Intellectual Disability/Mental Retardation - Description

Page Contents

• Other Names
• ICD-9
• Description
• Genetics
• Prognosis
• Prevalence
• Pearls And Alerts
• Helpful Articles

Other Names

intellectual disability, static encephalopathy

ICD-9

317, Mental Retardation (MR), mild

318.0, MR, moderate

318.1, MR, severe

318.2, MR, profound

319, MR, NOS

Also see ID-MR ICD9 ( 65 KB) ..

Description

Intellectual disability (ID), or mental retardation (MR), is a condition or syndrome and also a defining characteristic of other disorders, such as Down syndrome. ID describes a heterogeneous group of conditions characterized by low or very low intelligence and deficits in adaptive behaviors without reference to etiology. [Sattler: 1988] This Diagnosis Module will focus primarily on ID as a syndrome, with links to associated disorders and features. Autism Spectrum Disorders, Fragile X Syndrome (the most common inherited cause of mental retardation), Down syndrome, and Fetal Alcohol Syndrome are described in separate modules. Here we will use the terms ID and MR interchangeably, cknowledging that ID is being increasingly used as the term of choice. The severity of ID is classified by degree of disability, see Intellectual disability/mental retardation - classification.

ID is, by some, referred to as static encephalopathy, but this is confusing since "static encephalopathy" is often used in conjunction with cerebral palsy. Static encephalopathy is defined as "permanent or unchanging brain damage" which can lead to many kinds of brain dysfunction, including ID, cerebral palsy, and others. Although about 52% of those with cerebral palsy also have ID, cerebral palsy refers specifically to motor disorders caused by brain damage before, during or after birth. [Swaiman: 2006] See Cerebral Palsy.

ID is often confused with developmental delay. ID should only be diagnosed when there is clear evidence that cognitive abilities and adaptive behavior are significantly below average and that, although the individual might make progress in learning, they will always be significantly below average. This excludes individuals with conditions that might be temporary (e.g., the convalescent period after a brain insult such as meningitis or trauma, the response to early neglect, or children soon after foreign adoption). It also excludes the very young where cognitive ability and adaptive behavior are not easily measurable. This is especially true in mild cases, because children with mild developmental delay are more likely to "catch up" with their peers. Opinion in the literature is mixed regarding the earliest age at which a diagnosis of ID is reasonably possible. It is usually possible in the preschool years, earlier for more severe cases, but not reliably until age 5. [Shevell: 2003]

A diagnosis of ID is important to allow the family to begin making realistic plans for the education and future of the child. The diagnosis also allows the child to qualify for early intervention and special educational services and, depending on the financial status of the family, entitlement programs, such as disability services.

Genetics

There are many different etiologies for ID, some of which are genetic; when possible, all children with intellectual disability without a known etiology should have a genetics evaluation. Genetic testing is best guided by a geneticist, but information about available tests for conditions associated with ID can be found at MR (GeneTests). Information on specific genetic syndromes and gene defects resulting in ID can also be found in Online Mendelian Inheritance in Man (OMIM) - a catalog of human genetic disorders.

Prognosis

Measures of intellect and measures of adaptive behavior allowing classification of the degree of ID are somewhat predictive of the eventual ability of individuals with ID to be able to live independently. For instance, individuals with mild to moderate mental retardation should become relatively self-sufficient with appropriate family and community support. Individuals with severe and profound ID will need a great deal of support and do not usually live independently or in group homes. Individuals with severe and profound ID tend to have shortened life expectancies as well, often due to the conditions causing their ID.

The degree of intellectual disability is fairly stable throughout life, that is a child of 5 diagnosed with severe ID will usually have the same diagnosis at age 21. This may not be apparent to families, as younger children with ID are closer to their peers in terms of their abilities than older individuals, and it may seem that the child is getting more behind as he/she gets older.

Prevalence

ID is the most common developmental disorder. Estimates of prevalence vary, but range around 2-5% of the population. Mild MR is approximately three times more common than severe MR. MR is more common in older children than younger children, more common among black children than white children, and more common in boys than in girls. Mental Retardation, CDC review Those with familial ID tend to come from groups with low socioeconomic status.

Pearls And Alerts

Helpful Articles

PubMed Search for articles on Mental Retardation in children for last 2 years.

Curry CJ, Stevenson RE, Aughton D, Byrne J, Carey JC, Cassidy S, Cunniff C, Graham JM Jr, Jones MC, Kaback MM, Moeschler J, Schaefer GB, Schwartz S, Tarleton J, Opitz J.
Evaluation of mental retardation: recommendations of a Consensus Conference: American College of Medical Genetics.
Am J Med Genet. 1997;72(4):468-77. PubMed abstract / Full Text
A consensus statement regarding a rational clinical approach to a child with mental retardation including history, physical exam and recommended testing.

Moeschler JB, Shevell M.
Clinical genetic evaluation of the child with mental retardation or developmental delays.
Pediatrics. 2006;117(6):2304-16. PubMed abstract / Full Text
This report describes the "optimal clinical genetics evaluation" for children with developmental delay or mental retardation for medical home providers.

Intellectual Disability/Mental Retardation Module Authors

The authors listed above are responsible for the overall Intellectual Disability/Mental Retardation Module. Authors contributing to individual pages in the module are listed on those pages.

Page Bibliography

Sattler, J.
Assessment of Children.
Third Edition ed. San Diego: Jerome M. Sattler Publisher; 1988. 9780961820978

Shevell M, Ashwal S, Donley D, Flint J, Gingold M, Hirtz D, Majnemer A, Noetzel M, Sheth RD.
Practice parameter: evaluation of the child with global developmental delay: report of the Quality Standards Subcommittee of the American Academy of Neurology and The Practice Committee of the Child Neurology Society.
Neurology. 2003;60(3):367-80. PubMed abstract / Full Text

Swaiman, K.F., Ashwal, S., and Ferriero, D.M. (Eds).
Pediatric Neurology Principles and Practice.
Fourth Edition ed. Saint Louis: C.V. Mosby Company; 2006.