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.

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.

Missense mutations in the BCS1L gene as a cause of the Björnstad syndrome.

BACKGROUND: The Björnstad syndrome, an autosomal recessive disorder associated with sensorineural hearing loss and pili torti, is caused by mutation of a previously unidentified gene on chromosome 2q34-36. METHODS: Refined genetic mapping and DNA sequencing of 44 genes between D2S2210 and D2S2244 revealed BCS1L mutations. Functional analyses elucidated how BCS1L mutations cause the Björnstad syndrome. RESULTS: BCS1L encodes a member of the AAA family of ATPases that is necessary for the assembly of complex III in the mitochondria. In addition to the Björnstad syndrome, BCS1L mutations cause complex III deficiency and the GRACILE syndrome, which in neonates are lethal conditions that have multisystem and neurologic manifestations typifying severe mitochondrial disorders. Patients with the Björnstad syndrome have mutations that alter residues involved in protein-protein interactions, whereas mutations in patients with complex III deficiency alter ATP-binding residues, as deduced from the crystal structure of a related AAA-family ATPase. Biochemical studies provided evidence to support this model: complex III deficiency mutations prevented ATP-dependent assembly of BCS1L-associated complexes. All mutant BCS1L proteins disrupted the assembly of complex III, reduced the activity of the mitochondrial electron-transport chain, and increased the production of reactive oxygen species. However, only mutations associated with complex III deficiency increased mitochondrial content, which further increased the production of reactive oxygen species. CONCLUSIONS: BCS1L mutations cause disease phenotypes ranging from highly restricted pili torti and sensorineural hearing loss (the Björnstad syndrome) to profound multisystem organ failure (complex III deficiency and the GRACILE syndrome). All BCS1L mutations disrupted the assembly of mitochondrial respirasomes (the basic unit for respiration in human mitochondria), but the clinical expression of the mutations was correlated with the production of reactive oxygen species. Mutations that cause the Björnstad syndrome illustrate the exquisite sensitivity of ear and hair tissues to mitochondrial function, particularly to the production of reactive oxygen species.

Butterfly cartilage graft inlay tympanoplasty for large perforations.

OBJECTIVE: Butterfly graft inlay tympanoplasty is a well-established technique for the repair of small perforations. However, the efficacy of the technique for medium and large tympanic membrane perforations remains unknown. STUDY DESIGN: Retrospective case series. METHODS: Postauricular tympanoplasty and tympanomastoidectomy using a large butterfly cartilage inlay graft (>4 mm diameter to total drum replacement) were analyzed in 90 pediatric patients (99 ears). RESULTS: Patient ages ranged from 2 to 20 years; mean follow-up duration was 27.6 months. Successful closure occurred in 92% of the ears. No graft lateralized nor displaced into the middle ear. No retraction pocket occurred during the follow-up period. In 62 cases, intact canal wall or canal wall window tympanomastoidectomy was performed; Fifty-one (82.2%) of the patients having mastoidectomy procedures had chronic otitis media with cholesteatoma. The mean preoperative to postoperative four-tone air-bone gap improved from 23 to 21 dB; the number of patients with 0 to 10 dB hearing results increased from 16 ears preoperatively to 32 ears postoperatively. Postoperative suboptimal results included eight patients with postoperative perforations in the residual tympanic membrane adjacent to an intact cartilage graft; two of these patients were the only individuals who exhibited otorrhea. CONCLUSIONS: Cartilage butterfly graft inlay tympanoplasty is effective in the vast majority of patients with moderate to large perforations. The closure rate exceeded 90% with no graft displacement, postoperative adverse events were respectably low, and hearing results improved or remained stable despite the need for concurrent mastoidectomy in the majority of patients.

Tuberculous otitis in infants: temporal bone histopathology and clinical extrapolation.

HYPOTHESIS: The study of infant temporal bones with tuberculosis (TB) of the middle ear and mastoid could provide information to assist with clinical diagnosis in this population. BACKGROUND: The TB pandemic has become a critical global public health problem. With the rising incidence of the disease, otolaryngologists might encounter an increased frequency of otologic TB. Pediatric temporal bone reports of TB are rare. METHODS: Light microscopic examination was performed on both temporal bones from an infant who died as a result of miliary TB. RESULTS: The tympanic membranes were thickened with dilated blood vessels, yet were intact without perforations. Purulence, granulation tissue, and classic tubercles were observed in the middle ears and mastoids. Serous labyrinthitis and inflammatory cells surrounding the Cranial Nerve VIII in the internal auditory canal were observed in the inner ear. CONCLUSIONS: The histological findings suggest that a clinical presentation of infantile tuberculous otitis media and mastoiditis could be a patient with otoscopic findings consistent with common otitis media with an intact tympanic membrane, likely in conjunction with inner ear symptoms. Lacking the classic finding of multiple tympanic membrane perforations, tuberculous otitis might be underappreciated in this population.

Hamartoma of the parotid gland: report of a unique case.

Hamartomas of the parotid gland are very rare. We present the case of a parotid gland hamartoma with oncocytic and sebaceous metaplasia arising as a 3-cm mass in a 70-year-old man. To the best of our knowledge, there has been no previous report of a tumor with the same features. We present this case to create awareness of hamartomas as part of the differential diagnosis of parotid masses.