Damaging variants in FOXI3 cause microtia and craniofacial microsomia.

PURPOSE: Craniofacial microsomia (CFM) represents a spectrum of craniofacial malformations, ranging from isolated microtia with or without aural atresia to underdevelopment of the mandible, maxilla, orbit, facial soft tissue, and/or facial nerve. The genetic causes of CFM remain largely unknown. METHODS: We performed genome sequencing and linkage analysis in patients and families with microtia and CFM of unknown genetic etiology. The functional consequences of damaging missense variants were evaluated through expression of wild-type and mutant proteins in vitro. RESULTS: We studied a 5-generation kindred with microtia, identifying a missense variant in FOXI3 (p.Arg236Trp) as the cause of disease (logarithm of the odds = 3.33). We subsequently identified 6 individuals from 3 additional kindreds with microtia-CFM spectrum phenotypes harboring damaging variants in FOXI3, a regulator of ectodermal and neural crest development. Missense variants in the nuclear localization sequence were identified in cases with isolated microtia with aural atresia and found to affect subcellular localization of FOXI3. Loss of function variants were found in patients with microtia and mandibular hypoplasia (CFM), suggesting dosage sensitivity of FOXI3. CONCLUSION: Damaging variants in FOXI3 are the second most frequent genetic cause of CFM, causing 1% of all cases, including 13% of familial cases in our cohort.

An ancient founder mutation located between ROBO1 and ROBO2 is responsible for increased microtia risk in Amerindigenous populations.

Microtia is a congenital malformation that encompasses mild hypoplasia to complete loss of the external ear, or pinna. Although the contribution of genetic variation and environmental factors to microtia remains elusive, Amerindigenous populations have the highest reported incidence. Here, using both transmission disequilibrium tests and association studies in microtia trios (parents and affected child) and microtia cohorts enrolled in Latin America, we map an ∼10-kb microtia locus (odds ratio = 4.7; P = 6.78e-18) to the intergenic region between Roundabout 1 (ROBO1) and Roundabout 2 (ROBO2) (chr3: 78546526 to 78555137). While alleles at the microtia locus significantly increase the risk of microtia, their penetrance is low (<1%). We demonstrate that the microtia locus contains a polymorphic complex repeat element that is expanded in affected individuals. The locus is located near a chromatin loop region that regulates ROBO1 and ROBO2 expression in induced pluripotent stem cell­derived neural crest cells. Furthermore, we use single nuclear RNA sequencing to demonstrate ROBO1 and ROBO2 expression in both fibroblasts and chondrocytes of the mature human pinna. Because the microtia allele is enriched in Amerindigenous populations and is shared by some East Asian subjects with craniofacial malformations, we propose that both populations share a mutation that arose in a common ancestor prior to the ancient migration of Eurasian populations into the Americas and that the high incidence of microtia among Amerindigenous populations reflects the population bottleneck that occurred during the migration out of Eurasia.

HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.

Microtia is a rare, congenital malformation of the external ear that in some cases has a genetic etiology. We ascertained a three-generation family with bilateral microtia and hearing loss segregating as an autosomal dominant trait. Exome sequencing of affected family members detected only seven shared, rare, heterozygous, nonsynonymous variants, including one protein truncating variant, a HOXA2 nonsense change (c.703C>T, p.Q235*). The HOXA2 variant was segregated with microtia and hearing loss in the family and was not seen in 6,500 individuals sequenced by the NHLBI Exome Sequencing Project or in 218 control individuals sequenced in this study. HOXA2 has been shown to be critical for outer and middle ear development through mouse models and has previously been associated with autosomal recessive bilateral microtia. Our data extend these conclusions and define HOXA2 haploinsufficiency as the first genetic cause for autosomal-dominant nonsyndromic microtia.

A 20-year experience with the Brent technique of auricular reconstruction: pearls and pitfalls.

BACKGROUND: The surgical treatment of 291 patients with auricular deformities is reported. This series includes correction of acquired defects in 15 patients and congenital malformations in the remaining 276. In the latter group, 222 had unilateral microtia, 38 had bilateral microtia, and 16 deformities were attributable to failed reconstructions. METHODS: Technical details are given on the planning and executing of operations, including the following: positioning of the reconstructed ear; unconventional lobule transposition for selected patients with facial microsomia; costal cartilage harvesting; framework construction with absorbable sutures; tragus and auricular sulcus construction; and secondary reconstructions with temporal fascial flaps, radical framework revision using the same skin pocket, and total reconstructions with costal cartilage grafts using the original skin envelope. RESULTS: A total of 326 ears were reconstructed in 291 patients using autogenous costal cartilage: 222 in unilaterally affected microtia patients, 73 in 38 bilaterally affected microtia patients, 16 secondary reconstructions of microtia patients, and 15 in acquired deformities. Two hundred sixty-four of the 291 patients (90.7 percent) were examined at least 1 year after completing treatment. In the remaining 27 patients (9.3 percent), follow-up was not possible for several reasons. Surgery-related complications (hematoma, skin loss, and infection) totaled 1.9 percent. Hypertrophic scars and keloids with important aesthetic consequences were 5.3 percent. CONCLUSIONS: Consistently good results were associated with progressive experience and favorable conditions (i.e., isolated type II or III microtia, appropriate amount and quality of costal cartilage, and thin and elastic auricular skin). Recognizing unfavorable conditions helped with sound preoperative planning and discussion of expectations with patients and families.