Palmar atd angle greater than 45deg; is a special appearance of mental retardation congenital stupidity due to chromosomal abnormalities (syndrome 21III, Down syndrome). The symptom is present in approximately 40% of patients. Mental retardation (mentalretardation) is a syndrome in which an individual’s intellectual functioning is significantly lower than that of his or her peers due to mental retardation, impaired or impeded intellectual development prior to developmental maturity (usually defined as before the age of 18 years), accompanied by difficulties in social adjustment as the main feature. There are two main causes of mental retardation: 1. genetic factors; 2. environmental factors. Genetic factors include chromosomal aberrations and inherited metabolic single-gene disorders; environmental factors include harmful factors during pregnancy and childbirth, and harmful factors during neonatal and infancy. In addition, due to early cultural and emotional deprivation, lack of appropriate stimulation, long-term neglect, isolation, living in remote and poor, culturally backward, inaccessible areas. The degree of mental retardation due to psychosocial factors is generally mild. Once the unfavorable factors are eliminated, it is possible to improve the level of intelligence, the improvement depending on the age of the child, the degree of impairment and the conditions provided by the environment in which he or she lives.