br Methods br Results br Discussion Insufficiency of GCase a

Methods
Results
Discussion Insufficiency of GCase activity in chenodeoxycholic acid due to GBA1 gene mutations is the molecular mechanism of GD. However, it has been observed that patients with the same GCase mutations may have significant variably in disease presentation, from a life-threatening manifestation to almost asymptomatic (Biegstraaten et al., 2011; Elstein et al., 2010). Here we reported PGRN as another previously-unrecognized molecule associated with GD. In addition to low serum levels of PGRN in GD patients, whole GRN gene sequencing identified 4 SNP sites. Logistic regression analysis revealed a correlation with GRN mutations and serum level of PGRN (Figs. 1, 2). Although reporter gene assays indicated lower transcriptional activities of rs4792937 and rs5848 SNPs, the limitation of the study is noted and further investigations, including measuring the levels of PGRN mRNA and protein in large numbers of GD patients with particular GRN variants, are warranted to fully determine whether specific variants lead to lower PGRN levels. Given that mutations in the GRN gene identified here were present in around 70% GD patients, detecting these variants using a simple PCR assay could be employed as another genetic diagnostic approach for GD. In addition, identification of GRN variants in GD patients betters our understanding of the pathogenesis of GD, and especially our understanding of the extraordinarily diverse phenotypes among patients harboring identical GBA1 mutations (Elstein et al., 2010). The association between PGRN and GD is also supported by animal data. Both “aged” and OVA-challenged adult mice with PGRN deficiency, but with normal Gba1 gene, developed GD-like phenotypes, including typical Gaucher cell infiltration in multiple organs, tubular-like lysosomes in macrophages, and GCase substrate accumulation. In addition, these GD-like phenotypes can be ameliorated with imiglucerase, the drug used clinically to treat GD. More importantly, recombinant PGRN protein also facilitates the lysosomal appearance of mutated GCase, as evidenced by the significant reduction in lysosomal storage in fibroblasts from GD patients following treatment with rPGRN. Homozygous mutation of the GRN gene was reported to associate with neuronal ceroid lipofuscinosis (Smith et al., 2012; Gotzl et al., 2014). We also observed the accumulation of lipofuscin in “aged” PGRN KO mice (Supplementary data Fig. S7), suggesting that PGRN deficient mice may be also a useful model for studying additional lysosomal storage diseases in addition to Gaucher\'s diseases. GBA1 mutations, especially L444P and N370S, were also found in Ashkenazi Jews with Parkinson\'s disease (PD) (Sidransky et al., 2009), and mutated GCase has been considered to be a risk factor for parkinsonism (Migdalska-Richards and Schapira, 2016). The mechanisms underlying the association of GBA1 mutations with these two different diseases still remain unclear (Mazzulli et al., 2011). Isolation of PGRN as a novel genetic factor in GD may also better our understanding of the association between GBA1 mutations with both rare (i.e. GD) and common (i.e. PD) diseases. Previous reports that GRN mutations associated with PD and α-synuclein pathology (Mateo et al., 2013; Leverenz et al., 2007), together with this study\'s finding that GRN mutations are also linked to GD, indicates that there may exist a functional and a genetic linkage between the GRN and GBA1 genes, and their homozygous or heterozygous mutations cause or render some carriers vulnerable to rare and/or common diseases. In summary, the identification of PGRN deficiency/insufficiency as a risk factor for GD is certainly a source of considerable excitement in the field. Moreover, serum levels of PGRN and prevalent mutations in GRN gene may represent alternative approaches for clinical diagnosis of GD. Further, recombinant PGRN effectively corrected the aggregation of mutant GCase and the accumulation of glucosylceramide in several preclinical models, supporting the potential development of different therapeutic strategies for the treatment of GD. Thus, these findings may not only provide new insight into the pathogenesis of GD, but also have implications for diagnosis and targeted therapy of GD.