Confirmation of the association between LRRK2 R1628P variant and susceptibility to Parkinson's disease in the Thai population.

OBJECTIVE: LRRK2 p.R1628P (c.4883G > C) is associated with Parkinson's disease (PD) in Chinese and Thais. However, some studies in other East Asian ethnic groups did not observe this association. Carriers of p.R1628P are about 3-5% Chinese and Thais. In contrast, Japanese, Koreans and Malays are much less prevalent (0-<1%). The contradictory results may be caused by insufficient sample sizes especially studies in ethnic groups with low prevalence, which, theoretically need a much larger sample size. We conducted a case-control Thai PD study with appropriate size in order to support the role of p.R1628P related to susceptibility to PD. METHODS: Estimated total sample size of 958 Thai subjects was needed. 485 PD patients and 480 controls were recruited. The p.R1628P was screened by RFLP and confirmed by direct sequencing. Clinical characteristics were compared between PD patients with and without p.R1628P. RESULTS: 54 PD patients (11%) and 29 control subjects (6%) carried p.R1628P. Multiple logistic regression analysis showed that GC and CC genotypes were significantly higher in PD patients than in controls (OR = 1.81, 95%CI = 1.10-2.97). The PD patients carrying p.R1628P had earlier age at onset (56 ± 13 vs 60 ± 12; P = 0.021) and a more rapidly progressive course (P < 0.001) than the patients carrying wild-type nucleotide. CONCLUSIONS: We confirm the association between p.R1628P and risk of developing PD in the appropriated sample-sized cohort. Certain LRRK2 variants appear to be generally distributed among East Asians, however, in widely different frequencies. In order to study role of such variants in PD, it should be carefully estimated the appropriate sample size.

Clinical analysis of adult-onset spinocerebellar ataxias in Thailand.

BACKGROUND: Non-ataxic symptoms of spinocerebellar ataxias (SCAs) vary widely and often overlap with various types of SCAs. Duration and severity of the disease and genetic background may play a role in such phenotypic diversity. We conducted the study in order to study clinical characteristics of common SCAs in Thailand and the factors that may influence their phenotypes. METHODS: 131 (49.43%) out of 265 Thai ataxia families with cerebellar degeneration had positive tests for SCA1, SCA2, Machado-Joseph disease (MJD) or SCA6. The study evaluated 83 available families including SCA1 (21 patients), SCA2 (15), MJD (39) and SCA6 (8). Comparisons of frequency of each non-ataxic sign among different SCA subtypes were analysed. Multivariate logistic regression analyses were undertaken to analyze parameters in association with disease severity and size of CAG repeat. RESULTS: Mean ages at onset were not different among patients with different SCAs (40.31 ± 11.33 years, mean ± SD). Surprisingly, SCA6 patients often had age at onset and phenotypes indistinguishable from SCA1, SCA2 and MJD. Frequencies of ophthalmoparesis, nystagmus, hyperreflexia and areflexia were significantly different among the common SCAs, whilst frequency of slow saccade was not. In contrast to Caucasian patients, parkinsonism, dystonia, dementia, and facial fasciculation were uncommon in Thai patients. Multivariate logistic regression analysis demonstrated that ophthalmoparesis (p < 0.001) and sensory impairment (p = 0.025) were associated with the severity of the disease. CONCLUSIONS: We described clinical characteristics of the 4 most common SCAs in Thailand accounting for almost 90% of familial spinocerebellar ataxias. There were some different observations compared to Caucasian patients including earlier age at onset of SCA6 and the paucity of extrapyramidal features, cognitive impairment and facial fasciculation. Severity of the disease, size of the pathological CAG repeat allele, genetic background and somatic heterogeneity of pathological alleles may influence clinical expressions of these common SCAs.

CAG-Expansion Haplotype Analysis in a Population with a Low Prevalence of Huntington's Disease.

BACKGROUND AND PURPOSE: The prevalence of Huntington's disease (HD) among East Asians is less than one-tenth of that among Caucasians. Such a low prevalence may be attributable to a lack of carriers of specific predisposing haplogroups associated with the high instability of the Huntingtin gene (HTT). The aim of this study was to evaluate the association between specific HTT haplogroups and the occurrence of HD in a Thai population. METHODS: CAG-repeat sizes and HTT haplotypes were analyzed in 18 Thai HD patients and 215 control subjects. Twenty-two tagging single-nucleotide polymorphisms (tSNPs) were genotyped. RESULTS: Only 18 patients from 15 unrelated families were identified over the last 17 years. Pathological CAG-repeat alleles ranged from 39 to 48 repeats (43.5±3.0, mean±SD), and normal alleles ranged from 9 to 24 repeats (16.49±1.74). Only two of the chromosomes studied comprised intermediate alleles. Unlike the Caucasian data, all but 1 of the 22 tSNPs were not associated with the occurrence of HD. The predisposing haplogroups for Caucasian HD (haplogroups A1 and A2) are very rare in Thai patients (<4%). Both HD and normal chromosomes are commonly haplogroups A5 and C, in contrast to the case for Chinese and Japanese patients, in whom only haplogroup C was common in HD chromosomes. The frequency of CAG-repeat sizes of haplogroup A5 and C were also similarly distributed. CONCLUSIONS: HD chromosomes of Thai patients may arise randomly from each haplogroup, with a similar mutation rate. This rate is much lower than the CAG expansions from Caucasian HD haplogroups. These data suggest that the different mechanisms underlie CAG expansion in Thai and Caucasian patients.

Long-term effectiveness of acetazolamide on permanent weakness in hyperkalemic periodic paralysis.

Acetazolamide is commonly used as an empirical treatment for inherited periodic paralyses although some patients may develop deleterious effects. We report a 65 year-old man with hyperkalemic periodic paralysis and late-onset permanent weakness in association with the common T704M mutation in α-subunit, skeletal muscle voltage-gated sodium channel gene. He rapidly recovered from weakness after acetazolamide treatment. Magnetic resonance imaging of thighs comparing pre- and post-treatment revealed a significant increase in muscle bulk. The patient has been without any type of weakness for over 6 years. This data show the remarkable benefit of acetazolamide on permanent weakness of hyperkalemic periodic paralysis in association with the T704M mutation.

Paroxysmal neuromyotonia: a new sporadic channelopathy.

Neuromyotonia is a heterogeneous group of genetic and autoimmune channelopathies resulting in hyperexcitability of peripheral nerves. We report an unusual case of neuromyotonia, which to our knowledge has not been previously described. The patient developed intermittent attacks of severe painful muscle stiffness accompanied by sweating, myokymia and raised serum creatine kinase. Genetic analysis of KCNA1, KCNQ2 and SCN4A genes did not identify pathogenic mutation. Serum voltage-gated potassium channel antibody was also negative. He was successfully treated with acetazolamide and carbamazepine. This appears to be a new neuromuscular disease, "paroxysmal neuromyotonia", the etiology of which is still unknown.