Investigation of Genetic Causes in a Developmental Disorder: Oculoauriculovertebral Spectrum

Oculoauriculovertebral spectrum (OAVS) is a genetically and clinically heterogeneous disorder that occurs due to a developmental field defect of the first and second pharyngeal arches. Even though recent whole exome sequencing studies (WES) have led to identification of several genes associated with this spectrum in a subset of individuals, complete pathogenesis of OAVS remains unsolved. In this study, molecular genetic etiology of OAVS was systematically investigated.

A cohort of 23 Turkish patients with OAVS, referred to Hacettepe University Hospital, Department of Pediatric Genetics from 2008 to 2018, was included in this study. Minimal diagnostic criteria for OAVS were considered as unilateral microtia or hemifacial microsomia with preauricular skin tag. The cohort was clinically reevaluated for craniofacial and extracranial findings. Molecular etiology was investigated using candidate gene sequencing following copy number variant (CNV) analysis. WES was also performed for 2 of the selected patients.

Patients in the study cohort presented similar demographic and phenotypic characteristics to previously described patients in the literature except for a higher frequency of bilaterality, cardiac findings, and intellectual disability/developmental delay. CNV analysis revealed a possible genetic etiology for 3 patients (13%). Additional WES in 1 of the 2 patients uncovered a novel heterozygous nonsense variant in Elongation factor Tu GTP-binding domain-containing 2 (EFTUD2) causing mandibulofacial dysostosis with microcephaly (MFDM), which clinically overlaps with OAVS.

Detailed clinical evaluation for any patient with OAVS is recommended due to a high rate of accompanying systemic findings. We further expand the existing genetic heterogeneity of OAVS by identifying several CNVs and a phenotypically overlapping disorder, MFDM.