In Wonder, Auggie refers to his condition as Mandibulofacial Dysostosis that is also known as Treacher Collins syndrome (TCS).

This disease is an inherited disorder, and there are very few people affected (about 1 in 70,000 of births in the USA). When a person is affected by TCS, his/her cheekbones and jawbones do not develop well. Children with this condition have very small or partially absent cheekbones and weird eyelids. Frequently the ears are not normal, and parts of them are usually absent. There is a hearing loss associated with this syndrome too.

In Wonder, Auggie's condition is also more complicated by another syndrome that makes his particular set of craniofacial differences unique.

There are many children born every year with different types of craniofacial differences. When people get older, other things that happen can cause facial differences too. They include accidents, fires, or diseases.

Adapted from https://wonderthebook.com/for-teachers