Authors: Naif Ahmad Mahmood Almontashiri

Abstract

Background: We recently reported 10 heterozygous missense and loss-of-function (LoF) FOXP4 variants that cause neurodevelopmental disease and multiple congenital abnormalities in 13 patients. However, the functional impact of the reported variants is not yet characterized.

Methods: The variants were constructed and introduced into expression vectors and then transfected into cell lines along with an empty control. Western blotting was used to assess mutant FOXP4 protein expression.

Results: Western blot analysis confirmed that all heterozygous FOXP4 variants resulted in very low or undetectable levels of the overexpressed mutant FOXP4. Similarly, homozygous FOXP4 variants resulted in very low or undetectable levels of the overexpressed mutant proteins, consistent with the predicted impact of the frameshift variants. These data support the pathogenicity of these variants by causing a loss-of-function effect on protein expression.

Conclusion: This study provides a functional characterization supporting that autosomal recessive forms of FOXP4-related disease are likely caused by loss of function. These data warrant a future study to investigate how the same disease mechanism produces different inheritance patterns.

Keywords: FOXP4, heterozygous, homozygous, recessive, dominant, loss of function, neurodevelopmental.