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Pathogenic PINK1 mutations have been described in PARK6-linked Parkinson's disease (PD) patients of Asian origin. However, data on the frequency of PINK1 mutations in sporadic early-onset Parkinson's disease (EOPD) Asian patients are lacking. The objectives of this study were to report the frequency of PINK1 mutations of sporadic EOPD in an Asian cohort comprising of ethnic Chinese, Malays, and Indians, and to highlight a PINK1-positive patient who presented with restless legs symptoms. Eighty consecutive sporadic EOPD patients from the movement disorder clinics of two major tertiary institutions in the country were included. We performed sequence analysis of all the coding and exon-intron junctions of the PINK1 using specific primer sets. In addition, we genotyped polymorphisms detected from the analysis in a group of sporadic PD patients and controls. Three different mutations (two homozygous nonsense and one heterozygous missense) in the putative kinase domain were found in three patients, giving a 3.7% frequency of PINK1 mutations in our EOPD cohort. All the mutations were absent in 200 healthy controls. One patient with a novel homozygous nonsense PINK1 mutation presented unusually with restless legs symptoms. Separately, analysis of the frequency of four PINK1 polymorphisms in a group of sporadic PD and controls did not reveal any significant differences. We highlight a 3.7% frequency of PINK1 mutations in an Asian cohort (ethnic Chinese, Malay, and Indian) of EOPD. The phenotypic spectrum associated with PINK1-positive patients may be wider than previously reported. Polymorphisms of PINK1 do not appear to modulate risk of PD in our population.

We provided data to show that the transcriptional activity of wildtype -258T in the parkin promoter region was significantly higher than the -258G variant in human cell lines. The transcriptional activity of wildtype -258T was significantly increased under oxidative stress by hydrogen peroxide, but this was not observed for the -258G variant. The transcriptional upregulation was significantly higher for wildtype -258T compared to -258G variant at 0.1, 0.2 and 0.4 mM of hydrogen peroxide. Similar results were obtained when the cells were treated with a proteasome inhibitor, MG132.Furthermore, in a case control study involving 753 subjects, we demonstrated that the parkin promoter -258G variant was associated with an increased risk of sporadic Parkinson's disease (PD) in the elderly ethnic Chinese population. Our clinical and laboratory data provide corroborative evidence that some older individuals who have the -258G variant may have a higher risk of developing PD.

Background: Altered splicing of parkin under cellular stress could lead to changes in gene expression and altered protein activity. The causative role of parkin in sporadic Parkinson's disease (PD) is unknown., Objectives: We described a parkin splice variant (SV) in the substantia nigra and leukocytes of sporadic PD patients. Using a case control methodology, we investigated the exon 4 SV (E4SV) and wild-type parkin expression in the leukocytes of sporadic PD patients and healthy individuals., Methods/results: We identified a parkin E4SV in the substantia nigra and leukocytes of sporadic PD patients and controls by reverse transcriptase-polymerase chain reaction (PCR). The exon 4 (122 bp) deletion resulted in a reading frame shift over the junction of exons 3-5 and a stop codon (tga) 17 bp downstream from exon 3. The translated truncated protein was associated with a total loss of the two-RING finger functional domain. Utilizing TaqMan real-time PCR with probes located across the junction of exons 3-4 or 3-5, we demonstrated an over-expression of E4SV/wild-type parkin ratio in the leukocytes of sporadic PD patients compared to age-, gender-, and race-matched controls (p<0.0005). A multivariate regression analysis demonstrated that the ratio of E4SV/wild-type parkin expression increased with age in PD patients, but this was not observed in the controls (p<0.0005)., Conclusion: The relative expression of E4SV/wild type parkin was increased in sporadic PD compared to healthy controls. Based on our observations, further functional studies to determine the pathophysiologic role of E4SV in sporadic PD patients will be of importance.

A common heterozygous leucine-rich repeat kinase 2 (LRRK2) mutation 6055G > A transition (G2019S) accounts for about 3-7% of familial Parkinson's disease (PD) and 1-1.6% sporadic PD in a number of European populations. To determine the prevalence of the G1019S mutation in our Asian population, we conducted genetic analysis of this mutation in 1000 PD and healthy controls. The G2019S mutation was not detected in any of our study subjects. The prevalence of G2019S mutation is rare (< 0.1%) in our population, suggesting that occurrence of this mutation may vary amongst different ethnic races. This has important clinical implication when implementing guidelines for genetic testing.

Pyridoxal-5-phosphate, the biological active form of pyridoxine, is a cofactor for dopa-decarboxylase (DDC) enzyme. Pyridoxine may augment the conversion of levodopa to dopamine in the periphery and therefore decrease availability of levodopa to the brain. However, this effect can be negated in the presence of a DDC inhibitor, which potentiates plasma levodopa level. A single nucleotide polymorphism at the nucleotide 1947 in the catechol-O-methyltransferase (COMT) gene encodes the high (COMT(H)) and low activity (COMT(L)) forms of the enzyme. In this study, we examined the effect of the COMT(L) allele on the clinical response to pyridoxine in Parkinson's disease (PD) patients. PD patients who were on stable and optimized dose of levodopa were included in this study. Their mean motor and activities of living score improved after high dose pyridoxine (P = 0.09, P = 0.04), and worsened after a washout period (P = 0.005, P = 0.001). Using a multivariate model, the presence of the COMT(L) allele predicted response to pyridoxine, with the best outcome observed in COMT(L/L) homozygotes. Our observational study suggests that the status the functional COMT(L) variant may be potentially useful to select PD patients for high dose pyridoxine therapy., ((c) 2005 Wiley-Liss, Inc.)

The expression of alpha-synuclein gene can be influenced by the genomic load and/or epigenetic factors. By using quantitative real-time polymerase chain reaction techniques, we demonstrated that the alpha-synuclein gene mRNA expression in sporadic PD did not differ from healthy controls (median [range] 0.110 ]0.012-0.628] vs. 0.120 [0.028-0.447]; P = 0.15). There was no difference in the alpha-synuclein gene dosage between PD patients with high and low mRNA expression. Multivariate analysis did not reveal age, gender, or cigarette smoking as confounding variables. Our study suggests that there was no significant alteration of alpha-synuclein mRNA expression in our sporadic PD patients compared to controls. However, the role of alpha-synuclein mRNA expression in select groups of sporadic PD patients and its interaction with environmental agents need to be further determined., (Copyright 2005 Movement Disorder Society.)

The MDR1 multidrug transporter is important in regulating environmental xenobiotics and hence may play a causative role in Parkinson's disease (PD). MDR1 haplotype comprising 2677 G > T/A and 3435 C > T may be protective against PD. Using a case control methodology, we investigated the association of MDR1 haplotypes (single nucleotide polymorphisms (SNPs) 2677 G > T/A and 3435 C > T) in a Polish PD population. Seven SNPs, extending from the promoter to exon 28 of the MDR1 gene in 158 PD patients and 139 healthy controls were evaluated. Specifically we examined the association of haplotypes containing SNPs 2677 G > T/A and 3435 C > T and risk of PD. The multivariate logistic regression model was used to evaluate the effects of the covariates on the phenotypes. Haplotypes' frequencies were estimated using the Expectation-Maximization algorithm. The frequency of each individual SNPs; -41 A > G (intron -1), -145 C > G (exon 1), -129 T > C (exon 1), 1236 T > C (exon 12), 2677 G > T/A (exon 21), 3435 C > T (exon 26), and 4036 A > G (exon 28) did not differ between PD and controls. However, there was a trend towards significance in PD patients having the haplotype 2677G-3435C (p < 0.09, chi-square 2.85, odds ratio 0.25, 95% CI 0.06-1.08). Haplotype constructs of the other loci did not differ significantly between the two groups. There was a weak protective effect of the haplotype 2677G-3435C in our white population. However, the MDR1 haplotypes did not generally modulate the risk of PD.

We performed sequence analysis of all the exons and exon-intron boundaries in familial and young-onset Parkinson's disease (PD) in an Asian cohort. None of the patients carried any pathogenic mutations in the Nurr1 gene. We demonstrated a 5 to 10% prevalence of the intron 7 +33 C-->T variant among Malay and Indian PD and healthy controls, suggesting that this variant, which was previously described only in 1 Chinese patient, was not a silent mutation but a common polymorphic variant in some ethnic races., (2004 Movement Disorder Society.)

Mutations in the DJ-1 gene have been described in autosomal recessive Parkinson's disease patients (ARPD) of European ancestry and young onset (YOPD) Ashkenazi Jewish and Afro-Caribbean patients. There is little information on the prevalence of DJ-1 mutations amongst Asian PD populations. In this study, we examined for DJ-1 mutations in consecutive YOPD and ARPD in a multi-ethnic cohort (Chinese, Malays, and Indians) of PD patients in a tertiary referral center. Sequence analysis of all the exons and the exon and intron boundaries of the DJ-1 gene were carried out. We did not find any DJ-1 mutations in these patients. A number of intronic variants with genotype frequency ranging from 15 to 90% were detected. Unlike Parkin, pathogenic DJ-1 mutations appear to be restricted to certain populations and are unlikely to be of clinical importance in our Asian cohort.