Hypophrenia, a group of diseases, refers to the condition that the general intelligence level is obviously lower than that of the healthy children of the same age, accompanied by adaptive behavior defect during developmental stage. It is marked by retarded development of action and speech, difficulty in study, social maladaptation as well as psychological and emotional disturbances. The disease belongs to the categories of "wuchi" (five kinds of retardation), "wuruan" (five kinds of flaccidity), etc.

In TCM. The causes of the disease include biomedical factors as well as social, psychological and cultural ones. The former refers to the fact that the unfavourable influence of various factors on the brain during the cerebral development (prenatal and perinatal periods) makes the brain unable to develop into the right level, ultimately affecting the intelligence; the latter refers to the fact that cultural deprivation, improper education and breeding, sensory deprivation, etc. may make the postnatal information input inadequate or improper, accordingly affecting the intelligence level.