'Evolutionary Glitch' behind Childhood Ear Infections: Researchers Say

Researchers from the U.K. have found a possible reason behind glue ear or Otitis media with effusion in children. Children affected by this condition have a sticky fluid behind the eardrum in the middle ear. According to them, a flaw in the formation of the middle ear during evolution in humans has made this part of the ear more prone to infection.

The middle ear chamber has three bones that carry sound vibration from the eardrum to the middle ear. When the fluid builds up, the bones don't move freely and so the person experiences a temporary hearing loss.

The middle-ear infection is the most common ear infection in children, where parts of the ear are swollen and fluid is trapped behind the eardrum, says National Institute on Deafness and Other Communication Disorders.

The present study was conducted on mice. Researchers found that cells that line the middle ear originate from 'endoderm' and 'neural crest'.

Now, the part that arises from endoderm is covered in hair or cilia that help in keeping the ear clean. However, the part of ear that comes from neural crest has no such cilia, making it prone to infection.

Birds and reptiles have just one bone in the middle ear that conducts sound. Researchers say that evolution might have resulted in humans having three tiny bones to relay the sound vibrations. The mechanism that involves two cell lines to create an air sac must have evolved to accommodate the three tiny bones.

"Our study has uncovered a new mechanism for how the middle ear develops, identifying a possible reason for why it is prone to infection. The process of neural crest cells making up part of the middle ear appears fundamentally flawed as these cells are not capable of clearing the ear effectively. While this process may have evolved in order to create space in the ear for the three little bones essential for hearing, the same process has left mammals prone to infection - it's an evolutionary glitch," Dr. Abigail Tucker from the Department of Craniofacial Development at King's College London's Dental Institute said in a news release.

Tucker added that the study challenges the theory about the formation of the middle ear. "These findings are contrary to everything we thought we knew about the development of the ear - in all the textbooks it describes that the lining of the middle ear is made of endodermal cells and formed from an extension of another part of the middle ear - the Eustachian tube. The textbooks will need to be re-written!" Tucker concluded.

The study is published in the journal Science.