One to three percent of the general population has mental retardation. In some countries (such as the UK), the word learning disability is used instead to avoid the pejorative connotations associated with the word mental retardation. However, in this book, the term mental retardation is retained as it is the preferred term in both ICD-10 and DSM-IV-TR.
Mental retardation is characterized by significantly sub-average intellectual performance coupled with significant impairment in adaptive functioning; it manifests during the developmental period (before 18 years of age). An IQ below 70 indicates significantly sub-average intelligence, while adaptive behavior is the ability to accept responsibilities in social, personal, occupational, and interpersonal areas of life appropriate to age, socio-cultural background, and education level. A standardized assessment scale and clinical interviews measure adaptive behavior.
Very often, it is assumed that persons with mental retardation constitute a homogenous group. This is however not true. Persons with mental retardation vary in their behavioural, psychological, physical, and social characteristics as much as the so-called ‘normal’ general population does.
Another common error is taking the IQ score as the measure of someone’s intelligence. It should be remembered that a person with mental retardation must have a deficit in both general intellectual functioning and adaptive behaviour. A classification of mental retardation on the basis of IQ ( Intelligence Quotient, which is equal to mental age, i.e. MA, divided by chronological age, i.e. CA, multiplied by 100; i.e. IQ = MA/CA × 100).
Mild Mental Retardation
This type of mental retardation is the most common, accounting for 85-90% of all cases. Usually, diagnosis occurs later in life than in other types. They often develop as normal children do in the preschool period (before 5 years of age), with little to no deficits. They can often achieve social and vocational independence with little or no support after reaching the 6th grade (grade) in school. Supervised care may be required only in stressful situations or when another disease is present. In a previous educational classification of mental retardation, this group was referred to as ‘educable’
Moderate Mental Retardation
Around 10% of all persons with intellectual disabilities are between the ages of 35 and 50. These individuals were previously classified as ‘trainable’ in the educational field, although many of them are also academically capable. The children can learn to speak despite poor social awareness in the early years of their lives. Many drop out after the second class (grade). They can be taught to support themselves by engaging in unskilled, semi-skilled, or even light work. Stress may destabilize them and prevent them from adopting, so they are best suited for supervised jobs.
Severe Mental Retardation
The signs and symptoms of severe mental retardation are particularly notable in the early years of life, such as an inability to move well (significantly delayed developmental milestones) and difficulty communicating. During the latter stages of life, they can be trained in basic health care and taught how to talk. With close supervision, they can perform simple tasks. These people were classified as dependent in the earlier educational system.
Profound Mental Retardation
This group accounts for about 1-2% of all persons with mental retardation. A physical disorder often related to mental retardation occurs in this subtype. Significant developmental delays occur in this subtype. A carefully planned and structured environment (such as a group home or residential placement) is often necessary to provide nursing care or ‘life support’ to them.
Etiology of Mental Retardation:
Mental retardation is a condition that is caused not only by biological factors but also by psychosocial factors. In more than one-third of cases, no cause can be found despite an extensive search. There appears to be a preponderance of males among people with mental retardation. Some important causes of mental retardation are discussed below.
- Genetic (probably in 5% of cases)
- Chromosomal abnormalities (such as Down’s syndrome, Fragile-X syndrome, Turner’s syndrome, Klinefelter’s syndrome)
- Inborn errors of metabolism, involving aminoacids (phenylketonuria, homo-cystinuria, Hartnup’s disease), lipids (Tay-Sachs disease, Gaucher’s disease, Niemann-Pick disease), carbohydrates (galactosaemia, glycogen storage diseases), purines (Lesch-Nyhan syndrome), and mucopolysaccharides (Hurler’s disease, Hunter’s disease, Sanfi llipo’s disease).
- Single-gene disorders (such as tuberous sclerosis, neurofi bromatosis, dystrophia myotonica)
- Cranial anomalies (such as microcephaly)
- Perinatal causes (probably in 10% of cases)
- Infections (such as rubella, syphilis, toxoplasmosis, cytomegalo-inclusion body disease)
- Birth trauma
- Intrauterine growth retardation (IUGR)
- Placental abnormalities
- Drugs during fi rst trimester.
- Acquired physical disorders in childhood (probably in 2-5% of cases)
- Infections, especially encephalopathies
- Lead poisoning
- Cerebral palsy.
- Sociocultural causes (probably in 15% of cases)
- Deprivation of sociocultural stimulation.
- Psychiatric disorders (probably in 1-2% of cases)
- Pervasive developmental disorders (such as Infantile autism)
- Childhood onset schizophrenia.
The commonly used tests for measurement of intelligence:
- Seguin form board test.
- Stanford-Binet, Binet-Simon, or Binet-Kamath tests.
- Wechsler Intelligence Scale for Children (WISC) for 6½ to 16 years of age.
- Wechsler’s Preschool and Primary Scale of Intelligence (WPPSI) for 4 to 6½ years of age.
- Bhatia’s battery of performance tests.
- Raven’s progressive matrices (coloured, standard and advanced).
The tests used for the assessment of adaptive behaviour:
- Vineland Social Maturity Scale (VSMS).
- Denver Development Screening Test (DDST).
- Gessell’s Development Scale.
Differential Diagnosis for Mental Retardation
Generally, mental retardation is an easy diagnosis. The following conditions, however, must be taken into consideration when making this diagnosis, since they can easily be confused with mental retardation, with disastrous consequences.
- Deaf and dumb (This possibility must always be ruled out either by clinical examination and/or by audiometry).
- Deprived children, with inadequate social stimulation (Although this can also cause mental retardation, many children become ‘normal’ intellectually on providing adequate stimulation).
- Isolated speech defects.
- Psychiatric disorders (such as infantile autism, childhood-onset schizophrenia).
- Systemic disorders (without mental retardation but with physical debilitation).
Management of Mental Retardation
The management of mental retardation can be discussed under prevention at primary, secondary, and tertiary levels.
- Primary Prevention:
- Improvement in socioeconomic condition of society at large, aiming at elimination of under-stimulation, malnutrition, pre maturity and perinatal factors.
- Education of the lay public, aiming at the removal of the misconceptions about individuals with mental retardation.
- Medical measures for good perinatal care to prevent infection, trauma, excessive medication use, malnutrition, obstetric complications, and diseases associated with pregnancy.
- The immunization of all children with BCG, polio, DPT, and MMR.
- Conducting research to study the causes of mental retardation and their treatment.
- Genetic counselling in at-risk parents, e.g. in phenylketonuria, Down’s syndrome.
- Secondary Prevention
- Early detection and treatment of preventable disorders, e.g. phenylketonuria (low phenylalanine diet), maple syrup urine disease (low branched amino-acid diet) and others as discussed earlier; hypo thyroidism (thyroxine).
- Early detection of handicaps in sensory, motor or behavioural areas with early remedial measures and treatment.
- Early treatment of correctable disorders, e.g. infections (antibiotics), skull configuration abnormalities (surgical correction).
- Early recognition of the presence of mental retardation. A delay in diagnosis may cause an unfortunate delay in rehabilitation.
- People with mental retardation should be integrated with normal individuals as much as possible, and any kind of segregation or discrimination should be avoided. It is important to provide them with facilities to help them maximize their potential. Special schools can, however, be useful for people with more severe mental disabilities.
- Tertiary Prevention
- Mental health and behavioral problems must be treated appropriately.
- A method of behavior modification that uses positive reinforcement and negative reinforcement.
- Rehabilitation in vocational, physical, and social areas, according to level of handicap.
- In order to reduce levels of stress, parent counseling is extremely important, as well as teaching parents how to adapt to their situation, enlisting them as co-therapists, and encouraging the formation of parent organizations, or caregiver organizations.
- A profoundly retarded individual may require institutionalization or residential care.
- Legislation: The ‘Persons with Disability Act’ came into being in India in 1995. Aiming to improve the welfare of individuals with disabilities in general, and individuals with mental disabilities in particular, this act mandates support for prevention, early detection, education, employment, and other services. People with disabilities are protected by this Act from discrimination and affirmative action. The ‘National Trust Act’ was passed in 1999. In this Act, it is proposed that government funding be used to fund a variety of services and facilities for mentally challenged individuals and their families.