A novel PAX1 null homozygous mutation in autosomal recessive otofaciocervical syndrome associated with severe combined immunodeficiency

Otofaciocervical syndrome (OFCS) is a rare disorder characterized by facial anomalies, cup-shaped low-set ears, preauricular fistulas, hearing loss, branchial defects, skeletal anomalies, and mild intellectual disability. Autosomal dominant cases are caused by deletions or point mutations of EYA1. A single family with an autosomal recessive form of OFCS and a homozygous missense mutation in PAX1 gene has been described. We report whole exome sequencing of 4 members of a consanguineous family in which 2 children, showing features of OFCS, expired from severe combined immunodeficiency (SCID). To date, the co-occurrence of OFCS and SCID has never been reported. We found a nonsense homozygous mutation in PAX1 gene in the 2 affected children. In mice, Pax1 is required for the formation of specific skeletal structures as well as for the development of a fully functional thymus. The mouse model strongly supports the hypothesis that PAX1 depletion in our patients caused thymus aplasia responsible for SCID. This report provides evidence that bi-allelic null PAX1 mutations may lead to a multi-system autosomal recessive disorders, where SCID might represent the main feature.