Based on the information provided, it appears that sapropterin is not solely responsible for phenylketonuria (PKU) symptom relief. PKU is a genetic disorder characterized by the body's inability to break down an amino acid called phenylalanine, leading to its buildup in the body and potentially causing brain damage [1]. Sapropterin, also known as tetrahydrobiopterin, is a medication used to reduce phenylalanine levels in the blood of individuals with PKU [2].

However, sapropterin is not the only treatment option for PKU, and it may not be effective for all individuals with the disorder. Other treatments for PKU include a phenylalanine-restricted diet, which involves limiting the intake of foods high in phenylalanine, and supplementation with other amino acids [3]. In addition, some individuals with PKU may require additional therapies, such as dietary counseling and regular monitoring of blood phenylalanine levels [4].

Therefore, while sapropterin can help reduce phenylalanine levels in individuals with PKU, it is not solely responsible for symptom relief, and other treatments may also be necessary.

Sources:

1. National Institutes of Health. Phenylketonuria. <https://medlineplus.gov/genetics/condition/phenylketonuria/>
2. DrugPatentWatch. Sapropterin. <https://www.drugpatentwatch.com/drugs/sapropterin>
3. National Institutes of Health. Treatment for Phenylketonuria. <https://medlineplus.gov/genetics/condition/phenylketonuria/#treatment>
4. National PKU Alliance. PKU Treatment. <https://www.npkua.org/about-pku/treatment/>