Phenylketonuria (PKU) is a rare inherited disorder that results an amino acid known as phenylalanine to build up in the body.
PKU is caused by a mutation in the gene responsible for producing the enzyme needed to break down phenylalanine. Without the enzyme, a toxic buildup can develop for individuals with PKU when they ingest foods that contain protein or aspartame; eventually leading to serious health complications. Babies born in the United States and many other countries are screened for PKU after birth, in order to recognize it right away and avoid any major health problems. For the rest of their lives, individuals with PKU — babies, children, and adults — must follow a strict diet that is phenylalanine-free.
Until this most recently, one of the only non-diet treatment options for individuals of PKU consisted of replacement cofactor; BioMarin’s Kuvan (sapropterin dihydrochloride). Kuvan binds to and enhances the activity of phenylalanine hydroxylase (PAH), an enzyme that metabolizes phenylalanine. “While Kuvan has been helpful to some people, it doesn't really benefit the large portion of our community, and many of those people are still struggling,” states Christine Brown, executive director of the National PKU Alliance (NPKUA), a nonprofit patient advocacy group, and the mother of two boys with PKU, “For most people, even on Kuvan, they still have to take medical foods.” Now, the FDA has recently approved another non-diet therapy: an enzyme substitute known as pegvaliase (Palynziq).
Palynziq metabolizes phenylalanine, replacing the deficient PAH enzyme that in PKU patients. “It is great that the FDA has approved . . . [Palynziq],” writes Francjan van Spronsen, a pediatrician specializing in inherited metabolic diseases at the University of Groningen in the Netherlands. “We have heard very promising results [that patients’] whole lives have changed, as now at least some of them can do without [specialized] diets or have increased their phenylalanine tolerance to a large degree.” As of now, Palynziq is only approved for use in the U.S and only for adult patients with uncontrolled phenylalanine amounts. Palynziq also comes with a black box warning due to the risk of anaphylaxis, which is severe and may be fatal allergic reaction if not treated. BioMarin has stated has announced that the therapy is expected to cost approximately $192,000 per year.