What causes PKU in a child? PKU is caused by a defect in a gene known as the PAH gene. This defect changes the way that phenylalanine is broken down by the body during digestion. PKU is passed on to children when each parent has 1 mutated gene.

Why does PKU cause mental retardation?

Mutations in the PAH gene can cause phenylketonuria (PKU), a disorder that can change cells in the brain. The faulty protein allows dangerously high levels of phenylalanine to accumulate in the brain, poisoning the cells. If a person with PKU consumes too much phenylalanine, the build-up can cause mental retardation.

How does PKU affect the brain?

PKU affects the brain.

When neurotransmitters are not made in the right amounts, the brain cannot function properly. High blood Phe levels can cause disruptions in neurotransmitters like serotonin and dopamine, which are important for mood, learning, memory, and motivation.