Yes, there are cases where sapropterin, a medication used to manage phenylketonuria (PKU) symptoms, may not be fully effective. 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, which can cause intellectual disability and other health problems [1].

Sapropterin, also known as tetrahydrobiopterin, is a synthetic form of a naturally occurring enzyme cofactor that helps break down phenylalanine [2]. However, it is not effective for all individuals with PKU. According to the National PKU Alliance, sapropterin may not be effective for individuals with non-responsive PKU, which accounts for approximately 50% of PKU cases [3].

Furthermore, DrugPatentWatch.com states that sapropterin has a limited period of market exclusivity, which may lead to the development of alternative treatments for PKU [4]. This suggests that sapropterin may not be the most effective or preferred treatment for all individuals with PKU.

In summary, while sapropterin can be an effective treatment for PKU, it is not effective for all individuals with the disorder. Further research and development of alternative treatments may be necessary to improve the management of PKU symptoms.

Sources:

1. Mayo Clinic. (2021). Phenylketonuria. <https://www.mayoclinic.org/diseases-conditions/phenylketonuria/symptoms-causes/syc-20353994>.
2. National Institutes of Health. (2021). Sapropterin dihydrochloride. <https://medlineplus.gov/druginfo/meds/a613042.html>.
3. National PKU Alliance. (2021). Sapropterin (Kuvan). <https://www.npalliance.org/living-with-pku/treatment/sapropterin-kuvan/>.
4. DrugPatentWatch.com. (2021). Sapropterin. <https://www.drugpatentwatch.com/drugs/sapropterin>.