A healthy baby boy is the first person to be born with DNA from three people, according to a medical report released Tuesday.

In addition to inheriting nuclear DNA from his mother and father, the infant also has mitochondrial DNA from a second woman who served as an egg donor.

Mitochondrial DNA consists of just 37 genes, a tiny fraction of the genetic material inside a cell. Unlike nuclear DNA — which is bundled into 23 pairs of chromosomes and influences traits such as eye color, height and cancer risk — mitochondrial DNA contains instructions for the energy-producing structures inside cells. It is passed down virtually unchanged from mother to child.

That was a situation the infant’s mother wanted to avoid. Her mitochondrial DNA contains mutations that cause Leigh syndrome, a neurological disorder that is usually fatal during early childhood. The woman had already lost two children to the disease.