A palmar atd angle greater than 45deg; is a specific appearance of mental retardation congenital dysgenesis (21 III sign, Down syndrome) due to chromosomal abnormalities. This 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 hindered intellectual development, accompanied by difficulties in social adjustment as the main feature before maturity (usually before the age of 18). The cause of its pathogenesis are both genetic and environmental factors, how to prevent hereditary palmar atd angle greater than 45°? Mental retardation is difficult to reverse once it occurs, so emphasis should be placed on prevention. Monitoring of hereditary diseases, good perinatal health care, prevention and early treatment of central nervous system diseases are important measures for prevention. Some developed countries have implemented blood biochemical screening for several genetic metabolic diseases for all newborns based on special laws, providing conditions for early prevention and treatment. (1) Good premarital checkups Pregnancy care and family planning: insist on routine prenatal checkups to prevent difficult and emergency deliveries, and in remote areas, especially to prevent damage and infection of the central nervous system in infants and children. It is recommended that iodine be administered to early pregnant women in areas where endemic goiter is endemic, and that newborns be tested for micro cord blood T3, T4, and TSH levels, and those suspected be monitored to prevent the occurrence of endemic cretinism. (2) Prevention of hereditary diseases If there are parents with obvious hereditary diseases or children with hereditary diseases, or if there is an advanced maternal age, genetic counseling can be conducted, and if necessary, prenatal diagnosis can be made, and if the fetus is diagnosed with hereditary diseases, the pregnancy can be terminated in time. The purpose is to detect suspected cases for further diagnosis and to avoid the birth of a second child with the disease.