Ebonne Yulin Ng

SLC1A2 variant associated with essential tremor but not Parkinson disease in Chinese subjects.

Essential tremor (ET) is characterized by postural and action tremor.1–3 A genome-wide association study (GWAS) identified a LINGO1 gene variant to be associated with ET.4 Subsequent GWAS further identified an intronic variant (rs3794087) of the main glial glutamate transporter (SLC1A2) gene to be associated with ET with an odds ratio (OR) of approximately 1.4.5 We conducted a case-control study to examine the SLC1A2 gene variant in an Asian cohort of ET. In addition, we investigated the variant in patients with Parkinson disease (PD) because the GWAS LINGO1 variant has been implicated in both ET and PD and etiologic links between the conditions have been suggested.6

Greater motor progression in patients with Parkinson disease who carry LRRK2 risk variants

Objectives: In a longitudinal follow-up study, we compared the clinical features and motor progression of patients with Parkinson disease (PD) who are carriers of the leucine-rich repeat kinase 2 (LRRK2) gene risk variants with patients who are noncarriers. Methods: We prospectively evaluated a cohort of patients with PD for their clinical characteristics, disease severity, and LRRK2 genotype. Carriers of risk variants (G2385R, R1628P, S1647T) and noncarriers were classified separately. A longitudinal, linear mixed model analysis of motor score progression was performed to compare motor progression between the 2 groups. Motor score progression was defined as the difference between Unified Parkinsons Disease Rating Scale motor score at baseline and follow-up scores. Results: A total of 184 patients (122 risk variant carriers and 62 noncarriers) were evaluated and followed up for up to 6.5 years. No differences in demographics and baseline disease characteristics were found. In the longitudinal, linear mixed model analysis, risk variant carriers experienced greater rate of motor progression than noncarriers after 4 years from the date of diagnosis (p ≤ 0.018). Conclusions: PD LRRK2 risk variant carriers showed greater motor progression after 4 years of disease duration compared with noncarrier patients, suggesting that these risk variants may facilitate neurodegeneration with increasing disease duration.

Lrrk2 R1628P variant is a risk factor for essential tremor

Essential tremor (ET) and Parkinsons disease (PD) are two of the most common adult onset movement disorders with overlapping clinical features. PD patients with leucine-rich repeat kinase-2 (LRRK2) mutations may present initially with an ET phenotype. To address the possibility of a common genetic link between ET and PD, we examined the association between a common LRRK2 R1628P gene variant and ET. The LRRK2 R1628P was genotyped in ET cases and matched healthy controls. A total of 1277 subjects comprising of 450 ET cases and 827 controls were included. There were 40 heterozygote (GG to CG) variant out of 450 ET cases (genotypic frequency 8.9%) and 36 heterozygote variant (GG to CG, genotypic frequency 4.3%) and one homozygote variant (GG to CC) out of 827 controls. Subjects carrying the R1628P variant had a twofold increased risk of ET (p = 0.0035, OR = 2.20 and 95% confidence interval is 1.30–3.73). Using a case control methodology, we demonstrated an association between a known PD risk variant, LRRK2 R1628P, with ET. Subjects carrying the R1628P variant had twice the risk of developing ET. The sharing of a similar gene risk variant suggests a possible pathophysiologic link between PD and ET.

Mitochondrial serine protease HTRA2 gene mutation in Asians with coexistent essential tremor and Parkinson disease

The overlapping of essential tremor (ET) and Parkinson disease (PD) phenotype suggests that both conditions can coexist. Previously, we showed in our Asian population that ET patients have 5–10 times risk of developing PD [1]. Some disease-causing genes, such as LINGO1 and LINGO2, have been shown to modulate risk in both conditions [2]. A recent publication by Gulsuner and colleagues suggests that HTRA2 p.G399S may be responsible for hereditary ET, and homozygotes for this allele develop PD [3]. To address the possibility of a common genetic link between ET and PD, we examined the association between HTRA2 p.G399S and ET, PD and ET/PD. A total of 1777 individuals including 468 ET patients, 778 PD patients, 14 ET/PD patients and 517 age/gendermatched control subjects were included in this study. Consecutive patients with ET or PD who presented to tertiary referral centres and examined by movement disorders neurologists were included. The diagnosis of PD was based on the United Kingdom PD Society Brain Bank clinical diagnostic criteria without postmortem pathology examination [4]. The diagnosis of classic ET was based on the recommendations of the Consensus Statement of the Movement Disorders Society [5]. Healthy individuals of similar gender, race and age were included as controls. Subjects with evidence of other neurodegenerative diseases were excluded. Written informed consent from all the study subjects was obtained, and the work received approval from the institutional ethics committee. Genomic DNAwas extracted from blood samples, and HTRA2 p.G399S was genotyped by Taqman SNP genotyping (Life Technologies, Singapore). Fisher’s exact test for count data was used to compare the categorical and numerical variables. Statistical significance was defined at p<0.05. The median age of ET patients was 56 (15, 86) years, 67 (39, 92) years for PD patients, 68.5 (55, 82) for ET/PD patients and 51 (30, 89) years for controls. The sex ratio of ET, PD, ET/PD patients and controls were (male/female) 260/208, 446/332, 6/8 and 296/221, respectively. We found only one healthy control HTRA2 p.G399S heterozygote carrier (female, 78 years old), while no risk variant was identified in all our ET, PD, ET/PD cases and the rest of the controls (Table 1). ET and PD are two of the most common adult onset movement disorders with overlapping clinical features. Many studies indicate the possibility of a common genetic link between ET and PD. HTRA2 p.G399S mutation has recently been identified to be a risk factor with overlapping ET and PD. We examined the association of HTRA2 p.G399S mutation with essential tremor and Parkinson disease in Asians, and found that HTRA2 p.G399S is rare and does not appear to play a major role in subjects with Yin Xia Chao and Ebonne Yulin Ng contributed equally to this work.

Development of a human induced pluripotent stem cell (iPSC) line from a Parkinson's disease patient carrying the N551K variant in LRRK2 gene

Peripheral blood mononuclear cells (PBMCs) were collected from a clinically diagnosed 64-year old male Parkinsons disease (PD) patient with N551K variant in the LRRK2 gene. The PMBCs were reprogrammed with the human OSKM transcription factors using the Sendai-virus reprogramming system. The transgene-free iPSC showed pluripotency confirmed by immunofluorescent staining for pluripotency markers and differentiated into the 3 germ layers in vivo. The iPSC line also showed normal karyotype. This cellular model can complement in vivo PD models for pathophysiological studies and drug screening.

Reprogramming of a human induced pluripotent stem cell (iPSC) line from a Parkinson's disease patient with a R1628P variant in the LRRK2 gene

Peripheral blood mononuclear cells (PBMCs) were collected from a clinically diagnosed 59-year old male Parkinsons disease (PD) patient with R1628P variant in the LRRK2 gene. The PMBCs were reprogrammed with the human OSKM transcription factors using the Sendai-virus reprogramming system. The transgene-free iPSC showed pluripotency confirmed by immunofluorescent staining for pluripotency markers and differentiated into the 3 germ layers in vivo. The iPSC line also showed normal karyotype. This cellular model will provide a good resource for further pathophysiological studies of PD.

Vitamin D Deficiency and its Relation to Underlying Stroke Etiology in Ethnic Asian Ischemic Stroke Patients

Vitamin D deficiency increases stroke risk but there are limited data in relation to underlying stroke etiology. We examined the association of serum 25-hydroxyvitamin D (25-OHD) and stroke etiology in 144 Asian ischemic stroke patients (41% small artery, 14% large artery, 9% cardioembolic, 1% other and 35% undetermined etiology by TOAST classification). Serum 25-OHD was measured using Roche competitive electrochemiluminescence immunoassay from blood samples taken within 1 week of stroke. The majority had vitamin D insufficiency (50–100 nmol/L) (55%) or deficiency (<50 nmol/L) (40%). Patients with large versus small artery stroke had lower median serum 25-OHD (48·4 nmol/L, IQR 38·6–59·4 vs. 61·8 nmol/L, IQR 40·2– 77·8, P = 0·074) and higher vitamin D deficiency prevalence (60% vs. 36%, P = 0·057). After adjusting for age, gender, hypertension, hypercholesterolemia, diabetes, atrial fibrillation, smoking and ischemic heart disease, patients with large artery stroke had lower serum 25-OHD (P = 0·002) and were 3·5 times more likely to have vitamin D deficiency compared to small artery stroke patients (P = 0·022). This is the first cross-sectional study comparing serum 25-OHD between ischemic stroke etiologies. Our findings may be explained by a stronger relationship between vitamin D deficiency and large artery stroke. Alternatively, small cerebral arteries may be more susceptible to vitamin D deficiency as suggested in a case-control study of healthy female nurses showing a higher risk of small artery stroke among patients with lowest versus highest tertiles of serum 25-OHD, but no associated risk of large artery stroke (1). Longitudinal studies are needed to better understand the differential relationship between vitamin D deficiency and stroke etiologies. Furthermore, the benefit of vitamin D replacement may differ for large and small artery stroke prevention.

Serum uric acid level and its association with motor subtypes and non-motor symptoms in early Parkinson's disease: PALS study

OBJECTIVE Uric acid has been found to be potentially neuroprotective in Parkinsons disease (PD). We investigated the relationship between serum uric acid levels and both motor and non-motor features in a prospective early PD cohort study. METHODS Fasting serum uric acid levels were measured from 125 early PD patients. Demographic, clinical characteristics, motor and non-motor assessments were performed. Patients were categorized into three motor subtypes: tremor-dominant (TD), postural instability/gait difficulty (PIGD), and mixed. Non-motor symptoms were classified as present or absent based on the appropriate cut-offs for each non-motor instrument. RESULTS Most patients had TD (n = 51, 40.8%) and mixed (n = 63, 50.4%) motor subtypes, while a minority had PIGD (n = 11, 8.8%) motor subtype. The mean serum uric acid levels were significantly different between the three motor subtypes (p = 0.0106), with the mixed subtype having the lowest serum uric acid levels. Using the TD subtype as reference, patients with higher serum uric acid levels were less likely to have the mixed (OR = 0.684; p = 0.0312) subtype as opposed to the TD subtype. Uric acid levels were not significantly different between the TD and PIGD subtypes. For non-motor symptoms, higher serum uric acid levels were significantly associated with less fatigue (OR = 0.693; p = 0.0408). CONCLUSION Higher serum uric acid levels were associated with TD motor subtype and less fatigue in early PD, which could be related to its anti-oxidative properties. Uric acid could be an important biomarker for specific motor features and symptoms of fatigue in PD.

Targeted exome sequencing reveals homozygous TREM2 R47C mutation presenting with behavioral variant frontotemporal dementia without bone involvement.

To identify genes associated with frontotemporal dementia (FTD) in South-East Asia, targeted exome sequencing and C9orf72 genotyping was performed in 198 subjects (52 patients with FTD and 146 healthy controls) who were screened for mutations in 12 FTD-associated genes. We detected a homozygous TREM2 R47C mutation in a patient with behavioral variant FTD without bone cysts or bone-associated phenotype. Two novel nonsense GRN mutations in 3 FTD patients from the Philippines were detected, but no known pathogenic mutations in other FTD-associated genes were found. In 45 subjects screened for C9orf72 repeat expansions, no pathogenic expansion (≥30 repeats) was identified, but there was a higher proportion of intermediate length (≥10-29 repeats) alleles in patients compared with controls (8/90 alleles, 8.9% vs. 9/164 alleles, 5.5%). Overall, we detected a mutation rate of 7.7% (4/52 patients) in our cohort. Given recent findings of enrichment of rare TREM2 variants (including R47C) in Alzheimers disease, it is notable that we detected a homozygous TREM2 R47C carrier presenting with an FTD rather than an Alzheimers disease phenotype.

Screening for TMEM230 mutations in young-onset Parkinson's disease

TMEM230 gene mutations have been reported to be linked with Parkinsons disease (PD) recently. To investigate the prevalence of this gene in southeastern Chinese patients with PD, whole exome sequencing was performed in young-onset and familial PD patients and healthy controls in our Asian population. One heterozygous missense p.Phe121Ser mutation was detected in a healthy 76-year-old control subject and no other TMEM230 mutations were found in PD patients and controls. These data suggest that TMEM230 mutation might be a rare cause of Chinese familial and sporadic PD patients and a larger sample size will be needed to evaluate the association of TMEM230 polymorphic variants with PD.