The breakthrough problem
Here’s a blog post from CSIRO “Bloody data: biostatistics and the first blood test for Alzheimer’s”
Here are some of the media headlines:
New blood test detects Alzheimer’s disease up to 20 years before symptoms begin
New blood test could detect risk of Alzheimer’s disease 30 years early
World-first blood test to diagnose dementia
Science has created a simple blood test for Alzheimer’s
Here’s the research paper and two press releases about it: from the Florey Institute and from Melbourne Uni
As StatsChat readers will know, this isn’t the world-first early test for Alzheimer’s to end up in the media. And as you’ll expect, the test hasn’t actually been able to detect Alzheimer’s disease 20 or 30 years before symptoms begin. That would require either waiting 20 or 30 years to see who developed symptoms, or having a test that could be run with blood samples from 20 or 30 years ago.
What the test actually does is predict quite accurately how much amyloid-beta protein people have in their brain using just a blood sample. That’s useful, because the current ways of measuring amyloid in the brain are expensive and involve radiation and/or sampling fluid from the spine, and these aren’t things anyone wants to do at the level of population screening.
We don’t currently know if measuring amyloid in the brain gives good 20-year predictions of Alzheimer’s — there’s increasing suspicion that the relationship between Alzheimer’s and amyloid is more complicated than was thought. But it’s the best candidate we’ve got for an early test, and a low-cost, low-risk, low-pain version of it would be very useful in selecting people for clinical trials targeting amyloid levels — as I’ve said about a few of the other “first blood test for Alzheimer’s” candidates.
The research paper did look at using the test to distinguish people with definite, known Alzheimer’s from a healthy comparison group. They found the test picked up almost all of the Alzheimer’s cases, but gave false positives in nearly 20% of the healthy controls. Maybe that’s just saying that 20% of the controls will end up with the disease in 20-30 years, but there’s no way to know that in the short term.
This is good research, giving a genuine improvement on an important component of one step in testing potential future drugs to prevent Alzheimer’s. And the actual text of some of the stories is quite reasonable. The headlines, however, are actively misleading, because of the need to frame science stories as breakthroughs.
This isn’t the Holy Grail. Indiana Jones isn’t just ten minutes and three plot twists away from the final credits. That just isn’t how science typically works.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »