Acquired Renal Amyloidosis in a Patient With X-Linked Hyper-IgM Immunodeficiency With Novel Hemizygotic Pathogenic Variant in CD40LG Gene.

Introduction: Renal AA amyloidosis with X-linked hyper-IgM immunodeficiency is rare diseases, and their simultaneous presentation in the same patient is exceptional. Case Presentation: We present a case of renal AA amyloidosis in a 20-year-old man with nephrotic syndrome and reduced glomerular filtration rate (GFR). Clinically, serologically, histopathological, and genetically, we confirm renal amyloidosis in the presence of X-linked hyper-IgM syndrome; in turn, we detected a new hemizygous pathogenic variant in the CD40L gene (c.345delA). Conclusion: Our hypothesis suggests that these conditions predisposed the patient to a combined (cellular and humoral) immunodeficiency, leading to recurrent infectious episodes throughout his life, ultimately resulting in renal amyloidosis due to deposition of serum amyloid protein.