Diabetes With Multiple Autoimmune and Inflammatory Conditions Linked to an Activating SKAP2 Mutation

• DOI: 10.2337/figshare.14192315
• Publication Date: 2021-06-16T21:55:41Z
• Authors: Niklas Rutsch; Chester E. Chambe...; Wesley Dixon; Lauren Spector; Lisa R. Letournea...; Wint W. Lwin; Louis H. Philipson; Alexander Zarbock; Karline Saintus; Juehu Wang; Michael S. German; Mark S. Anderson; Clifford A. Lowell
• Keywords: Adult; Biomedical and clinical sciences; Immunology; Autoimmune Disease; Medical and Health Sciences; Autoimmune Diseases; Endocrinology & Metabolism; Young Adult; 03 medical and health sciences; 0302 clinical medicine; Genetics; Diabetes Mellitus; 2.1 Biological and endogenous factors; Humans; Aetiology; Metabolic and endocrine; Pediatric; Biomedical and Clinical Sciences; Prevention; Inflammatory and immune system; Human Genome; Diabetes; Intracellular Signaling Peptides and Proteins; Health sciences; 3. Good health; Diabetes Mellitus, Type 1; Phenotype; Mutation; Type 1; Genome-Wide Association Study

<b>OBJECTIVE: </b>Multiple genome-wide association studies (GWAS) have identified a strong genetic linkage between the <i>SKAP2</i> locus and type 1 diabetes (T1D) but how this leads to disease remains obscure. Here, we characterized the functional consequence of a novel <i>SKAP2</i> coding mutation in a T1D patient to gain further insight into how this impacts immune tolerance.

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<p><b>RESEARCH DESIGN AND METHODS: </b>We identified a 24-year-old individual with T1D and other autoimmune and inflammatory conditions. The proband and first-degree relatives were recruited for whole exome sequencing. Functional studies of the protein variant were performed using a cell line and primary myeloid immune cells collected from family members.</p>

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<p><b>RESULTS: </b>Sequencing identified a <i>de novo</i> <i>SKAP2</i> variant (c.457G>A, p.Gly153Arg) in the proband. Assays using monocyte-derived macrophages from the individual revealed enhanced activity of integrin pathways and a migratory phenotype in the absence of chemokine stimulation, consistent with SKAP2 p.Gly153Arg being constitutively active. The p.Gly153Arg variant, located in the well-conserved lipid-binding loop, induced similar phenotypes when expressed in a human macrophage cell line. SKAP2 p.Gly153Arg is a gain-of-function, pathogenic mutation that disrupts myeloid immune cell function, likely resulting in a break in immune tolerance and T1D.</p>

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<p><b>CONCLUSIONS: </b>SKAP2 plays a key role in myeloid cell activation and migration. This particular mutation in a patient with T1D and multiple autoimmunity implicates a role for activating <i>SKAP2</i> variants in autoimmune T1D. <br> </p>