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Intellectual disability

As  per Census  2011,  there  were  1.5  million  persons  with  intellectual disability  in  India. However  other  estimates  vary  significantly,  and it  is  difficult  to  collect  the  accurate prevalence rate of intellectual disability in a country like India.


The Rights of Persons with Disabilities Act, 2016 defines Intellectual Disability as a condition characterised by significant limitations both in intellectual functioning (reasoning, learning, problem solving) and in adaptive behaviour which covers a range of everyday, social and practical skills, including:

  • Specific learning disabilities refer a heterogeneous group of conditions wherein there is a deficit in processing language, spoken or written, that may manifest itself as a difficulty to comprehend, speak, read, write, spell, or to do mathematical calculations and includes such conditions as perceptual disabilities, dyslexia, dysgraphia, dyscalculia, dyspraxia and developmental aphasia;
  • Autism spectrum disorder refers to a neuro-developmental condition typically appearing in the first three years of life that significantly affects a person's ability to communicate, understand relationships and relate to others, and is frequently associated with unusual or stereotypical rituals or behaviours.

Globally and in practice it is generally defined by an IQ under 70-75, in addition to deficits in two or more adaptive behaviors that affect every day, general living. Adaptive skills are skills needed for daily life including the ability to produce and understand language (communication); home-living skills; use of community resources; health, safety, leisure, self-care, and social skills; self-direction; functional academic skills (reading, writing, and arithmetic); and work skills.


  • Mild Intellectual Disability: Approximately 85 percent of the mentally retarded population globally are categorized as having a mild disability. Their IQ score ranges from 50 to 75 and they can often acquire academic skills up to the sixth grade level. They can become fairly self-sufficient and in some cases live independently, with community and social support.
  • Moderate Intellectual Disability: About 10 percent of the mentally retarded population is considered moderately retarded. Individuals with moderate disability have IQ scores ranging from 35 to 55. They can carry out work and self-care tasks with moderate supervision. They typically acquire communication skills in childhood and are able to live and function successfully within the community in a supervised environment such as a group home.
  • Severe Intellectual Disability: About 3 to 4 percent of the itellectual disability population is severely disabled. Individuals with severe intellectual disability have IQ scores of 20 to 40. They may master very basic self-care skills and some communication skills. Many are able to live in a group home.
  • Profound Intellectual Disability: Only 1 to 2 percent of the intellectually disability population is classified as profoundly retarded. Individuals with profound disability have IQ scores under 20 to 25. They may be able to develop basic self-care and communication skills with appropriate support and training. Their disability is often caused by an accompanying neurological disorder. Those with profound disabilities need a high levelof structure and supervision.

Intellectual disability is also subdivided into syndromic intellectual disability, in which intellectual deficits associated with other medical and behavioral signs and symptoms are present, and non-syndromic intellectual disability, in which intellectual deficits appear without other abnormalities. Down syndrome and fragile X syndrome are examples of syndromic intellectual disabilities.

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Prenatal causes (causes before birth)

  • Chromosomal Disorders: Down’s syndrome, fragile X syndrome, prader wili syndrome, klinfelter’s syndrome
  • Single Gene Disorders: Inborn errors of metabolism like galactosemia, phenyl ketonuria, hypothyroidism, muco polysaccaridoses, tay sachs disease
  • Neuro Cutaneous Syndromes: Tuberous sclerosis, neurofibromatosis
  • Dysmorphic Syndromes: Laurence Moon Biedl syndrome
  • Brain Malformations: Microcephaly, hydrocephalus, myelo meningocele

Abnormal maternal environmental influences

  • Deficiencies: Iodine deficiency and folic acid deficiency, severe malnutrition
  • Substance use: Alcohol, nicotine, cocaine
  • Exposure to harmful chemicals: Pollutants, heavy metals, harmful drugs like thalidomide, phenytoin, warfarin sodium etc.
  • Maternal infections: Rubella, toxoplasmosis, cytomegalovirus infection, syphilis, HIVExposure to: Radiation and Rh incompatibility
  • Complications of Pregnancy: Pregnancy induced hypertension, ante partum hemorrhage, placental dysfunction
  • Maternal Disease: Diabetes, heart and kidney disease
  • During delivery: Difficult and/or complicated delivery, severe prematurity, very low birth weight, birth asphyxia, birth trauma
  • Neonatal period: Septicemia, jaundice, hypoglycemia, neonatal convulsions
  • Infancy and childhood: Brain infections like tuberculosis, Japanese encephalitis, bacterial meningitis, Head trauma, chronic lead exposure, severe and prolonged malnutrition, gross under stimulation


  • Treatment for Intellectual Disability is not designed to "cure" the disorder. Rather, therapy goals include reducing safety risks (e.g., helping an individual maintain safety at home or school) and teaching appropriate and relevant life skills. Interventions should be based on the specific needs of individuals and their families, with the primary goal of developing the person's potential to the fullest.
  • Medications are required to treat co morbidities like aggression, mood disorders, self injurious behaviour, other behavioral problems and convulsions which occur in 40%to 70% of cases.

Statistics in India

As  per Census  2011,  there  were  1.5  million  persons  with  intellectual disability  in  India. However  other  estimates  vary  significantly,  and it  is  difficult  to  collect  the  accurate prevalence rate of intellectual disability in a country like India.

References for More Reading and Understanding/Sources

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