[1] Chulalongkorn Univ, Fac Med, Dept Med, Chulalongkorn Ctr Excellence Parkinsons Dis & Rel, Bangkok 10330, Thailand
[2] King Chulalongkorn Mem Hosp, Thai Red Cross Soc, Bangkok 10330, Thailand
[3] Chulalongkorn Univ, Fac Med, Dept Med, Div Gastroenterol, Bangkok 10330, Thailand
[4] Univ Calif Los Angeles, Geffen Sch Med, Dept Neurol, Los Angeles, CA 90095 USA