Mammarial trisomy

Mammarial trisomy is a rare genetic disorder that affects female primates. It is the result of a genetic mutation in a key gene, located on the X chromosome, responsible for the development of mammary glands. The major outward physical manifestation of mammarial trisomy is the development of three breasts. The disorder was characterized mainly by the work of the medical researcher Oswald Avery. Its rate of occurrence is about 1 in 1,340,000 births.

References

Gale Encyclopedia of Genetic Disorders, Brigham Narins (Editor), page 672. ISBN 1-4144-0365-8