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

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

RESEARCH DESIGN AND METHODS: 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.

RESULTS: Sequencing identified a de novo SKAP2 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.

CONCLUSIONS: 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 SKAP2 variants in autoimmune T1D.