Pompe disease is a storage disorder characterized by deficient or absent activity of the enzyme acid alpha-glucosidase. As a result of ineffective metabolism, glycogen accumulates in muscle tissues. Patients with a classic infantile-onset form present by the first few months of life with hypertrophic cardiomyopathy and muscle weakness. If left untreated, these patients rapidly die of cardiorespiratory failure. A cross-reactive immunological material (CRIM)-negative status is predictive of high anti-alglucosidase alpha antibody titers. However, CRIM-positive patients also sometimes develop robust antibody titers. High antibody titers complicate therapeutic management, and those patients have a worse clinical outcome of enzyme replacement therapy (ERT).
Four years ago, we successfully used an immune modulation therapy (IMT) protocol in a CRIM-positive infantile-onset patient with Pompe disease in whom ERT had to be discontinued because of severe infusion-associated reactions. She was found to be positive for anti-alglucosidase alpha antibodies. IMT (rituximab, methotrexate, and intravenous gammaglobulin) was started, and ERT was safely reintroduced during the IMT induction phase without any complications. Antibodies disappeared; IMT was tapered and discontinued; and cardiomyopathy steadily improved. During more than 3 years of follow-up, she remained ventilator dependent, and no gains in motor skills were noticed. The antibodies are still undetectable, and no adverse reactions associated with IMT had occurred. The cardiomyopathy is gradually increasing, but there is still ~ 50 % reduction as compared with the highest value measured. Although the reversal of clinical decline in our CRIM-positive and antibody-positive infant cannot be solely attributed to IMT, this protocol proved itself efficient and safe.