There are many reasons for this - prematurity, chronic illness, physical disability, poor stimulation, etc. The mentally retarded child has difficulty in learning, remembering, and using ideas and skill. This affects not only the ability to learn academic skills such as reading and arithmetic, but also the ability to function in everyday life, to communicate with others and to care for oneself. Unlike developmental delay, mental retardation is a permanent condition that can be helped by special training, but not cured.
Mental retardation has many possible causes.
Mental retardation can also be related to infection or injury during the birth process, to prematurity, and to breathing problems or brain injury after birth. Sometimes mental retardation is the result of physical abuse, severe neglect, or lack of opportunity to learn. Parents are often the first to suspect that their child has developmental problems. Sometimes, the problems are first observed during a medical examination. Doctors sometimes prefer to watch the child over time, to be sure that the problem is not a normal variation.