Progranulin Peripheral Levels as a Screening Tool for the Identification of Subjects with Progranulin Mutations in a Portuguese Cohort

Abstract

Background: Progranulin (PGRN) mutations are associated with different clinical phenotypes, including frontotemporal lobar degeneration (FTLD), corticobasal syndrome (CBS) and Alzheimer's disease (AD). As all pathogenic PGRN mutations identified so far cause disease through haploinsufficiency, determination of PGRN levels has been proposed as a reliable method to identify mutation carriers. Objective: To evaluate the accuracy of peripheral PGRN levels in the identification of the PGRN mutation carriers detected thus far in our Portuguese cohort. Methods: Serum PGRN levels were measured in 244 subjects (124 patients in the spectrum of FTLD, 2 asymptomatic descendants of a FTLD patient, 56 AD patients and 64 controls) by a novel commercial ELISA kit. Results: Low PGRN levels were detected in 7 individuals (5 behavioral variant frontotemporal dementia, 1 CBS, and 1 still clinically unaffected) that constituted the group of the null PGRN mutation carriers previously identified in our molecular diagnostic laboratory. The pathogenic mutations found consisted of 4 insertion-deletions, causing frameshifts resulting in premature stop codons, 3 of which were novel. In addition, a normal PGRN level was found in a patient harboring a novel missense variant. For this novel ELISA kit, we established a PGRN cut-off level that identified with 100% accuracy the pathogenic mutation carriers. Conclusion: This study supports the use of a novel assay for the determination of PGRN levels as a screening procedure to identify patients harboring null PGRN mutations. This approach would significantly decrease the required PGRN mutation analysis workload and should be extended to other clinical phenotypes than behavioral variant frontotemporal dementia and to apparently sporadic cases.