Mongolian idiocy, also known as trisomy 21 syndrome, is a form of mental subnormality due to a chromosome defect (there are three no.21 chromosomes instead of the usual two). The disease is divided into three types: 21-trisome type, mosaic type and translocation type. It is reported that the incidence of the disease is 0.32-3‰ in foreign countries and 0.56-0.64‰ at home.
The pathogenesis of the disease remains unclear. It is generally believed that viral infection before or at the early stage of pregnancy, autoimmune disease, repeated use of chemical abortifacient in pregnancy, administration of such drugs as contraceptive, antipyretic analgesic, neuroleptic, antiepileptic, antithyroid drug, progesterone and adrenocortical hormone, or exposure to radioactive rays and to certain chemical substance may be possible etiological factors. The incidence of mongolian idiocy is related to the age of pregnancy of mother. Report from Shanghai showed that the age group of less than 30 years had an incidence of 0.1‰, that of 30-39 years had an incidence of 1.45‰ and that of more than 40 years had an incidence of 12.8‰. Recently, there is also report that father's exposure to some mutagens such as beryllium, cyclophosphamide, etc. may also lead to development of mongolian idiocy.
The main pathological change of mongolian idiocy is the abnormal development of cerebrum, brain stem and cerebellum, manifested as reduction in volume

Author's unit: Guangdong Gaoming Medical and Medicinal Institute of Encephalopathy, Gaoming, Guangdong 528500

and weight, asymmetric development of cerebrum and cerebellum, thinning of cortex, broadening and deepening of cerebral sulci, narrowing of gyri, hypothalamic hypoplasia, and particularly the marked shrink of posterior temple and superior temporal gyrus. Studies at home and abroad have shown that all patients with mongolian idiocy aged more than 35 years have pathological changes similar to Alzheimer's senile dementia.
The clinical manifestations of mongolian idiocy are feeblemindedness, characteristic facies, hypomyotonia, deformity of fingers and toes, abnormal cleavage lines and malformation of heart. The main physical features are a slightly oblique slant to the eyes, a round head, flat nasal bridge, fissured tongue, exophthalmus, ectropion of thick lower lip, cyrturanus, small round ears, low hair line, abnormalities of the palms including single transverse creases and characteristic ridges, osteodysplasty of little and middle fingers, a tongue often stuck out, salivation, foolish laugh, short stature, lack of the twelfth pair of rib, maldevelopment of male genital organs, often with undescended testis and improcreance, delay of female sexual maturity, delayed menarche, involuntary movement and ataxia in a small number of patients and convulsion in part of the patients, feeblemindedness is one of the main characteristics of the disease.
The prognosis of the disease is unfavourable, abortion occurs in 70% of the cases before delivery, the average life span of the affected infants is short, the mortality rate is the highest one year after birth, and about two thirds of the affected infants die before 10 years of age. The length of life span depends on complications, the main lethal causes are congenital heart disease and leukemia, followed in turn by malformation of digestive tract, infection, etc.
Mongolian idiocy is the chromosomal disease with the highest morbidity rate among newborns, it has greater hazard to the whole society and is a big burden of the patient's family. Prophylactic measures may be taken: (1) Many of the above-mentioned features are present at birth, enabling an early diagnosis, the condition can also be diagnosed prenatally by amniocentesis. (2) The various above-mentioned pathogenic factors should be avoided, child bearing should be of right age, and prenatal diagnosis should be given to infants at high risk. (3) Sterilization should be practised for father or mother who is the carrier of balanced translocation or the person of t (Dq 21 q) translocation. (4) One of the parents is mosaic, mosaic type is generally believed to be hereditable. (5) Exposure to various gene mutagens should be decreased as far as possible, the use of chemical abortifacient in pregnancy or the oral administration of sulfonamides should be avoided, infectious hepatitis should be prevented and exposure to x-ray should be avoided.
At present, there are no specific remedies for the disease, long-term patient education and social behaviour training are recommended. Chinese drugs activate and nourish nerve cells and improve functions of central nervous system, thus improving the social adaptive capacity and life quality of the patients.