The biopsy revealed endoneural IgM deposition, consistent with paraproteinemic neuropathy, thereby raising clinical suspicion for WM and warranting further evaluation with a bone marrow biopsy, which revealed 30% involvement of the bone marrow by a low-grade B cell lymphoma with plasmacytic differentiation and a MYD88 L265P mutation. The gene discussed is CD40LG; the disease is B-cell non-Hodgkin lymphoma.