Occurrence of different external ear deformities in monozygotic twins: report of 2 cases.

SUMMARY: Microtia is a spectrum of congenital deformities, which varies from barely discernable to anotia. Twinning is a well-known risk factor for congenital defects including external ear deformities. Monozygotic twins usually show identical appearances as well as congenital malformations. In special conditions as ear deformities, "mirror-image" may also occur. We report 2 cases of monozygotic twins with different ear deformities. The 8-year-old propositus with lobule type microtia and her identical female twin presented with facial symmetry. Patient A had sausage-type right microtia with absence of external auditory canal. The left external ear showed normal appearance. Patient B presented with left-sided preauricular skin tag and right-sided malformation of tragus with skin tag combined with hyperplasia of underlying cartilage. A granule-size skin tag was also noticed at crus of right helix. A 7-year-old male patient with right-sided conchal type microtia presented to an ear reconstruction center. The patient's mother showed normal auricular appearance. Her monozygotic twin sister, whose son and daughter had normal ear appearance, was diagnosed with a leftsided lobule type microtia.

Microtia is a spectrum of congenital deformities, which varies from barely discernible to anotia. Approximately half of the cases are associated with hemifacial microtia. The birth rate of microtia ranges from 2 per 10,000 to 17.4 per 10,000.[1]

Twinning is a well-known risk factor for congenital defect including external ear deformities. Pathopoiesis of many congenital craniofacial deformities were thought to be vascular disturbances during embryonic or fetal development.[2] Monozygotic twins usually show identical appearances and congenital malformations.[3] In special conditions such as ear deformities, “mirror image” may also occur.[4]

An 8-year-old propositus with lobule-type microtia presented to ear reconstruction center for surgical treatment. The identical female twins were born at 37 weeks of pregnancy. Other congenital defects were excluded, such as congenital heart disease, deformities of extremity, perineal abnormality, facial hypoplasia, cleft lip, and cleft palate. Two years later, DNA testing showed monozygosity. On physical examination, both patients show facial symmetry. Patient A had sausage-type right microtia with the absence of external auditory canal. The left external ear showed normal appearance. Patient B presented with left-sided preauricular skin tag and right-sided malformation of tragus with skin tag combined with hyperplasia of underlying cartilage. A granule-sized skin tag was also noticed at crus of right helix (Figs. 1–3).

Fig. 1.

Lateral view of the right microtia (propositus, 8 years old).

Fig. 3.

Front view of the monozygotic twins (10 years old).

Lateral view of deformity of right tragus (patient B, 10 years old).

A 7-year-old male patient with right-sided conchal-type microtia presented to ear reconstruction center. The patient’s mother showed normal auricular appearance. Her monozygotic twin sister, whose son and daughter had normal ear appearance, was diagnosed with left-sided lobule-type microtia. The monozygotic female twins were born at 38 weeks of pregnancy. Other congenital defects were also excluded. On physical examination, patient C showed bilateral normal ear appearance and external acoustic meatus, the cranioauricular angle was 80 degree. Patient D had left-sided lobule-type right microtia with atresia of external auditory canal.

In theory, monozygotic twins have the same genetic background, embryonic development, and living environment. Discordant monozygotic twins may result from gene mutation, chromosomal abnormality, X-inactivation, genomic imprinting, DNA methylation, or human endogenous retrovirus. Artunduaga et al[5] studied 13 monozygotic and 22 dizygotic twins. The concordance for ear malformation is higher in monozygotic twins than dizygotic twins (61.5% and 4.5%). Through comparative analysis in discordant monozygotic twins, the interference by other factors can be excluded, the research scope better focused, and thus, the pathogenic genes or related factors be more accurately identified. Analysis of discordant monozygotic twins could be an advantageous and potential tool in the genetic research.

PATIENT CONSENT

Parents or guardians provided written consent for the use of the patients’ image.