Blood serum levels of progranulin, a key protein to both neuronal survival and neurodegenerative diseases, are not adequate measures of progranulin levels in the brain. As such, they cannot serve as a biomarker for diseases ranging from Alzheimer’s to amyotrophic lateral sclerosis (ALS), researchers report in a study titled “Serum Levels of Progranulin Do Not Reflect Cerebrospinal Fluid Levels in Neurodegenerative Disease,” published in the journal Current Alzheimer’s Research.
Because progranulin can be easily measured in the blood, it was seen as a potential marker of diseases affected by the protein, and, importantly, as a way of gauging the effectiveness of future treatments. But researchers with the Hertie-Institute for Clinical Brain Research & German Center for Neurodegenerative Diseases (DZNE), in Tübingen, Germany, have found that accurate progranulin measurements are not as simple as a noninvasive blood test.
Carlo Wilke and Matthis Synofzik, the study’s co-leaders, reported that blood levels of progranulin are distinct from levels found in the cerebrospinal fluid (the liquid surrounding the brain) in Alzheimer’s, ALS, and frontotemporal dementia. Since these are diseases that affect the brain, progranulin levels there are essential to determining both disease progression and response to treatments.
“We here demonstrate that cerebrospinal fluid progranulin levels do not correlate with its serum levels in AD, FTD and ALS, indicating a differential regulation of its central and peripheral levels in neurodegeneration,” the researchers wrote. “Blood progranulin levels thus do not reliably predict central nervous progranulin levels and their response to future progranulin-increasing therapeutics.”
Even though the results seem disappointing, they are useful to the extent that future research can focus on other potential biomarkers for neurodegenerative diseases like ALS.