There are many causes of intellectual disabilities. Some are preventable; others are not. These causes can be grouped into four categories:
1. Medical conditions;
2. Brain injury;
3. Genetic conditions;
4. Psychiatric conditions.
The leading causes are Autism, Down syndrome, Fragile X syndrome, and fetal alcohol syndrome or FAS. Among these, the only preventable cause is fetal alcohol syndrome.
Medical conditions that lead to intellectual disabilities fall into three groups. These are: 1) prenatal exposure to alcohol and other drugs; 2) exposure to certain toxins; and 3) some types of infections. Prenatal exposure to alcohol and drugs is entirely preventable. Even drinking three drinks a day during pregnancy can cause fetal alcohol syndrome (FAS). FAS is a leading cause of intellectual disabilities. It is not clear how much alcohol is safe. Therefore, most doctors recommend pregnant women do not drink. Other drugs also harm a developing fetus. This includes nicotine, cocaine, and heroin. A pregnant woman should tell her doctor if she uses alcohol or drugs. Her doctor may be able to help her reduce the risks to her unborn child.
Pre- and post-natal exposure to toxins can cause intellectual disabilities. Of particular concern are lead, mercury, and radiation. Avoiding exposure to these toxins reduces the risk of developing an intellectual disability. Large fish such as shark, mackerel, and swordfish contain higher amounts of mercury. Low mercury fish include shrimp, salmon, and Pollack. Lead based paints are present in pre-1970s homes and in the soil surrounding older homes. Families can find lead abatement programs through their county and state public services. High radiation exposure is associated with intellectual disabilities. Fortunately, modern radiation equipment has drastically reduced the amount of radiation exposure. However, it is uncertain what a safe level of exposure is. For this reason, women who may be pregnant should speak up before receiving any radiation procedures.
Certain types of infections can also lead to intellectual disabilities. Pregnant women can take simple steps to reduce these risks. Pregnant women should avoid any contact with cat feces. Cats can carry a parasite that causes Toxoplasma infection. This infection is known to cause intellectual disabilities. Pregnant women should not handle cat liter boxes. They should not garden in places where cats may have defecated.
Several sexually transmitted diseases can lead to intellectual disabilities if a fetus or infant is exposed to these diseases. These include Hepatitis B, syphilis, and herpes simplex II. Pregnant women should practice safe sex and use condoms to reduce the risk of exposure. Children should receive immunizations for infections known to cause intellectual disabilities. These immunizations and protocols are constantly evolving. Parents should ask their child's doctor for recommendations. .
Brain injury is another cause of intellectual disability. Many brain injuries are preventable. Children should always ride in an approved child safety seat. The seat must be installed and used correctly. Follow the manufacturer's instructions for installation and use. If a family cannot afford a safety seat, there are agencies that can provide them. Ask your healthcare provider for information. Children should always wear helmets when riding bikes, skateboards, etc.
Brain injury also occurs when infants are shaken or dropped. This unfortunate situation often occurs when caregivers are frustrated. Caring for infants can be extremely stressful. It is natural to feel frustrated. Ask your healthcare provider to refer you to someone who can teach you better ways to cope stress.
There are many genetic causes of intellectual disability. The two most common are Down syndrome and fragile X syndrome. Genetic causes of intellectual disability cannot be considered preventable.
Lastly, certain psychiatric conditions are associated with intellectual disabilities. The most common disorder is called autism spectrum disorder (ASD). Like genetic abnormalities, there is no known way to predict or prevent ASD.
More complete and detailed information can be found in our Intellectual Disabilities Topic Center.