Mental retardation is a developmental disorder characterized by a significantly below-average intelligence (an intelligence quotient [IQ] below 70) and an inability to function in and adapt to daily life without assistance. According to the Centers for Disease Control and Prevention (CDC), mental retardation affects about 12 out of every 1,000 schoolchildren in the United States, making it the most common developmental disorder.

Any brain injury or developmental problem in the brain may result in mental retardation. Such problems may occur before, during or after birth. Prenatal causes of mental retardation include genetic disorders (e.g., Down syndrome), infections in the mother or fetus during pregnancy (e.g., rubella, chickenpox) and exposure to various harmful substances (e.g., medications, alcohol, recreational drugs, radiation) during pregnancy. Serious infections in infancy (e.g., meningitis, measles) and serious head injuries (e.g., head trauma, shaken baby syndrome) in infants and children can also cause mental retardation. However, in many cases, the cause of mental retardation is not known.

Children with mental retardation tend to have trouble learning. They develop many skills and reach many developmental milestones at a later age than other children. These children may have trouble learning in school, especially difficulty solving problems or thinking logically.

Diagnosis of mental retardation relies on an evaluation of how well the patient thinks and functions. It includes standardized intelligence tests and an evaluation of how well the child functions in daily life. In general, the more severe the retardation, the earlier it is noticed. Mild cases may not be detected until the child begins school.

All children with mental retardation require an ever-changing educational and training program that is individualized especially for their abilities and needs. Young children with mental retardation may need assistance developing certain basic skills (e.g., motor skills, speech and language skills). Children with mental retardation require a special setting for education, including individual attention and support. However, those with mild retardation may be able to attend regular classes with other children their age with special assistance from a teacher or aide, both in and out of the classroom.

As a child with mental retardation enters adolescence, their education may focus more on developing independent living skills, such as work skills, using public transportation, social adaptation and managing money. Adolescents with mild retardation can usually look forward to living at least semi-independently once they reach adulthood. Those with more severe forms may require more direct care from a family member or other caretaker throughout their lives.

Many methods to prevent mental retardation begin before and during pregnancy. These include genetic counseling to evaluate a couple’s risk of having a child with mental retardation. It is also important to ensure that a woman is healthy both before and during pregnancy. When an infant is born, newborn screening tests are used to detect any conditions that need to be treated (e.g., phenylketonuria). After this point, mental retardation can often be avoided by avoiding brain injuries.