Woman Shares Decision to Take Early-Onset Alzheimer's Gene Test

A genetic test can determine with 99.999% certainty whether a person carries the mutation behind a rare, inherited form of early-onset Alzheimer's disease, a specialist told Laura Sides in 2013, according to the BBC. For years before that, the number that mattered most to Sides was simpler: 50/50, the odds a doctor gave her of inheriting the same condition that had already claimed her father.

Sides, whose father was a GP diagnosed with the so-called "London variant" of early-onset Alzheimer's in his 40s, eventually took the test in her 30s after declining it once before, the BBC reported Nov. 5. The result was positive. She has since discussed the decision with Dr Sian Williams, host of BBC Radio 4's Life Changing podcast, in an episode that aired Nov. 4.

What is the "London variant" of early-onset Alzheimer's?

Early-onset Alzheimer's refers to the disease appearing before the more typical retirement-age onset; the London variant is the specific inherited form that affected Sides' father, according to the BBC. He was diagnosed in his 40s, and Sides left university to help care for him as his symptoms worsened. He died in 2009, a year after her mother's death, the outlet reported.

How accurate is the predictive test, and what did the numbers show?

A specialist Sides saw in Melbourne in 2013 told her a blood test could confirm, with 99.999% certainty, whether she carried the gene, the BBC reported. Predictive testing — a genetic test run on someone without symptoms to gauge future risk, as opposed to a diagnostic test confirming a disease already present — came with a second figure attached: if positive, the specialist said her expected age of cognitive decline would fall between 46 and 48, according to the broadcaster.

At that first meeting, Sides turned the test down. "I just thought, I'm not there yet. I don't want to do that," she told the BBC.

Why did she wait years before testing?

The 50/50 figure first surfaced years earlier, at a hospital appointment with her father, when a doctor told Sides she had even odds of carrying the gene. "All I could think was, that's a toss of a coin," she said, according to the BBC. She said she pushed the thought aside while caring for her father and, after his death, left the UK on a solo trip that ended with her settling in Melbourne. It was there, as she entered her 30s, that she decided she wanted a definitive answer, the outlet reported.

What did the testing process involve, and what was the result?

Before the test, Sides underwent six months of genetic counseling, followed by a six-week wait for results, according to the BBC. She described going into the results appointment alone despite having booked a lunch with a friend afterward. "We're really sorry, it's not good news, and you have inherited the gene," she was told, she said. Her immediate reaction was "almost a white blurry noise," she told the broadcaster; the anger and confusion, she said, came later: "I was angry. I felt it was so unjust. I was just too confused at how I was meant to live now."

By the numbers

• 50/50 — odds Sides was first given of inheriting the gene, per a doctor's statement at her father's hospital appointment, per the BBC
• 99.999% — certainty level a specialist attached to the predictive test in 2013, per the BBC
• 46 to 48 — expected age range for onset of decline if the gene is present, according to the specialist cited by the BBC
• 6 months — length of required genetic counseling before testing, per the outlet
• 6 weeks — wait time for results after the test, per the BBC

What's next for Sides and her story

• The interview is available as a BBC Radio 4 Life Changing podcast episode, "'Toss of a coin' if I'd inherit dementia gene," released Nov. 4, 2026, on BBC Sounds, per the BBC.
• Sides has continued speaking publicly about living with a confirmed diagnosis of the inherited gene, according to the broadcaster's report.
• The two figures at the center of her case — 99.999% test certainty and a 46-to-48 estimated age range for decline — are the same numbers any patient offered similar predictive testing for the London variant would be weighing, based on the specialist's comments to the BBC.

Key terms

• Early-onset Alzheimer's: Alzheimer's disease with symptoms appearing well before typical retirement age.
• Predictive genetic testing: A test given to someone without symptoms to determine future disease risk, as distinct from a diagnostic test for existing illness.
• Genetic counseling: Structured consultation, in Sides' case six months long, required before a predictive test is administered.

Artiglio is A coming-soon iPhone chief of staff for briefings and drafts. Not on the App Store yet.