What is Mental Retardation?
Mental retardation is a condition characterized by limitations in performance that result from significant impairments in measured intelligence and adaptive behavior that occurs before age 18.

This is a condition of both clinical and social importance.

Introduction

Mental retardation also confers a social status that can be more handicapping than the specific disability itself. The determinants of competence in any individual are complex and multifactorial. Regardless of his or her level of performance, each child's abilities are influenced by both the integrity and the maturational status of the nervous system and by the nature and quality of his or her life experience. Some children sustain significant neurological insults and develop normal skills. Others manifest severe cognitive impairment despite the absence of recognizable focal neurological findings or historical evidence of significant risk factors for CNS dysfunction.

Incidences

Approximately 3% of the general population has an IQ less than two standard deviations below the mean. It has been estimated that 80-90% of persons with mental retardation function within the mild range, whereas only 5% of the population with mental retardation is severely to profoundly impair.

Causes

Table 1 lists potential contributing factors in the pathogenesis of mental retardation from preconception through the early childhood years.

Clinical Menifestation

• Failure to meet intellectual developmental markers
• Persistence of infantile behavior
• Lack of curiosity
• Decreased learning ability
• Inability to meet educational demands of school

Table 2 lists a number of atypical physical features that have been associated with a higher incidence of mental retardation.

Mental retardation may suggest syndromes that are associated with mental retardation should be identified at birth or during early infancy e.g. Down syndrome, fetal alcohol syndrome, and primary microcephaly are examples of such conditions.

Deviations in normal adaptive behaviors depend on the severity of the condition. Mild retardation may be associated with a lack of curiosity and quiet behavior. Severe mental retardation is associated with infantile behavior throughout life.

Although youngsters with severe impairment show marked delays in psychomotor skills in the first year of life, children with moderate retardation typically exhibit normal motor development and present with delayed speech and language abilities in the toddler years. Mild retardation, on the other hand, may not be suspected until after entry into school, although participation in an organized preschool or child-care program can highlight discrepancies in the performance of a young child with significantly sub average abilities.

Classification
Recently categories of mild, moderate, severe and profound retardation have been replaced by a classification system that specifies four levels of support systems needed for daily functioning (i.e., intermittent, limited, extensive and pervasive).

Mental efficiency

Ultimately, the diagnosis of mental retardation requires confirmation of significantly sub average general intellectual functioning (i.e., an IQ standard score of 70-75 or below) in association with deficits in two more of the following ten adaptive skill areas: communication, self-care, home living, social skills, community use, self-direction, health and safety, functional academics, leisure, and work.

Diagnosis

• Parental report, and, caregiver or teacher report gives the initial clue that this child needs further evaluation.
• A comprehensive history, physical examination, and laboratory evaluation often lead to identification of specific factors.
• This finding follows developmental assessment and systemic evaluation. A range of laboratory studies must be considered in the medical evaluation including karyotypes.
• It should be kept in mind that a diagnosis of mental retardation relies on an assessment of adaptive behavior and not solely on IQ, the epidemiology varies with the life cycle.

Neuropathology

Mental retardation is multifactor and neuropathology varies with the cause.

Biological studies

It has been observed that irrespective of the cause of mental retardation, brain perfusion defects have been observed in various areas of brain. This finding is of significance since the central theme of treatment common to all efforts to treat and prevent mental retardation is the promotion of healthy brain development and the provision of a nurturing and growth-promoting environment.