The poor utility of IgG and IgA measurements may be related to the following:1) Changes in hematocrit and blood volume occur in MM leading serum Ig concentrations to vary by 50% or more, independently of changes in tumor production [3]; 2) Serum IgG concentrations are affected by variable clearance rates, so measurements do not reliably relate to tumor production. The gene discussed is CD79A; the disease is Miyoshi myopathy.