For years, researchers have been striving to develop reliable and simple methods to detect Alzheimer’s disease (AD) in its early stages. To date, several phosphorylated (p)-tau species, of which p-tau 181 and p-tau 217 are the most studied, have been shown to be elevated in cerebrospinal fluid (CSF) of people with AD compared to those without AD. More recently, blood p-tau 181 and p-tau 217 have been proposed as accurate biomarkers of AD pathology. However, a new study showed that blood p-tau tests for the early detection of AD are not as disease-specific as previously thought. Published in the journal Nature Communications, the study showed that the levels of p-tau were elevated in blood of people with AD but also in blood of people with Amyotrophic Lateral Sclerosis (ALS), a degenerative disease of the motor nervous system.
Researchers examined a multicentre cohort of ALS, AD cases and disease controls (with no signs of AD or ALS) recruited from four different centres. By measuring serum levels of p-tau 181 and p-tau 217, they discovered that both people with AD and ALS exhibited higher levels of these biomarkers compared to the control group. Using mass spectrometry and immunohistochemistry, scientists also documented the presence of p-tau 181 and 217 in muscle biopsies from both ALS cases and disease controls, with ALS samples showing increased p-tau reactivity in atrophic muscle fibres. Scientists suggested that p-tau species could potentially be used to diagnose both ALS and AD, thus calling into question the recently proposed inclusion of blood p-tau 181 and p-tau 217 as accurate screening tests for AD pathology.