Mental retardation in children is defined as the ‘sub-average intellectual functioning resulting from any insult during the period of development, co-existing with limitations in at least two of the following 10 areas of adaptive behaviors – communication, self-care, home living, social skills, community use, self-direction, health and safety, functional academics, leisure and work.

Practically, it may be defined as an intelligence quotient (IQ) below 2 SD for chronological age, corresponding to a range of 70-75 on standard psychometric tests. Early identification of Mental retardation in children is crucial to achieve best possible functional outcome.

Classification: Conventional classification is based on IQ scores has been largely replaced by the revised classification systems based on need for support system necessary for daily functioning.

Incidence: It is estimated that —3% of general population fulfills the diagnostic criteria for Mental retardation in children, though> 80% of them have only mild disease.

Mental retardation in children is relatively more common in males and children with following risk factors — a) similar family history, b) consanguinity, c) elderly mothers, d) low birth weight or other perinatal complications.

Etiology: It may be genetic, environmental or mixed in origin, though the exact cause is identifiable in only 40-60% cases.

Mild to moderate Mental retardation in children is usually idiopathic or familial in origin, with recurrence risk in the offspring being 40% if both parents are affected and — 20% if only one parent is retarded. Down syndrome is the commonest cause of genetic MR in Indian children.

PKU: Phenylkenonuria, ALT5: Acute Life-threatening Events

Clinical presentation: Severe or profound Mental retardation in children is easily identified in early infancy due to delayed milestones. However mild to moderate cases are often missed till school entry or even later age. Important early indicators include Developmental delay on early surveillance, Poor scholastic performance, Neurosensory deficits like cerebral palsy, visual hearing defects, seizures, language delay etc, Presence of physical stigmata and Behavioral problems like attention deficit, hyperactivity, impulsivity, clumsy movements.

Diagnostic Evaluation of Mental retardation involves confirmation the diagnosis, identification of underlying etiology and identification of limiting neurosensory defects

Step I: Confirmation of diagnosis: Mental retardation in children is a shattering diagnosis for parents and should be made only after careful developmental or IQ assessment. As the single assessment may he abnormal due to temporary variability in performance or environmental influences, an abnormal observations needs to be reconfirmed before disclosing the diagnosis to parents. Other causes for poor performance on developmental or IQ testing like Hearing or visual defects, should also be considered to eliminate secondary delays in development.

Development or intelligence quotient (DQ or IQ) is a ratio (mental age/chronological age x 100), commonly used to denote presence and severity of Mental retardation in children. It may be assessed by a number of age-appropriate screening tests to evaluate various domains of cognitive and adaptive behavior, with due consideration for ethnic and linguistic variations as well as adequacy of sensory inputs like hearing and vision.

In India, commonly used age-appropriate developmental tests are – Bayley’s Scales of Infant Development (< 2.5 years), Kamat’s test or Wechsler Preschool and Primary Scale of Intelligence — WPPSI (3-7 years), Wechsler Intelligence Scale for Children — WISC (6-16 years) and Wechsler Adult Intelligence Scale — WAIS (>16 years). Adaptive skills are generally tested using neland Adaptive Behavior scale.

Step II: Etiological diagnosis is often difficult, though every effort should be made to identify preventable! treatable causes. Important steps in etiological diagnosis include —

a) Detailed history, with special reference to similar family history (pedigree analysis), consanguinity, adverse antenatal/perinatal events and behavioral problems like attention-deficit.

b) Developmental evaluation with sequential recording of milestones to — i) distinguish between non progressive Mental retardation in children (delay since birth) and neurodegenerative disorders (regression of milestones); and ii) identify or exclude discrepancy between motor, social, adaptive and language skills.

Mental retardation in children is the global delay in all spheres of psychosocial development, while selective delay in only one or two fields indicates sensory problems (hearing for language, vision for adaptive milestones) or neuromuscular disorders like cerebral palsy (isolated delay in motor milestones).

c) Physical examination with special reference to anthropometry, physical stigmata, vision/hearing problems and neurological signs. Ophthalmoscopic examination is highly informative in etiological diagnosis of Mental retardation in children, like chorioretinitis in intrauterine infections, cherry-red spot in neurodegenerative disorders, papilledema in hydrocephalus etc.

d) Relevant Investigations, depending on suspected etiology, mainly include cytogentic, biochemical and neuroimaging tests.

e) Family screening: Once a genetic diagnosis is firmly established in the index case, parents and siblings should be screened for computing the recurrence risk and genetic counseling.

Step III: Identification offunction-limiting defects i.e. hearing & vision defects, neuromotor problems, seizures, behavioral problems and parent-child relationship.

Management: Except few conditions like hypothyroidism, phenylketonuria and lead intoxication, for which specific therapy is available, majority of the disorders with MR have no treatment. In such cases, primary aim of the management is to achieve maximum functional independence and eliminate function-limiting factors like vision or hearing correction.

Management and rehabilitation program of each child needs to be individualized, according to their needs and potential.

A multidisciplinary team-approach is essential in these cases, involving following interventions —

1) Physio/occupational therapy for neuromuscular dysfunctions

Common physical stigmata in Mental retardation in children

  • Size : Tall/short stature, Obesity, Failure to thrive
  • Head : Microcephaly, Hydrocephalus
  • Eyes : Slanting eyes, Microphthalmia, Cataract
  • Ears : Deformed or Low-set ears
  • Face : Coarse fades, Retro-/prognathia
  • Mouth : Cleft lip/palate, Macroglossia
  • Hair : Sparse, kinky, light-colored
  • Neck : Short or Webbed neck
  • Limb : Brachy-/arachnodactyly, poly-/syndactyly Abnormal dermatoglyphics
  • Skin : Café au alt spots, Adenoma sebaceum
  • Genitals: Hypogonadism, hypospadias

Laboratory investigations in Mental retardation in children

  • Skeletal survey for bone age
  • Neuroimaging – CT/MRI for structural CNS lesions
  • Electrophysiological studies: EEG, EMG, BERA
  • Serologicaltests for Intrauterine infections
  • Hormonal assays like Thyroid function tests
  • Toxin screening: Lead, Uric acid
  • Cytogenetic studies: Karyotyping, Barr bodies, others
  • Urinalysis for Inborn errors of metabolism like Benedict test, Ferric chloride test, AA chromatography
  • Enzyme assays for neurodegenerative disorders AA: Amino acid

2) Management of associated deficits like hearing, vision and speech delay, seizures etc.

3) Psychotherapy or behavioral modification

4) Family counseling and social support

5) Schooling – Efforts should be made to educate mild! moderate Mental retardation in children in a regular school as far as possible.

I) Institutionalization is the last resort, often needed in severe/profound condition.

Prevention of MR and associated handicaps may be broadly divided into —

I) Primary prevention includes following interventions in all prospective mothers —

a) Pre-conceptional measures like Control of goiter in adult population and MMR immunization in girls

b) Antenatal measures like Serological screening for intrauterine infections, Folic acid supplements for neural tube defects, Anti-D prophylaxis in Rh-negative mothers and  Appropriate obstetrical and neonatal care

c) Neonatal screening for hypothyroidism, PKU etc.

II) Secondary prevention includes prenatal diagnosis and genetic counseling in cases with family history of Mental retardation in children in parents or previous siblings. Familial MR is usually multifactorial in origin with recurrence risk of 20-40%. Although prenatal diagnosis is difficult in these cases, prenatal genetic studies may be used to avoid recurrence of other genetic!chromosomal defects.

III) Tertiary prevention includes minimization of functional handicaps in established by early diagnosis and treatment of limiting factors.

IV) Legislative support – Mental retardation in children has been included as a disability under ‘The Person with Disabilities (Equal opportunities, Protection of rights and Full participation) Act, 1995’ that provides for screening of children at-risk, awareness campaigns via mass media and improve perinatal care. It also provides for free education, research and setting up of special teacher’s training institutes.