What You Will Learn
After reading this note, you should be able to...
- This content is not available yet.
Read More 🍪
- It is a condition of both medical and social importance defined as significantly subaverage general intellectual functioning observed during the developmental period, characterized by inadequacy of adaptive behavior.
- The diagnosis depends on:
- IQ below 2 standard deviations from the mean
- Manifestation before 18 years of age
- Presence of maladaptive behavior
- IQ is calculated as Mental Age × 100 / Chronological Age
- In general terms:
- There are two overlapping populations of children with intellectual disability:
- Mild/moderate mental retardation (IQ >50), which is more associated with environmental influences;
- Severe mental retardation (IQ <50), which is more frequently linked to biologic causes.
- Mild mental retardation is four times more likely to be found in the offspring of women who have not completed high school than in women who have graduated. This is presumably a consequence of both genetic (children may inherit an intellectual impairment) and socioeconomic (poverty, undernutrition) factors.
- The specific causes of mild mental retardation are currently identifiable in <50% of affected individuals.
- The most common biologic causes of mild mental retardation include:
- Genetic syndromes with multiple minor congenital anomalies,
- Fetal deprivation,
- Prematurity,
- Perinatal insults,
- Intrauterine exposure to drugs of abuse,
- Sex chromosomal abnormalities.
- Familial clustering is frequent.
- In children with severe mental retardation, a biologic cause (most commonly prenatal) can be identified in >75% of cases. Causes include:
- Chromosomal (e.g., Down syndrome),
- Other genetic syndromes (e.g., fragile X syndrome),
- Abnormalities of brain development (e.g., lissencephaly),
- Inborn errors of metabolism/neurodegenerative disorders (e.g., mucopolysaccharidoses).
Causes of Mental Retardation
- Chromosomal abnormalities such as Klinefelter syndrome, Prader-Willi syndrome, Fragile X syndrome.
- Developmental brain abnormalities such as hydrocephalus.
- Inborn errors of metabolism.
- Congenital infections.
- Hypoxic Ischemic Encephalopathy.
- Trauma, meningitis, and metabolic disorders such as hypothyroidism amongst others.
- Most children with intellectual disability first come to the pediatrician’s attention in infancy because of dysmorphisms, associated dysfunctions, or failure to meet age-appropriate developmental milestones.
- There are no specific physical characteristics of intellectual disability, but dysmorphisms are the earliest signs that bring children to the attention of the pediatrician.
- Dysmorphisms may comprise a genetic syndrome such as Down syndrome or be isolated, as in microcephaly.
- Associated dysfunctions include neurologic disorders (e.g., seizures, cerebral palsy, autism) that are seen more frequently in conjunction with mental retardation than in the general population.
- Most children with intellectual disability do not keep up with their peers and fail to meet age-expected norms.
- In early infancy, failure to meet age-appropriate expectations may include:
- Lack of visual or auditory responsiveness,
- Unusual muscle tone (hypo- or hypertonia) or posture,
- Feeding difficulties.
- Between 6 and 18 months of age, motor delay (lack of sitting, crawling, walking) is the most common complaint.
- Language delay and behavior problems are common concerns after 18 months.
- Earlier identification of atypical development is likely to occur with more severe impairments; mental retardation is usually identifiable by age 3 years.
- Newborn – Dysmorphic syndromes, microcephaly, major organ system dysfunction (e.g., feeding and breathing)
- Early infancy (2–4 months) – Failure to interact with the environment, concerns about vision and hearing impairments
- Later infancy (6–18 months) – Gross motor delay
- Toddlers (2–3 years) – Language delays or difficulties
- Preschool (3–5 years) – Language difficulties or delays, behavior difficulties, including play, delays in fine motor skills: cutting, coloring, drawing
- School age (>5 years) – Academic underachievement, behavior difficulties (e.g., attention, anxiety, mood, conduct)
| IQ | Educational Terminology | Psychosocial Terminology | Usual Time of Diagnosis | Academic Potential |
|---|---|---|---|---|
| 70-84 | Slow learner | Borderline | Increasing academic difficulties | Eventually complete school with help |
| 55-69 | Educable | Mild MR | Nursery school | Primary school |
| 40-54 | Trainable | Moderate MR | Pre-school, when there is delayed developmental milestone | Can be taught survival words, self-help, social and vocational skills |
| 25-39, <25 | Sub-trainable | Severe MR / Profound | Infancy and Early childhood | Needs assistance even in self-help |
Severity of Mental Retardation and Adult-Age Functioning
- Mild – 9-11 years
- Moderate – 6-8 years
- Severe – 3-5 years
- Profound – <3 years
- In-depth history
- Detailed physical examination
- Basic tests to include visual and hearing evaluation
- Neuroimaging may be necessary.
- Chromosomal studies and hormonal assays, especially thyroid assays
- The diagnosis of mental retardation is clinical and involves the determination of Intelligence Quotient using specified tools such as:
- Bayley Scales of Infant Development
- Wechsler Scales
- Vineland Adaptive Behavior Scale (VABS)
- Woodcock-Johnson Scales of Independent Behavior
- American Association on Mental Retardation Adaptive Behavior Scale (ABS)
- “Draw-a-man test”
- Ziler’s “Draw-a-man” test has been validated for use in Nigerian children by Izuora and Ebigbo. It requires pencil and paper with a simple instruction to the child to draw a person.
- Multidisciplinary, with the pediatrician as the coordinator.
- Increasing public awareness of the adverse effects of drugs of abuse in pregnancy.
- Adequate antenatal care
- Prevention of early teenage pregnancy
- Keeping medicines and potential poisons out of reach of children
- Promote early prenatal care
- Promote immunization
- Children with mental retardation have higher rates of vision, hearing, orthopedic, and behavioral/emotional disorders than typically developing children.
- These and some other problems are identified later in children with mental retardation.
Practice Questions
Check how well you grasp the concepts by answering the following questions...
- This content is not available yet.
Read More 🍪
Contributors
Jane Smith
She is not a real contributor.
John Doe
He is not a real contributor.
Send your comments, corrections, explanations/clarifications and requests/suggestions