Novel FOXA2 mutation causes Hyperinsulinism, Hypopituitarism with Craniofacial and Endoderm-derived organ abnormalities

Abstract

Congenital hypopituitarism (CH) is characterized by the deficiency of one or more pituitary hormones and can present alone or in association with complex disorders. Congenital hyperinsulinism (CHI) is a disorder of unregulated insulin secretion despite hypoglycaemia that can occur in isolation or as part of a wider syndrome. Molecular diagnosis is unknown in many cases of CH and CHI. The underlying genetic etiology causing the complex phenotype of CH and CHI is unknown. In this study, we identified a de novo heterozygous mutation in the developmental transcription factor, forkhead box A2, FOXA2 (c.505T>C, p.S169P) in a child with CHI and CH with craniofacial dysmorphic features, choroidal coloboma and endoderm-derived organ malformations in liver, lung and gastrointestinal tract by whole exome sequencing. The mutation is at a highly conserved residue within the DNA binding domain. We demonstrated strong expression of Foxa2 mRNA in the developing hypothalamus, pituitary, pancreas, lungs and oesophagus of mouse embryos using in situ hybridization. Expression profiling on human embryos by immunohistochemistry showed strong expression of hFOXA2 in the neural tube, third ventricle, diencephalon and pancreas. Transient transfection of HEK293T cells with Wt (Wild type) hFOXA2 or mutant hFOXA2 showed an impairment in transcriptional reporter activity by the mutant hFOXA2. Further analyses using western blot assays showed that the FOXA2 p.(S169P) variant is pathogenic resulting in lower expression levels when compared with Wt hFOXA2. Our results show, for the first time, the causative role of FOXA2 in a complex congenital syndrome with hypopituitarism, hyperinsulinism and endoderm-derived organ abnormalities.