Auriculo-condylar syndrome is a condition that affects facial development, particularly development of the ears and lower jaw.
Most people with auriculo-condylar syndrome have deformed outer ears (auriculo refers to the ears). A unique feature of this condition is an ear abnormality called a “question-mark ear,” in which the ears have a distinctive question-mark shape caused by a split that separates the upper part of the ear from the earlobe. Other ear irregularities that can occur in auriculo-condylar syndrome include cupped ears, ears with fewer folds and grooves than usual, narrow ear canals, small skin tags in front of or behind the ears, and ears that are rotated backward. Some affected people may suffer from hearing loss.
Abnormalities of the lower jaw are another feature of auriculo-condylar syndrome. These abnormalities often include an abnormal small chin and malfunction of the temporomandibular joint (TMJ), which connects the lower jaw to the skull. Problems with the temporomandibular joint affect how the upper and lower jaws fit together and can make it difficult to open and close the mouth. The term “condylar” in auriculo-condylar is the upper portion of the lower jaw that forms part of the temporomandibular joint.
Other characteristics of auriculo-condylar syndrome can include prominent cheeks, an unusually small mouth , differences in the size and shape of facial structures between the right and left sides of the face (facial asymmetry), and an opening in the roof of the mouth (cleft palate). These characteristics differ, even among affected members of the same family.
How prevalent is auriculo-condylar syndrome?
Auriculo-condylar syndrome is an extremely uncommon health condition. Only a few dozen affected patients have been recorded in the medical history.
Which genes are involved in auriculo-condylar syndrome?
Auriculo-condylar syndrome can be caused by mutations in either the GNAI3 or PLCB4 gene. These genes provide instructions for making proteins that are involved in chemical signalling within cells. They help transmit information from outside the cell to inside the cell, which instructs the cell to grow, divide, or take on specialized functions.
Research shows that the proteins produced from the GNAI3 or PLCB4 genes contribute to the development of the first and second pharyngeal arches, which are structures in the embryo that ultimately develop into the jawbones, facial muscles, middle ear bones, ear canals, outer ears, and related tissues. Mutations in these genes alter the formation of the lower jaw. Instead of developing normally, the lower jaw becomes shaped more like the smaller upper jaw. This abnormal shape leads to micrognathia and problems with TMJ function.
How individuals inherit auriculo-condylar syndrome?
Auriculo-condylar syndrome is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is typically sufficient to cause the disorder. In some cases, an affected person inherits the mutation from one affected parent. Other cases result from new mutations in the gene and occur in people with no history of the disorder in their family.