Textbooks may have to be re-written after researchers in England discovered why some children are prone to repeated bouts of glue ear – it’s an evolutionary glitch in the development of the middle ear.
Scientists at King’s College London, UK, found that the cells lining the middle ear cavity originate from two different tissue types – endoderm and neural crest cells.
The part of the lining that originates from the endoderm is covered in cilia that help to clear debris from the ear, but the lining derived from neural crest cells do not have cilia and that makes the area of the middle ear less efficient at self-cleaning and susceptible to infection.
The process of the middle ear transforming into an air-filled space is different in birds and reptiles, which have just one small ear bone, so researchers believe that mammals may have evolved this new mechanism to house the additional bones.
The process of two distinct cell types to create the lining of the middle ear cavity could be why there are three tiny sound-conducting bones from the eardrum to the inner ear.
When fluid builds up in the chamber, the three bones cannot move freely and are unable to pass sound vibrations to the inner ear, causing temporary hearing loss.
Until now, it was largely unknown as to why some children appear more prone than others to developing chronic ear problems, with repeated bouts of glue ear.
Dr Abigail Tucker from the Department of Craniofacial Development at King’s College London’s Dental Institute, whose report is published in Science said: “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.
“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 A, Thompson S. Dual Origin of the Epithelium of the Mammalian Middle Ear. Science 21 March 2013
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