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The mental retardation is one of the factors affecting the evolution of language development, and specialized studies to indicate the multiplicity of reasons for its occurrence,
The causes of mental disability are classified into nine groups and noted that some of these reasons may occur before birth, during birth and some others after birth, and these reasons include:

2- Cross Brain Diseases: It is the most important meningitis and inflammation and brain tumors.

 3- Trauma or Physical Agents: Kasabat head as a result of accidents or falls from high places, and frequent exposure to childhood diseases, especially high fever.
4- Unknown Prenatal Influences: Introduces including genetic factors and health status of the mother during pregnancy and pharmacological doses dealt with or exposure to the amounts of harmful radiation, also falls within these factors, the psychological state of the mother during pregnancyMetabolic
5- Nutrition: One of these disorders is known as the status of PKU, as that malnourished pregnant and the baby of the factors that may affect

6- Sensory Impairment: Included among these injuries visual and auditory difficulties may lead to such extreme deprivation in experience, which could affect the growth of mental ability.

 7- Psychiatric Disorder.

8- Environmental Influences: a combination of factors related to the cultural and economic status of the family
9- Chromosomal Abnormality: refers to a bug that exposed the process of a fertilized egg splits).