1. Department of Medicine, College of Medicine, King Saud University, P.O. Box 2925 (38), Riyadh 11461, Saudi Arabia
2. Clinical Chemistry Unit, Department of Pathology, College of Medicine, King Saud University, P.O. Box 2925 (30), Riyadh 11461, Saudi Arabia
3. Department of Medical Biochemistry, Faculty of Medicine, Ain Shams University, Abbassia, Cairo 11566, Egypt
4. National Neuroscience Institute, King Fahad Medical City, Riyadh 11525, Saudi Arabia
5. Neurology Department, King Faisal Specialist Hospital & Research Center, Riyadh 11211, Saudi Arabia