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INTRODUCTION: Apathy is a neuropsychiatric symptom in Parkinson's Disease (PD) which has a negative impact on quality of life and might be related in part to damage of presynaptic dopaminergic system. Little is known about relationship between striatal dopamine levels and apathy in PD patients without dementia and/or depression. The aim of the present study was to investigate the relationship between "pure apathy" and striatal dopamine uptake in untreated, drug-naïve PD patients without clinically significant dementia and/or depression. METHODS: Fourteen PD patients with pure apathy and 14 PD patients without apathy, matched for age, side of motor symptoms at onset, motor disability and disease duration, underwent both neuropsychological and behavioral examination including self-rated version of the Apathy Evaluation Scale (AES-S). All patients underwent 123 I-FP-CIT (DaT-SCAN) SPECT to assess dopamine transporter (DAT) striatal uptake. RESULTS: PD patients with apathy showed lower DAT levels in the striatum than non-apathetic patients. After Bonferroni correction the difference between groups was significant in the right caudate. CONCLUSIONS: Apathy is associated with reduced striatal dopamine transporter levels, independent of motor disability and depression in non-demented PD patients. These findings suggest that dysfunction of dopaminergic innervation in the striatum and particularly in the right caudate may contribute to development of apathy in early PD.

Background and purpose: Cognitive impairment is common in Parkinson's disease (PD), even in the early stages. We aimed to assess the relationship between insulin-like growth factor-1 (IGF-1) and cognitive functions in early, drug-naïve patients with PD. Methods: Serum IGF-1 was measured in 65 early, drug-naïve patients with PD that underwent a complete neuropsychological battery at baseline and after 2years. Linear regression analysis was used to evaluate the relationships between neuropsychological scores and IGF-1. Repeated-measures anova was applied to assess changes in neuropsychological variables over time. Results: At baseline, IGF-1 levels were related to phonological fluency. At follow-up, IGF-1 levels were associated with the Rey auditory verbal learning test (RAVLT) - immediate and delayed recall, Frontal Assessment Battery, verbal span and Benton judgement of the line orientation test. Patients with low IGF-1 levels at baseline showed a significantly faster decline of performances than patients with high IGF-1 levels on immediate and delayed recall of the RAVLT and interference task of the Stroop test. Conclusions: Low serum IGF-1 levels are related to poor performance on executive tasks in early, drug-naïve patients with PD, and may predict poor performance on attention/executive and verbal memory tasks after a 2-year follow-up. © 2013 The Author(s) European Journal of Neurology © 2013 EFNS.

BackgroundThe variability in the clinical phenotype of Parkinson's disease seems to suggest the existence of several subtypes of the disease. To test this hypothesis we performed a cluster analysis using data assessing both motor and non-motor symptoms in a large cohort of newly diagnosed untreated PD patients.MethodsWe collected data on demographic, motor, and the whole complex of non-motor symptoms from 100 consecutive newly diagnosed untreated outpatients. Statistical cluster analysis allowed the identification of different subgroups, which have been subsequently explored.ResultsThe data driven approach identified four distinct groups of patients, we have labeled: 1) Benign Pure Motor; 2) Benign mixed Motor-Non-Motor; 3) Non-Motor Dominant; and 4) Motor Dominant.ConclusionOur results confirmed the existence of different subgroups of early PD patients. Cluster analysis revealed the presence of distinct subtypes of patients profiled according to the relevance of both motor and non-motor symptoms. Identification of such subtypes may have important implications for generating pathogenetic hypotheses and therapeutic strategies.

Both low serum uric acid (UA) levels and apathy are considered biomarkers of cognitive decline and dementia in Parkinson’s disease (PD). There is an urgent need to combine different biomarkers to predict disease course in PD. Data on the relationship between serum UA levels and apathy in PD are lacking. The aim of this study is to evaluate the relationship between serum UA levels and pure apathy in early, drug-naïve PD patients. Forty-nine early, drug-naïve PD patients were enrolled and stratified into two groups using the median serum UA levels at diagnosis (Group 1 serum UA ≤ 4.8 mg/dl; Group 2 serum UA > 4.8 mg/dl). The cohort was followed for the first 2 years of disease. Apathy was evaluated with the Apathy Evaluation Scale (AES). Patients with lower serum UA levels presented significant higher AES score compared to patients with higher serum UA levels. Regression analysis showed that baseline serum UA levels were significant determinants of AES scores at both baseline and 2-year follow up, irrespective of gender, age, attention/executive functions and dopamine replacement therapy when applicable. This is the first study showing a link between serum UA levels and apathy in non-demented, non-depressed, early, drug-naïve PD, being lower serum UA levels associated with greater apathy. Further follow up of our patients and replication of this observation in independent cohorts are needed to establish if this combination of biomarkers may help in characterizing a subgroup of PD patients at diagnosis.

Introduction Higher caffeine consumption has been associated with reduced risk of Parkinson's disease (PD), and with a more benign progression of motor and non-motor symptoms (NMS). The present observational cohort study investigated motor and non-motor correlates of caffeine consumption in de novo PD. Methods 79 newly diagnosed, drug naive PD patients have been included and followed up for 4 years. The total caffeine use was calculated with the Caffeine Consumption Questionnaire. Following study variables were recorded at baseline, and after 2 and 4 years: UPDRS part III, UPDRS part IV, l -dopa Equivalent Daily Dose (LEDD), NMS Questionnaire (NMSQuest), and the time occurring from PD diagnosis to the need for l -dopa treatment. Age, gender and disease duration were included as covariates in the statistical models. Results The average daily caffeine consumption was 296.1 ± 157.2 mg. At Cox regression models, higher caffeine consumption was associated with a lower rate of starting l -Dopa treatment (HR = 0.630; 95%CI = 0.382–0.996). At the mixed-effects linear regression models considering the whole study period, each additional espresso cup per day (50 mg of caffeine) was more likely associated with 5-point lower UPDRS part III total score (Coef = −0.01; 95%CI = −0.02 to 0.00), with 50% reduced LEDD (Coef = −0.01; 95%CI = −0.15 to 0.00; p = 0.021), and with 5-point lower NMSQuest total score (Coef = −0.01; 95%CI = −0.01 to 0.00), but not with UPDRS part IV total score (Coef = −0.00; 95%CI = −0.00 to 0.00). Conclusion Caffeine consumption was associated with a reduced accrual of motor and non-motor disability during 4-year follow-up in de novo PD, highlighting the rationale for using adenosine A2A antagonists since the early phases of PD.

Lateral trunk flexion is a very common clinical observation in patients affected by Parkinson's disease. Postural control is known to depend on vestibular, visual, and somatosensory information. The aim of this study was to investigate whether impairment of vestibular function can account for the postural alterations observed in parkinsonian patients with lateral trunk flexion. We evaluated vestibular function in 11 parkinsonian patients with lateral trunk flexion and in 11 age-, sex-, and disease duration-matched patients without lateral trunk flexion. The following vestibular tests were performed: infrared videonystagmography including fast and slow ocular movements, spontaneous-positional and evoked nystagmus search with and without visual fixation, fast positioning maneuvers, the bithermal caloric test, and the vibration test. A peripheral, unilateral vestibular hypofunction was identified in all patients with lateral trunk flexion. The vestibular hypofunction was ipsilateral to the leaning side and contralateral to the most affected parkinsonian side in all patients. In the control group, 7 subjects had no vestibular signs; 4 subjects had unilateral vestibular hypofunction without clinically evident lateral trunk flexion. Two of the latter patients subsequently developed lateral trunk flexion ipsilateral to the vestibular deficit and contralateral to the side most affected by Parkinson's disease. The processing of vestibular information was impaired in parkinsonian patients affected by lateral trunk flexion. The impairment was at least in part responsible for the patients' postural abnormality. We propose that the acronym PISA (Postural Imbalance Syndrome with vestibular Alterations) be used to describe the specific postural change observed in parkinsonian patients affected by a vestibular defect and lateral trunk flexion.

To explore the relationship between depression and cognitive impairment in non-demented PD patients, we evaluated neurological and neuropsychological asset in 65 patients with a diagnosis of major depressive disorder (dPD) according to DSM-IV criteria and 60 patients without depression (nPD). Compared with nPD patients, dPD patients had significantly higher scores on behavioral rating scales and performed worse on the Frontal Assessment Battery (FAB), Semantic Fluency Task, Copying Task (CT), and Stroop Test. Three dPD subgroups were identified based on the first two DSM-IV criteria: patients fulfilling criterion 1 (depressed mood; group 1); patients fulfilling criterion 2 (apathy/anhedonia; group 2); patients fulfilling criteria 1 and 2 (group 3). Patients of group 2 scored significantly lower than patients of group 1 on the CT, FAB and phonological fluency task. Patients of groups 2 and 3 scored significantly lower than nPD patients on visuoconstructional and frontal tasks. Similar results were obtained in dPD patients stratified in four subgroups based on cut-off scores of the Apathy Evaluation Scale and the Snaith Hamilton Pleasure Scale. In summary, PD patients with concomitant apathy and anhedonia may show more severe cognitive impairments. Since such patients are diagnosed to be affected by depression according to clinical DSM-IV criteria, we suggest that DSM-IV criteria may not distinguish an affective from a cognitive disorder in PD.

Introduction In PD, Mild Cognitive Impairment (PD-MCI) occurs since early stages of disease. The aims were to assess presence of PD-MCI in untreated, drug-naive PD patients, and to follow-up the sample over 4 years to ascertain evolution of neurocognitive profile. Methods Seventy-six patients underwent neuropsychological testing at baseline (T0), and after 2 (T1:n = 62) and 4 years (T2:n = 55). Diagnosis of PD-MCI and PD-associated dementia (PDD) was made according to current consensus criteria. Results PD-MCI occurred in 25/76 patients (32.9%) at baseline, and 4 of them reverted from PD-MCI to Normal Cognition (Reverters), 7 remained stable (Non-Reverters) and 2 developed PDD at T2; 12 patients were lost to the follow-up. Among the 51 patients with normal cognition (PD-CN) at T0, 27 had normal cognition at T2 (5 of them were Reverters with respect to diagnosis at T1), 5 had MCI at T1 and T2 (Non-Reverters), 9 had MCI at T2 only, whereas 1 developed PDD; 9 patients were lost to the follow-up. At baseline, Reverters (n = 9) had younger age at onset and better performance on constructional visuospatial task than Non-Reverters (n = 12). Compared to patients without PD-MCI at all evaluations (n = 19), Reverters had poorer performance on verbal immediate recall and attention tasks and higher level of apathy at T0. Reduced performance on the Stroop Test at baseline predicted PD-MCI at T2. Conclusion Executive dysfunctions predicted development of PD-MCI after few years from onset. Reversal from PD-MCI to PD-CN was related to young age at onset and high level of apathy at baseline evaluation.

Background and purpose Oxidative stress is a central pathogenic mechanism of Parkinson's disease (PD), and the heme oxygenase (HO) bilirubin pathway is one of the main mammalian antioxidative defences. Indeed, there is growing evidence of HO−bilirubin upregulation from early phases of PD. Our aim was to investigate bilirubin as a possible biomarker of PD diagnosis and progression. Methods A cross-sectional case−control study was performed to evaluate differences in bilirubin levels between newly diagnosed, drug-naive PD subjects and controls. Afterwards, PD subjects were included in a 2-year longitudinal study to evaluate disease progression in relation to baseline bilirubin levels. Results Seventy-five de novo PD subjects were selected and matched with 75 controls by propensity score. Analysis of variance showed higher bilirubin levels in PD patients compared with controls (P

The variability in the clinical pheno- type of Parkinson's disease (PD) suggests the existence of several subtypes of the disease. Motor heterogeneity of PD is well established, but not nonmotor heterogeneity. At present, we are unable to predict the rate of progression of PD based on robust biomarkers. We aimed to examine the heterogeneity of PD by attempting to identify nonmotor fac- tors associated with the rate of motor progression and functional decline, as measured by the time to reach the need for levodopa therapy during the first 4 years from diagnosis in a cohort of de novo PD patients. The median time to introduction of L-dopa for patients with urinary symptoms was significantly shorter than that for those with- out (20 vs. 37 months; P 5 0.001). Cox's regression models showed that the urinary domain was associated with a higher probability of starting L-dopa (hazard ratio: 2.1; P 5 0.002). There was no influence of such confounders as sex, age, baseline motor features, use of dopamine ago- nists and/or monoamine oxidase B inhibitors, and total L- dopa equivalent daily dosage. Patients with urinary symp- toms had higher baseline and follow-up motor and nonmo- tor disturbances than those without. Our study suggests the existence of a subgroup of patients who show urinary symptoms along with an overall higher motor and nonmotor burden. Such patients are prone to manifest a rapid func- tional decline over the first 4 years of the disease. Urinary symptoms might be a clinical marker of severity as well as a possible nonmotor subtype of PD. V C 2015 International Parkinson and Movement Disorder Society

Objectives Mild cognitive impairment (MCI) is a common feature in Parkinson's disease (PD). We performed an exploratory study to investigate dopaminergic nigrostriatal innervation and its cognitive correlates in early untreated PD patients with MCI as compared to cognitively intact patients. Patients and methods A consecutive series of 34-de-novo, drug-naive patients with PD were enrolled. They underwent [123-I] FP-CIT SPECT and comprehensive neuropsychological battery. MCI was identified in 15 of 34 patients with PD. Results The two groups did not show any statistically significant difference in age, sex, disease duration, education, lateralization, and H&Y and Hospital Anxiety and Depression Scale scores. Logistic regression analysis showed that UPDRS-III was weakly associated with MCI (P = 0.034). Partial correlation analysis controlling for UPDRS-III and age suggested that in PD patients with MCI reduced V3″ values in the more affected caudate were correlated with reduced performances in frontal assessment battery, Trail Making Test: part B minus Part A and copy task of the Rey–Osterrieth complex figure test. Reduced V3″ values in the more and less affected putamen were significantly related with reduced performance in frontal assessment battery and in copy task of Rey–Osterrieth complex figure test, respectively. No correlation was found between neuropsychological scores and DAT availability in PD patients without MCI. Conclusions Although preliminary, our results suggest that striatal dopamine depletion may contribute to some cognitive deficit in early never treated PD patients with MCI.

Background and purpose Apathy may be either a symptom of major depression or a behavioral disturbance occurring in concomitance with depression or alone in Parkinson's disease (PD). The aim of the present study was to determine the progression of cognitive impairment in drug-naive untreated PD patients with or without clinically significant apathy. Methods Sixty-two PD patients with a disease duration

Background Diagnosing Parkinson's disease (PD) and tracking its progression may require the combination of reliable biomarkers. Among them, both serum uric acid (UA) and dopamine transporter (DaT) binding deserve more investigations. Aims of the study We aimed to investigate the relationship between serum UA levels and DaT availability in newly diagnosed, drug-naive PD patients, by means of semiquantitative [(123) I]FP-CIT-SPECT. Methods We recruited 52 newly diagnosed, drug-naive PD patients, and performed serum UA dosage and [(123) I]FP-CIT-SPECT. Results Pearson's correlation analysis showed that UA levels were significantly higher in patients with higher averaged, ipsilateral and contralateral DaT binding in caudate, putamen, and striatum. Conclusions We showed, for the first time, by regional semiquantitative analysis of DaT binding in PD patients that UA levels significantly correlates with the severity of dopaminergic impairment in caudate, putamen, and striatum. This study broadens our knowledge on the importance of UA as a biomarker of PD.

Background and purpose Uric acid (UA) has been studied extensively as a valuable biomarker of Parkinson's disease (PD), but its relationship with non-motor symptoms (NMS) in de novo PD has been poorly investigated. Our aim was to evaluate the usefulness of baseline serum UA as a marker of NMS progression in newly diagnosed PD. Methods Sixty-nine newly diagnosed PD patients were enrolled. At baseline, all patients completed the NMS questionnaire (NMSQuest), and serum UA levels were measured. After 2 years, the NMSQuest was completed again and patients were categorized into four groups: NMS improvement (domain involvement at baseline but not at 2-year follow-up visit), NMS absence (domain not involved at baseline or 2-year follow-up visits), NMS presence (domain involvement both at baseline and 2-year follow-up visits) and NMS worsening (domain not involved at baseline but involved at 2-year follow-up). Results anova with post hoc Bonferroni correction showed that patients with NMS absence presented significantly higher UA values than patients with NMS presence with regard to the attention/memory (P = 0.023), depression/anxiety (P = 0.028) and cardiovascular domains (P = 0.002), whilst no differences were found with regard to both the NMS improvement and worsening groups. In addition, multinomial regression analysis showed that the lowest tertile of NMS progression presented higher UA levels (P = 0.023; odds ratio 0.488) compared with patients with greater NMS progression. Conclusions This is the first report of a relationship between serum UA and presence/progression of multiple NMS in de novo PD, providing additional evidence of the reliability of UA as a biomarker of PD and opening new insights on PD neuroprotection.

Gender differences in brain structure and function may lead to differences in the clinical expression of neurological diseases, including Parkinson's disease (PD). Few studies reported gender-related differences in the burden of non-motor symptoms (NMS) in treated PD patients, but this matter has not been previously explored in drug-naïve PD patients. This study is to assess gender differences in the prevalence of NMS in a large sample of early, drug-naïve PD patients compared with age and sex-matched healthy controls. Two hundred early, drug-naïve PD patients and ninety-three age and sex-matched healthy controls were included in the study. Frequency of NMS was evaluated by means of the Non-Motor Symptoms Questionnaire. The difference in gender distribution of NMS was evaluated with the χ (2) exact test; multiple comparisons were corrected with the Benjamini-Hochberg method. Male PD patients complained of problems having sex and taste/smelling difficulties significantly more frequently than female PD patients. Furthermore, men with PD complained more frequently of dribbling, sadness/blues, loss of interest, anxiety, acting during dreams, and taste/smelling difficulties as compared to healthy control men, while female PD patients reported more frequently loss of interest and anxiety as compared with healthy control women. This study shows specific sex-related patterns of NMS in drug-naïve PD. In contrast with previous data, female PD patients did not present higher prevalence of mood symptoms as compared to male PD patients. Comparison with healthy controls showed that some NMS classically present in premotor and early stage of disease (i.e., acting out during dreams, taste/smelling difficulties) are more frequent in male than in female patients.

Background Non-motor symptoms are very common among patients with Parkinson9s disease since the earliest stage, but little is known about their progression and their relationship with dopaminergic replacement therapy. Methods We studied non-motor symptoms before and after 2 years from dopaminergic therapy introduction in ninety-one newly diagnosed previously untreated PD patients. Results At baseline, nearly all patients (97.8%) referred at least one non-motor symptom. At follow-up, only few non-motor symptoms significantly changed. Particularly, depression and concentration became less frequent, while weight change significantly increased after introduction of dopamine agonists. Conclusions We reported for the first time a 2-year prospective study on non-motor symptoms before and after starting therapy in newly diagnosed PD patients. Even if non-motor symptoms are very frequent in early stage, they tend to remain stable during the early phase of disease, being only few non-motor symptoms affected from dopaminergic therapy and, specifically, by the use of dopamine agonists.

Background A relation between the side of motor onset and cognitive impairment in early PD has been reported, suggesting that the asymmetric degeneration affecting subcortical regions may play a pivotal role in lateralized cognitive function. However, evidences are controversial and all previous studies were performed on treated patients, though it is known that dopaminergic therapy can affect cognition in PD. Methods Sixty-nine early untreated PD patients underwent an extensive neuropsychological battery exploring memory, visuospatial and attention/executive functions. Patients were divided with respect of the side of onset (right vs. left) and further grouped according to motor phenotype (tremor vs. rigidity-bradykinesia). Multivariate analysis of variance has been carried out to compare clinical and neuropsychological data between subgroups. Results There were no differences in any neuropsychological task between right-sided and left-sided onset subgroups, irrespective of tremor dominant or rigid-bradykinetic phenotype. Age at onset was significantly higher in patients with any cognitive impairment as compared with patients without (66.7 ± 3.2 vs. 56.3 ± 6.8 years, p = 0.001). Conclusion Side of motor onset is not a major determinant for developing lateralized cognitive deficits in newly diagnosed untreated PD patients.

Background Anxiety is a common non-motor symptom among patients with Parkinson's disease (PD). Although the etiology of anxiety in PD is likely to be multifactorial, a dysfunction in the dopaminergic system might be implicated in its pathogenesis. The aim of our study was to investigate a possible dopaminergic mechanism involved in anxiety in newly diagnosed never-medicated PD patients using SPECT and 123I-FP-CIT as the dopamine transporter ligand. Methods Thirty-four newly diagnosed, untreated PD patients with asymmetric motor symptoms were included in the study: 17 patients with right- and 17 with left-motor onset, matched for age, disease duration and motor disability constituted the group. They were all evaluated for anxiety and depression and underwent an SPECT with 123I-FP-CIT. Dopamine transporter (DAT) availability values for right and left caudate and putamen were calculated and compared between patients with and without anxiety. Regression analyses were also performed in order to correlate DAT availability with the severity of the anxiety symptoms. Results Comparison between PD patients with and those without anxiety revealed significant differences of DAT availability in all the examined regions except the right putamen. In the group of patients considered as a whole, a significant correlation was found between increased anxiety severity and decreased DAT availability in right caudate. Conclusions We reported an association between nigrostriatal DAT availability deficits and anxiety symptoms in newly diagnosed, untreated PD patients. Our results suggest that hypofunction of the nigrostriatal dopaminergic system may represent one of the functional anomalies involved in anxiety in PD from the earliest stages of disease and irrespective of any therapy.

The objective of this study was to evaluate hearing impairment in patients affected by Parkinson's disease compared with hearing scores observed in normal age- and sex-matched controls. One hundred eighteen consecutive patients with a clinical diagnosis of Parkinson's disease were screened. Severity of motor symptoms and staging were measured with the Unified Parkinson's Disease Rating Scale (section III) and the Hoehn and Yahr scale. Audiometric evaluation consisted of a comprehensive audiologic case history and questionnaire, visual otoscopic examination, acoustic immittance measures (tympanogram and acoustic reflexes), pure tone audiometry, and measurement of brain stem auditory-evoked potentials. Healthy age- and sex-matched subjects were selected as the control group. One hundred six of 118 patients were enrolled. Pure tone audiometry revealed age-dependent high-frequency hearing loss in patients with Parkinson's disease compared with both normative values and values for healthy age- and sex-matched controls (75/106 [71%], χ(2) = 5.959, P = .02; 92/106 [86.8%] vs 60/106 [56.6%], χ(2) = 23.804, P < .001, respectively). Pure tone audiometry scores correlated with Hoehn and Yahr scale scores (P < .05). Brain stem auditory-evoked potentials were normal in all patients. Our patients with Parkinson's disease showed age-dependent peripheral, unilateral, or bilateral hearing impairment. Whether these auditory deficits are intrinsic to Parkinson's disease or secondary to a more complex impaired processing of sensorial inputs occurring over the course of illness remains to be determined. Because α-synuclein is located predominately in the efferent neuronal system within the inner ear, it could affect susceptibility to noise-induced hearing loss or presbycusis. It is feasible that the natural aging process combined with neurodegenerative changes intrinsic to Parkinson's disease might interfere with cochlear transduction mechanisms, thus anticipating presbycusis.

Little is known about the relationship between cognitive dysfunctions and the non-motor complex in subjects with newly diagnosed untreated Parkinson's disease (PD). The aim of this study was to explore the association between non-motor symptoms (NMS) and cognitive dysfunctions in an incident cohort of de novo, drug-naive, PD patients. Sixty-six non-demented, early, untreated PD patients completed a semi-structured interview on NMS and a battery of neuropsychological tests that assess verbal memory, visuospatial abilities, and attention/executive functions. Scores were age- and education-corrected. Patients who failed at least two tests for each cognitive domain were diagnosed as having mild cognitive impairment (MCI). All but three (95.4%) PD patients complained of at least one NMS. A total of 37.8% was diagnosed with MCI. There was a relationship between sleep-NMS and cognitive dysfunctions. Specifically, both REM behavioral sleep disorders (RBD) and insomnia were associated with lower scores on several cognitive tests. Moreover, RBD was closely related to MCI. NMS and MCI are very common even in the early phase of PD, before patients are treated. Given the correlation between sleep disturbances and cognitive impairment, it is possible that sleep symptoms in PD patients might be considered as an early marker of dementia.

Hyperhomocysteinaemia was reported in patients with Parkinson's disease (PD) treated with l-Dopa. The increase in plasma concentration of this sulfur compound arises from the massive methylation of the drug operated by the enzyme catechol-O-methyltransferase (COMT), which acts as a powerful sink of methyl groups. The contemporary occurrence of C677T polymorphism in homozygosity, leading to a temperature-labile variant of the MTHFR enzyme, induces an even more marked increase in tHcy. Here we show that l-Dopa administration in hyperhomocysteinemic PD patients is able to lower intracellular concentration of S-Adenosylmethionine (AdoMet) in erythrocytes (RBC), while the occurrence of hyperhomocysteinaemia causes a significant increase in S-Adenosylhomocysteine (AdoHcy) level. In patients with PD treated with l-Dopa and hyperhomocysteinemic, the remarkable decrease in AdoMet and the concurrent increase in AdoHcy concentration both contribute to significantly lower the transmethylation potential ([AdoMet]/[AdoHcy]), a useful index of the effectiveness of methyl group transfer by methyltransferases. This decrease could indeed contribute to partly attenuate, through a self-limiting kinetic mechanism, the tendency of developing drug resistance, partly mediated in these patients by COMT upregulation. Our results also support the conclusion that COMT inhibitors (entacapone or tolcapone), when administered in PD patients treated with l-Dopa, may potentiate the endogenous AdoHcy-dependent COMT inhibition mechanism already operative in a variable fashion.