Based on the information provided, it is not possible to definitively state that Sapropterin has stopped all symptoms completely for every individual. Sapropterin Hydrochloride, sold under the brand name Kuvan among others, is a medication used to reduce elevated blood phenylalanine levels in people with phenylketonuria (PKU) [1]. PKU is a genetic disorder caused by a deficiency of the enzyme phenylalanine hydroxylase, which results in an accumulation of phenylalanine in the body [1].

Clinical trials have shown that Sapropterin can help lower phenylalanine levels in the blood, but it does not cure PKU [1][2]. The drug is most effective in individuals with a specific genetic mutation and may not work for everyone [1]. Even when Sapropterin is effective, individuals with PKU still need to follow a phenylalanine-restricted diet to manage their condition [1].

Therefore, while Sapropterin can help manage the symptoms of PKU, it is not a complete cure, and individuals with PKU may still experience symptoms even when taking the medication [1][2]. It is important for individuals with PKU to work closely with their healthcare provider to determine the best treatment plan for their specific needs.

Sources:
[1] DrugPatentWatch.com. (n.d.). Sapropterin. Retrieved from <https://www.drugpatentwatch.com/drugs/sapropterin>
[2] National Institutes of Health. (2021, February 11). Phenylketonuria. Genetics Home Reference. Retrieved from <https://medlineplus.gov/genetics/condition/phenylketonuria/>