A boy born with three penises is the first-ever reported case of human triphallia, a condition in which three phalluses form during embryonic development.
The child, first seen by doctors as a 3-month-old, was from Duhok, Iraq. He underwent surgery to remove two of the phalluses, which were small projections at the base of the penis and scrotum. The third phallus was in the usual location.
According to a case study published in the International Journal of Surgery Case Reports in November, the boy was doing well at a follow-up visit a year after surgery.
Extra, or "supernumerary" penises are a rare congenital condition, occurring only once every 5 million to 6 million live births, according to the researchers.
The level of development of these extra phalluses differs in different individuals. In the case of the child in Iraq, the two additional penises contained the erectile tissue, called corpus cavernosum, which becomes engorged with blood during arousal, as well as a tissue called corpus spongiosum, which helps support the urethra, the tube through which urine passes.
But the extra penises didn't have urethras. This made surgical removal of the extra organs simple.
Not much is known about why supernumerary penises occur, said John Martin, an anatomy professor at the St. Louis University School of Medicine, who was not involved in the case study.
Martin and his colleagues teach anatomy using a body-donation program and once discovered that one of their body donors had diphallia, or two penises. The man, who died at age 84, had two full-size phalluses with a urethral opening between them at their base.
The donor didn't make any mention of the condition on his body-donation forms. He had two children, Martin said, but the researchers don't know whether they were biological children or whether any reproductive technologies were necessary for the man to have children.
"He died in the early 2000s, so when he was growing up surgery wasn't an option, perhaps," Martin told Live Science. "It's just very different from today where anything like that would have been detected early on and most likely surgery would have been done."
Martin and his colleagues did genetic testing on the donor to see if they could determine the reason for the unusual development. They found several mutations in genes known to be involved in genital development, including some that contribute to forming hairlike structures called cilia on embryonic cells.
These cilia are very important in development, Martin told Live Science, because they flutter in specific directions, wafting proteins toward one side or the other of the developing embryo.
Abnormalities in the cilia genes have also been seen in other cases of congenital abnormalities, he said, such as situs inversus, in which the organs in the torso are flip-flopped so that they are on opposite sides from their normal positions.
The researchers also found mutations in genes that help regulate the activity of other genes in development and in genes involved in receptors for androgens, hormones that have a masculinizing influence and that are involved in genital development.
Another gene commonly associated with genital development is the quirkily named sonic hedgehog, Martin said, which is important throughout the body for promoting growth during embryonic development.
It's not clear how similar the genetics are between different cases of diphallia or whether these findings apply to the one-of-a-kind case of triphallia.
The doctors who treated the Iraqi baby found nothing in the child's family history or medical history, such as exposure to medications or chemicals during pregnancy, that would explain the congenital abnormality.
The child was otherwise healthy except for some fluid buildup in the scrotum, which is a common and easily treated condition in infancy.