Our knowledge of the significance of nutrients in the treatment of degenerative diseases of tne nervous system and muscle is poor. In addition to scarcity of vitamins in the diet, a tissue-specific vitamin deficiency may underlie these diseases. Gene defects of folate or thiamine transport proteins cause severe pediatric encephalopathies that can partly or completely be prevented with early vitamin therapy. In other words, a vitamin deficiency restricted to an individual tissue develops in degenerative diseases despite a well-balanced diet. The focus is especially on B vitamins, the effects of which as regulators of cell growth and energy metabolism are only beginning to be understood.