Mental Retardation | intellectual disability

Mental retardation (MR) is one of the most commonly observed neuropsychiatric disorders among children and adolescents. Its prevalence among young individuals is of 1%, however, some authors report rates of 2 to 3%, with estimates of up to 10%. It is commonly agreed that MR is more frequent in males, a finding that is attributed to numerous gene mutations in X chromosome. The male/female ratio is 1.3 to 1.9: When affected children visit the general pediatrician, they often present with speech delay, behavioral disorders, or low school performance.

Mental Retardation | intellectual disability
Mental retardation word cloud

What causes Mental Retardation?

● Genetic factors

● Hereditary factors or chromosomal abnormalities Pregnancy and birth factors

● e.g. misuse of drugs or excessive alcohol intake during pregnancy, complication of birth, prematurity
Infancy and childhood

● Infections and brain injuries, e.g. meningitis, brain trauma, etc. Unknown factors

● The cause in most cases is unknown

Diagnosis of mental retardation

The diagnosis of MR is established according to three criteria: onset of symptoms before the age of 18 years; intellectual function significantly lower than average, with an IQ equal to or less than 70; and poor adaptive skills in at least two of the following areas: communication, self-care, social/interpersonal skills, self-guidance, school performance, work, leisure, health and safety.

An IQ greater than 85 is considered normal, and individuals with an IQ between 71 and 84 are regarded as having a borderline IQ level. IQ tests are more valid and reliable in children older than five years, therefore, many authors prefer to use other names for MR, such as developmental delay, learning disabilities, developmental disorder, or developmental deficiency.

Moreover, since IQ tests are not always available, there is a natural tendency towards the use of developmental delay and MR as synonyms, but we should bear in mind that not every young child with developmental delay will have MR when formally tested at a later age

How does Mental Retardation affect the child?

Developmental aspects affected by MR:

● Attention

● Memory

● Language ability

● Gross and fine motor coordination

● Learning and problem-solving abilities

● Social and self-care skills

● Ability to control emotion and behavior As the child’s abilities in the above aspects are significantly lower than children of comparable age, his/her adaptability in daily life would be affected.

● Ability to communicate

● Self-care

● Housework

● Social skills

● Working and learning

● Community life

What are the different grades of Mental Retardation?

According to the prevailing international classification system, MR can be classified into the following grades according to its severity:

● Persons with “mild” to “moderate” MR face relatively fewer obstacles during their development. They can acquire general daily living and self-care skills with proper training and assistance.


● Persons with “severe” to “profound” MR require intensive training and support in various aspects to cope with basic needs in daily life.


● A “three-tier system” is normally used in Hong Kong for operational classification, i.e. MR is classified into “mild”, “moderate” and “severe” (including severe and profound) grades for the provision of special educational and training services.

How can parents help their child with Mental Retardation?

● Arrange early assessment for the child so as to understand and accept his/her developmental problems

● Involve in the child’s training so as to master the training methods and communicate with the instructors

● Join parent self-help groups and make good use of community resources

● Share feelings with others to relieve negative emotion and stress


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