The causes of MGUS have long remained unknown, but recent studies of the antigen specificity of monoclonal Igs indicate that chronic antigenic stimulation by an infectious pathogen or by a self-antigen, notably glucosylsphingosine (GlcSph)—also called lysoglucosylceramide (LGL1)—appears to be a frequent pathogenic mechanism involved both in sporadic MGUS and MM and in monoclonal gammopathies associated with Gaucher disease (GD) [5,6,7,8,9]. The gene discussed is CUBN; the disease is Gaucher disease.