Re-focusing on Agnathia-Otocephaly complex

Objectives Agnathia-otocephaly complex is a rare condition characterized by mandibular hypoplasia or agnathia, ear anomalies (melotia/synotia) and microstomia with aglossia. This severe anomaly of the first branchial arch is most often lethal. The estimated incidence is less than 1 in 70.000 births, with etiologies linked to both genetic and teratogenic factors. Most of the cases are sporadic. To date, two genes have been described in humans to be involved in this condition:OTX2andPRRX1. Nevertheless, the overall proportion of mutated cases is unknown and a significant number of patients remain without molecular diagnosis. Thus, the involvement of other genes thanOTX2andPRRX1in the agnathia-otocephaly complex is not unlikely. Heterozygous mutations inCnbpin mice are responsible for mandibular and eye defects mimicking the agnathia-otocephaly complex in humans and appear as a good candidate. Therefore, in this study, we aimed (i) to collect patients presenting with agnathia-otocephaly complex for screeningCNBP, in parallel withOTX2andPRRX1, to check its possible implication in the human phenotype and (ii) to compare our results with the literature data to estimate the proportion of mutated cases after genetic testing. Materials and methods In this work, we describe 10 patients suffering from the agnathia-otocephaly complex. All of them benefited from array-CGH and Sanger sequencing ofOTX2,PRRX1andCNBP. A complete review of the literature was made using thePubmeddatabase to collect all the patients described with a phenotype of agnathia-otocephaly complex during the 20 last years (1998-2019) in order (i) to study etiology (genetic causes, iatrogenic causes horizontal ellipsis ) and (ii), when genetic testing was performed, to study which genes were tested and by which type of technologies. Results In our 10 patients' cohort, no point mutation in the three tested genes was detected by Sanger sequencing, while array-CGH has allowed identifying a 107-kb deletion encompassingOTX2responsible for the agnathia-otocephaly complex phenotype in 1 of them. In 4 of the 70 cases described in the literature, a toxic cause was identified and 22 out the 66 remaining cases benefited from genetic testing. Among those 22 patients, 6 were carrying mutation or deletion in theOTX2gene and 4 in thePRRX1gene. Thus, when compiling results from our cohort and the literature, a total of 32 patients benefited from genetic testing, with only 34% (11/32) of patients having a mutation in one of the two known genes,OTX2orPRRX1. Conclusions From our work and the literature review, only mutations inOTX2andPRRX1have been found to date in patients, explaining around one third of the etiologies after genetic testing. Thus, agnathia-otocephaly complex remains unexplained in the majority of the patients, which indicates that other factors might be involved. Although involved in first branchial arch defects, no mutation in theCNBPgene was found in this study. This suggests that mutations inCNBPmight not be involved in such phenotype in humans or that, unlike in mice, a compensatory effect might exist in humans. Nevertheless, given that agnathia-otocephaly complex is a rare phenotype, more patients have to be screened forCNBPmutations before we definitively conclude about its potential implication. Therefore, this work presents the current state of knowledge on agnathia-otocephaly complex and underlines the need to expand further the understanding of the genetic bases of this disorder, which remains largely unknown.