Mental Handicap

Synonyms: mental retardation, learning disability

Mental retardation is a condition of arrested or incomplete development of the mind, which is especially characterised by impairment of skills manifested during the developmental period, contributing to the overall level of intelligence, i.e. cognitive, language, motor and social abilities. The DSM-IV definition is:

• IQ less than 70.
• Dysfunction or impairment in more than 2 of the following areas: communication, self-care, home living, social/interpersonal skills, use of community resources, self-direction, functional academic skills, work, leisure, health and safety.
• Onset during childhood (before age 18)

• Mild learning disability: IQ 50-70, approximately 85% of cases; most can lead normal lives except may need assistance in handling difficult situations.
• Moderate: IQ 35-49, approximately 10% cases; use simple language when talking but understand speech better. Patient can generally attend to the basic tasks of life after training but more complex activities such as using money usually require support within a special residential environment.
• Severe: IQ 20-34, approximately 3-4% cases: many able to look after themselves with careful supervision.
• Profound: IQ less than 20, approximately 1-2% cases: development level of one year old baby across a range of parameters and so require intensive help and supervision in all activities.

The prevalence is 20-30/1,000 population of all ages but less than 50% of these require special provision.

• Genetic: chromosome disorders: trisomy (e.g. Down's syndrome), deletion (e.g. cri du chat), sex chromosome anomaly (e.g. Fragile X, Klinefelter's, Turner's)
• Metabolic: amino acid (e.g. phenylketonuria), carbohydrate (e.g. galactosaemia), lipid (e.g. Tay-Sach's, Gaucher's, Niemann-Pick), mucopolysaccharidoses (e.g. Hurler's syndrome)
• Cerebral degeneration: e.g. gangliosidoses, leucodystrophies
• Structural disorders: e.g. tuberose sclerosis, familial hydrocephalus, neurofibromatosis
• Intrauterine:
  • Nutritional deficiency: e.g. iodine deficiency
  • Congenital infection: e.g. CMV, rubella, toxoplasmosis
• Drugs: e.g. phenytoin, alcohol
• Cerebral malformations: e.g. holoprosencephaly, lissencephaly
• Perinatal:
  • Antenatal: e.g. pre-eclampsia, antepartum haemorrhage, premature labour
  • Intrapartum: e.g. prolonged labour, trauma, asphyxia
• Neonatal: e.g. intraventricular haemorrhage, hypoglycaemia, meningitis, severe neonatal jaundice
• Postnatal:
  • Accidental or non-accidental injury
  • Infection: e.g. encephalitis, meningitis
  • Anoxia: asphyxia, status epilepticus, near drowning
  • Metabolic, endocrine: hypoglycaemia, hypernatraemia, hypothyroidism
  • Poisoning: lead, carbon monoxide
  • Malnutrition

• The presentation will depend on the cause.
• Generally poor performance on tasks such as learning, short term memory and problem solving.
• Frequently associated with specific congenital syndromes e.g. Down's syndrome, fragile X syndrome.
• Assessment needs to consider the possible cause, e.g. family history, birth history, functional disability and associated medical, psychological and social difficulties.

• Physical:
  • Motor and mobility problems
  • Abnormalities of movement
  • Speech, hearing and visual impairment
  • Epilepsy
  • Urinary and faecal incontinence
• Psychological (the following are more common in patients with learning disabilities):
  • Schizophrenia
  • Anxiety and depressive disorders
  • Personality disorder
  • Early onset dementia
  • Autism
  • Hyperactivity and attention-deficit hyperactivity disorder
  • Eating disorders, including rumination, food faddiness, and anorexia nervosa and bulimia nervosa are common
• Behaviour:
  • Threatening safety of themselves or others
  • Seemingly violent but harmless behaviour is often interpreted as aggression.¹
  • Temper tantrums
  • Criminal activity
• Sleep disorders

• Management includes multidisciplinary support for both the child and the rest of their family. The person with mental handicap and their carer(s) and family need a great deal of physical and emotional support.
• Psychological, psychosocial, and educational interventions for deprived children with low IQ have been shown to have positive effects on behaviour, overall adjustment, and possibly also on IQ.¹
• Behavioural treatment methods for self-injury in learning disability are probably effective if used systematically by people who are well trained in such methods.¹
• Psychotropic drugs are often used but rarely produce significant benefits.
• Direct support and coaching of young people with learning disability are efficient ways to improve their integration into employment.¹

• Behaviour problems: includes distractible, overactive, impulsive, repeated self-injury, stereotyped repetitive and purposeless activities.
• Sexual problems: curiosity about other people's bodies may be misunderstood as sexual; inappropriate behaviour, e.g. masturbation, in public.
• Physical disorders are more frequent, e.g. sensory or motor disabilities, epilepsy. disorders of vision and hearing are more frequent.
• Effects on the family: parental rejection, physical and emotional stress in caring for a child with learning disability, difficulty with family dynamics with other sibs, increasing difficulty as the child gets older with isolation, contraception etc.

• Most adults with learning disability have very limited economic resources.
• People with severe learning disability have a particularly poor outlook. Those with mild learning disability and borderline intelligence also do poorly in terms of the adaptive functioning.¹
• Life expectancy is reduced in those with learning disability. Non-mobile children and those incapable of feeding themselves may be at particular risk of a short life expectancy.
• Both the scope and pattern of disease mortality and cause-specific mortality tend to become increasingly similar to those of the general population after the age of 40 years.¹

• Early and effective management of problems and effective antenatal and intrapartum care.
• Early and effective management of problems in the neonatal period and early childhood.