PKU symptoms can range from mild to severe. The most severe form of this disorder is known as classic PKU. An infant with classic PKU may appear normal for the first few months of their life. If the baby isn’t treated for PKU during this time, they’ll start to develop the following symptoms:
seizures
tremors, or trembling and shaking
stunted growth
hyperactivity
skin conditions, such as eczema
a musty odor of their breath, skin, or urine