Enzyme replacement therapy: efficacy and limitations

Area of Science:

• Biochemistry
• Genetics
• Pediatrics

Background:

• Enzyme replacement therapy (ERT) is an established treatment for specific types of mucopolysaccharidoses (MPS), including MPS I, MPS II, MPS VI, and MPS IVA.
• Long-term follow-up studies have assessed ERT efficacy in MPS I, MPS II, and MPS VI, providing valuable data on its effectiveness and limitations.

Purpose of the Study:

• To evaluate the efficacy and limitations of current enzyme replacement therapy (ERT) for various types of mucopolysaccharidoses (MPS).
• To discuss alternative treatments and future directions, including stem cell transplantation and neonatal screening, for improving patient outcomes.

Main Methods:

• Review of clinical trials and post-marketing studies evaluating ERT in MPS patients.
• Analysis of ERT's impact on biochemical markers (urinary GAGs), organ volumes, and specific tissue penetration.
• Consideration of factors affecting ERT efficacy, such as antibody formation and blood-brain barrier penetration.

Main Results:

• ERT effectively reduces urinary glycosaminoglycans (GAGs) and liver/spleen volumes in MPS patients.
• Cartilaginous organs, bones, and eyes show limited improvement with ERT due to poor tissue penetration.
• ERT does not cross the blood-brain barrier, leaving the central nervous system untreated, which is critical for severe MPS forms with cognitive decline.

Conclusions:

• While ERT offers benefits for certain MPS manifestations, its limitations in treating skeletal, ocular, and neurological aspects necessitate alternative or adjunctive therapies.
• Hematopoietic stem cell transplantation is considered the gold standard for severe MPS I (Hurler syndrome), though its role in MPS II is debated.
• Early, possibly pre-symptomatic, treatment through neonatal screening is recommended to improve prognosis for treatable MPS, with ongoing studies exploring its potential.