GRN

Progranulin (GRN) is a massive, multi-functional lysosomal protein critical for maintaining proper microglial degradative capacity. While its exact receptor interactions span sortilin and potentially EphA2, its primary biological duty is regulating the processing and flux of lipids and protein aggregates through the microglial endolysosomal network.

Heterozygous loss-of-function mutations in GRN cause profound haploinsufficiency, making it one of the leading genetic drivers of Frontotemporal Dementia (FTD). Without sufficient progranulin, microglial lysosomes fail to acidify properly or process complex lipids, causing pathological catastrophic swelling of the lysosomal compartment. This forces microglia into a hyper-inflammatory, senescent state where they can engulf debris but cannot digest it.

Conversely, complete bi-allelic loss of GRN results in Neuronal Ceroid Lipofuscinosis (NCL), a devastating pediatric lysosomal storage disorder. Therapeutically, GRN haploinsufficiency represents one of the most promising precision-medicine targets in neurology; companies like Alector are actively developing monoclonal antibodies (like latozinemab) to block sortilin-mediated degradation of progranulin, artificially elevating GRN levels back to operational thresholds in order to rescue microglial lysosomal function.