Per the European public assessment report (EPAR), Myozyme® is designated as an “orphan medicine” used in treating rare diseases. The Committee for Medicinal Products for Human Use (CHMP) has assessed Myozyme and granted authorization for marketing with recommendations for conditional use. The drug is available as a powder that can be used to prepare a solution for intravenous infusion. The active substance in Myozyme, alglucosidase alfa, is effective in treating Pompe disease, a rare inherited disorder. Patients with Pompe disease lack the enzyme alpha-glucosidase (GAA), which breaks down glycogen to form glucose, used by the body’s cells for energy. A lack of alpha-glucosidase results in the accumulation of glycogen in muscles, including the diaphragm and heart. The buildup of glycogen can cause a wide range of symptoms, including muscle weakness, breathing difficulties, and an enlarged heart. Myozyme can be obtained with a prescription to treat Pompe disease.¹

Get prescribing information about Myozyme on Rare Disease Advisor’s drug monograph.

In March of 2006, the European Medicines Agency granted a license to Myozyme as an enzyme substitute drug, and it is considered a promising new therapy for Pompe disease. The drug molecule has an additional mannose-6-phosphate remnant on its surface and is otherwise identical to the human enzyme molecule. The sugar remnant is used by cells to take up the molecule during endocytosis. Drug production involves cell culture or the milk of transgenic animals. Myozyme was licensed after several phase II studies conducted in infants with a diagnosis of Pompe disease showed that all of them survived the first year of life, and two-thirds survived the fourth year.²

Myozyme Enzyme Replacement Therapy

Per the authorization from the European Medicines Agency, Myozyme is administered as an intravenous infusion. Studies have shown that treatment with Myozyme can decrease heart size and improve cardiac function. Patients with infantile-onset Pompe disease die within the first year of life, and enzyme replacement therapy (ERT) with Myozyme has shown remarkable efficacy in these children.² Features of Pompe disease include slowly progressive myopathy along with respiratory muscle involvement. Several reports and one randomized placebo-controlled study have shown stabilization of respiratory function and improvement in walking distance after treatment with Myozyme in patients with a late-onset form of Pompe disease. 

ERT is achieved with recombinant human GAA (rhGAA, Myozyme). In a randomized trial, ERT did not prove efficacious in patients with advanced Pompe disease, who may require ventilator assistance. Few studies have addressed the respiratory function of affected patients. Most have assessed the short-term effects (no longer than 2 years) of ERT with Myozyme. Studies of patients with severe, advanced of Pompe disease are needed to determine whether ERT with Myozyme provides any long-term benefits.³

Myozyme Treatment in Early-Onset Pompe Disease

Myozyme treatment consists of periodic intravenous infusions of the drug. It has been observed that a relatively small proportion of drug reaches striated and cardiac muscle. Most goes to the liver and is taken up by hepatic cells. Myozyme cannot cross the blood-brain barrier. Glycogen deposits form in neurons over many years. The long-term development of neuronal involvement is concerning, but studies have not shown it to be significant.

After the administration of Myozyme, cardiac muscle function appears to improve more than skeletal muscle function. More mannose-6-phosphate receptors are present on cardiac muscle cells than on skeletal muscle cells. The response to rhGAA is better in peripheral nerves and endothelial tissues than in muscles. Many factors may affect a patient’s response to Myozyme, such as the development of antibodies to GAA, age, severity of disease, and type of muscle fibers affected (type II fibers are less sensitive to Myozyme). In patients with classic Pompe disease, Myozyme has brought about improvement in cardiac function and survival. However, improvement in the function of multiple organs does necessarily result in a significant improvement in quality of life or body function.⁴

Long-term Exposure to Myozyme in Late-Onset Pompe Disease

Since the approval of Myozyme, the life expectancy and quality of life of patients with Pompe disease have improved. Late-onset Pompe disease can lead to a progressive deterioration of skeletal muscle and significant disability. Currently, ERT with Myozyme is approved for both pediatric patients and those with late-onset Pompe disease. However, the symptoms of children being treated with ERT may not disappear completely. Long-term follow-up is required to monitor symptoms. Studies have been conducted to address efficacy and safety concerns regarding Myozyme ERT. The cellular and humoral responses to ERT are still poorly understood. The level of anti-rhGAA antibodies peaks within 1000 days after ERT administration. The administration of Myozyme can lead to a residual production of non-neutralizing immunoglobulin G and clearance of antibodies. In vitro research has shown that the administration of rhGAA can also lead to detectable T-cell reactivity. Both treated and untreated patients with late-onset Pompe disease show an upregulation of chemokines and cytokines. Overall, patients with late-onset Pompe disease show a decrease in the residual production of non-inhibitory immunoglobulin G antibody titers.⁵

References

  1. European Medicines Agency. Myozyme. Updated April 28, 2021. Accessed July 22, 2021.
  2. Merk T, Wibmer T, Schumann C, Krüger S. Glycogen storage disease type II (Pompe disease)–influence of enzyme replacement therapy in adults. Eur J Neurol. 2009;16(2):274-277. doi:10.1111/j.1468-1331.2008.02377.x
  3. Papadopoulos C, Orlikowski D, Prigent H, et al. Effect of enzyme replacement therapy with alglucosidase alfa (Myozyme®) in 12 patients with advanced late-onset Pompe disease. Mol Genet Metab. 2017;122(1-2):80-85. doi:10.1016/j.ymgme.2017.06.007
  4. Pascual SI. Phenotype variations in early onset Pompe disease: diagnosis and treatment results with Myozyme®. In: Espinos C, Felipo V, Palau F, eds. Inherited Neuromuscular Diseases. Advances in Experimental Medicine and Biology, vol 652. Dordrecht: Springer; 2009:39-46. doi:10.1007/978-90-481-2813-6_4
  5. Masat E, Laforêt P, De Antonio M, et al. Long-term exposure to Myozyme results in a decrease of anti-drug antibodies in late-onset Pompe disease patients. Sci Rep. 2016;6:36182. doi:10.1038/srep36182

Reviewed by Harshi Dhingra, MD, on 7/27/2021.

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