According to the latest UNFPA survey, mentally retarded children account for approximately 5.4% of the total child population. Of these, 3% have an IQ below 70 (diminished intelligence) and 8% have an IQ between 70 and 79 (critical intelligence). There are many reasons for the formation of mental retardation previously identified, except for a few children who have a single cause, the majority are caused by multiple factors. The first is prenatal factors, including genetic factors, maternal illness and medication during pregnancy, maternal emotional depression during pregnancy, maternal smoking and alcohol abuse during pregnancy, the effects of X-ray radiation, and advanced maternal age. The next factors are the delivery process, such as asphyxia and hypoxia, intracranial hemorrhage, prematurity and low weight (within 260 days of pregnancy and weighing less than 2,500 grams), poor health status during delivery, and postpartum factors, such as pathological jaundice, traumatic brain injury, brain diseases, high fever and convulsions, various kinds of poisoning, etc. With the development of medical science, the causes of mental retardation in children are constantly being discovered. The following key factors have been identified in medical research to date: i. Embryonic period The first peak of brain cell development occurs at 3 months of gestation, and at 4-5 months, brain cells are still at their peak and occasional memory traces appear. at 6 months, grooves appear on the surface of the brain and the hierarchical structure of the cerebral cortex is basically set from the embryonic period. At this stage, the main cause of fetal mental development is the mother’s physiological state. Mutation of the MTHFR enzyme, which converts folic acid into a useful nutrient in the mother’s body, and hypothyroidism can affect the fetus’ mental development. At this time, conventional folic acid supplementation is ineffective or inefficient, and intensive supplementation of methyltetrahydrofolate and VB12 and VB6 is needed. Second, childhood The child’s brain develops fastest before the age of 3, and 80% of the brain development has been completed before the age of 5. The brain off the ball continues to develop in children aged 7-8, and the brain weight increases from 1200 grams at the age of 6 to 1300 grams, which is close to the brain weight of adults, and in children aged 9-16, the brain weight does not increase much. Therefore, the early development and cultivation of children’s intelligence is of decisive importance. All people’s brain intelligence is formed before the age of 3, so why later people grow up some will be more intelligent, some people in general, smart people are more perfect brain development in infancy. At this stage, there are more reasons that affect the development of fetal intelligence. Among them are congenital hypothyroidism, phenylketonuria, Down’s syndrome and other rare genetic diseases. The rapid development of medical science in recent years has made it clear that the genetic mutation of type II deiodinase and hypothyroidism are involved in the intellectual development of more children. If a child has a mutation in the type II deiodinase gene, along with acquired hypothyroidism, these two factors are superimposed on one child and act simultaneously to cause the child to have an IQ score of less than 85 (mental retardation). Neither of these two factors, alone, is abnormal and does not result in an impaired IQ in children. In the UK, 13.5% of children are type II deiodinase gene mutants. Some of these children also have hypothyroidism, which causes 3.71% of children to become mentally retarded. By the time these children are found to be mentally retarded at the age of 7-9 years, they have missed the optimal intervention period. Considering that 5.4% of children worldwide have unexplained mental retardation, it is important to find the cause of 3.71% of children with mental retardation and to take timely interventions to promote the intellectual health of children. In China, about 23% of children are type II deiodinase gene mutants, and more children are involved. These children are also likely to be mentally retarded if they also have hypothyroidism. Our newborns are screened for blood free T4 levels at birth, but this only screens for the child’s congenital T4 level, not later into adulthood. After birth, there are many factors that can cause free T4 levels to drop, such as diet, environment, and medications. These acquired factors lead to decreased T4 levels and are the main cause of childhood mental retardation. Therefore, children need to be screened for the type II deiodinase gene first, and for children with genetic abnormalities, their blood free T4 levels need to be monitored continuously (once or twice a year until the age of eight) for timely intervention in case of abnormalities. Third, the later intellectual growth The later growth is not the development of intelligence, but cognitive power. 6-9 years old, is the peak of the child’s cognitive development. It is now clear that the 169C15orf60 (G>A) gene (chromosome 15, gene 60 open reading frame), is associated with the child’s cognitive ability. Children with this gene, type AA, have a slightly thinner left cerebral cortex than types AG and GG, resulting in slightly lower verbal and nonverbal IQ scores. However, it does not affect overall IQ. For such children, intensive verbal and behavioral training should be provided to improve certification. Treatment: 1. Type II deiodinase gene mutation with hypothyroidism T4: We cannot change the child’s gene, but we can treat the child by taking thyroxine to improve the thyroid function and make the child’s intelligence develop healthily. 2. People with MTHFR 677 and 1298 gene mutations take nutritional supplements such as tri-generation folic acid to cross over the genetic defect and directly replenish the active metabolites and neurotrophic factors required by the body. 3. 169C15orf60 (G>A) mutants should have intensive language and behavior training to improve cognitive ability.