Nutritional and systemic metabolic disorders.

Vitamin deficiency disorders display a wide variety of neurologic signs and symptoms, the pathogenesis of which is not clearly understood. Metabolic encephalopathies (hepatic, hypoglycemic, and uremic) have to be considered in the differential diagnosis of patients with cognitive impairment, motor disturbances, psychiatric symptoms, seizures, and neuropathies. Calcifications (vascular wall and parenchymal) occur in the normal aging brain and in neurodegeneration; some associated genes are already described.