Condition in which a person has failed to attain the intelligence qoutient (IQ) range appropriate for his or her age. Symptoms vary from slightly disturbed to mentally defective. There are many causes: hereditary disorders, infection before and after birth, nutritional deficiency (including iodine and vitamin deficiency), lack of oxygen in the brain (anoxia), and injuries. Environmental factors such as education, physical and mental neglect (affective deficiencies) can also be significant. Often the cause cannot be found, and the symptoms are not always immediately perceptible, so that all too often slight deficiencies are only discovered and dealt with when it is too late. Precise monitoring of the development of babies and young children is important: motor backwardness is often a sign of mental problems. If physical abnormalities are discovered an impression of the degree of backwardness can be gained from IQ and other psychological tests. Support and advice from those around them are important to the parents of a backward child. Placing the child in a home is often difficult, but necessary for child and family.