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Blood obtained by pricking a baby’s heel was collected on filter paper and tested for phenylketonuria, a rare metabolic condition that, if untreated, causes intellectual disability.

However, for individuals with a rare genetic disorder called phenylketonuria, phenylalanine can accumulate and cause health issues, so they are sometimes instructed to avoid it.

These are people with an inherited disease called phenylketonuria or PKU, who are born unable to metabolise the phenylalanine that is released as aspartame is broken down.

At Children’s Hospital, Richard Koch devoted most of his career to developmental disabilities, especially the early detection and prevention of phenylketonuria, commonly called PKU.

But that approach is not unprecedented: People born with the metabolic disorder phenylketonuria, for whom the amino acid phenylalanine is a neurotoxin, stay healthy by getting amino acids from a phenylalanine-free drink.