GENE THERAPY for an enzyme deficiency causing severe disease in children appears to have been successful. A single CSF injection of the gene encoding the enzyme in a harmless virus restored enzyme replacement. Enzyme Replacement Therapy (ERT) is available for about six diseases, and involves IV enzyme infusion twice a month for life (in some cases generating neutralizing antibodies), and at an enormous cost. Pioneered by Genzyme and followed by Biomarin, this has been the state of the art treatment to date. Gene therapy can be a game changer, with infrequent inoculations.
http://www.sciencedaily.com/releases/2013/07/130702100344.htm?goback=.gde_1955065_member_255195820