Sepiapterin for treating phenylketonuria

Sepiapterin is being developed as a treatment for phenylketonuria (PKU). People with PKU cannot break down the amino acid phenylalanine (Phe), which then builds up in their blood and brain. This can lead to brain damage. PKU is characterised by absence or deficiency of an enzyme called phenylalanine hydroxylase (PAH), responsible for processing Phe. The genetic cause (mutation) for PKU is passed on by the parents, who are usually carriers and do not have any symptoms of the condition themselves. PKU can be diagnosed during the first days of life with routine newborn screening and does not usually cause any symptoms if treatment is started early. Without treatment, PKU can damage the brain and nervous system, which can lead to learning disabilities. The main treatment is a low-protein diet and controlled intake of many other foods, such as potatoes and cereals. As there is currently no cure for PKU, the diet is recommended for life. Therefore, there is an unmet need for a treatment that allows patients to loosen their highly restrictive diets and still maintain Phe control.