Classification of mental impairment on the basis of causes.. Primary mental impairment, such as family mental impairment and dark family dementia. Secondary mental impairment, such as brain aspiration and squamous conditions

Classification based on causes includes:
A - Initial mental impairment: It includes cases where mental impairment is due to genetic factors such as gene errors, chromosomes, etc. It occurs in about 80% of cases of mental impairment. Examples include family mental impairment and dark family dementia.
B - Secondary mental impairment: It includes cases where mental impairment to environmental factors lead to the nervous system at any stage of growth after the process of fertilization, and occurs in about (20%) of cases of mental impairment. Examples of cases include brain aspiration, and cases of bronchitis.