F is for the amino acid Phenylalanine. Use this bead as a charm on a bracelet. The genetic disorder phenylketonuria (PKU) is the inability to metabolize phenylalanine. Individuals with this disorder are known as "phenylketonurics" and must regulate their intake of phenylalanine. Pregnant women with hyperphenylalaninemia may show similar symptoms of the disorder (high levels of phenylalanine in blood) but these indicators will usually disappear at the end of gestation. Individuals who cannot metabolize phenylalanine for whatever reason must monitor their intake of protein to control the buildup of phenylalanine as their bodies convert protein into its component amino acids. A non-food source of phenylalanine is the artificial sweetener aspartame.