# Dementia: hereditary?

**URL:** <https://boards.straightdope.com/t/dementia-hereditary/309333>\
**Category:** Factual Questions\
**Created:** [June 22, 2005, 10:22am UTC](https://boards.straightdope.com/t/dementia-hereditary/309333 "2005-06-22T10:22:48Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![auRa](https://avatars.discourse-cdn.com/v4/letter/a/c4cdca/32.png) [@auRa](https://boards.straightdope.com/u/auRa)\
**Post date:** [June 22, 2005, 10:22am UTC](https://boards.straightdope.com/t/dementia-hereditary/309333/1 "2005-06-22T10:22:48Z")

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My grandmother was diagnosed with [dementia with Lewy bodies](http://www.ninds.nih.gov/disorders/dementiawithlewybodies/dementiawithlewybodies.htm) about two years ago. Watching the disease progress, I’ve started wondering: to what extent is dementia hereditary? [This](http://www.pdsg.org.uk/Factsheets/LewyBody.htm) link states (in reference do DLB)

> [@](#):
>
> Genetic studies are making some progress in revealing a matrix of different genes, which may contribute to development of DLB. This appears to be complex but may explain firstly the relationship of DLB to the other primary Lewy body disorders including Parkinson’s disease and secondly the association with Alzheimer’s disease. It remains to be seen whether genetic testing will be sufficiently simple to help in clinical diagnosis.

As far as I know, no-one else on my father’s side has been diagnosed with dementia, but then again, those diagnoses probably wouldn’t go too far back into history anyway. Women on both sides of my family have been traditionally long-lived; when I get old and gray, will I have to worry about dementia in addition to arthritis and excessive hair loss? In general, how much do doctors and scientists know about the hereditary nature of diseases like dementia?

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**Author:** ![irishgirl](https://avatars.discourse-cdn.com/v4/letter/i/8edcca/32.png) [@irishgirl](https://boards.straightdope.com/u/irishgirl)\
**Post date:** [June 22, 2005, 1:45pm UTC](https://boards.straightdope.com/t/dementia-hereditary/309333/2 "2005-06-22T13:45:59Z")

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I’m sorry about your grandmother’s illness.

There are genes on chromosome 21 that have been associated with Alzheimers. There are other genes, too, but that is the best known one. The gene was discovered because people with Down’s Syndrome often develop Alzheimer’s in their 40s and 50s-since they have 3 copies of chromosome 21, it was thought that a gene on that chromosome was to blame. This has been backed up by research on Alzheimer’s patients without Down’s Syndrome.

However, it’s not a 100% correlation, you can have the genes and not get Alzheimer’s, you can get Alzheimer’s without the genes.

A family history of lots of long-lived, healthy relatives is probably more important than a history of 1 relative with DLB. Even if your grandmother DID have the gene, you have only a 25% chance of having inherited it from her, and as I said, you can develop dementia whether you have the gene or not, and a significant proportion of people with the gene don’t develop dementia at all.

Basically, don’t let this worry you.