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The Many Causes of Intellectual Disabilities, Fetal Alcohol Syndrome and Environmental Exposure to Toxins

Tammy Reynolds, B.A., C.E. Zupanick, Psy.D. & Mark Dombeck, Ph.D.

Intellectual disabilities (ID, formerly mental retardation) have many causes. Some of these causes are preventable. Others are not. These causes can be grouped into four categories.

1) Medical Conditions;
2) Brain Damage;
3) Genetic Conditions;
4) Psychiatric Conditions.

Four conditions are the most common causes of ID ( First, there is autism. This is a psychiatric cause. Next are two genetic conditions. These are Down syndrome and Fragile X syndrome. Lastly, Fetal Alcohol Syndrome (FAS) is a medical condition. However, among these common causes, only FAS is completely preventable.

Medical Causes of Intellectual Disabilities

Pre- and post-natal exposure to alcohol, drugs, toxins, and certain infections can have a devastating effect on brain development. This exposure can result in physical and mental defects, and even death of an infant.

Prenatal exposure to alcohol and other drugs

Fetal Alcohol Syndrome (FAS) is one of the leading causes of preventable birth defects and intellectual disabilities (source: The American College of Obstetricians and Gynecologist). Alcohol passes directly from the blood stream of a pregnant woman, through the placenta, to the developing fetus' brain. It is not clear how much alcohol is safe. Therefore, most doctors recommend pregnant women avoid alcohol. Even drinking three drinks a day during pregnancy can cause fetal alcohol syndrome (FAS). 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.

Environmental exposure to toxins

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.

Mercury is found in polluted waters. Fish that swim in these waters contain mercury. Large fish such as shark, mackerel, and swordfish contain higher amounts of mercury. Because large fish live longer, the mercury builds up to higher levels. When women consume these large fish, the mercury can pass through the placenta, and to the fetus. Women can reduce this risk by switching to low mercury fish. Low mercury fish are smaller. This includes shrimp, salmon, and Pollack. Some farm-raised fish are also safer than ocean dwelling fish.

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.

Life Expectany and Severity

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  • Articles

    • Introduction to Intellectual Disabilities
    • Causes of Intellectual Disabilities
    • Diagnosis of Intellectual Disabilities
      • The Diagnosis of Intellectual Disabilities
      • Psychological Tests and Intellectual Disabilities
      • Psychological Tests and Intellectual Disabilities Continued
      • Tests of Adaptive Functioning
      • Diagnostic Criteria for Intellectual Disabilities: DSM-5 Criteria
      • The American Association on Intellectual and Developmental Disabilities (AAIDD) Diagnostic Criteria for Intellectual Disability
      • Comparing the APA and the AAIDD Diagnostic Criteria for Intellectual Disability
      • Intellectual Disability and Severity Codes
      • Intellectual Disability and Other Psychiatric Disorders
    • Historical & Contemporary Perspectives of Intellectual Disabilities
      • Historical And Contemporary Perspectives on Intellectual Disabilities
      • Early Medical Explanations of Intellectual Disability
      • History of Stigmatizing Names for Intellectual Disabilities
      • History of Stigmatizing Names for Intellectual Disabilities Continued
      • Reducing the Stigma of Intellectual Disabilities: The Evolution of Modern Medical Explanations
      • Paving the Way to a Modern Conception of Intellectual Disability: Advancements in Intelligence Testing
      • Advancements in Genetic Research
      • Social and Political Controversies Associated with Intellectual Disabilities
      • Reproductive Rights for People with Intellectual Disabilities
    • Intellectual Disabilities & Supportive Rehabilitation
      • Intellectual Disabilities and Supportive Rehabilitation: Developing an Individualized Support Plan (ISP)
      • Educational Supports and Individual Educational Plans (IEPs)
      • The Choice of Educational Settings: The Pros and Cons of Mainstreaming Children With Intellectual Disabilities
      • Effective Teaching Methods for People With Intellectual Disabilities
      • Applied Behavioral Analysis (ABA) and Intellectual Disabilities
      • Physical Therapy and Sensory Skills Training
      • Individualized Support Plans: Adaptive Functioning & Life Skills
      • Social Skills Training
      • Supported Employment and Integrated Work Sites
      • Supported Housing and Community Integration
      • Therapies for Intellectual Disabilities and Outdated/Unproven Treatments
    • Support for Families of People with Intellectual Disabilities
      • Additional Support Services for People with Intellectual Disabilities and Their Families: Community Supports
      • Additional Support Services: Financial Supports
      • Additional Support Services: Family Supports
      • Additional Support Services: Advocacy and Legal Supports
    • Intellectual Disabilities Summary & Conclusion
      • Intellectual Disabilities Summary and Conclusion
    • Intellectual Disabilities Resources & References
      • Intellectual Disabilities Resources and References
      • Intellectual Disabilities Document Revision History
  • Book & Media Reviews

    • A Special Education
    • Living with Mild Cognitive Impairment
  • Videos

    • What is Intellectual Disability?
    • Let's Talk About Intellectual Disabilities: Loretta Claiborne
    • What Causes an Intellectual Disability?
    • What Is An Intellectual Disability?
    • What's disability to me? Mia's story.
    • Primary Care of Children and Young Adults with Down Syndrome
    • Dr. Tim Shriver: Intellectually Different ... Not Disabled
    • Living with Down Syndrome: Parents, Health Professionals and Personal Perspectives