The MAG expression promoter of the present invention contains a compound of the formula (I)
 wherein each symbol is as defined in the specification, an optically active form thereof or a pharmaceutically acceptable salt thereof. As a compound of the formula (I), 4-[α-hydroxy-5-(1-imidazolyl)-2-methylbenzyl]-3,5-dimethylbenzoic acid is exemplified. The MAG expression promoter of the present invention is useful as an agent for the prophylaxis and/or treatment of a disease of mammals inclusive of human, which mainly presents hypomyelination, further, dysmyelination or demyelination.
                            本发明的 MAG 表达启动子含有式(I)化合物
 其中各符号如说明书中所定义,是其光学活性形式或其药学上可接受的盐。作为式(I)的化合物,以4-[α-羟基-5-(1-
咪唑基)-2-甲基苄基]-
3,5-二甲基苯甲酸为例。本发明的 MAG 表达启动子可用作预防和/或治疗哺乳动物(包括人类)疾病的药物,这些疾病主要表现为髓鞘功能减退,进一步表现为髓鞘功能障碍或脱髓鞘。