Biomarkers play a crucial role in guiding sapropterin treatment, a medication used to reduce elevated phenylalanine (Phe) levels in individuals with phenylketonuria (PKU) [1][2]. PKU is a genetic disorder characterized by the body's inability to break down Phe, an amino acid found in proteins [1]. Sapropterin is a synthetic form of tetrahydrobiopterin (BH4), a cofactor that helps the enzyme phenylalanine hydroxylase (PAH) function properly in breaking down Phe [1][2].

Biomarkers are biological indicators that measure the body's biological state and can be used to monitor disease progression, evaluate therapeutic responses, and inform treatment decisions [3]. In the context of sapropterin treatment, the primary biomarker used is Phe levels in the blood [2].

Before initiating sapropterin treatment, biochemical and genetic testing is performed to determine if the patient has PKU and if they are a candidate for sapropterin therapy [2]. Specifically, BH4 loading tests are conducted to assess the patient's response to BH4, which can predict their response to sapropterin [2]. Patients with a significant decrease in Phe levels (typically ≥30%) after a BH4 loading test are considered good candidates for sapropterin therapy [2].

During sapropterin treatment, Phe levels are closely monitored to assess the effectiveness of the therapy and adjust the dosage as needed [2]. If Phe levels do not decrease or remain elevated, sapropterin therapy may be discontinued or modified [2].

In summary, biomarkers, particularly Phe levels, guide sapropterin treatment by informing treatment decisions, monitoring therapy effectiveness, and adjusting dosages as needed.

Sources:

[1] DrugPatentWatch. (n.d.). SAPROPTERIN. Retrieved from <https://www.drugpatentwatch.com/p/tradename/SAPROPTERIN>

[2] Blau, N., van Spronsen, F. J., & Levy, H. L. (2010). Phenylketonuria. The Lancet, 376(9754), 1417-1431. doi:10.1016/s0140-6736(10)60827-3

[3] National Center for Biotechnology Information. (2021). Biomarkers. In National Library of Medicine. Retrieved from <https://www.ncbi.nlm.nih.gov/books/NBK221531/>