Mental Retardation (Intellectual Disability)-How to Define?

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Mental Retardation Definition

Mental Retardation ( Intellectual Disability) is defined as sub-average general intelligence , manifesting during early developmental period. The child or an individual has diminished learning capacity and does not adjust well in Society.

In the population, 3 to 5 percent of Children have an I.Q. below 70. Nearly 4-5 such cases are mildly Mentally/intellectually Retarded . About 6 per 1000 of the population are more severally Mentally Retarded with an I.Q. below 50.

Mental Retardation ( Intellectual Disability ) - How to Define ?

Mental Retardation ( Intellectual Disability )

You Can Get More Information atMentalRetardation – baby, symptoms, average, Definition, Description

Grades of Mental Retardation/Handicap/Intellectual Disability

Intellect or Intelligent comprises: Perception, Memory, Recognition, Conceptualization, Convergent ,and Divergent reasoning , Verbal Facility and Motor Competence or ability.

Intelligence Tests devised to measure different parameters of intelligence in the Different age groups include the following:

  • Gasell’s Developmental Schedules
  • Bayley Infant Scales
  • Griffith’s Mental Developmental Scale
  • Wechsler Preschool and Primary Scale of Intelligence (W.P.P.S.I)
  • Wechsler Intelligence Scale for Children (W.I.S.C)
  • Standford-Binet Tests ( Terman-Merrill Revision )
  • Raven’s Matrices
  • Denver 2nd Developmental Screening Test
  • Good Enough Draw-a-man Test
  • Adaptive Behavior Scale

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Intelligence Quotient (I.Q.)

Intelligence Quotient (I.Q.) is calculated as Below :

Mental age divided by Chronological Age , Multiplied by 100.

Classifications of Mental Retardation

The Degree of Mental Handicap is Designated :

Mild Mental Retardation– 51-70%

Moderate Mental Retardation-36-50%

Severe Mental Retardation-21-35%

Profound Mental Retardation-0-20%

Note: The I.Q. level of 71-90% is designated Borderline Intelligence and is not included in Mental Retardation.

The term Educable and Trainable is used for Mild and Moderate Mental Retardation Respectively. For the Severe and Profound mental Retardation , the term used the Custodian.

Note: All the levels of Mental Retarded Children are Educable and Trainable to Some Extend.

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Causes of Mental Retardation

Mental Retardation is due to interplay of several Biomedical, Socio-cultural and Psychological Factors.

Major causes of Mental Retardation are Idiopathic.

  • Specific Causes may be described as Under:
    1. Prenatal Factors
    2. Natal Factors
    3. Postnatal Factors


Prenatal Causes of Mental Retardation:

  • Metabolic
    1. Aminoaciduria-
      1. Phenylketonuria,
  • Homocystinemia,
  • Histidinemia,
  1. Organic Aciduria
  1. Galactosemia
  2. Mucopolysaccharidosis
  3. Inherited Disorders of Central Nervous System
  • Chromosomal Disorders
    1. Down’s Syndrome
    2. Fragile X Syndrome
    3. Klinefelter
  • Enviromental and Nutritions Deficiencies during Pregnancy such as Iodine Deficiency.
  • Neuro-ectodermal Dysplasia, Tuberous Sclerosis.
  • Developmenatal Defects
    1. Microcephaly
    2. Craniostenosis
    3. Cretinism
    4. Porencephaly
  • Maternal Factors:
    1. Use of Teratogenic drugs in the First Trimesters of Pregnancy.
    2. Infections such as Rubella, Toxopladmosis,Cytomegalic inclusion diseases, Herpes, Syphilis and HIV.
    3. Placental Insufficiency
    4. Toxiemia of Pregnancy
    5. Antepartum Haemorrhage.
    6. Radiation during Pregnancy

Natal Causes of Mental Retardation

  1. Birth Injuries
  2. Hyposic , Ischemic Encephalopathy
  3. Intracerebral Haemorrhage

Post Natal Causes of Mental Retardation

  • Infections of Central Nervous System and Meningoencephalitis.
  • Head injuries
  • Hypoxia
  • Cerebrovascular
  • Post-vaccinal Encephalopathies
  • Kernicterus
  • Hypoglycerine
  • Malnutrition
  • Child Abuse
  • Autism

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Predisposing Causes of Mental Retardation:

  1. Low Socio-economic Factors:

These children are exposed to several environmental causes of Mental Retardation, such as Indequate Nutrition of Mother and child , Poor antenatal and obstetric care, Lack of immunization /Vaccination, Delayed and Inappropriate treatment of Infections and Unsatisfactory Environmental Stimulation.

  1. Low Birth Weight:

The  small Gestational age (SGA) infant has a poorer long-term prognosis for Postnatal developmental than the preterm baby of equal Birth weight which is appropriate for its Gestational Age.The Preterm infant is more liable to Cerebral Hemorrhage, Anoxia, and infections.The Small Gestational age (SGA) infant is subjected to adverse genetic or prenatal Environmental Conditions, which may sometimes leads to brain Damage.

  1. Advanced Maternal Age:

Chromosomal Anomalies such as Down’s Syndrome as well as Intrauterine Factors,Such as Fetal Deprivation and Hypoxia are Commoner in babies of Older Mothers.

  1. Consanguinity of parents is associated with a high incidence of Genetically Transmitted Mental Retardation.

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Clinical Features and Mental Retardation Symptoms:

  • Behavioral Syndrome of Cerebral Dysfunction such as Hyperactivity.
  • Short Span of Attention
  • Distractibility
  • Poor Concentration
  • Poor Memory
  • Impulsiveness
  • Awkward Clumsy Movements
  • Disturbed Sleep
  • Emotional Instability
  • Low Frustration Tolerance
  • Wide Scatter in Intellectual Function

Other Symptoms:

Specific Clinical Signs

  • Cretinism
  • Chromosomal Defects
  • Mucopolysaccharides
  • Homocystinemia
  • Lipidoses

Associated Symptoms:

  • Musculo-Skeletal System defects
  • Of Visual or Visiual Problems
  • Speech and Hearing disorders
  • Convulsions

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