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Mental retardation is characterized by limitations in performance that result from significant impairments in measured intelligence and adaptive behavior. It also confers a social status that can be more handicapping than the specific disability itself. Because the boundaries between "normality" and "retardation" frequently are difficult to delineate, the pediatric identification, evaluation, and care of

The American Association on Mental Retardation revised its official definition to formalize the paradigm shift from viewing mental retardation as an individual trait to thinking of it as an expression of the interaction between a person with limited intellectual functioning and the environment. Consequently, categories of mild, moderate, severe, and profound retardation have been replaced by a classification system that specifies four levels of support systems needed for daily functioning (i.e., intermittent, limited, extensive, and pervasive). Four assumptions were articulated as essential to the appropriate application of the new definition as follows: (1) valid assessment considers cultural and linguistic diversities; (2) limitations in adaptive skills occur within the context of community environments typical of age peers and indexed to individualized needs for supports; (3) adaptive limitations coexist with strengths; and (4) with appropriate and sustained supports, the life functioning of individuals with mental retardation will generally improve mental retardation, MR, mentally retarded, mentaly retarded.


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 maturational status of the nervous system and by the nature and quality of his or her life experience. Some children sustain


Approximately 3% of the general population has an intelligence quotient (IQ) less than two standard deviations below the mean. It has been estimated that 

Potential Contributing Factors in the Pathogenesis of Mental Retardation
Preconceptual Disorders
Single gene abnormalities (e.g., inborn errors of metabolism, neurocutaneous disorders)
Chromosomal abnormalities (e.g., X-linked disorders, translocations, fragile X)
Polygenic familial syndromes
Early Embryonic Disruptions
Chromosomal disorders (e.g., trisomies, mosaics)
Infections (e.g., cytomegalovirus, rubella, toxoplasmosis, human immunodeficiency virus)
Teratogens (e.g., alcohol, radiation)
Placental dysfunction
Congenital central nervous system malformations (idiopathic)
Fetal Brain Insults
Infections (e.g., human immunodeficiency virus, toxoplasmosis, cytomegalovirus, herpes simplex)
Toxins (e.g., alcohol, cocaine, lead, maternal phenylketonuria)
Placental insufficiency/intrauterine malnutrition
Perinatal Difficulties
Extreme prematurity
Hypoxic-ischemic injury
Intracranial hemorrhage
Metabolic disorders (e.g., hypoglycemia, hyperbilirubinemia)
Infections (e.g., herpes simplex, bacterial meningitis)
Postnatal Brain Insults
Infections (e.g., encephalitis, meningitis)
Trauma (e.g., severe head injury)
Asphyxia (e.g., near drowning, prolonged apnea, suffocation)
Metabolic disorders (e.g., hypoglycemia, hypernatremia)
Toxins (e.g., lead)
Intracranial hemorrhage
Postnatal Experiential Disruptions
Poverty and family disorganization
Dysfunctional infant-caregiver interaction
Parental psychopathology
Parental substance abuse
Unknown Influences


Children with physical findings suggestive of recognizable syndromes that are associated with mental retardation should be identified at birth or during early infancy. Down syndrome and primary microcephaly are examples of such conditions. These disorders, however, represent a 

Delayed achievement of developmental milestones is the cardinal symptom of mental retardation. 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

The natural history of mental retardation is highly variable and dependent on the availability of appropriate educational and therapeutic experiences as well as on neuromaturation and the presence of associated disabilities. Although many youngsters may experience transient "plateau periods" during which measurable progress may be minimal, most individuals with mental retardation acquire new skills

A thorough pediatric history is essential to identify relevant contributing factors as well as to document the evolving pattern of the child's developmental skills over time. The product of the history should be a

A systematic physical examination may reveal findings that help to explain the etiology of the child's disability or that identify particular treatment needs. Table 40-4 lists a number of atypical physical features that have been associated with a

Atypical Physical Features That May Be Associated with Increased Incidence of Mental Retardation
Double whorl
Fine, inable, prematurely gray or white locks
sparse or absent hair
Upward-and-outward or downward-and-outward slant
Inner or outer epicanthal folds
Coloboma of iris or retina
Brushfield spots
Eccentrically placed pupil
Low-set pinna
Simple or abnormal helix formation
Flattened bridge
Small size
Upturned nares
Increased length of philtrum
Hypoplasia of maxilla or mandible
Inverted V shape of upper lip
Wide or high-arched palate
Short 4th or 5th metacarpals
Short, stubby fingers
Long, thin tapered fingers
Broad thumbs
Abnormal dermatoglyphics (e.g., distal triradius)
Transverse palmar crease
Abnormal nails
Short 4th or 5th metatarsals
Overlap of toes
Short, stubby toes
Broad, large big toes
Deep crease leading from angle of 1st and 2nd toes
Abnormal dermatoglyphics
Ambiguous genitalia
Large testicles
Cafe-au-lait spots
Depigmented nevi
Evidence of abnormal enamelogenesis
Abnormal odontogenesis


The primary care pediatrician is strategically situated to identify young children with possible mental retardation through routine developmental surveillance in the context of general pediatric care. Parental report of a child's typical skills and behaviors in conjunction with the use of in-office screening procedures are important complementary sources of information. For young children involved in a

Ultimately, the diagnosis of mental retardation requires confirmation of significantly subaverage general intellectual functioning (i.e., an IQ standard score of 70-75 or below) in association with deficits in two or more of the following 10 adaptive skill areas: communication, self-care, home living, social skills, community use, self-direction, health and safety, functional academics, leisure, and work.


Management of a child with mental retardation is multidimensional and highly individualized. Although the potential need for a highly specialized multidisciplinary effort should be considered, not all children with mental retardation are 

One of the critical and most demanding roles played by the physician involves the initial synthesis and presentation of diagnostic findings to the family. This process involves a highly sensitive interaction the details of which are often remembered and recounted verbatim by parents for 

Specialized educational and therapeutic services are central elements in the multidisciplinary treatment of children with mental retardation. During the adolescent years, issues related to sexuality, vocational training, and community living become more prominent than at earlier stages. The role of 

Collaboration between the primary care physician and an early intervention service system is particularly important in the management of children with developmental impairments in the first years of life. Early identification and prompt referral ensure access to individualized therapeutic and educational services for