Karen’s* 80-year-old mother, Joy, has Alzheimer’s disease. It started innocuously about 10 years ago with occasional memory lapses. Today Joy can’t discern jam from Vaseline, eating both on bread as if starving. Although she used to be a highly respected clinical psychologist, Joy is now incontinent, no longer recognises her husband and uses mash-up words that nobody understands. 

Alzheimer’s disease is the most common form of dementia, which is an umbrella term for disorders affecting memory and thinking. 

Both Karen’s maternal grandmother and great-grandmother died late in life of the disease that’s now afflicting her mother too. She’s thinking about taking a gene test that could tell her whether she’s likely to be next. 

Is it in your genes?

In South Africa you can buy a “direct-to-consumer” gene test for about R3,600, which claims to show whether your genetic make-up puts you at risk for developing any of up to 33 different diseases, such as rheumatoid arthritis, bladder and bowel cancer, some forms of heart disease – and Alzheimer’s. 

Test kits like these are generally delivered to your home. You then swab the inside of your cheek or spit into a tube, put the sample back into the collection packet and a courier picks it up to take it to the lab. Results are returned to you by email after a few weeks. Although companies offering these tests may advise that you talk to a health worker to help you interpret the results, such counselling is not mandatory. 

An increased risk [because of having the gene] does not mean that someone is guaranteed to develop Alzheimer’s. Similarly, not having the gene doesn’t make it sure that a person will not develop the condition.

Testing for Alzheimer’s in this way is a contentious issue, because the disease is complex. For one, there are two types of Alzheimer’s – and genes do not have an equal role in determining the outcome in the two. 

One form of the disease, which usually shows up before the age of 65, is purely genetic, which means that if someone has a specific change in any one of three genes (called APP, PSEN1 and PSEN2) associated with Alzheimer’s, they’re guaranteed to develop the condition. A tell-tale sign of this genetically inherited form of Alzheimer’s is when a close family member dies of the disease anywhere from the age of 40. 

The role of genes in the other type of Alzheimer’s, which normally shows up after the age of 65, is much more murky. Up to 40% of people who develop this later-onset form of the disease have a gene called apolipoprotein E (APOE) type 4. But it’s not to say that everyone who’s a carrier will necessarily develop Alzheimer’s.

So, you have an Alzheimer’s gene. What now?

Genes are passed on in pairs, one from each parent. In South Africa about a quarter of the population inherited a copy of the APOE4 gene from one of their parents and about 3% got a copy from each parent. It’s this gene that the consumer test kits screen for. 

Unlike with the rare, purely genetic type of Alzheimer’s, having APOE4 genes simply increases the risk of getting the more common late-onset Alzheimer’s. Research shows that people with a single APOE4 copy may be twice as likely to get Alzheimer’s as those who don’t have that form of the gene, while in people with two copies the risk is 10 times higher.

Read more in Daily Maverick: Looking after family members with dementia: Alzheimer’s disease

Bianca Rossouw, a genetic counsellor at the National Health Laboratory Service, explains: “An increased risk [because of having the gene] does not mean that someone is guaranteed to develop Alzheimer’s. Similarly, not having the gene doesn’t make it sure that a person will not develop the condition.”

Genetics are among many factors that can contribute to someone developing the more commonly seen form of Alzheimer’s. Age is the biggest thing that ups your risk. If one of or both your parents or a sibling has the disease, your chances for developing it too may be higher, as it might be for women and people of colour. These risk factors cannot be changed. 

But conditions such as obesity, high blood pressure, diabetes and high cholesterol or behaviours such as drinking and smoking can also add to someone’s risk for developing Alzheimer’s. And because these are often linked to lifestyle, they can be changed (and are therefore said to be modifiable risk factors).  

Regular exercise, a healthy diet, getting enough sleep and minimising stress protect against Alzheimer’s, as does being socially active, doing mentally challenging activities and having a high level of education in early life. 

Your ancestry and where you live may also matter. West Africans with APOE4 genes living in Africa do not have an increased risk of disease, yet those who live in North America do.

Direct-to-consumer testing can be dangerous if people don’t fully grasp what the results may mean.

Because variations in the APOE4 gene are just one part of the picture, many health professionals and authoritative organisations, including Alzheimer’s South Africa, as well as the National Institute of Aging in the US, caution against testing for APOE4 at all.

According to Rossouw “this kind of testing may cause significant anxiety for fear of developing the condition [if one tests positive] or, on the other hand, cause a false sense of reassurance [if one tests negative]”.

Can testing positive be positive?

A survey of people who had tested positive for APOE4 revealed that while they felt distressed shortly after hearing their result, which was worse if they didn’t have a counsellor to help them interpret their results, they were generally glad that they had taken the test. Knowing that you are at risk can bring about lifestyle changes, and a study published in the British Medical Journal in January suggests that living healthier, particularly eating a healthy diet, can significantly reduce the risk of developing Alzheimer’s even if you have the APOE4 gene.

Karen is now 57 and has never smoked. Six months ago she was drinking regularly and her weight was up 20kg. At a routine medical her cholesterol and blood sugar levels were higher than they should have been. She was stressed at work, not sleeping well and did not exercise regularly. 

Studies show that even if Karen tests negative for the APOE4 gene, her risk factors could still make her more likely to develop Alzheimer’s than somebody who tests positive for two copies of the gene but has no other risk factors for the disease. 

Read more in Daily Maverick: Why is my loved one with dementia sometimes ‘there’ and sometimes not?

Rossouw explains: “Direct-to-consumer testing can be dangerous if people don’t fully grasp what the results may mean. Understanding the difference between being affected with disease and having an increased risk to develop a condition is crucial. Appropriate [genetic] counselling is important.” 

After giving it some thought, Karen has accepted that no matter her APOE4 status, her risk for developing Alzheimer’s disease is likely to be high, and she would rather spend her time and money on things she can change, such as eating better and exercising more, than on genetic tests.

“I choose to live proactively and with hope, even though science doesn’t yet offer any certainty for whether I will get Alzheimer’s.” DM/MC

* Karen’s full name has been omitted for privacy reasons.

Martinique Stilwell is an anaesthetist, writer and occasional freelance journalist with an interest in science and medical communication. She is the author of Thinking Up A Hurricane.

This story was produced by the Bhekisisa Centre for Health Journalism. Sign up for the newsletter.