Short inward curvature of the terminal finger or only two knuckles are the clinical symptoms of mental retardation. Mental retardation is a group of diseases caused by genetic factors, environmental factors or psychosocial factors during the developmental stage before the age of 18, and is mainly characterized by significant mental retardation and social adaptation deficits. There are two main causes of mental retardation: (1) Biological factors (1) Genetic factors (1) Chromosomal aberrations: including changes in the number and structure of chromosomes. Changes in number include polyploidy and aneuploidy, and changes in structure include chromosome breaks, deletions, duplications, inversions and translocations. For example, Down syndrome, fragile X syndrome, Turner syndrome, etc. With the development of molecular biology techniques, the study of genes associated with mental retardation has received much attention in recent years. Currently, more than 20 genes related to X-linked mental retardation (XLMR) have been reported, and the JARIDI C (Jumonji, AT-rich, interactive domain 1C) gene is one of them. The JARIDlC gene is a member of the highly conserved ARID family, which encodes a protein involved in a series of biological effects such as chromatin remodeling, cell proliferation and division, individual development, and regulation of gene transcription, and is abundantly expressed in the brain, thus playing an important role in the normal development and maintenance of normal function of the nervous system. It has been found that small mutations within this gene such as insertions, deletions, and translocations can cause mental retardation, thus becoming one of the current hot spots for research on mental retardation and human cognitive ability related genes. (ii) Monogenic genetic disorders: such as phenylketonuria, tuberous sclerosis, neurofibromatosis, galactosemia, familial microcephaly, etc., which often cause mental deficits. (iii) Polygenic diseases: Polygenic diseases are the result of multiple genes acting together. Although each gene acts individually and minimally, there is a cumulative effect, which, together with the influence of environmental factors, determines the susceptibility of an individual to a trait or disease. If the susceptibility is high and exceeds the threshold for the disease, it will lead to the disease. Common polygenic genetic disorders with mental retardation are: neural tube malformations, mental retardation without clinical symptoms, i.e. familial mild mental retardation without meditative organic features. (2) Maternal exposure to harmful factors during pregnancy: ① viral and toxoplasma infections: among viral infections, rubella virus, herpes simplex virus, cytomegalovirus have the greatest impact on the fetus, and if the infection occurs in the first trimester of pregnancy, the damage is more severe. ②Drugs and chemical toxins: such as salicylates, diazepam, Librium, phenytoin sodium, progesterone, and lead, mercury, alcohol, etc. ③Radiation. ④Maternal health condition: mother suffering from serious physical diseases during pregnancy, such as hypertension, heart disease, diabetes, severe anemia, severe malnutrition, iodine deficiency, etc. may affect fetal development and lead to mental retardation. The mother’s gestational age is more than 40 years old, which may lead to chromosomal aberrations. ⑤ Insufficient placental function. (6) emotional factors: long-term anxiety, depression or acute trauma during pregnancy may adversely affect the development of the central nervous system of the fetus. 2, intrapartum factors: intrauterine distress, birth asphyxia, birth injuries resulting in cranio-cerebral injury and intracranial hemorrhage, nuclear jaundice, etc. may lead to fetal and neonatal central nervous system damage, resulting in mental retardation. Premature infants, very low birth weight children are often affected by the development of the central nervous system, which may appear behind the intellectual development. 3, postnatal factors: central nervous system infection, severe cranial trauma, various causes of cerebral hypoxia, metabolic or toxic encephalopathy, severe malnutrition, hypothyroidism, heavy metal or chemical poisoning, cranial suture premature closure, etc. may lead to mental retardation. For example, lead is the most prevalent neurotoxin in the environment, and studies have shown that there is a significant association between blood lead levels and cognitive deficits in childhood, but excessive blood lead cannot be easily taken as the main cause of mental retardation. Psychosocial factors: severe social isolation in early childhood due to poverty or neglect or abuse, lack of benign environmental stimulation, and lack of cultural and educational opportunities can lead to mental retardation.