Both SLE and IIM can, at times, have an associated underlying immunodeficiency, more so in children.29 Apart from inherited complement defects, most common being C4 deficiency, seen with both SLE and IIM, polymorphisms and copy number variations in C2, C4, and C4A gene have associated with both SLE and polymyositis.30,31,32 Of particular note, Mannose Binding Lectin (MBL) deficiency is reasonably common and confers a high risk of Tuberculosis.33 This evidence concerns the gene MBL2 and polymyositis.