There are also acquired neurobiological factors (an illness or injury that affects the brain early in life) that cause learning disabilities. This could include traumatic conditions during the birth process, particularly those resulting in lack of oxygen during birth (eg. cerebral palsy resulting from anoxia). This can cause brain damage and result in learning disabilities. At birth, both low birth weight (which is significantly more common for women who smoke during pregnancy) and prematurity (especially in combination with Respiratory Distress Syndrome) are associated with a variety of negative outcomes, which sometimes can include learning disabilities. Following birth, any source of acquired brain injury may result in a range of effects including learning disabilities. These include:

• traumatic events ("shaken baby syndrome", falls, accidents);
• exposure to toxic chemicals (eg., to heavy metals such as mercury or lead from contaminated soil, through solvent inhalation or "gas sniffing");
• hypoxia (loss of oxygen to the brain as a result of suffocation or choking);
• infections (especially meningitis and encephalitis);
• and inflammation of the brain (eg. Reyes Syndrome).²³

Causes of Intellectual Disability

There are many causes of intellectual disability with some being more predominant than others. Some of these causes include:

Before Birth

1. Inheritance

   Intellectual disability may occur through heredity (i.e. genetic transmission of traits from parents to offspring).

2. Chromosomal Abnormality

   There are 23 pairs of chromosomes in each human cell. Chromosomes are structures which contain the genetic material for the transmission of human traits. Certain syndromes (which encompass intellectual disability) arise when the chromosomes of an individual have an abnormal arrangement or structure. Affected persons will have intellectual disability and characteristic physical features (i.e. Down's Syndrome).