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Most, if not all, people living with Down syndrome eventually develop Alzheimer's disease, and they tend to develop it relatively early in life. The common connection between the two conditions is chromosome 21.

Down syndrome was once considered a death sentence for a child. In the 1920's the average life expectancy of a child born with Down syndrome was just nine years. Children who were born with Down syndromes often died of respiratory infections, circulatory problems, or medical neglect. By the 1960's, the situation had improved slightly. More children born with Down syndrome than not could be expected to reach the age of 30. As stories of successful adult living accumulated, medical intervention to extend life in the syndrome became more common. Nowadays it is assumed that a child who is born with Down syndrome can experience quality of life and a measure of independence as an adult, and by 1993, the life expectancy for a one-year-old diagnosed with the condition was 55, and in 2019, some are living to the age of 70.

Nearly all people born with Down syndrome who grow up to live past the age of 50, however, live with some form of dementia, most commonly Alzheimer's disease.

Alzheimer's disease is usually a condition of old age, 75 and older. Because so few children born with Down syndrome even survived to adulthood before the twenty-first century, scientists weren't aware of a connection between Down syndrome and dementia. But as more and more people living with Down syndrome get better and better care, the distressing observation is that nearly everyone who has Down's will eventually develop dementia. It turns out that the two conditions may be expressions of the same issue in brain chemistry.

What's the connection between Down Syndrome and Alzheimer's?

Every person who has Down syndrome has an extra copy of a chromosome identified as chromosome 21. Instead of two copies of certain genes, they have three.

Every kind of Alzheimer's disease involves increased production of a protein in the brain called amyloid beta. Genes on the twenty-first chromosome code the production of this protein. People who have Down syndrome have an extra gene that codes the production of more of this protein earlier in life. 

Amyloid beta has been detected in the brains of people who have Down syndrome as early as age eight. The production of the protein accelerates through the teenage years through the twenties As people living with Down syndrome get older, more and more of this destructive protein accumulates in their brains. However, there is no direct relationship between how much of the protein has been made in the brain and the development of Alzheimer's disease in addition to Down syndrome. There are possibly some ways to slow down the development of the second disability.

The first symptom of Alzheimer's in people living with Down syndrome is usually a combination of memory problems with attention problems. Symptoms of Alzheimer's usually appear about age 55. 

What might delay the appearance of Alzheimer's symptoms in Down Syndrome?

Scientists don't really know what might delay the onset of Alzheimer's in people who have Down syndrome, but the research suggests these approaches might help:

  • Higher cholesterol is associated with higher risk of developing Alzheimer's, and lower cholesterol is linked to lower risk of developing Alzheimer's. The target level for total cholesterol seems to be 200 mg/dl (5.2 mmol/L). A study of 123 people with Down syndrome found that those who had cholesterol levels over 200 mg/dl were twice as likely to be diagnosed with Alzheimer's as those who had cholesterol levels below 200 mg/dl. Lowering cholesterol with statins lowered the risk of Alzheimer's. It's possible that even those volunteers in the study who had lower cholesterol levels would eventually develop dementia, but that didn't happen in the five years of the study.
  • "Intellectual reserve" is probably associated with a delay in the symptoms of Alzheimer's. People who have Down's who have had at least eight years in school develop Alzheimer's later in life than those who were not schooled. The more life skills someone acquires, the later they are diagnosed with Alzheimer's.
  • There have been studies that have found that diet can delay Alzheimer's in people who don't have Down syndrome if they have a gene known as alpha-epsilon 4. Scientists really don't know that the intermittent fasting that seems to delay Alzheimer's in people who don't have Down syndrome would also work in people who do. However, there are enough benefits to portion control and planned mealtimes that limiting nighttime eating is probably a good idea.

What about other forms of dementia in Down Syndrome?

Although people who have Down syndrome are especially susceptible to Alzheimer's disease, they can develop other forms of dementia, especially Lewy body disease. It's also possible to have Down syndrome, Alzheimer's, and frontotemporal dementia. The best approach to dealing with these dire possibilities is still the same: Encourage development of life skills, and manage cholesterol. These may add years and quality to life.

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  • Photo courtesy of SteadyHealth
  • https://www.karger.com/Article/FullText/442941 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6374283/

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