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Mental retardation

The topic describes issues related to mental retardation.

What is mental retardation?

It is defined as an intellectual functioning level (as measured by standard tests for intelligence quotient) well below average and significant limitations in daily living skills (adaptive functioning).

Description of MR

  • According to the ‘Centre for Disease Control and Prevention’, in the 1990s, mental retardation occured in 2.5 to 3 percent of the general population. Mental retardation begins in childhood or adolescence before the age of 18.
  • It persists throughout adulthood. Intellectual functioning level is defined by standardized tests (Weschsler-Intelligence Scales) that measure the ability to reason in terms of mental age (intelligence quotient or IQ). Diagnosis of mental retardation is made if an individual has an intellectual functioning level well below average and significant limitations in two or more adaptive skill areas.
  • Mental retardation is defined as IQ score below 70 to 75.
  • Adaptive skills are the skills needed for daily life. Such skills include 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.
  • In general, mentally retarded children reach developmental milestones such as walking and talking much later than the general population.
  • Symptoms of mental retardation may appear at birth or later in childhood. Time of onset depends on the suspected cause of the disability.
  • Some cases of mild mental retardation are not diagnosed before the child enters pre-school.
  • These children typically have difficulties with social, communication, and functional academic skills.
  • Children who have a neurological disorder or illness such as encephalitis or meningitis may suddenly show signs of cognitive impairment and adaptive difficulties.

Categories of mental retardation

Mild Mental Retardation

Approximately 85 percent of the mentally retarded population is in the mildly retarded category. 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 Mental Retardation

About 10 percent of the mentally retarded population is considered moderately retarded. Moderately retarded individuals 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 Mental Retardation

About 3 to 4 percent of the mentally retarded population is severely retarded. Severely retarded individuals have IQ scores of 20 to 40. They may master very basic self-care skills and some communication skills. Many severely retarded individuals are able to live in a group home.

Profound Mental Retardation

Only 1 to 2 percent of the mentally retarded population is classified as profoundly retarded. Profoundly retarded individuals 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 retardation is often caused by an accompanying neurological disorder. The profoundly retarded need a high level of structure and supervision

Causes of Mental Retardation

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, HIV
  • Exposure 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

Symptoms of Mental Retardation

  • Failure to meet intellectual developmental markers
  • Failure to meet developmental milestones such as sitting, crawling, walking, or talking, in a timely manner
  • Persistence of childlike behaviour, possibly demonstrated in speaking style, or by a failure to understand social rules or consequences of behaviour
  • Lack of curiosity and difficulty solving problems
  • Decreased learning ability and ability to think logically
  • Trouble remembering things
  • An inability to meet educational demands required by school


  • Treatment for Mental Retardation 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

Source: Dr Sudha Rani, Assistant Professor of Psychiatry, Institute of Mental Health, Hyderabad

Ayesha Feb 26, 2019 10:25 PM

How do we give reference for this article in APA Style?

Anita Jain Jun 24, 2016 09:40 PM

It is very difficult to leave an MR child alone so there should be some provision of some EOL for suffering parents.If in Govt . Job should be posted nearby.So that they can do justice to the child as well as job.

devendar Mar 16, 2014 12:40 PM

to do any physical activity every movement exept sleeping

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