Mental challenge has been defined as deficits in cognitive and adaptive functioning with the onset during development. mentally challenged can be caused by any condition that impairs development of the brain before birth, during birth or in the childhood years. 

The causes of mentally challenged are many. There are over 250 known causes of mentally challenged. In few cases of MR there is a known biological cause. But in the majority of cases, the cause is unknown. Here MR could be caused by the factors other than biological ones, such as psychosocial factors.

The various causes of mentally challenged include chromosomal and genetic defects, disorders that occur as a foetus develops during pregnancy and also the problems during or after birth. Some cases of mentally challenged have multiple causes.

Knowledge of the causes of mentally challenged is essential for all groups involved in the care of people with MR. However, it must be recognized that only a small percentage of people with MR have identifiable causative factors or can be placed within a common group or syndrome.

Importance of knowing the Causes
It is important to have knowledge of the causes for a number of reasons such as:
1.	The need for the parents, caretakers and individuals to understand why mentally challenged has occurred.
2.	The individual and also the family's basic right to know.
3.	Relief from uncertainty regarding the cause of the disabilities.
4.	Relief from the guilt that family and/or social factors were the cause of the mentally challenged.
5.	Facilitating the resolution of grief.
6.	Focusing towards the future.
7.	Initiating interventions relevant to strengths and needs.
8.	Potential for identifying with and belonging to a support group.
9.	Essential genetic counselling where ever appropriate, for the entire extended family.
10.	Risks for other family members that MR may re-occur in their offspring.
11.	Possible treatment of specific conditions.
12.	Identification of complications of the condition and an understanding of how the condition may develop over a period of time.

Background knowledge of the causes of mentally challenged can
	Enable staff in hospitals and community settings to provide the most appropriate care.
	Play a role in the prevention of mentally challenged at a primary and secondary level.
	Help and support the families of people with MR.
	Give meaningful advice and counselling.
	An understanding of the causes of MR -genetic, toxic, trauma or infection etc. can enable the professionals/families to take measures to prevent the reoccurrence of mentally challenged in subsequent pregnancies.