Recurrent FOXP4 nonsense variant in two unrelated patients: Association with neurodevelopmental disease and congenital diaphragmatic hernia

De novo variants in FOXP4 were recently associated with a neurodevelopmental disorder characterized by speech and language delay, growth abnormalities, hypotonia, and variable congenital abnormalities, including congenital diaphragmatic hernia, cervical spine abnormalities, strabismus, cryptorchidism, and ptosis. The variant spectrum in this small cohort was limited to de novo missense except for one frameshift, the inheritance of which was unknown. Variants tested in vitro exhibited reduced repressor transcriptional activity, indicating loss of function is the likely mechanism of disease, but only one frameshift variant was reported. Here, we report four affected individuals from two unrelated families heterozygous for a nonsense variant, c.1893C > G, p.Tyr631*, in FOXP4. The phenotype of the affected children includes developmental delay, feeding difficulties in infancy, and similar facial features. In both cases, the variant was inherited from a parent with mild or even subclinical features. Interestingly, one patient presented with congenital diaphragmatic hernia, as reported in two other FOXP4 patients. This report implicates FOXP4 truncating variants in human disease and highlights the wide phenotypic spectrum and variable expressivity.