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    Replacement of Cysteine at Position 46 in the First Cysteine-Rich Repeat of the LDL Receptor

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    Background and aims Pathogenic mutations in the Low Density Lipoprotein Receptor gene (LDLR) cause Familial Hypercholesterolemia (FH), one of the most common genetic disorders with a prevalence as high as 1 in 200 in some populations. FH is an autosomal dominant disorder of lipoprotein metabolism characterized by high blood cholesterol levels, deposits of cholesterol in peripheral tissues such as tendon xanthomas and accelerated atherosclerosis. To date, 2500 LDLRvariants have been identified in the LDLR gene; however, only a minority of them have been experimentally characterized and proven to be pathogenic. Here we investigated the role of Cys46 located in the first repeat of the LDL receptor binding domain in recognition of apolipoproteins. Methods Activity of the p.(Cys46Gly) LDLR variant was assessed by immunoblotting and flow cytometry in CHO-/d/A7 expressing the receptor variant. Affinity of p.(Cys46Gly) for LDL and VLDL was determined by solid-phase immunoassays and in silico analysis was used to predict mutation effects. Results and conclusion Functional characterization of p.(Cys46Gly) LDLRvariant showed impaired LDL and VLDL binding and uptake activity. Consistent with this, solid-phase immunoassays showed the p. (Cys46Gly) LDLR variant has decreased binding affinity for apolipoproteins. These results indicate the important role of Cys46 in LDL receptor activity and highlight the role of LR1 in LDLr activity modulation. This study reinforces the significance of in vitro functional characterization of LDL receptor activity in developing an accurate approach to FH genetic diagnosis. This is of particular importance because it enables clinicians to tailor personalized treatments for patients' mutation profile.Progenika Biopharma SA, is an Spanish biotech company founded in 2000 with headquarters in Derio, Bizkaia (SPAIN). Progenika Biopharma SA did not play a role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript and only provided financial support in the form of authors' salaries to M.S. and L.P. This work was supported by Gobernio Vasco, ELKARTEK BIOGUNE 2015 (Codigo KK-2015/0000089) and Basque Government (Grupos Consolidados IT849-13). A. B-V. was supported by a grant (PIF 2014/2015) Eusko Jaurlaritza and S.J. was supported by grant (PIF 2018/2019) Eusko Jaurlaritza. The funders did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript
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