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 cell–derived 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.

Massive pneumatosis without necrosis: A case report of Clostridium perfringens sepsis in an extremely low birth weight infant

Pneumatosis intestinalis and free intraperitoneal air on abdominal radiographs are considered pathognomonic signs of necrotizing enterocolitis (NEC). We report a unique case of late-onset fulminant sepsis due to Clostridium perfringens presenting with shock, extensive pneumatosis intestinalis and free intraperitoneal air in an extremely low birth weight infant without histopathological evidence of bowel necrosis or NEC.

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.

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.

Tobacco cembranoids block behavioral sensitization to nicotine and inhibit neuronal acetylcholine receptor function

Cembranoids are cyclic diterpenoids found in tobacco and in marine invertebrates. The present study established that tobacco cembranoids inhibit behavioral sensitization to nicotine in rats and block several types of nicotine acetylcholine receptors (AChRs). 1) At the behavioral level, rat locomotor activity induced by nicotine was significantly increased after seven daily nicotine injections. This sensitization to nicotine was blocked by mecamylamine (1 mg/kg) and by the cembranoids eunicin, eupalmerin acetate (EUAC), and (4R)-2,7,11-cembratriene-4-6-diol (4R), each at 6 mg/kg. None of these compounds modified locomotor activity of nonsensitized rats. 2) In cells expressing human AChRs, cembranoids blocked carbamoylcholine-induced (86)Rb(+) flux with IC(50) in the low micromolar range. The cell lines used were the SH-EP1-halpha4beta2 cell line heterologously expressing human alpha4beta2-AChR, the SH-SY5Y neuroblastoma line naturally expressing human ganglionic alpha3beta4-AChR, and the TE671/RD cell line naturally expressing embryonic muscle alpha1beta1gammadelta-AChR. The tobacco cembranoids tested were 4R and its diastereoisomer 4S, and marine cembranoids tested were EUAC and 12,13-bisepieupalmerin. 3) At the molecular level, tobacco (4R and 4S) and marine (EUAC) cembranoids blocked binding of the noncompetitive inhibitor [(3)H]tenocyclidine to AChR from Torpedo californica electric organ. IC(50) values were in the submicromolar to low-micromolar range, with 4R displaying an order of magnitude higher potency than its diastereoisomer, 4S.