Analytical and clinical validation of a blood progranulin ELISA in frontotemporal dementias

Objectives: Heterozygous mutations in the granulin (GRN) gene may result in haploinsufficiency of progranulin (PGRN), which might lead to frontotemporal dementia (FTD). In this study, we aimed to perform analytical and clinical validation of a commercial progranulin kit for clinical use. Methods: Analytical validation parameters including assay precision, selectivity, measurement range, dilution linearity, interferences and sample stability were tested according to previously described procedures. For clinical validation, PGRN levels were measured in plasma from 32 cognitively healthy individuals, 52 confirmed GRN mutation carriers, 25 C9orf72 mutation carriers and 216 patients with different neurodegenerative diseases of which 70 were confirmed as non-mutation carriers. Results: Among the analytical validation parameters, assay precision and repeatability were very stable (coefficients of variation <7 %). Spike recovery was 96 %, the measurement range was 6.25-400 mu g/L and dilution linearity ranged from 1:50-1:200. Hemolysis did not interfere with progranulin levels, and these were resistant to freeze/thaw cycles and storage at different temperatures. For the clinical validation, the assay was capable of distinguishing GRN mutation carriers from controls and non-GRN mutation carriers with very good sensitivity and specificity at a cut-off of 57 mu g/L (97 %, 100 %, respectively). Conclusions: In this study, we demonstrate robust analytical and diagnostic performance of this commercial progranulin kit for implementation in clinical laboratory practice. This easy-to-use test allows identification of potential GRN mutation carriers, which may guide further evaluation of the patient. This assay might also be used to evaluate the effect of novel PGRN-targeting drugs and therapies.