a group of diseases that is characterized by defective mental development. Oligophrenic diseases can be congenital or acquired in early childhood. Oligophrenia can result from diseases in the mother during pregnancy, including syphilis, rubella, toxoplasmosis, vitamin deficiencies, thyroid diseases, and diabetes mellitus. Other causes of oligophrenia include Rh-incompatibility of maternal and fetal blood, trauma, asphyxia of the fetus during childbirth, residual effects of meningitis, and encephalitis. Oligophrenia can also be inherited, as with Down’s syndrome (seeDOWN’S SYNDROME). Feeblemindedness is often accompanied by sequelae of focal lesions in the brain, including seizures, motor disturbances, and sensitivity. Abnormalities in physical development are also common.

The mental changes that occur in oligophrenia are stable and do not progress. This disease course differentiates oligophrenia from other mental diseases that originate in childhood but proceed with progressive feeblemindedness and an increasingly complex clinical picture.

Three degrees of oligophrenia are distinguished for purposes of raising, treating, and educating oligophrenics: idiocy is characterized by severe feeblemindedness, imbecility by moderate feeblemindedness, and moronity by mild feeblemindedness (seeIDIOCY). These degrees of mental inadequacy apply regardless of the etiology of the condition. The mental functioning of idiots is essentially limited to reflex acts. Imbeciles can learn how to tend to some of their own needs. Morons are able to acquire some knowledge and to master some occupational skills despite their poor judgment, narrow perspective, poor vocabulary, weak memory, and the slowness and concreteness of their thought processes.

Treatment of oligophrenia is mostly symptomatic, with pedagogical influences and the quality of care being of the utmost importance.