Membranoproliferative glomerulonephritis in a young adult with X-linked agammaglobulinaemia.

X-linked agammaglobulinaemia (XLA) is a rare congenital immunodeficiency caused by pathogenic mutations in the Bruton's tyrosine kinase (BTK) gene, characterised by a reduction in mature B cells and low levels of immunoglobulins, which predispose patients to recurrent infections. However, renal involvement in adult XLA patients is extremely rare. Here, we report a man in his early 20s with XLA who experienced recurrent severe infections, resulting in elevated serum creatinine, nephrotic-range proteinuria and haematuria. Laboratory analysis revealed the absence of mature B cells and significantly reduced immunoglobulin levels. A kidney biopsy confirmed a diagnosis of membranoproliferative glomerulonephritis (MPGN), and genetic testing identified a BTK gene mutation. This is a rare case of XLA complicated by MPGN prior to intravenous immunoglobulin therapy, which expands the pathological spectrum of renal involvement.