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Why Are Some People Born With Two Heads?

posted: 11/12/15
by: Danny Clemens
Two-headed girl born in November 2015
STR/AFP/Getty Images

A woman in Bangladesh gave birth late Wednesday evening to a daughter with two heads. The unnamed child reportedly only has one set of vital organs, and is currently receiving treatment for 'breathing difficulties," the AFP reports.

It's not immediately clear why the Bangladeshi girl was born with two heads. Throughout history, rare cases of both humans and animals with two heads have been reported. In 2007, paleontologists uncovered a 120-million-year-old fossil of an ancient reptile that had two distinct heads and necks, an abnormality still seen in reptiles in the present day.

Although most are not well-understood, there are many different congenital cephalic disorders that can result in the birth of a child with two heads and/or faces:

Craniopagus parasiticus is an extremely rare condition that occurs when an embryo containing identical twins fails to split completely, leaving an underdeveloped parasitic twin that remains attached to a fully developed child.

In February 2005, doctors in Egypt performed the first "successful separation" of a craniopagus parasiticus case. During a 9-month surgery, doctors removed the underdeveloped twin from a 10-month-old child. Throughout the procedure, the child experienced severe bleeding, requiring a staggering four liters of blood. Skin and bone grafts from the parasite were used to repair the wound left by the surgery.

Although child lived for more than a year "without neurological deficit," she died suddenly after coming down with a fever in March 2006.

An infant with craniofacial duplication (also known as diprosopus) has two sets of facial features -- although not necessarily two heads -- and an outwardly regular trunk. The condition's causes are not well understood, although many experts believe that the conditions originates during an "embryological disturbance in the separation of the twins during the 2nd week of pregnancy."

According to the U.S. National Library of medicine, varying degrees of craniofacial duplication can be indicative of internal abnormalities. "A complete duplication is associated with a high incidence of anomalies in the central nervous system, cardiovascular system, gastrointestinal system and the respiratory system, whereas no major anomalies are found in the infants with a partial duplication."

The condition disproportionately affects females over males. Fewer than 50 cases have been reported in the past 150 years; many infants that suffer from the condition are stillborn.

Conjoined twins occur when a fertilized egg doesn't split fully following fertilization. The resulting twins have two separate heads and, oftentimes, two sets of vital organs.

"The developing embryo starts to split into identical twins during the first few weeks after conception, but stops before the process is complete," the University of Maryland Medical Center explains. "The partially separated egg develops into a conjoined fetus."

For conjoined twins, the chances of survival are relatively good: up to 25% of conjoined twins survive beyond birth, although female conjoined twins are statistically far more likely to survive than males. Separation surgeries, however, are still risky.

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