Alzheimer's Disease in Individuals with Down Syndrome

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Medical Author:

Norberto Alvarez, MD

Medical Editor:

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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• Alzheimer's Disease and Down Syndrome Overview
• The Link Between Down syndrome and Alzheimer's Disease
• Alzheimer's Disease in People with Down syndrome - Symptoms
• Alzheimer's Disease in People with Down syndrome - Diagnosis
• Alzheimer's Disease in People with Down syndrome - Treatment
• Alzheimer's Functional Assessment Tool
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• Authors and Editors

Alzheimer's Disease and Down syndrome Overview

Alzheimer's disease (AD) is the most common form of dementia. The disease is progressive, and the brain degenerates. Alzheimer's disease is strongly associated with old age. However, it should not be considered a normal part of aging.

Down syndrome (DS) is a genetic disorder (the chromosome abnormality is acquired at the time of conception) in which a person has extra genes because of extra chromosome 21 material. The syndrome causes delays and limitations in physical and intellectual development. The extra chromosome material can be inherited from either parent. Common characteristics of the syndrome include:

• Low muscle tone



• Flat face (low nasal bridge and small nose)



• Eye openings that slant downward and inward
  
  
• Single crease across the centre of the palm



• Smaller than normal size



• Delay of both physical and intellectual development

People with Down syndrome, also called trisomy 21, develop a syndrome of dementia that has the same characteristics of Alzheimer's disease that occurs in individuals without Down syndrome. The only difference is that Alzheimer's disease occurs much earlier in people with Down syndrome; patients with Down syndrome begin to have symptoms in their late 40s or early 50s.

Most (and maybe all) people with Down syndrome develop the brain changes associated with Alzheimer's disease. However, Alzheimer's disease is not more common in individuals with intellectual disabilities from causes other than Down syndrome. An estimated 10%-25% of patients with Down syndrome have Alzheimer's disease at age 40-49 years, 20%-50% have Alzheimer's disease at age 50-59 years, and 60%-75% have Alzheimer's disease when older than 60 years of age. Alzheimer's disease decreases survival in people with Down syndrome who are older than 45 years of age.

The Link Between Down syndrome and Alzheimer's Disease

The reason Alzheimer's disease is more common in people with Down syndrome is not completely known. Alzheimer's disease is associated with increased production of a compound called amyloid beta in the brain. Amyloid beta accumulates and causes loss of brain cells called neurons. Exactly how neuron loss occurs is not well understood. The higher risk for Alzheimer's disease in people with Down syndrome may be related to the extra copy of chromosome 21 (which causes Down syndrome) because it leads to increased production of amyloid beta.

The age when symptoms of Alzheimer's disease actually develop may be related to a person's mental capacity (cognitive reserve) or some anatomic characteristics of the brain. That means people with greater brain weight, more brain cells (neurons), and more education may not have symptoms of Alzheimer's disease as early as people with less cognitive reserve. People with Down syndrome may develop symptoms of Alzheimer's disease earlier in life than other people because of their increased production of amyloid beta and their smaller cognitive reserve.