Human ear deformities usually develop during pregnancy, and a few of these cases may be severe enough to cause hearing loss. Based on data from the Plastic and Craniofacial Surgery for Infants and Children, ear deformities can range from the mild case of the ear displaying too prominently to the more serious absence of ear cartilage.
When there is missing ear cartilage, this deformity is called microtia. Hearing loss may occur as a result of microtia. In severe cases when the ear is completely missing, this condition is referred to as anotia.
Microtia is the developmental malformation of the external ear. It can vary in appearance and most cases will cause the appearance of peanut-shaped ears. There are cases where the ear canal has not opened; this condition is associated with aural atresia, which can cause partial deafness. The condition can occur unilaterally or bilaterally.
Causes of Microtia
As a congenital condition, missing ear cartilage microtia occurs in 0.8 to 4.2 in every 10,000 births. It is more prevalent among males. In majority of the cases, the cause of microtia is unknown, and is referred to as idiopathic microtia.
The missing ear cartilage may be due to either genetics or environmental factors. Risk factors include gestosis, high paternal or maternal age, diabetes, anemia, race, multiple births, and certain medications. For example, the acne medication Accutane (isotretinoin) is known to cause microtia during the development of the embryo, due to the very high doses of vitamin A it contains.
Genetics of Microtia
Is missing ear cartilage genetic? It is believed that genetics of ear cartilage play a role in the occurrence of microtia. Based on different studies, there exists a wide range of 3% to 34% of familial cases out of the total microtia cases. Moreover, several studies also reported hereditary forms of this ear deformity with autosomal recessive or dominant mode of inheritance with incomplete penetrance and variable expression.
Genetics can be the clear cut cause of the problem. The already identified missing ear cartilage genetic problems include the trisomy of chromosomes 13, 18, and 22. Complex chromosomal rearrangements, microldeletions, and distinct hereditary genomic copy number variants were also implicated to be causes of this deformity.
There are cases where complex genetic problems can also lead to other associated syndromes aside from the missing cartilage in the ear. The chromosomal translocations affecting the 6p24 region have also been linked to bilateral microtia and associated facial deformity like orofacial clefting. In the case of Treacher Collins syndrome, the absence of cartilage in both ears and the deformities in other facial structures can be attributed to the mutation in the Treacher Collins-Franceschetti 1 or TCOF1 gene.
In other cases, the genetic cause can only be inferred as a possible cause. Microtia can demonstrate an inherited pattern among several family members but the specific genes causing the problem may not be identified by science. Furthermore, some ethnic groups have higher chances of having the condition. Nevertheless, this does not prove a genetic population disposition.
Microtia or missing ear cartilage is a developmental disorder with a genetic as well as environmental etiology. A number of vital genes that is essential to the development of the auditory system can be involved in the occurrence of this abnormal condition. However, the genetics of ear cartilage can only be implicated directly in only a percentage of all cases.
Further research on the identification of microtia-causing genes is very important to identify the molecular mechanisms involved in the ear development. A deeper understanding of the genetics and pathogenesis of this condition will lead to better treatments and possible prevention of the problem.
In the end, the goal is to detect the problem as early as possible. The missing ear cartilage genetic problem could have been detected during prenatal screening as well as with genetic testing with parents who have family history of the condition. After birth, parents should also seek immediate treatment upon discovery of an ear deformity in one or both ears of the child.