The pathogenesis of WD likely involves TH cells in patients with AR CD4 deficiency, but it remains unknown whether IRF4 haploinsufficiency operates via lymphocytes capable of killing T. whipplei-infected cells and/or via myeloid or epithelial cells in which T. whipplei can replicate. Here, CD4 is linked to hyperinsulinemic hypoglycemia, familial, 4.