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Mental retardation

Mental retardation (also called mental handicap and, as defined by the UK Mental Health Act 1983, mental impairment and severe mental impairment) is a term for a pattern of persistently slow learning of basic motor and language skills ("milestones") during childhood, and a significantly below-normal global intellectual capacity as an adult. One common criterion for diagnosis of what used to be called mental retardation is a tested intelligence quotient (IQ) below 70. more...

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Alternate terms

The term mental retardation has gradually acquired pejorative and shameful connotations over the last few decades and is now used almost exclusively in technical or scientific contexts where exactness is necessary.

  • In North America, the broad term developmental delay has become an increasingly preferred synonym by many parents and caregivers. Elsewhere however, developmental delay is generally used to imply that appropriate intervention will improve or completely eliminate the condition, allowing for "catching up." Importantly, this term carries the emotionally powerful idea that the individual's current difficulties are likely to be temporary.
  • Developmental disability is preferred by most physicians, but can also refer to any other physical or psychiatric delay, such as delayed puberty.
  • Intellectual disability is increasingly used as a synonym for people with significantly below-average IQ, primarily as a means of separating general intellectual limitations from specific, limited deficits as well as indicating that it is not an emotional or psychological disability. Intellectual disability is also used to describe the outcome of traumatic brain injury or lead poisoning or dementing conditions such as Alzheimer's disease. It is not specific to congenital conditions like Down Syndrome.

The American Association on Mental Retardation continues to use the term mental retardation .


There are many signs. For example, children with developmental disabilities may learn to sit up, to crawl, or to walk later than other children, or they may learn to talk later. Both adults and children with intellectual disabilities may also:

  • have trouble speaking,
  • find it hard to remember things,
  • not understand how to pay for things,
  • have trouble understanding social rules,
  • have trouble seeing the consequences of their actions,
  • have trouble solving problems, and/or
  • have trouble thinking logically.

In early childhood, mild disability (IQ 60-70) may not be obvious, and may not be diagnosed until they begin school. Even when poor academic performance is recognized, it may take expert assessment to distinguish mild mental disability from learning disability or behavior problems. As they become adults, many people can live independently and may be considered by others in their community as "slow" rather than "retarded".

Moderate disability (IQ 50-60) is nearly always obvious within the first years of life. These people will encounter difficulty in school, at home, and in the community. In many cases they will need to join special, usually separate, classes in school, but they can still progress to become functioning members of society. As adults, they may live with their parents, in a supportive group home, or even semi-independently with significant supportive services to help them, for example, manage their finances.


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Aging with mental retardation: increasing population of older adults with MR require health interventions and prevention strategies
From Geriatrics, 4/1/05 by Kathleen Fisher

Improvements in institutional care and residential placements as well as advances in assistive technology and public health programs have enhanced the quality of life for individuals with mental retardation (MR). Indeed, gains in life expectancy for those with MR are one of the clear public health success stories for the second half of the 20th century. Currently, the average life expectancy of persons with MR is 66 years. (1) However, younger adults with MR can expect to live as long as their non-MR peers--76.9 years.1 Individuals with Down's Syndrome (DS), the most common cause of MR in America, have experienced a doubling in life expectancy. In 1983, the average lifespan for an individual with DS was 25 years; by 1997, it had increased to 49 years. (2)

Because of increased longevity, individuals with MR confront the same chronic illnesses (ie, cardiovascular disease, cancer, diabetes) that affect the general aging population. Management of these illnesses is typically accomplished with caregiver supervision or, in some cases, independently. In either situation, providers will need to allow additional time for health education and health maintenance practices with this population. These individuals experience an increased prevalence of certain conditions including thyroid disease, seizure disorders, mental health disorders, obesity, ocular anomalies, and poor oral health. (3) Health interventions and prevention strategies exist to address the chronic illnesses and special needs of the MR patient, but not everyone benefits equally or has access to health care. Those with MR are less likely to receive adequate medical services compared with those in the general population, even though they have more physical and chronic health problems. (1,4)

The emerging population of older patients with MR will add costs to an already strapped healthcare system. An analysis of costs in the Netherlands attributes 9% of all disease-specific costs of health care to MR. (5) Primary care providers (PCPs) therefore must be familiar with managing the health care needs of this "new" geriatric population. The challenge is to enhance the overall functioning of the aging individual with MR, while allowing them to retain independence for as long as possible. This article will identify common health problems in elders with MR, especially those with DS.

Systemic age-related changes

Visual impairment Visual impairment, including cataracts, keratoconus, refractive errors, strabismus, nystagmus, corneal abnormalities, and hyperplasia are common in patients with MR. Uncorrected refractive errors are identified as the most common cause of decreased vision within this population. (1) While these are typical age-related changes, those with MR may not receive routine eye care. Routine annual eye examinations are recommended for all adults over age 65 and include visual acuity and glaucoma screening. (6) Moreover, severity of MR is associated with an increased prevalence of visual impairments. (7)

Adults with DS are at higher risk for vision problems and experience these changes (including cataracts, refractive errors, retinopathy, and glaucoma) at earlier ages (ie, >age 35). In one study examining the vision of patients with DS between ages 50 and 59, approximately one-half had moderate to severe visual loss. (8) Another survey found that 50% of those with DS over age 50 had cataracts, (9) while in the non-MR population only mild lens opacities are typically evident at age 50. (10)

Hearing loss Individuals with DS are also prone to hearing loss and may experience age-related loss by age 50. For example, 70% of institutionalized DS individuals age 50 to 59 had moderate, severe, or very severe hearing loss on health screening. (7) By comparison, hearing loss affects the non-MR population much later, ie, only 25% of adults age 65 to 74 experience hearing loss, which increases to 50% for those over age 85. (6)

Oral health Poor oral health and limited access to dental care can impact the quality of life for those with MR, contributing to difficulties with eating, speech, pain, and sleep. Studies show that individuals with MR have a higher prevalence of dental caries and other periodontal diseases compared with the general population. (1) Acquiring dental care for this population continues to be a challenge, as individuals may not always cooperate in a dental chair and often have poor insurance coverage. A study of 116 elder institutionalized residents with mental or physical disabilities examined the effectiveness of a dental health promotion program. It showed that caries incidence decreased, but plaque build-up and oral streptococci colonization were not affected. (11)

If problems with vision, hearing, and oral health among older persons with MR are not corrected, managing other health problems becomes more difficult. Attention to routine screening for these problems is critical. We recommend dental examinations continue throughout one's lifetime as in the non-MR population, and that annual hearing and visual screening be done in this population beginning at age 45.

Health conditions

Thyroid abnormalities are more common in those with MR. Increased thyroid stimulating hormone (TSH) was found in 48% of persons with DS living in an institutional setting. (8) In another study, 50% of those with DS had never had a thyroid test, despite a known higher prevalence of thyroid dysfunction with DS. (12) We recommend annual thyroid screening for those with DS over the age of 40.

Obesity, a major risk factor for diabetes and heart disease, is more prevalent among individuals with MR compared with the general population. (13) A study of adults with DS found 31% of males and 22% of females were overweight, defined as body mass index (BMI) 25-29, while 48% of males and 47% of females were obese (BMI Z 30). Causes of obesity in this population are thought to be multifactorial: poor eating behaviors, high/inappropriate caloric intake, depressed metabolic rate, reduced exercise, hypotonia, and endocrine abnormalities. (14)

Cardiovascular disease presents at younger ages in this population, and prevalence of disease is predicted to increase with aging. Increased risk factors for cardiovascular disease were found in a study of 202 adults with MR ages 20 to 50. The study group averaged 5.4 medical disorders per person including: hypertension, obesity, epilepsy, asthma, and visual (including blindness) and hearing conditions. Fifty percent of the medical disorders identified on physical examinations had previously been undetected in the study group. (15) Moreover, this study found that even when chronic conditions were recognized in this group, they were not being appropriately managed. Other studies have identified untreated congenital heart disease, acquired heart disease, pulmonary hypertension, and chronic pulmonary interstitial disease in aging individuals with DS. (9)

Osteoporosis may be a larger problem in those with severe MR. One survey of 23 bedridden MR adults with proper nutrition including good calcium intake, found low bone mineral density and low vitamin D levels. Those over age 50 were especially more likely to have long bone fractures and vertebral fractures. (16)

Individuals with DS are also more likely to experience complications of bone disease, including osteoarthritis. In one residential center, one-third of individuals with DS had osteoarthritis, one-half had fractures of the long bones, and 8% had untreated atlanto- occipital instability. (9)

High rates of osteoarthritis and bone fractures in those with MR can lead to unexplained agitation, decreased activity, and social interaction. As cognitive impairment increases, reporting of pain decreases. (17) When caring for the aging patient with MR, a suspicion of pain--especially joint pain--should be prominent and factored in the differential diagnosis of agitation or violence in this group.

Behavioral problems

The recognition of mental health disorders is difficult in individuals with MR, due in part to atypical symptom presentation, communication difficulties, and "diagnostic overshadowing." With diagnostic overshadowing, abnormal symptoms and behaviors are attributed to mental retardation, while coexisting psychopathology is often overlooked. (15) Severe and persistent mental illnesses, including mood disorders or schizophrenia, are more common than in the general population, as are behavioral symptoms, such as agitation or aggression, sleep disturbances, anxiety disorders, and self-injurious behaviors. In long-term care facilities, residents with MR are more likely to be on psychotropic medications than residents without intellectual disability. (18)

As individuals with MR age, they often continue to receive psychotropic medications. While these medications may be required chronically, some, especially when used in combination with other medications, could be discontinued. Reviewing all medications of these patients periodically--particularly antipsychotics and anticonvulsants given for agitation--will help to promote health and minimize side effects. (19)

Patients with mental disabilities often do not receive appropriate psychiatric care20 and little data is available on psychiatric disorders specific to elders with MR. One recent study compared psychiatric disorders in older and younger adults with learning disabilities. Researchers found that older adults with MR are more likely to have psychiatric symptoms than their younger peers. Fully 68.7% of those over age 65 had some kind of psychiatric morbidity compared with 47.9% of those who were younger. (21) Similar rates of schizophrenia (about 3% in both groups) and past history of depression (about 9%) were seen in both groups. However, 21.6% of the elder group also had dementia, compared with only 2.7% of the younger group. (22) Thus, much of the difference in psychiatric morbidity between the two groups is accounted for by the higher risk of dementia and its associated psychiatric symptoms. Figure 1 shows psychiatric morbidity in elders with mental retardation compared with the general population. (23)



Frequency of dementia in individuals with MR is unknown. Primary care physicians should interview caregivers to see if there is a change over time in the patient's ability to care for ADLs, or in pleasurable activities, such as playing games. More formal cognitive screening tools, such as the Mini-Mental Status Exam (MMSE) can be useful in high-functioning adults with mild MR, especially following declines over time.

Initially, it was thought that virtually all individuals with DS would develop Alzheimer's disease (AD). (24) While those with DS do suffer from dementia more often than their peers with other kinds of MR and have a much higher rate than the general population (Figure 2), the disease is not universally present in those with DS.


A survey of 134 adults with MR of all types (age Z65) showed that 20% had dementia. (21) As age advances, so does the risk of dementia. By age 88, 52% of adults with non-Down's MR had developed dementing illnesses. (25) Psychotic symptoms, particularly delusions of theft or persecution, complicate the task of caring for older adults with MR. (21) Other psychiatric symptoms of dementia, including aggression, sleep disturbance, hallucinations, and wandering, occur commonly. (26)

Two separate surveys show the rate of dementia in individuals over age 50 with DS to be 42%. (8,9) Before age 50, rates of dementia in DS varied widely according to the study, with remarkably high rates of dementia in aging individuals with DS. Dementia is found in 56% of those over age 60 with DS, and in 67% by age 72. (25) Patients with DS and dementia are more likely than their peers with MR and dementia to suffer from low mood, restlessness, disturbed sleep and hallucinations, but are less likely to be aggressive than are other patients with dementia and MR. (26) Antidepressants, antipsychotics, and mood stabilizers are routinely used in this population to treat the behavioral sequelae of dementia.

The use of cholinesterase inhibitors has been investigated for treatment of Alzheimer's dementia in those with DS. In a 5-month study, donepezil significantly improved cognitive scores in the study group. (27) Similarly, in a 24-week trial of donepezil in those with Alzheimer's dementia and DS, patients treated with donepezil had less deterioration in dementia rating scales, but no clear change in behavioral symptoms. (28) However, in a 12-week trial, no clear improvement was demonstrated in DS patients treated with donepezil. (29) The use of cholinesterase inhibitors may lead to lessened decline in those with DS and Alzheimer's disease.

An analysis of health care costs in the Netherlands for those with intellectual disability shows that there are 2 peaks of expenditures. The first occurs between ages 25 and 35, and the second occurs between ages 75 and 85. Researchers observe, "The costs will inevitably increase because of the aging of the population and increasing life expectancy among people with disabilities." (5)

Given this added burden, it is imperative that behavioral symptoms of dementia be treated early in aging patients with MR. No data is available on the standard treatments for AD in this population. However, the prudent clinician should make use of these treatments in those with MR as in any other patient.


Deinstitutionalization has moved individuals with MR into community-based systems and primary care practices. As such, more comprehensive routine screening and interventions for medical and mental health disorders have become necessary. Lingering medical and psychiatric problems combined with aging and dementia present a challenge for physicians. Clearly, more research is needed to better define health care needs and improved treatment paradigms and service systems. Physicians are reminded that treatment of individuals with MR requires input from providers from multiple disciplines, including special educators, behavior therapists, and occupational therapists.


(1.) Horwitz SM, Kerker BD, Owens PL, Zigler E. The health status and needs of individuals with mental retardation. Available at: /English/Initiatives/Research/Health+Status+Report.htm. Accessed February 18, 2005.

(2.) Yang Q, Rasmussen SA, Friedman JM. Mortality associated with Down's syndrome in the USA from 1983 to 1997: A population-based study. Lancet 2002; 359(9311):1019-25.

(3.) Cooper SA. Clinical study of the effects of age on the physical health of adults with mental retardation. Am J Ment Retard 1998; 102(6):582-9.

(4.) Closing the Gap: A National Blueprint to Improve the Health of Persons with Mental Retardation. Available at: Accessed February 18, 2005.

(5.) Polder JJ, Meerding WJ, Bonneux L, van der Maas PJ. Healthcare costs of intellectual disability in the Netherlands: A cost-of-illness perspective. J Intellect Disabil Res 2002; 46(Pt 2):168-78.

(6.) U.S. Preventive Services Task Force. Guide to clinical preventive services. 2nd ed. Baltimore, Md: Lippincott Williams & Wilkins; 1996.

(7.) McCulloch DL, Sludden PA, McKeown K, Kerr A. Vision care requirements among intellectually disabled adults: A residence-based pilot study. J Intellect Disabil Res 1996; 40(Pt 2):140-50.

(8.) Van Buggenhout GJ, Trommelen JC, Schoenmaker A, et al. Down syndrome in a population of elderly mentally retarded patients: Genetic-diagnostic survey and implications for medical care. Am J Med Genet 1999; 85(4):376-84.

(9.) van Allen MI, Fung J, Jurenka SB. Health care concerns and guidelines for adults with Down syndrome. Am J Med Genet 1999; 89(2):100-10.

(10.) Branch, WT. Office Practice of Medicine. 4th ed. Philadelphia, Pa: W.B. Saunders; 2003.

(11.) Mojon P, Rentsch A, Budtz-Jorgensen E, Baehni PC. Effects of an oral health program on selected clinical parameters and salivary bacteria in a long-term care facility. Eur J Oral Sci 1998; 106(4):827-34.

(12.) Jones RG, Kerr MP. A randomized control trial of an opportunistic health screening tool in primary care for people with intellectual disability. J Intellect Disabil Res 1997; 41(Pt 5):409-15.

(13.) Bell A, Bhate M. Prevalence of overweight and obesity in Down's syndrome and other mentally handicapped adults living in the community. J Intellect Disabil Res 1992; 36(Pt 4):359-64.

(14.) Prasher VP. Overweight and obesity amongst Down's syndrome adults. J Intellect Disabil Res 1995; 39(Pt 5):437-41.

(15.) Beange H, McElduff A, Baker W. Medical disorders of adults with mental retardation: A population study. Am J Ment Retard 1995; 99(6):595-604.

(16.) Wagemans AM, Fiolet JF, van der Linden ES, Menheere PP. Osteoporosis and intellectual disability: Is there any relation? J Intellect Disabil Res 1998; 42(Pt 5):370-4.

(17.) Gabre P, Sjoquist K. Experience and assessment of pain in individuals with cognitive impairments. Spec Care Dentist 2002; 22(5):174-80.

(18.) Hughes CM, Lapane KL, Mor V. Influence of facility characteristics on use of antipsychotic medications in nursing homes. Med Care 2000; 38(12): 1164-73.

(19.) Tyler CV Jr, Bourguet C. Primary care of adults with mental retardation. J Fam Pract 1997; 44(5):487-94.

(20.) Moss S, Emerson E, Bouras N, Holland A. Mental disorders and problematic behaviours in people with intellectual disability: Future directions for research. J of Intellect Disabil Res 1997; 41(Pt 6):440-7.

(21.) Cooper SA. Epidemiology of psychiatric disorders in elderly compared with younger adults with learning disabilities. Br J Psychiatry 1997; 170:375-80.

(22.) Cooper SA. Psychiatric symptoms of dementia among elderly people with learning disabilities. Int J Geriatr Psychiatry 1997; 12(6):662-6.

(23.) Sadock BJ, Sadock VA. Kaplan and Sadock's Synopsis of Psychiatry. 9th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2003.

(24.) Geldmacher DS. Contemporary diagnosis and management of Alzheimer's Dementia. Newtown, PA: Handbooks in Health Care Co.; 2003.

(25.) Zigman WB, Schupf N, Urv T, Zigman A, Silverman W. Incidence and temporal patterns of adaptive behavior change in adults with mental retardation. Am J Ment Retard 2002; 107(3):161-74.

(26.) Cooper SA, Prasher VP. Maladaptive behaviours and symptoms of dementia in adults with Down's syndrome compared with adults with intellectual disability of other aetiologies. J Intellect Disabil Res 1998; 42(Pt 4):293-300.

(27.) Lott IT, Osann K, Doran E, Nelson L. Down syndrome and Alzheimer disease: Response to donepezil. Arch Neurol 2002; 59(7):1133-6.

(28.) Prasher VP, Huxley A, Haque MS, and the Down Syndrome Ageing Study Group. A 24-week, double-blind, placebo-controlled trial of donepezil in patients with Down syndrome and Alzheimer's disease--pilot study. Int J Geriatr Psychiatry. 2002; 17(3): 270-8.

(29.) Johnson N, Fahey C, Chicoine B, Chong G, Gitelman D. Effects of donepezil on cognitive functioning in Down syndrome. 2003. Am J Ment Retard 108(6):367-72.

Dr. Fisher is associate professor, college of nursing and health professions, Drexel University, Philadelphia.

Dr. Kettl is professor of psychiatry, Milton S. Hershey Medical Center, Penn State College of Medicine, Hershey, Pa.

Disclosure: Dr. Fisher has no conflict of interest related to the subject presented. Dr. Kettl discloses that he has received research grants from Bristol-Myers Squibb, Janssen, and Forest, and was a speaker or consultant for AstraZeneca, Bristol-Myers Squibb, Lilly, and Pfizer.

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