Symptoms of Mental Retardation

Symptoms of MR include:

• Failure to meet intellectual developmental markers
• Failure to meet developmental milestones such as sitting, crawling, walking, or talking, in a timely manner
• Persistence of childlike behavior, possibly demonstrated in speaking style, or by a failure to understand social rules or consequences of behaviors
• Lack of curiosity and difficulty solving problems
• Decreased learning ability and ability to think logically
• Trouble remembering things
• An inability to meet educational demands required by school

It may be difficult to assess very young children for MR, so most clinicians will not give a definitive diagnosis of mental retardation to children under the age of two unless their symptoms are extremely severe and/or they have a condition that is highly associated with this condition (such as Down's Syndrome). Often, particularly with mild or moderate mental retardation, it is not until children have difficulties in school that symptoms are recognized.

Although factors such as cause and degree of severity vary from individual to individual, there are some common predisposing factors linked with MR. The first of these is heredity- for example, a child may suffer from inborn errors of metabolism (which occur when the body cannot properly turn food into energy, such as in the disorder Phenylketonuria), single-gene abnormalities (e.g., Fragile X syndrome, which is caused by the presence of a single non-working gene on the X chromosome), or various chromosomal aberrations (e.g., Down's Syndrome, which is caused by having an extra copy of chromosome 21).

Another cause of mental retardation is maternal exposure to teratogens, or outside elements that the mother may encounter during pregnancy that are damaging to the developing baby. Teratogens can include toxins (e.g., a mother who drinks or uses drugs during pregnancy), medications, infections or diseases. Other factors during pregnancy that can predispose an individual to developing MR are fetal malnutrition, prematurity, hypoxia (lack of oxygen), or trauma. Environmental influences may play a part as well; for example, children who are raised in extremely impoverished environments who lack social, linguistic, or other forms of necessary stimulation may develop MR. In addition, some other mental disorders may predispose someone for Mental Retardation, such as an Autism Spectrum Disorder (neurological disorders that cause severe communication, language and social deficits) or other Pervasive Developmental Disorders (delays in the development of basic communication and socialization skills). Finally, general medical conditions acquired in infancy or childhood may also cause Mental Retardation. These can include infections such as meningitis or measles that are not properly treated, or exposure to toxins (e.g., mercury or lead).

Over the past few decades, there have been many changes in the definition of Mental Retardation. These changes have occurred due to a variety of factors, ranging from the scientific acquisition of new information to changes in clinical practice or beliefs (e.g., an enhanced awareness that many individuals with MR can highly benefit from appropriate therapeutic interventions). As a result, modifications in IQ score categories as well as changes in name (prior to the name mental retardation, the proper term was "mental deficiency") have occurred across time. There have also been changes regarding societal attitudes and treatment of individuals with MR (for example, in the early part of the 20th century, MR was believed to be a disease with a specific "cure", and there were "training schools" designed to cure mental retardation), as well as an expansion of available services. We now have better home-based care, group housing, and therapies aimed at helping individuals to improve their life skills.

According to the DSM, approximately 1.25%-3% of the population has some form of mental retardation. Among school-age children, prevalence rates appear to be between 0.3% and 2.5%. Mental retardation is more common among older children (ages 6-10) than younger children (under age 6), and is also more common in boys than in girls.