INTELLECTUAL DISABILITIES

 Definitions and Classification:  

"A delayed intellectual growth that is manifested in immature reactions to environmental stimuli and below average social and academic performance. Intellectual disabilities are also known as Developmental Disabilities." (Winzer) 

To be classified with an intellectual disability an individual must meet the following criteria:

• have a score below 70 on a standardized IQ test.
• have deficits in adaptive behaviour (including self care, home living, social skills, health and safety).

There are four degrees of intellectual disabilities measured by a standardized IQ test:

• Mild (IQ= 55-70): The student is capable of basic academic subjects.
• Moderate (IQ= 40-55): The student is capable of attaining self-help skills, communication skills, and social adjustment skills.
• Severe (IQ= 25-40): The student shows basic communication and self-help skills.

• Profound (IQ= below 25): The student can learn basic self-help and communication skills with intensive intervention.  

 Etiology: 

Chromosomal:

• individuals can have too many, too few or attached chromosomes.
• abnormalities in structure and number of chromosomes can be caused by natural mutations of genes, radiation and other factors.

Genetic Defects: 

• specific disorders are associated with distinctive behavioural phenotypes, which play a key role in a child's behaviour and learning styles. 
• 1/3 of intellectual disabilities come from genetic defects.

Infections/Intoxicant: 

• occurs in pregnant mothers passed on to their unborn children (rubella,syphilis etc.), infants and young children.
• intoxicants and poison (alcohol, nicotine etc.)  in a mother can cause an intellectual disability.

Environmental Influences:

• deprived background.
• psychological disadvantages.
• poverty 
•  inadequate nutrition.
• dysfunctional family dynamics.
• lack of educational opportunities.
• unstimulating infant environment. 

Prevalence:   

In the case of intellectual disabilities, mild conditions prove elusive and difficult to accurately pinpoint. Mild cases go unreported, although this is not true in the case of significant intellectual impairments.
Theoretically 2.27% of the populatoin may fall into the classification of intellectually disabled. In reality about 1 to 1.5% of the population meet the A.A.M.R definition of "retarded" in both intellectual and adaptive behaviour. 

• more than 75% of those identified are in the mild range.
• moderate, severe and profound account for 3 to 4 persons out of 1000, with severe and profound being extremely low-incidence conditions.
•  for a variety of reasons the number of boys identified is greater than that of girls by factors of five to ten. (Bennett) 
• the disablility also has a significantly higher prevalence in children from lower socio-economic classes.(Bennet)

The following is a list of the more common conditions with their prevalences. For a more detailed list see Winzer p184,185, table 6.5

Down Syndrome ( trisomy 21)         1 in 1,000.
Turners Syndrome                          1 in 2,500.
Prader-Willi Syndrome                    1 in 10,000 to 25,00.
Angleman Syndrome                       1 in 12,000 to 20,000.
Williams Syndrome                         1 in 20,000 to 25,000
Fragile X Syndrome                         1 in 25,000 to 1 in 40,000.

*Fetal Alcohol Syndrome (F.A.S.) is now considered to be the second major cause of intellectual and developmental disability in Western countries. Although conclusive data on the prevalence of F.A.S. are still being developed, there is concensus that the numbers are rising.