Snijders Blok, L., Vino, A., Den Hoed, J., Underhill, H. R., Monteil, D., Li, H., Reynoso Santos, F. J., Chung, W. K., Amaral, M. D., Schnur, R. E., Santiago-Sim, T., Si, Y., Brunner, H. G., Kleefstra, T., & Fisher, S. E.
(2020). Heterozygous variants that disturb the transcriptional repressor activity of FOXP4 cause a developmental disorder with speech/language delays and multiple congenital abnormalities. Genetics in Medicine. Advance online publication. doi:10.1038/s41436-020-01016-6.
Heterozygous pathogenic variants in various FOXP genes cause specific developmental disorders. The phenotype associated with heterozygous variants in FOXP4 has not been previously described.
We assembled a cohort of eight individuals with heterozygous and mostly de novo variants in FOXP4: seven individuals with six different missense variants and one individual with a frameshift variant. We collected clinical data to delineate the phenotypic spectrum, and used in silico analyses and functional cell-based assays to assess pathogenicity of the variants.
We collected clinical data for six individuals: five individuals with a missense variant in the forkhead box DNA-binding domain of FOXP4, and one individual with a truncating variant. Overlapping features included speech and language delays, growth abnormalities, congenital diaphragmatic hernia, cervical spine abnormalities, and ptosis. Luciferase assays showed loss-of-function effects for all these variants, and aberrant subcellular localization patterns were seen in a subset. The remaining two missense variants were located outside the functional domains of FOXP4, and showed transcriptional repressor capacities and localization patterns similar to the wild-type protein.
Collectively, our findings show that heterozygous loss-of-function variants in FOXP4 are associated with an autosomal dominant neurodevelopmental disorder with speech/language delays, growth defects, and variable congenital abnormalities.