYP2D6 and M/M gene of PON1 was modified by the age at onset. The genotypes were associated with early onset of PD (p = 0.001, p = 0.004). The carriers of the A and M alleles in homozygote had 2.4 and 4.2 years respectively earlier onset of PD than carriers of other genotypes with these polymorphisms. The frequency allele ?4 gene of APOE was higher in the PD patients with early onset (20%) than in PD with later onset (7.4%), while the genotype ?3/?3 was associated with PD late onset (p = 0.024). Combined genotype I (carriers of the two risk allels in homozygote and one alleles risk in heterozygote) and combined genotype II (carriers of the three alleles risk in homozygote) caused early PD. Combined genotype II was detected in 12.7% of the patients in the group of early onset, and in 2.4% of the patients with the onset after 45 years. Conclusion. The results of our study suggest that the genotypes A/A and M/M genes of CYP2D6 and PON1, and allele ?4 gene are an important risk for the development of PD, causing its early onset. The cumulative effects of the risk genes cause an early onset of PD.

Gene-environment interactions in sporadic Parkinson's disease

Much has been learned in recent years about the genetics of familial Parkinson's disease. However, far less is known about those malfunctioning genes which contribute to the emergence and/or progression of the vast majority of cases, the 'sporadic Parkinson's disease', which is the focus of our current review. Drastic differences in the reported prevalence of Parkinson's disease in different continents and countries suggest ethnic and/or environmental-associated multigenic contributions to this disease. Numerous association studies showing variable involvement of multiple tested genes in these distinct locations support this notion. Also, variable increases in the risk of Parkinson's disease due to exposure to agricultural insecticides indicate complex gene-environment interactions, especially when genes involved in protection from oxidative stress are explored. Further consideration of the brain regions damaged in Parkinson's disease points at the age-vulnerable cholinergic-dopaminergic balance as being involved in the emergence of sporadic Parkinson's disease in general and in the exposure-induced risks in particular. More specifically, the chromosome 7 ACHE/PON1 locus emerges as a key region controlling this sensitive balance, and animal model experiments are compatible with this concept. Future progress in the understanding of the genetics of sporadic Parkinson's disease depends on globally coordinated, multileveled studies of gene-environment interactions.

Role of chronic infection and inflammation in the gastrointestinal tract in the etiology and pathogenesis of idiopathic parkinsonism. Part 1: eradication of Helicobacter in the cachexia of idiopathic parkinsonism

BACKGROUND

Neuronal damage in idiopathic parkinsonism may be in response to ubiquitous occult infection. Since peptic ulceration is prodromal, Helicobacter is a prime candidate.

AIM

To consider the candidature of Helicobacter in parkinsonism with cachexia.

METHODS

We explore the relationship between being underweight and inflammatory products in 124 subjects with idiopathic parkinsonism and 195 controls, and present the first case-series evidence of efficacy of Helicobacter eradication, in parkinsonism advanced to the stage of cachexia.

RESULTS

Association of a low body mass index with circulating interleukin-6 was specific to parkinsonism (p = .002), unlike that with antibodies against Helicobacter vacuolating-toxin and cytotoxicity-associated gene product (p < .04). Marked reversibility in both cachexia and disability of idiopathic parkinsonism followed Helicobacter heilmannii eradication in one case, Helicobacter pylori eradication in another, follow-up being > or = 3.5 years. The latter presented with postprandial bloating, and persistent nausea: following eradication, radioisotope gastric-emptying returned towards normal, and upper abdominal symptoms regressed. Reversibility of their cachexia/disability contrasts with the outcome of anti-Helicobacter therapy where eradication repeatedly failed (one case), and in non-Helicobacter gastritis (three cases). Anti-parkinsonian medication remained constant. Intestinal absorption and barrier function were normal in all.

CONCLUSION

Categorization, according to presence or absence of Helicobacter infection, was a useful therapeutic tool in late idiopathic parkinsonism.

How frequent is altered gene expression among susceptibility genes to human complex disorders?

It is regularly thought that human complex disorder susceptibility genes show differences in gene expression between normal and pathologic tissues. Thus, differences of transcript amounts could be indicative of complex disorder susceptibility loci and, therefore, be used for the discovery or the validation of human susceptibility genes to complex disorders/traits. Whether human complex disorder susceptibility genes effectively display differences in transcript amounts was tested by meta-analysis of the published literature comparing transcript amounts of well-validated human susceptibility genes to complex traits/disorders. A total of 94 gene-disease associations, which were studied in at least three independent studies and showed strong evidence of positive association, were analyzed. For 23 out of these 94 well-validated gene-disease associations, 120 gene expression studies comparing normal and pathologic human tissues were found. For 60 out of these 120 gene expression studies, the difference of level expression between normal and pathologic human tissues was statistically significant. This result was highly significant, as only 6 significant results were expected randomly under the null hypothesis (P < 10(-112)). A large excess of replication studies were also found, which were in agreement with the original report (P = 6 x 10(-4)). However, the overall level of expression change between normal and pathologic human tissues was relatively moderate, because only 36 (60%) and 19 (31.6%) out of the 62 statistically significant gene expression studies reached 2- or 3-fold changes in expression level, respectively. The present meta-analysis confirms statistical differences of expression levels between normal and pathologic human tissues for human susceptibility genes to complex traits/disorders. However, the levels of differences in transcript amounts appear to be relatively weak. These findings rationalize the use of gene expression for the discovery/validation of human susceptibility genes, but the weak differences of expression typically found should be taken into account for the design of such studies.

Studies on the pathogenesis of Parkinson's disease in Japan

Studies on the pathogenesis of nigral cell death in Parkinson's disease (PD) are reviewed. Discussions are focused mainly on studies performed by Japanese investigators because of the purpose of this issue. We and other groups found a decrease in complex I of the mitochondrial electron transfer complex in the substantia nigra of patients with PD, and in addition to complex I deficiency, we reported loss of alpha-ketoglutarate dehydrogenase complex of the tricarboxylic acid cycle (TCA cycle) by immunohistochemistry. Thus mitochondrial respiratory failure and resultant energy crisis appear to be one of the most important mechanisms that lead nigral neurons to cell death. The primary cause of mitochondrial respiratory failure has not been elucidated yet; however, environmental neurotoxins such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) may be responsible for nigral cell death in PD; in this respect a number of candidate toxins including tetrahydroisoquinolines and beta-carbolines have extensively been studied for nigral as well as mitochondrial toxicity. Recent progress in this field is also reviewed. Even if an environmental neurotoxin is involved in PD, exposure to such a neurotoxin alone may not account for its pathogenesis, as most of us are probably being exposed to the same toxin. Therefore, genetic predisposition appears to be essential for the development of PD. The genetic predisposition may involve hepatic detoxifying enzymes for such neurotoxins, the transport mechanism of those toxins to the brain, bioactivation of those toxins in the brain, the uptake mechanism to the nigral neurons, and the activity levels of target enzymes or proteins; all of these factors are being extensively studied in many laboratories at a molecular level.

Environmental factors and Parkinson's disease: a case–control study in the Tuscany region of Italy

To date the aetiology of Parkinson's disease (PD) is unknown although both genetic susceptibility and environmental factors appear to play an important role in the development of the disease. Recent data have also indicated that chronic exposure to a common pesticide can reproduce the neurochemical, behavioral and neuropathological features of PD. The epidemiological studies previously carried on the prevalence of PD in population exposed to environmental factors have produced controversial results, probably because of different trial design and different analysis methods. A case-control retrospective study was conducted in a well-defined geographic area in Tuscany-Italy with the aim to identify environmental factors possibly related to PD. No significant difference between PD patients and control subjects was observed in time spent in rural or industrial residence, in well water drinking and in the exposure to herbicides and pesticides. A significant difference between patients with PD and controls was reported for cigarette smoking, controls resulting more likely cigarette smokers in comparison with PD patients. The present findings support the view of a protective effect of cigarette smoking and do not show any significant association between environmental factors and the risk of development of PD.

Genetic testing in Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disorder of adulthood characterized clinically by rigidity, bradykinesia, resting tremor, and postural instability. The annual incidence of PD ranges between 16 and 19 individuals per 100,000 (Twelves et al., Mov Disord 2003;18:19-31). Historically, PD has been commonly viewed as an idiopathic or environmentally triggered condition. However, as is true with most common conditions, there have been several families reported with PD who demonstrate a classic Mendelian pattern of inheritance. To date, nine genetic loci have been reported and four pathogenic genes have been identified: alpha-synuclein, parkin, DJ1, and PINK1. Families with alterations in these genes or linked sites demonstrate either recessive or dominant inheritance patterns and may have typical and/or atypical symptoms, with an age of onset extending from the second to the sixth decade. Commercial tests for parkin and alpha-synuclein mutations are now available. We predict that physicians, particularly neurologists, increasingly will be approached for information and referrals regarding genetic testing. To assist patients and their families, physicians will not only need to know when such testing is likely to yield a meaningful result but also be aware of the possible social and emotional consequences of testing. The following is a review of what is currently known about the genetics of PD within this context. We discuss what is known about genetic testing for Huntington's disease, a well-described model for genetic testing in a neurodegenerative disorder. We explore the utility, appropriateness, and possible implications of genetic testing for diagnostic and presymptomatic purposes.

Potential role of cerebral cytochrome P450 in clinical pharmacokinetics: modulation by endogenous compounds

Cytochrome P450 (CYP) enzymes catalyse phase I metabolic reactions of psychotropic drugs. The main isoenzymes responsible for this biotransformation are CYP1A2, CYP2D6, CYP3A and those of the subfamily CYP2C. Although these enzymes are present in the human brain, their specific role in this tissue remains unclear. However, because CYP enzymatic activities have been reported in the human brain and because brain microsomes have been shown to metabolise the same probe substrates used to assess specific hepatic CYP activities and substrates of known hepatic CYPs, local drug metabolism is believed to be likely. There are also indications that CYP2D6 is involved in the metabolism of endogenous substrates in the brain. This, along with the fact that several neurotransmitters modulate CYP enzyme activities in human liver microsomes, indicates that CYP enzymes present in brain could be under various regulatory mechanisms and that those mechanisms could influence drug pharmacokinetics and, hence, drug response. In this paper we review the presence of CYP1A2, CYP2C9, CYP2D6 and CYP3A in brain, as well as the possible existence of local brain metabolism, and discuss the putative implications of endogenous modulation of these isoenzymes by neurotransmitters.

Interaction between GSTM1-null and CYP2D6-deficient alleles in the pathogenesis of Parkinson's disease

The present study was conducted to examine the interaction between cytochrome p450 2D6: CYP2D6 (phase I) poor metabolizer (PM) and glutathione S-transferase M1: GSTM1 (phase II) null genotypes, among 103 unrelated French Parkinson's disease (PD) patients. Both genes are involved in the biotransformation process, and the main objective of that work is to assess synergic effect between CYP2D6 PM and GSTM1 null genotypes in PD patients. Patients with both GSTM1 null genotype and poor metabolizer CYP2D6 have shown a strong dependency of multiplicative interaction (9.50; P = 0.016); this have also been observed when combining GSTM1 null with CYP2D6*4 deficient alleles, but were at the limit of significance (2.18; P = 0.076). Such a combination of polymorphic peculiarities in studied metabolic genes might represent additional risk factor for development of sporadic PD.

Septin 3 gene polymorphism in Alzheimer's disease

Septin 3 is a novel member of the septin subfamily of GTPase domain proteins that was recently identified in human neuronal cells. These proteins are involved in vesicle trafficking, neurite outgrowth, and neurofibrillary tangle formation; however, the expression and functional role of septin 3 in normal neuronal tissues and as an etiological agent in neurological disorders is currently unclear. To further characterize these parameters, the present study analyzed the expression of three isoforms of septin 3 (A, B, and C) in fetal and adult human brains and polymorphism of the septin 3 exon 11 microsatellite in control, pure Alzheimer's disease (AD), Lewy body variant (LBV) of AD, and Parkinson's disease. Septin 3 mRNAs for isoforms A and B, but not C, were detected in the frontal cortex of fetus and adult human samples, as measured by reverse transcription-coupled polymerase chain reaction. Genotype analyses indicated that polymorphic septin 3 alleles were distributed in two peaks of frequency in both control and disease groups. Categorization of the alleles into short (S) and long (L) types revealed a significant difference between AD patients and controls (p = 0.034 by chi-square test). Furthermore, the S-allele homozygosity was significantly underrepresented in AD compared with control (p = 0.015 by chi-square test). These results suggest that polymorphism in exon 11 of septin 3 may have a determinative role in the pathogenesis of AD.

Parkinson's disease and CYP2D6 polymorphism in Asian populations: A meta-analysis

Polymorphism of CYP2D6 and its relationship with the development of Parkinson's disease (PD) has been controversial. The distribution of the B-mutation of CYP2D6, a mutation that results in the absence of a functional protein, differs by ethnicity and accounts for less than 1% of the 'poor metabolizer' phenotype in Asians. Thus, a meta-analysis was conducted to determine if polymorphism, other than the B-mutation, within the CYP2D6 gene confers a greater susceptibility to PD outcome among Asian populations. Eleven studies were identified, two of which were excluded due to unavailability in the English language or availability of the same original data in more detail in another publication. None of the studies showed a statistically significant association between CYP2D6 polymorphism and PD (p<0.05). The overall odds ratio was 0.84 (95% confidence interval 0.66-1.08). We conclude that among Asian populations, there is no convincing evidence of an association between CYP2D6 polymorphism and the risk of developing PD.

Cytochrome P450 II D6 gene polymorphisms and the neuroleptic-induced extrapyramidal symptoms in Japanese schizophrenic patients

OBJECTIVE

The purpose of this study was to examine whether the neuroleptic-induced extrapyramidal symptoms are associated with the CYP2D6 activity.

METHODS

The CYP2D6 gene polymorphisms (CYP2D6*2, CYP2D6*3, CYP2D6*4, CYP2D6*10, and CYP2D6*12) were genotyped in 196 normal controls and 320 schizophrenic patients receiving neuroleptics. The relationships with susceptibility to extrapyramidal symptoms (EPS) and tardive dyskinesia, and with steady-state serum haloperidol levels in maintenance therapy, were investigated.

RESULTS

The allele frequency of CYP2D6*2 was significantly higher, while that of CYP2D6*10 tended to be higher in the schizophrenic patients susceptible to acute EPS. The steady-state serum haloperidol levels per daily dosage were observed to be significantly higher in schizophrenic patients with the mutant-type homozygote of CYP2D6*2, while this difference was trend level in those of CYP2D6*10. However, no significant difference was observed in the distribution of both CYP2D6*2 (C2938T) and CYP2D6*10 (C188T) polymorphisms between schizophrenic patients with or without tardive dyskinesia.

CONCLUSION

The present results suggest that the homozygotes of CYP2D6*2 and CYP2D6*10 appear to be a susceptibility factor for developing acute EPS in schizophrenic patients and for impaired neuroleptic metabolism in Japanese schizophrenic patients.

Genetic and environmental factors in the cause of Parkinson's disease

Despite being the subject of intense study, the pathogenesis of Parkinson's disease still remains unclear. In recent years, however, there has been increasing evidence to support a role for genetic factors in its cause. This has come from twin and family studies, the mapping and cloning of PARK genes that are associated with the development of PD, and analysis of potential susceptibility genes. There is also evidence indicating that environmental factors may play a role in the disease process. It is likely that for most cases, there is a complex interplay between these genetic and environmental influences in the causation of Parkinson's disease. This article reviews the evidence in support of genetic and environmental factors in the cause of PD.

Familial Lewy body diseases

Lewy body disease includes clinically and pathologically defined disorders in which Lewy bodies occur in the nervous system. In recent years, the molecular features of these disorders have been emerging. Several genetic loci have been identified in association with familial Lewy body disease; however, the genetic risks underlying most cases of familial Lewy body disease remain to be discovered. The fact that Lewy bodies stain strongly with antibodies to asynuclein and that mutations in the alpha-synuclein gene lead to syndromes in which parkinsonism and dementia occur gives us important clues regarding the biologic processes leading to disease. Pursuit of additional mendelian causes of familial Lewy body disease and study of the factors contributing to the complex phenotypes associated with Lewy body disorders will elucidate underlying disease pathways and, thus, possible targets for therapeutic intervention.

Mammalian longevity under the protection of PARP-1's multi-facets

Given the presence of continuous endogenous and exogenous sources of stress, mammalian species have evolved complex systems of protection, detoxification and repair, in order to maintain homeostasis during development and until reproductive maturity for the sake of the species. However, since no system is perfect, complete prevention of damage is unlikely to occur. Accumulation of macromolecular damage, including damage to DNA and genomic instability, is considered a driving force for the ageing process and age-related diseases. One of the immediate eukaryotic cellular responses to DNA breakage is the covalent post-translational modification of nuclear proteins with poly(ADP-ribose) from NAD+ as precursor, mostly catalysed by poly(ADP-ribose) polymerase-1 (PARP-1). Poly(ADP-ribosyl)ation is involved in DNA base-excision repair (BER), DNA-damage signalling and regulation of genomic stability. In recent years, many groups have become involved in PARP field, shedding light on new partners for PARP-1, new members of the PARP family and new physiological and pathophysiological properties for the founding member of the poly(ADP-ribose) polymerase super family. The present review focuses on PARP-1 and its role in the maintenance of genome stability and in mammalian longevity.

Serotonin syndrome and other serotonergic disorders

Serotonin syndrome is an iatrogenic disorder induced by pharmacologic treatment with serotonergic agents that increases serotonin activity. In addition, there is a wide variety of clinical disorders associated with serotonin excess. The frequent concurrent use of serotonergic and neuroleptic drugs and similarities between serotonin syndrome and neuroleptic malignant syndrome can present the clinician with a diagnostic challenge. In this article, we review the pathophysiology, diagnosis, and treatment of serotonin syndrome as well as other serotonergic disorders.

CYP2D in the Brain

CYP2D1, 2D2, 2D3, and 2D4 are major CYP2D isoforms expressed in the rat. In humans, only CYP2D6 is expressed. In rat brain, the mRNA for CYP2D4 is most abundant in cerebellum, striatum, pons and medulla oblongata. In human brain, CYP2D6 mRNA expression was detected in all regions with highest levels observed in cerebellum. CYP2D isoforms are involved in the metabolism of not only xenobiotics such as antidepressants, beta-adrenergic blockers, antiarrhysthmics, and antihypertensives, but also endogenous compounds such as trace amine and neurosteroids. Among 11 isoforms of human recombinant P450s, only CYP2D6 exhibited an ability to efficiently convert tyramine which exists in the brain, to dopamine. CYP2D4 and CYP2D6 which are the predominant CYP2D isoforms in the rat and human brain, respectively, possess 21-hydroxylation activity for both progesterone and allopregnanolone. CYP2D4, not P450c21, works as a steroid 21-hydroxylase in the brain. These results suggested that CYP2D in the brain may be involved in the metabolism of neuronal amines and steroids and in the regulation of the central nervous system.

14-3-3 protein is a component of Lewy bodies in Parkinson's disease-mutation analysis and association studies of 14-3-3 eta

Mutations in alpha-synuclein have been identified in some rare families with autosomal dominant Parkinson's disease (PD). The synuclein gene family shares physical and functional homology with 14-3-3 proteins and binds to 14-3-3 proteins and to its ligands. We therefore investigated whether 14-3-3 proteins are also involved in the pathogenesis of PD. Here we demonstrate that 14-3-3 proteins are colocalized with Lewy bodies in PD. We investigated the 14-3-3 eta (YWHAH) gene by mutation analysis and association studies as it maps to human chromosome 22q12.1-q13.1, a region which has been recently implicated in PD and carried out immunohistochemical studies of Lewy bodies with two different 14-3-3 eta antibodies. In 358 sporadic and familial PD patients, disease causing mutations were not identified. Furthermore, association studies with intragenic polymorphisms do not provide evidence for an involvement of 14-3-3 eta in the pathogenesis of PD. In accordance with these findings, there was no staining of substantia nigra Lewy bodies with antibodies specific for the 14-3-3 eta subunit.

Familial and environmental risk factors in Parkinson's disease: a case-control study in north-east Italy

BACKGROUND AND OBJECTIVE

The aetiology of Parkinson's disease remains unknown, although both genetic susceptibility and environmental factors are considered putative contributors to its origin. We performed a case-control study to investigate the association of familial and environmental risk factors with Parkinson's disease (PD).

METHODS

We studied 136 patients with neurologist confirmed PD and 272 age- and sex-matched controls, affected by neurological diseases not related to PD. The risk of developing idiopathic PD associated with the following familial and environmental factors: positive family history of PD, positive family history of essential tremor (ET), age of mother at subject's birth, rural birth, rural living, well water use, farming as an occupation, exposure to pesticides, head tremor, exposure to general anaesthesia and to ionizing radiations, food restriction, concentration camp imprisonment and smoking has been assessed by using univariate and multivariate statistical techniques.

RESULTS

In the conditional multiple logistic regression analysis, positive family history of PD (OR 41.7, 95% CI 12.2-142.5, P < 0.0001), positive family history of ET (OR 10.8, 95% CI 2.6-43.7, P < 0.0001), age of mother at subject's birth (OR 2.6, 95% CI 1.4-3.7, P=0.0013), exposure to general anaesthesia (OR 2.2, 95% CI 1.3-3.8, P=0.0024), farming as an occupation (OR 7.7, 95% CI 1.4-44.1, P=0.0212) and well water use (OR 2.0, 95% CI 1.1-3.6, P=0.0308) exhibited a significant positive association with PD, whereas smoking showed a trend toward an inverse relationship with PD (OR 0.7, 95% CI 0.4-1.1, P < 0.06).

CONCLUSIONS

We conclude that both familial and environmental factors may contribute to PD aetiology.

A review of xenobiotic metabolism enzymes in Parkinson's disease and motor neuron disease

The role of xenobiotic metabolising enzymes (XMEs) in disease aetiology has been under investigation by numerous researchers around the world for the last two decades. The association of a number of defects in both phase I and phase II reactions with Parkinson's disease (PD) and motor neuron disease (MND) have been extensively studied. This review of the work of the group based initially at the University of Birmingham into the functional genomics of XMEs and neurodegenerative diseases has indicated that: 1. Sub-groups of patients with PD and MND can be identified with problems in xenobiotic metabolism by in vivo or in vitro methods. 2. 38-39% of the patients with MND/PD have a defect in the S-oxidation of the mucoactive drug, carbocysteine, by an unknown cytosolic oxidase(s). The odds risk ratio for the association of this defect with these diseases was calculated to be 10.21 for MND and 10.50 for PD. 3. Patients with PD appear to have an altered substrate specificity for monoamine oxidase B substrates in an in vitro platelet assay. 4. Patients with MND have an increased capacity to S-methylate aliphatic sulphydryl compounds in an in vivo challenge as well as an in vitro erythrocyte thiol methyltransferase assay. The results of over a decade of investigations into both PD and MND indicate that these are diseases with mutifactorial origins that encompass both genetic predisposition and environmental insult.

CYP2D6*4 polymorphism is not associated with Parkinson's disease and has no protective role against Alzheimer's disease in the Korean population

CYP2D6*4 polymorphism is reported to be associated with Parkinson's disease (PD) and to have protective role against Alzheimer's disease (AD). Such findings are not extensively studied in the Oriental population, especially Koreans. The effects of CYP2D6*4 polymorphism on AD and PD were investigated by polymerase chain reaction-restriction fragment length polymorphism in Korean subjects. Heterozygous mutant allele was found in four of 93 patients with PD, 0 of 32 patients with AD and one of 121 control subjects (59 stroke, 59 normal controls and four other psychiatric disorders), but no homozygous mutant allele was found. There were no statistically significant differences between the AD group and controls, and between the PD group and controls. In conclusion, we suggest that CYP2D6*4 polymorphism does not confer susceptibility to PD in the Korean population. Also, due to such a rare occurrence of the CYP2D6*4 polymorphism, we can not confirm the protective role of the polymorphism against AD in the Korean population.

No evidence of an association between CYP2D6 polymorphisms among Japanese and dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is the second most frequent degenerative dementia among the elderly, following Alzheimer-type dementia (ATD). An association of DLB with CYP2D6*4, one of the cytochrome P450IID6 (debrisoquine 4-hydroxylase; CYP2D6) gene polymorphisms, was reported previously, but this is controversial. Moreover, these reports have been restricted to Caucasian populations. Therefore, we compared frequencies of CYP2D6*3, *4, and *10 mutant alleles in 17 Japanese DLB patients to those among Alzheimer-type dementia (ATD) patients and healthy controls. Polymerase chain reaction amplification and restriction fragment length polymorphism analyses were used for genotyping. No significant difference of genotype or mutant allele frequencies was detected between DLB, ATD, and healthy controls. The present results do not support the suggestion that the CYP2D6 gene is related to DLB susceptibility, at least in the Japanese population.

Cellular localization and regional distribution of CYP2D6 mRNA and protein expression in human brain

The cytochrome P4502D6 (CYP2D6) is involved in the biotransformation of many drugs which predominantly act in the central nervous system (CNS), including opioids, various psychotrophic drugs and neurotoxins. Until now, however, only controversial information is available regarding the presence of CYP2D6 in CNS. In this study, the regional and cellular expression of CYP2D6 transcripts and proteins in postmortem brain tissues of three individuals was analysed. A combination of in-situ hybridization coupled with immunohistochemistry on adjacent sections allowed simultaneous detection of CYP2D6 mRNA and protein. However, discrepancies existed in the results such that the mRNA was more widely distributed in the brain areas analysed compared to the protein. Neuronal cells, as well as glial cells, showed labelling for mRNA in brain regions such as the neocortex, caudate nucleus, putamen, globus pallidus, hippocampus, hypothalamus, thalamus, substantia nigra and cerebellum. In contrast, CYP2D6 protein was primarily localized in large principal neurons such as pyramidal cells of the cortex, pyramidal cells of the hippocampus, and Purkinje cells of the cerebellum. In glial cells, CYP2D6 protein was absent. These results provide clear evidence of CYP2D6 expression in certain regions of the CNS and may indicate the role CYP2D6 plays in a number of drug interactions that are of potential clinical importance for neurological diseases.

Allelic association between the DRD2 TaqI A polymorphism and Parkinson's disease

Genes encoding proteins involved in dopaminergic transmission have been of special interest during the evaluation of candidate genes for Parkinson's disease (PD). The dopamine D2 receptor gene (DRD2) is located on chromosome 11 q22-q23, and several polymorphisms of the gene have been described. The DRD2 gene has a TaqI A restriction fragment length polymorphism that is located in the untranslated region, approximately 10 kilobases from the 3' end of the gene. This polymorphism creates the two alleles A1 (variant) and A2. In this study, we investigated the hypothesis that a TaqI repeat fragment length polymorphism in the dopamine D2 receptor gene may be associated with PD. DNA from 72 patients with PD, classified as definite, probable, or atypical PD, and from 81 controls was genotyped by polymerase chain reaction and gel electrophoresis for the presence of the TaqI A1 polymorphism. The controls were matched for age, race, and geographic origin. There were significant differences in allelic distribution between the overall PD group and control groups (chi2 = 5.009, p = 0.025). When only patients with definite PD were considered an even more significant association was found (chi2 = 8.2121, p = 0.004). Among the overall PD group, the odds ratio for having the variant allele A1 was found to be 2.2 (95% confidence interval, [1.1; 4.4]), whereas it was calculated to be 3.0 (95% confidence interval, [1.4; 6.4]) when only patients with definite PD were considered. The current study showed that there is a statistically significant association between the DRD2 variant allele A1 and PD. This association is most pronounced in patients with definite PD and becomes nonsignificant when the clinical picture is classified as atypical PD.

CYP2D6 HhaI genotype and the neuroleptic malignant syndrome

To investigate the relationship between CYP2D6 genotypes (reported to be associated with the susceptibilities to Parkinson's disease and multisystem atrophy) and the possible susceptibility to neuroleptic malignant syndrome (NMS) and subacute myelo-optico-neuropathy (SMON), we analyzed the CYP2D6 gene by polymerase chain reaction and restriction fragment length polymorphism in Japanese schizophrenia patients with a history of NMS. There was no significant difference in the frequency of the poor metabolizer genotype of CYP2D6 between the cases with a history of NMS and controls (p > 0.05). The frequency of the mutation located at the HhaI site in exon 6 of CYP2D6 in the cases was higher, but not significantly (p > 0.05; the mutated allele frequency was 0.25), than that in the controls, schizophrenia patients without NMS (0.11) and healthy controls (0.09). The frequency (0.10) of the HhaI mutation type in patients with a diagnosis of SMON was also not significantly higher than in healthy controls. These results suggest that the poor metabolizer and HhaI polymorphism of CYP2D6 may not be a useful molecular marker for predicting the onset of NMS and SMON.

Pharmacologic profile of perphenazine's metabolites

The authors have previously reported that in elderly patients treated with low doses of perphenazine, few extrapyramidal symptoms (EPS) developed in those who were not poor CYP2D6 metabolizers. The authors hypothesized that this atypical side effect profile is due to perphenazine's principal metabolite, n-dealkylperphenazine (DAPZ), which is usually present in vivo at concentrations 1.5 to 2 times that of the parent drug. Perphenazine, DAPZ, and 7-hydroxyperphenazine affinities were examined in vitro by competition-binding analysis to isolated human receptors expressed in transfected cell lines. Perphenazine and metabolite effects were examined in vivo in 54 older patients who were treated with perphenazine, at a target dose of 0.1 mg/kg, for 10 to 17 days. Drug concentrations were determined by high-performance liquid chromatography with electrochemical detection. In in vitro binding studies, DAPZ demonstrated a higher affinity for serotonin-2A receptors than for dopamine-2 receptors to an extent comparable to that of some atypical neuroleptic agents. In contrast, perphenazine and 7-hydroxyperphenazine demonstrated a higher affinity for dopamine-2 receptors than for serotonin-2A receptors. The mean +/- SD concentrations in the 54 subjects were the following: perphenazine, 1.5 +/- 1.4 ng/mL; DAPZ, 2.0 +/-1.6 ng/mL; and 7-hydroxyperphenazine, 0.8 +/- 1.9 ng/mL. The mean +/- SD quotient for the DAPZ/perphenazine concentration was 1.7 +/- 1.1 and for the 7-hydroxyperphenazine/perphenazine was 0.54 +/-1.6. EPS onset was not correlated with the perphenazine concentration, the metabolite concentrations, the DAPZ/perphenazine quotient, or the 7-hydroxyperphenazine/perphenazine quotient. Despite a moderately atypical receptor-binding profile, DAPZ does not seem to moderate perphenazine effects in vivo in older patients. This outcome likely reflects the low potency of DAPZ for dopamine-2 and serotonin-2A receptors relative to the potency of perphenazine for these receptors. Further exploration of atypical properties of DAPZ should include de novo administration of this metabolite in animal models.

Neuroprotective effects of estradiol in mesencephalic dopaminergic neurons

There is a gender difference, or male predominance, in Parkinson's disease and attention deficit hyperactivity disorder (ADHD). Although the reason why it is predominantly the male who suffers from the diseases is still unknown, the female steroid hormone may be involved in the pathogenesis. Estrogen is a female sex hormone with a steroid structure. Like other steroid hormones, it binds to specific receptors in the nuclei and regulates gene transcription (genomic effects). In addition to the genomic effects, it can act as an antioxidant, a process not mediated by the estrogen receptor (nongenomic effects). Further, estrogen can have a novel action through a specific receptor located in the plasma membrane. In the central nervous system, estrogen provides neuroprotection mediated through multiple mechanisms. In this article, we review several possible mechanisms for the neuroprotective effects including antiapoptotic protection by estrogens as transcription factors, protection against oxidative stress by estrogens acting as antioxidants, and neurotrophic cross talk through the signal cascade shared with neurotrophic factors.

Genetic association analysis between CYP2D6*2 allele and tardive dyskinesia in schizophrenic patients

Previous studies have shown a possible association between tardive dyskinesia (TD) and debrisoquine 4-hydroxylase (CYP2D6) polymorphisms, which result in absent enzyme activity. We have recently found a positive association between TD and the CYP2D6*10 allele, which codes for the intermediate metabolizer (IM) phenotype and is characterized by decreased but not absent CYP2D6 activity in Japanese schizophrenic patients. In addition, the CYP2D6* 2 allele with the HhaI site mutation in exon 6 has also been reported to be an IM allele and a risk factor for Parkinson's disease (PD) in the Japanese population. In the present study, we investigated potential contributions of the CYP2D6*2 allele to TD using case-control and regression analysis in 99 schizophrenic patients. No significant differences in genotypic and allelic frequencies were found between patients with and without TD. Even after using regression analysis to adjust for the confounding variables, there was no significant association of the CYP2D6*2 genotype with either outcome variable, the occurrence of TD or the total AIMS score. These results suggest that the CYP2D6*2 allele may not contribute to the pathogenesis of TD.

Dopamine receptor D2 intronic polymorphism in patients with Parkinson's disease

An association between the intronic allele 3 of the dopamine receptor D2 (DRD2) gene and European Parkinson's disease (PD) cases has been reported recently. We initiated the present work in order to determine whether this association between the DRD2 locus and PD is also present in our population from Spain. The DRD2 gene polymorphism has been genotyped in 154 patients and in 125 controls. The allele 3 is present in 60.3% of the patients and in 55.2% of the controls. The genotype 3/3 is present in 36.3% of the patients and in 34.4% of the controls. No statistical differences in the genotype and allelic frequencies between the two groups have been found. No differences were also found when the patients were classified according to different criteria such as onset, family history, gender or clinical presentation. Thus our results do not support a role for the DRD2 locus to develop PD.

CYP2D6 mutations and therapeutic outcome in schizophrenic patients

STUDY OBJECTIVE

To investigate whether a relationship exists between the most common known cytochrome P450 (CYP) isozyme 2D6 mutations and schizophrenia. Because most antipsychotic and antidepressant agents interact with CYP2D6, we also investigated clinical outcomes in schizophrenic poor metabolizers (PMs) and extensive metabolizers (EMs).

DESIGN

Prospective, observational study.

SETTING

Two psychiatric hospitals and a university-affiliated nonpsychiatric hospital.

SUBJECTS

Thirty-nine consecutive schizophrenic patients (POP 1), 89 schizophrenics of French Canadian origin (POP 2), and 384 healthy French Canadians (POP 3).

INTERVENTION

All study subjects were genotyped for CYP2D6 mutant alleles. POP 1 patients were evaluated before and after 21 or more days of treatment with antipsychotic drugs metabolized at least in part by CYP2D6.

MEASUREMENTS AND MAIN RESULTS

Whole blood was collected to determine CYP2D6 alleles *1, *3, *4, *5, *6, and *7 using standard restriction fragment length polymorphisms and polymerase chain reaction techniques. In comparison, CYP2D6 genotypes were determined in POP 2 and POP 3. Twenty-three (59.0%) of 39 patients in POP 1 were genotypically EM homozygotes, 15 (38.4%) were EM heterozygotes, and 1 (2.6%) was a PM. Similar genotype distributions were determined in POP 2 and in POP 3. Genotype distributions for all three populations were in Hardy-Weinberg equilibrium (p>0.05), and there was no significant difference among them (p=0.857). In POP 1, no differences were seen among genotypes in disease symptom severity, number and severity of adverse drug effects, or attitudes toward drug treatment at baseline and at the end of the study. In fact, all patients improved significantly during their hospital stay (all p<0.05), although independent of the CYP2D6 genotype.

CONCLUSION

Common CYP2D6 mutant alleles were not associated with schizophrenia or with disease symptoms, antipsychotic-related adverse effects, or attitudes toward treatment.

The genetics of Parkinson's disease

Since the first description of Parkinson's disease in 1817 there have been numerous attempts to clarify the relative contribution of hereditary and environmental factors in its aetiology. Epidemiological and case-control studies as well as the existence of families with monogenic Parkinson's disease point clearly to a genetic contribution. Insights into the genetic basis of Parkinson's disease will lead to a greater understanding of the condition at a molecular level which will in turn allow the development of new rational therapeutic option.

[Genetics of Parkinson disease]

INTRODUCTION

What is the role of genetic factors in the pathophysiology of idiopathic Parkinson's disease, one of the most frequent neurodegenerative disorders? In the past two years, identification of two genes and localization of a third one have supported the hypothesis that genetics factors are involved in idiopathic Parkinson's disease. We present arguments that support such hypothesis, and describe recent advances in genetic studies of idiopathic Parkinson's disease.

CURRENT KNOWLEDGE AND KEY POINTS

The first gene identified on chromosome 4 encodes alpha-synuclein. It causes a rare form of autosomal dominant Parkinson's disease. A locus on the short arm of chromosome 2 was recently identified in families with autosomal dominant Parkinson's disease. More recently, the gene encoding Parkin (located on chromosome 6) has been described. It already appears to be an important locus for juvenile parkinsonism with autosomal recessive transmission.

CONCLUSION

We now have to understand how mutations in these genes lead to selective degeneration of dopaminergic neurons, and to determine whether or not they participate in the genetic susceptibility of idiopathic Parkinson's disease.

Absence of effect of seven functional mutations in the CYP2D6 gene in Parkinson's disease

The reduction or loss of cytochrome P450 enzyme activity as a result of mutations in the CYP2D6 gene has been suggested as a risk factor for Parkinson's disease (PD). Conflicting results among reported studies of the prevalence of mutations among patients with PD suggested a more comprehensive genotyping and an analysis of the interactions with other suspected risk factors and family history. We determined the frequency of seven CYP2D6 mutations among 109 patients with PD and 110 control subjects. Family history of PD, age of onset, exposure to pesticides or herbicides, and well-water consumption were obtained for all cases. There was no significant difference in frequency between patients with PD and control subjects for any mutant allele and no significant association with family history, onset age, or environmental exposures. We sought to increase the power of our study by combining reports from the literature, choosing allele frequencies as the most informative measure. Although we found variability in reported allele frequencies for control subjects that made a meta-analysis problematic, summing all reports demonstrated no difference in CYP2D6 mutation frequency between patients with PD and control subjects. This comprehensive study of CYP2D6 mutations demonstrates that other genes or shared environmental exposures account for the familial risk of PD.

Polymorphic cytochromes P450 and drugs used in psychiatry

1. The cytochrome P450 monooxygenases, CYP2D6, CYP2C19, and CYP2C9, display polymorphism. CYP2D6 and CYP2C19 have been studied extensively, and despite their low abundance in the liver, they catalyze the metabolism of many drugs. 2. CYP2D6 has numerous allelic variants, whereas CYP2C19 has only two. Most variants are translated into inactive, truncated protein or fail to express protein. 3. CYP2C9 is expressed as the wild-type enzyme and has two variants, in each of which one amino acid residue has been replaced. 4. The nucleotide base sequences of the cDNAs of the three polymorphic genes and their variants have been determined, and the proteins derived from these genes have been characterized. 5. An absence of CYP2D6 and/or CYP2C19 in an individual produces a poor metabolizer (PM) of drugs that are substrates of these enzymes. 6. When two drugs that are substrates for a polymorphic CYP enzyme are administered concomitantly, each will compete for that enzyme and competitively inhibit the metabolism of the other substrate. This can result in toxicity. 7. Patients can be readily phenotyped or genotyped to determine their CYP2D6 or CYP2C19 enzymatic status. Poor metabolizers (PMs), extensive metabolizers (EMs), and ultrarapid metabolizers (URMs) can be identified. 8. Numerous substrates and inhibitors of CYP2D6, CYP2C19, and CYP2C9 are identified. 9. An individual's diet and age can influence CYP enzyme activity. 10. CYP2D6 polymorphism has been associated with the risk of onset of various illnesses, including cancer, schizophrenia, Parkinson's disease, Alzheimer's disease, and epilepsy.

Behavioral disturbances of dementia

Behavioral disturbances are common in patients with dementia. Medical intervention is needed if, for example, these behaviors threaten a patient's safety or jeopardize his or her ability to perform activities of daily living. Typical antipsychotic agents are associated with troublesome adverse effects in the elderly (e.g., anticholinergic effects, extrapyramidal symptoms). Atypical antipsychotics have reduced potential to cause these types of side effects but are not free from side effects. Recently, there has been a greater focus on the use of antidepressants to treat behavioral disturbances in dementia. Among these, selective serotonin reuptake inhibitors have been studied more commonly due to their safety profile in the elderly. Citalopram, in particular, has demonstrated efficacy in improving dementia-related behavioral symptoms.

Cytochrome P4502D6 (debrisoquine 4-hydroxylase) and Parkinson's disease in Chinese and Caucasians

Four polymorphic sites (C/T188, C/T2938, G/C4268, G/A1934) in the cytochrome P4502D6 (debrisoquine 4-hydroxylase) gene were investigated for their association with sporadic Parkinson's disease (PD). Three mutant alleles (C/T188, C/T2938 and G/C4268) result in amino acid changes which could alter the substrate specificity or alter its ability to metabolize their substrates; the fourth (G/A1934) causes a loss of enzyme activity. The study was carried out in two ethnically homogenous populations: Chinese (123 PD patients, 124 controls); and Caucasian (95 PD patients, 62 controls). Haplotype status, which took into account amino acid changes at three polymorphic sites, was deduced from genotyping results in order to investigate whether substrate specificity was important rather than loss of enzyme activity. There was no gender difference in the distribution of the alleles in either race. There was, however, significant association among the three polymorphic sites (C/T188, C/T2938, G/C4268) in both ethnic groups. T/T188:C/C2938:C/C4268 is the most common genotype in the Chinese population, in contrast to C/C188:C/T2938:C/G4268 (followed by C/C188:C/C2938:G/G4268) in Caucasians. All 69 of the sub-group of Chinese patients tested were homozygous for the wild-type allele at the G/A1934 polymorphic site. Neither the CYP2D6 allele nor haplotype was associated with PD in either ethnic group.