1. Brain degenerative diseases: The most common is Alzheimer’s disease dementia, which is also called early senile dementia when it develops in pre-mature old age. There are also Pick’s disease, Parkinson’s disease dementia, etc. 2, cerebrovascular disease: common are multiple cerebral infarction dementia, subcortical vascular dementia, etc. 3, genetic factors: the mode of inheritance is still unclear. Some studies believe that it is dominant genetic inheritance; some studies believe that it is recessive genetic inheritance; some believe that it is polygenic autosomal recessive inheritance, and the inheritance is affected by environmental factors and mutations of genetic factors. Some studies have also concluded that Alzheimer’s disease is non-genetic, such as vascular dementia, which is not directly related to heredity.