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Intellectual Disability/Mental Retardation - Initial Diagnosis

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Overview

Important steps in the clinical assessment of a child with intellectual disability (ID)/ mental retardation (MR) include:
  1. Suspicion of developmental delay/mental retardation (DD/MR), prompted by parent interview and/or direct observation of the child, should be confirmed with norm-referenced testing for IQ and adaptive functioning (see Psychometric testing (general)). Treatable diagnoses that might mimic DD/MR, such as severe auditory or visual impairment or neurologic disorders, must be ruled out.
  2. Identification of the etiology, if possible, through medical history, family history, and/or physical exam (e.g., a large head circumference may indicate fragile X syndrome or facial features might suggest Cornelia de Lange syndrome). An etiology can be found in about two-thirds of individuals with severe MR but in only about one-third of those with mild MR (see Intellectual disability/mental retardation - classification). A very small number of etiologies for ID may be treatable. [Engbers: 2008] [Mueller: 2008] Knowing the cause can be helpful in determining prognosis and risk of recurrence in the family and for predicting the child's ability to live independently in the future.
  3. Determining the severity of ID, with psychometric and adaptive function testing can be helpful in prognosis for independent living.
  4. Determining the needs for educational interventions and support for the child and family, through testing and comprehensive evaluation by the school and/or community agencies and professionals.

Etiology: There are hundreds of known causes of ID. In about half of children with ID, the cause is thought to be exogenous, such as prenatal exposure to infection or toxins. The other half are likely due to genetic causes. [Battaglia: 2003] Note that scientific knowledge regarding genetic etiologies of ID is increasing rapidly. When seeking the cause for a particular child, it is often useful to consider broad categories of etiologies, including:
  • Inherited/chromosomal: PKU, hypothyroidism, fragile X syndrome, Down syndrome, tuberous sclerosis, autism
  • Factors associated with pregnancy: intrauterine infections, toxins (including drug and alcohol abuse, prescription drug effects), abnormal brain development (e.g., cortical dysplasia), and hypoxia/ischemia (placental insufficiency)
  • Birth-related: hypoxic-ischemic encephalopathy, extreme prematurity
  • Post-natal: infection, head injury, abuse/neglect, malnutrition, lead/mercury exposure

The likelihood of finding an etiology for ID in a given child is not correlated with the severity of ID. ([Battaglia: 2003])

Screening and Initial Evaluation: Developmental screening, an important component of routine well-child care, should identify children with developmental delay early in life, depending on the severity. Use of a standardized screening tool provides the best combination of sensitivity (not missing children with delays) and specificity (minimizing the evaluation of children with no delays). See the Developmental Screening section for an overview of screening strategies and tools.

A positive screening test should lead to a confirmatory evaluation and, if significant developmental delay is found, then full psychometric testing. Testing strategies will depend on age and degree of developmental delay. Evaluating sustained and focused attention and impulse control is also important, since treating attention problems behaviorally and/or pharmacologically might maximize the child's potential by helping him/her to be more cognitively "available" for instruction and intervention. Such evaluation should be performed by specialists and may include: assessment of speech, language, gross and fine motor development, social and emotional responsivity, play imitation, non-verbal communication, attention and impulse control, intelligence, learning abilities, and more. See Services (below) for details on neuropsychological testing resources and Psychometric testing (general) for more information about these tests.

Diagnostic Criteria

Classification of ID allows the examiner to clarify the severity and the level of support that will be required in the educational system and beyond. Both intelligence (measured as IQ) and adaptive behavior scales are important in the evaluation. Potential confounding factors should be kept in mind. Children with motor, auditory, or visual impairments, might perform lower than their measured IQ would predict, while similar impaiements might result in a child scoring lower than their potential on IQ testing. Adaptive measures, which are typically conducted by interview, may vary depending on the reliability of the informant.

IQ scores from the ICD-9 [National: 2007] classification and the DSM-IV [American: 2000] classification (in parentheses) are indicated below. Typically the definition of mental retardation requires that a child score below the population average by at least two standard deviations on measures of intelligence.
  • Borderline Intellectual Functioning - IQ=67-85 (71-84, DSM-IV).
  • Mild MR - IQ=52-68, ICD9 (50-55 to 70, DSM-IV) Affected children are able to speak and to learn some social skills. They can usually be expected to care for themselves as adults, with some guidance.
  • Moderate MR - IQ=36-51, ICD9 (35-40 to 50-55, DSM-IV) Affected children, although they are able to learn some language, usually have poor social skills. They will be able to achieve in school to about the elementary school level. Because their early motor milestones are usually attained in the normal range, children at this IQ level and above tend to be diagnosed around the preschool period. However, language development and achievement of activities of daily living and social skills are often delayed. They will generally need complete supervision as an adult, often in a group home setting. They may be capable of unskilled occupations in a supported-employment setting.
  • Severe MR - IQ=20-35, ICD-9 (20-25 to 35-40, DSM-IV) Affected children will be able to learn a few words and a few self-help skills, but will need a protected environment as an adult. A living situation in a group home with increased support will sometimes be possible. Children with severe and profound MR are often diagnosed very early because acquisition of even the earliest motor milestones are delayed.
  • Profound MR - IQ=19 and below, ICD-9 (less than 20-25, DSM-IV) Affected children will generally need full care as adults, often in a nursing home type environment.

Pearls And Alerts

Children with autism may have normal intelligence or intellectual disability. IQ tests on children with autism may underestimate IQ because the testing is often language based.

A perceived worsening of ID may occur as children get older. Even children with profound intellectual disability may differ little from their peers at 1 year of age, but are very different at age 10. This should be discussed with families in early visits with the Medical Home.

A multidisciplinary team in the Netherlands evaluated 433 patients with ID with no identified etiology. They found genetic and metabolic etiologies in 14%, some of which were treatable (GLUT1, hyperoxaluria, 5-MTHF reductase deficiency, and creatine synthase deficiency) and several of which are very new in the literature (creatine synthase deficiency). [Engbers: 2008] [Mueller: 2008] Children should receive full evaluations for the etiology of their ID.

Practice Guidelines

The guidelines below focus on evaluation. Some of the syndromes that cause ID have their own guidelines, for example Down syndrome [American: 2001], Williams syndrome [American: 2001], and fragile X syndrome [American: 1996].

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

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

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

Szymanski L, King BH.
Practice parameters for the assessment and treatment of children, adolescents, and adults with mental retardation and comorbid mental disorders. American Academy of Child and Adolescent Psychiatry Working Group on Quality Issues.
J Am Acad Child Adolesc Psychiatry. 1999;38(12 Suppl):5S-31S. PubMed abstract

Differential Diagnosis

Autism spectrum disorders, specific language problems, and hearing problems may be confused with ID in young children, or may coexist with ID. A full evaluation of the child will help sort this out.

History And Examination

Family History

Knowledge of others in the extended family (back 3 generations, if possible) with ID may provide clues to a genetic etiology, prognosis, and prior understanding or concern on the part of the family. Family history should include ethnic background, metabolic diseases, parental consanguinity, relatives with autistic features, multiple miscarriages, or unexplained infant/childhood deaths. Attention should be paid to the sex of affected relatives because there are several X-linked ID syndromes.

Pregnancy/Perinatal History

Pregnancy: difficulty conceiving, intrauterine infections or maternal illness, toxins (including drug and alcohol abuse, prescription drug effects), abnormal brain development (e.g., cortical dysplasia), and hypoxia/ischemia (placental insufficiency). Ask about birth-related factors such as hypoxic-ischemic encephalopathy during labor (and Apgar scores) and extreme prematurity. Also ask about birth weight/height for evidence of placental insufficiency or a genetic syndrome. Ask about prenatal screening or testing, type of delivery and why, and weight gain and difficulty feeding during the first few weeks. Ask about bonding/attachment.

Medical History

Ask about possible post-natal problems: decreased growth or overgrowth, infection, head injury, abuse/neglect, malnutrition, lead/mercury exposure. Ask about hearing and vision problems and previous testing.

Developmental and Educational History

Ask about time of achievement of developmental milestones. Children with more severe ID are likely to have all developmental milestones delayed from an early age, whereas children with mild ID are more likely to display normal early milestones.

Social and Family History

Ask about family functioning, parental jobs, financial resources for caring for a child with intellectual disability, and family support systems.

Physical Exam

General

Observe behavior and interaction, including quality of eye contact, attention/focus, interaction, repetitive movements, hand flapping, aggression

Growth Parameters

Ht | Wt | OFC, head shape, presence of fontanels (FTT, compare to parents), asymmetry?

HEENT

Note head size and shape. Look at facies - similar to family members? Look for epicanthal folds, ear position/shape/size, prominence of chin or forehead, size and shape of eyes, ears, mouth, philtrum. Check hair for abnormal texture or color.

Skin

Look for the presence of abnormal textures, hyper- or hypopigmentation, eczema, Wood's lamp findings, hemangiomata

Extremities

Look for single palmar creases, clinodactyly, size of hands/feet, nail abnormalities, presence of contractures, hyperextensibility

Abdomen

hepatosplenomegaly

Neurologic Exam

Check for spasticity, tone, balance, coordination, dystonia, chorea

Genitalia

size, structure

Testing

Sensory Testing

Because hearing and vision impairments are relatively common in children with MR, testing is important to rule them out as a cause or contributor. Periodic retesting is indicated, particularly if a deterioration in function is noted.

Laboratory Testing

Metabolic testing: - Newborn screening should identify many of the congenital causes of ID (see the Newborn Screening section), some of which are treatable (e.g., congenital hypothyrodism). A full evaluation for the etiology of the child's ID by specialists in this area may include further metabolic testing. [Engbers: 2008] Other signs/symptoms that might prompt targeted testing include: stigmata of hypothyrodism, seizures, lethargy, vomiting, abnormal urinary odors, and failure to thrive. Deterioration of a child's developmental status should lead to further testing because deterioration is not consistent with ID alone, rather suggesting a degenerative disease.

Imaging and EEG

Imaging: In patients with specific findings, such as microcephaly or a focal neurologic abnormality, brain MRI will identify an abnormality in about 40%; in the absence of clinical clues, the yield is only about 14%. When an etiology cannot be identified, an MRI may still be cost-effective as a once-in-a-lifetime test, particularly when results might be important in family planning and genetic counseling. The American Academy of Neurology and Child Neurology Society [Shevell: 2003]) recommend neuro-imaging as part of an evaluation of the child with ID, whereas the American College of Medical Genetics [Curry: 1997] does not feel that neuroimaging should be considered "standard of care" in the absence of specific neurologic findings. Battaglia and Carey [Battaglia: 2003] suggest MRI and magnetic resonance spectroscopy be performed in children with otherwise unexplained ID. MRI is preferred over CT in almost all cases (unless the examiner is looking for calcifications, as in congenital CMV). The risk of sedation for an MRI and the parents' desires should be considered, along with the potential helpfulness of the information gained.

EEG: An EEG should be performed when clinical seizures or a seizure syndrome are suspected.

Skeletal survey, other imaging may be recommended as part of a genetics consultation.

Genetic Testing

The American College of Medical Genetics has offered recommendations for the evaluation of children with ID without a definite diagnosis. [Curry: 1997] The American Academy of Pediatrics Committee on Genetics has also weighed in, and has included a Clinical Genetic Evaluation Algorithm (AAP) (PDF Document 520 KB) . [Moeschler: 2006] Newer recommendations, prompted by a study finding etiologies in 14% of previously evaluated children with ID, may be forthcoming. [Engbers: 2008] Tests that may prove helpful, depending on the clinical assessment, include:
  1. High resolution karyotyping is able to diagnose syndromes with relatively large gene alterations (e.g., cri du chat syndrome, due to deletion of the telomere of the short arm (p) of chromosome 5).
  2. Fluorescent in situ hybridization (FISH) looks for smaller duplications and/or deletions such as 1pter and 1qter deletion, syndromes not well known to pediatricians.
  3. Microarray comparative genomic hybridization (MCGH) can detect very small deletions and duplications of chromosomes. One study found 10% of children with ID with unclear etiology had microimbalances detectable with DNA microarray analysis. [Engels: 2007]
  4. Guided by history or physical exam, tests for specific genetic syndromes, such as fragile X or Rett syndrome may be indicated.
  5. If no etiology is found, testing for fragile X symdrome may be warranted even when the child does not fit the clinical syndrome, particularly if history or exam findings are suggestive of a genetic cause. ([Curry: 1997]) Genetic testing is best guided by a genetist, but information about available tests for conditions associated with ID can be found at MR (GeneTests). See the Fragile X Syndrome module.

Other Testing

Norm-referenced testing for IQ and adaptive functioning is critically important to confirm the diagnosis of intellectual disability, guide a diagnostic workup in some cases, to guide therapeutic interventions, to provide some idea of the child's prognosis.

Subspecialist Evaluations

Once the diagnosis of developmental delay/intellectual disability is suspected, the Medical Home should have the child tested by psychology (via the educational or medical systems) and then decide whether to refer to neurology, genetics, etc. based on the history and physical exam. Such referrals may be useful to aid in the diagnosis or to help with ongoing care of the child.

Pediatric Medical Genetics (see Services below for relevant providers)

When a diagnosis of intellectual disability is confirmed, a genetic evaluation is recommended. Genetic counseling may also be appropriate for the family. See Clinical Genetic Evaluation Algorithm (AAP) (PDF Document 520 KB) for an overview of the recommended genetic evaluation.

Pediatric Metabolic Genetics (see Services below for relevant providers)

If a metabolic etiology is suspected, the child with ID should be evaluated by a metabolic geneticist.

Pediatric Neurology (see Services below for relevant providers)

Children with specific neurologic problems, such as seizures or hemiplegia, should be seen by neurology and followed as needed for ongoing management.

Pediatric Physical Medicine & Rehab (see Services below for relevant providers)

A physiatrist may be helpful in directing services such as physical therapy, occupational therapy, feeding management, etc., as well as evaluating for needed adaptations at school.

Pediatric Ophthalmology (see Services below for relevant providers)

In addition to finding and treating visual impairment, a pediatric ophthalmologist may find etiologic clues on exam.

Developmental Pediatrics (see Services below for relevant providers)

Developmental pediatricians can offer a complete developmental evaluation and assist in coordinating services.

Child Psychology (see Services below for relevant providers)

Specialists in this field provide comprehensive assessment of the domains of intellectual, social, cognitive, behavioral, academic and emotional functioning. This assessment process is helpful in identifying strengths and weaknesses, providing diagnostic information, and in formulating a diagnosis and recommendations for interventions.

Neuropsychology (see Services below for relevant providers)

Neuropsychologc assessment of functioning is particularly important when the child has neurological deficits, such as brain injury or seizures. This process is helpful in identifying strengths and weaknesses, providing diagnostic information, and in formulating a diagnosis and recommendations for interventions.

Resources

Information & Support

More specific information and support groups may be available to those individuals and families and providers where the etiology for the intellectual disability is known, e.g., syndrome-specific support groups.

For Professionals

Developmental disabilities information (ddhealthinfo.org)
Information and links for families and professionals on developmental disabilities and associated medical condtions. This site is funded by the California Department of Developmental Services and coordinated by the University of California San Diego, School of Medicine.

Developmental disabilities information (dbpeds.org)
Type developmental disabilities in the search box on this website to find information about developmental disabilites and links to associated sites.

For Parents and Patients

Support

Arc of the United States
Publishes A Family Handbook on Future Planning which is a guide to help families develop a future plan that provides personal, financial, and legal protections for their children after the parents either die or can no longer provide care or support. The book is free and available on their website.

Developmental Delay/Mental Retardation resources
A listing of international resources related to ID/MR, compiled by the University of Kansas Medical Center's Genetics Education Center.

Arc of Utah
May be able to recommend attorneys and/or financial planners.

General

Developmental disabilities information (ddhealthinfo.org)
Information and links for families and professionals on developmental disabilities and associated medical condtions. This site is funded by the California Department of Developmental Services and coordinated by the University of California San Diego, School of Medicine.

Mental Retardation (MedlinePlus Encyclopedia)
Overview of mental retardation with links to much more information; from the National Library of Medicine and National Institutes of Health.

Developmental Disabilities (MedlinePlus)
Comprehensive compilation of reliable links to information about developmental disabilities and intellectual disability/mental retardation; from the National Library of Medicine and National Institutes of Health.

Practice Guidelines

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.

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

Szymanski L, King BH.
Practice parameters for the assessment and treatment of children, adolescents, and adults with mental retardation and comorbid mental disorders. American Academy of Child and Adolescent Psychiatry Working Group on Quality Issues.
J Am Acad Child Adolesc Psychiatry. 1999;38(12 Suppl):5S-31S. PubMed abstract
A review of mental health disorders in the DD/MR population. Although possibly more frequent in this population, psychiatric disorders are essentially the same as in normally developing children; however, behavioral observations are very important due to decreased verbal skills in this population.

Tools

Clinical Genetic Evaluation Algorithm (AAP) (PDF Document 520 KB)

Services

Child Psychology

See all Child Psychology services providers (43) in our database.

Developmental Pediatrics

See all Developmental Pediatrics services providers (2) in our database.

Neuropsychology

See all Neuropsychology services providers (4) in our database.

Pediatric Medical Genetics

See all Pediatric Medical Genetics services providers (4) in our database.

Pediatric Metabolic Genetics

Metabolic Clinic, more info...
100 Mario Capecchi Drive
Salt Lake City, UT 84113
Phone: 801-585-2457
Fax: 585-7252
http://www.ped.med.utah.edu/pku/contact.html

See all Pediatric Metabolic Genetics services providers (2) in our database.

Pediatric Neurology

Pediatric Neurology, more info...
100 N. Mario Capecchi Dr.
Salt Lake City, UT 84158
Phone: 801-662-5696
Fax: 801-587-7539
http://medicine.utah.edu/pedsneurology/

See all Pediatric Neurology services providers (3) in our database.

Pediatric Ophthalmology

See all Pediatric Ophthalmology services providers (4) in our database.

Pediatric Physical Medicine & Rehab

Primary Children's Rehabilitation Salt Lake, more info...
100 Mario Capecchi Drive, Ste. 4400
Salt Lake City, UT 84113
Phone: 801-662-4949
Fax: 801-662-4964
http://intermountainhealthcare.org/hospitals/primarychildrens/services/pages/Service.aspx?index=Physical%20Medicine%20and%20Inpatient%20Rehabilitation

See all Pediatric Physical Medicine & Rehab services providers (2) in our database.

For other services related to this condition, browse our Services categories or search our database.

Studies

Mental Retardation (clinicaltrials.gov)
Many clinical trials are underway related to mental retardation. Some may be relevant and of interest to your patients.

Helpful Articles

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

Battaglia A, Carey JC.
Diagnostic evaluation of developmental delay/mental retardation: An overview.
Am J Med Genet C Semin Med Genet. 2003;117(1):3-14. PubMed abstract

Authors

Authors: Lynne M Kerr MD, PhD, 5/2009
Chuck Norlin MD, 7/2008
Contributing Author: Dorothee Serpas Ph.D., 7/2008
Content Last Updated: 5/2009

Page Bibliography

American Academy of Pediatrics - Committee on Genetics.
Health supervision for children with Down syndrome.
Pediatrics. 2001;107(2):442-9. PubMed abstract / Full Text

American Academy of Pediatrics Committee on Genetics.
Health care supervision for children with Williams syndrome.
Pediatrics. 2001;107(5):1192-204. PubMed abstract / Full Text

American Academy of Pediatrics Committee on Genetics.
Health supervision for children with fragile X syndrome.
Pediatrics. 1996;98(2 Pt 1):297-300. PubMed abstract / Full Text
Guidelines reaffirmed in 2007 by the AAP.

American Psychiatric Association.
Diagnostic and Statistical Manual of Mental Disorders DSM-IV-TR (Text Revision).
4th edition (June 2000) ed. Washington, DC: American Psychiatric Association; 2000. 0890420254

Battaglia A, Carey JC.
Diagnostic evaluation of developmental delay/mental retardation: An overview.
Am J Med Genet C Semin Med Genet. 2003;117(1):3-14. PubMed abstract

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.

Engbers HM, Berger R, van Hasselt P, de Koning T, de Sain-van der Velden MG, Kroes HY, Visser G.
Yield of additional metabolic studies in neurodevelopmental disorders.
Ann Neurol. 2008;64(2):212-7. PubMed abstract

Engels H, Brockschmidt A, Hoischen A, Landwehr C, Bosse K, Walldorf C, Toedt G, Radlwimmer B, Propping P, Lichter P, Weber RG.
DNA microarray analysis identifies candidate regions and genes in unexplained mental retardation.
Neurology. 2007;68(10):743-50. PubMed abstract

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.

Mueller S, Sherr EH.
The importance of metabolic testing in the evaluation of intellectual disability.
Ann Neurol. 2008;64(2):113-4. PubMed abstract

National Center for Health Statistics (NCHS) and the Centers for Medicare and Medicaid Services .
International Classification of Diseases, Ninth Revision, Clinical Modification.
10th revision ed. Various Publishers; 2007. http://icd9cm.chrisendres.com/

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