Modern Medical Explanations for Mental Retardation

By the middle 1800s, the cultural tide was turning away from the older view of mental retardation as a divine punishment and toward a medical understanding.

John Langston Down is well known for his classification of a genetic disorder of chromosome 21 (Trisomy 21) that carries relatively similar characteristics among its carriers. His 1866 paper, "Observations on the Ethnic Classification of Idiots," postulated that physical ethnic characteristics could help physicians to pinpoint different conditions.

Down noticed similar characteristics among a certain group of individuals. However, he did not have the technology or the information necessary to understand that the characteristics were expressions of an underlying genetic disorder. This key genetic information would be discovered later by other researchers. John Down's description of individuals with Trisomy 21 included a flat face and distinctively almond-shaped eyes placed widely apart. He thought these individuals looked like Mongolian people (e.g., Asians), which was inaccurate. As noted above, the term "Mongolian" was used for years, until the World Health Organization renamed Mongolian syndrome as Down syndrome in the 1960s.

William Ireland attributed most of the cases of mental retardation to heredity in an influential article titled, "On the Diagnosis and Prognosis of Idiocy and Imbecility," published in the June 1882 edition of the Edinburgh Medical Journal. He associated mental retardation with the existence of neurotic disorders, insanity, and relatives with mental retardation. Ireland also believed that illnesses such as consumption and scrofula could contribute to the occurrence of mental retardation. He further postulated that nervous conditions such as epilepsy might result in mental retardation. Ireland suggested that infant tantrums (usually occurring during the teething stage of infant development) might cause irreversible brain injury.

Ireland's observations included many physical features associated with mental retardation, specifically that retarded people tended to have a generally smaller head size than normal. He noted that there were many deformities in the palate and in the teeth. His descriptions of cleft palates and widely spaced teeth were quite detailed.