True dementia can be divided into two broad categories

True dementia according to their origin can be divided into congenital and acquired Alzheimer's dementia that two major categories. Dementia is congenital mental retardation, It refers to the time of birth or fetal period onset, brain damage or inherited metabolic diseases, the development of the brain is obstructed, the development of smart is not a situation. Along with the growth of age, significantly lower than its peers intelligent children. Acquired dementia is that the onset in childhood or adulthood, patients with normal brain development was later due to a serious illness caused by the defect intelligent another situation. The large number of patients with congenital dementia, their average domestic investigation prevalence rate of 4.3 per 1,000, some scholars even believe that the crowd at any time in almost 1% of all people with mental retardation, it is considered disease caused human disabled the largest category of disease. The male than female patients about more than twice. In congenital dementia due to various reasons, generally summarized as follows: 1. Genetic abnormalities including chromosomal aberrations, such as gene mutation. 2. Infection factors infection especially viral infection occurred in the first three months of pregnancy for fetal damage from the most serious. Early perinatal and infant various infections, such as bacterial, tuberculosis or purulent meningitis, and various viral infections may cause brain damage and mental retardation. 3. Physical injury include: ① mechanical injury; such as dystocia delivery of the child or because of accidents such as collisions, such as brain injury caused. ② radioactive damage: early pregnancy such as abdominal X-ray irradiation to accept may cause congenital malformations and accompanied by mental retardation. 4. Easements such as chemical damage caused by certain drugs deformities, such as lead poisoning. 5. Premature babies and low birth weight babies. 6. Endocrine dysfunction such as congenital hypothyroidism. 7. The vast majority of neonatal jaundice caused due to mother-to-child blood group incompatibility caused by neonatal hemolytic. 8. Psycho-social factors of the development of brain function of children need a suitable external stimulation, in the early years of life on the psychological and social factors also affect intellectual development. If children live in a lonely time of the environment, because of a lack of abundant thorns and adequate care, can significantly lower intelligence in children. Many such families, there are one or more mental retardation, they think this is the interaction of genetic and environmental factors the results.