Newborns and Alzheimer's patients have elevated blood levels of phosphorylated tau

Newborn babies and patients with Alzheimer's disease share an unexpected biological trait: elevated levels of a well-known biomarker for Alzheimer's. This is shown in a study led by researchers at the University of Gothenburg.

What do the brains of newborns and patients with Alzheimer's disease have in common? Researchers from the University of Gothenburg, led by first author Fernando Gonzalez-Ortiz and senior author Professor Kaj Blennow, recently reported that both newborns and Alzheimer's patients have elevated blood levels of a protein called phosphorylated tau, specifically a form called p-tau217.

While this protein has been largely used as a diagnostic test for Alzheimer’s disease, with an increase in p-tau217 blood levels proposed to be driven by another process, namely aggregation of b-amyloid protein into amyloid plaques. Newborns (for natural reasons) do not have this type of pathological change, so interestingly, in newborns increased plasma p-tau217 seems to reflect a completely different - and entirely healthy - mechanism.

In a large international study that involved Sweden, Spain and Australia, researchers analyzed blood samples from over 400 individuals, including healthy newborns, premature infants, young adults, elderly adults, and people diagnosed with Alzheimer’s disease. They found that newborn babies had the highest levels of p-tau217 - even higher than those found in people with Alzheimer’s. These levels were particularly elevated in premature babies and started to decrease over the first few months of life, eventually settling to adult levels.

First time in the blood of newborns

Previous research, largely based on animal models, had hinted at the role of phosphorylated tau in early brain development. This is the first time scientists have directly measured p-tau217 concentrations in the blood of human newborns, opening the door to a much clearer understanding of its developmental role.

But here’s where it gets fascinating, while in Alzheimer’s disease p-tau217 is associated with tau aggregation into harmful clumps called tangles, believed to cause the breakdown of brain cells and subsequent cognitive decline. In contrast, in newborns this surge in tau appears to support healthy brain development, helping neurons grow and to form new connections with other neurons, thereby shaping the structure of the young brain.

The study also revealed that in both healthy and premature babies, p-tau217 levels were closely linked to how early they were born. The earlier the birth, the higher the levels of this protein, suggesting a role in supporting rapid brain growth under challenging developmental conditions.

Potential roadmap for new treatments 

What’s perhaps most compelling about these findings, published in the journal Brain Communications, is the hint that our brains may once have had built-in protection against the damaging effects of tau, so that newborns can tolerate, and even benefit from, high levels of phosphorylated tau without triggering the kinds of damage seen in Alzheimer’s.

We believe that understanding how this natural protection works - and why we lose it as we age - could offer a roadmap for new treatments. If we can learn how the newborn brain keeps tau in check, we might one day mimic those processes to slow or stop Alzheimer’s in its tracks.”

Fernando Gonzalez-Ortiz, first author

So while an increase of p-tau217 is a danger signal in older brains, in newborns it might be a vital part of building one. The same molecule, two dramatically different roles - one building the brain, the other marking its decline.

Plasma p-tau217 has recently received FDA approval for use in diagnosing Alzheimer’s disease, making it an increasingly important tool in clinical settings. The authors emphasize the need to also understand the mechanism for the increase in p-tau217, especially for interpreting it as an outcome in clinical and epidemiological research and in drug development. This study indicate that amyloid plaques may not be the main driver of increases in p-tau217.