The BILU syndrome is an autosomal dominant primary immunodeficiency that combines B cells Immunodeficiency, Limb abnormalities and Urogenital malformations. Recently, we discovered the genetic basis of this disorder using whole exome sequencing. The causative mutation affects the protein that is involved in mediating transcriptional responses after activation of nuclear receptors (e.g. sex hormone receptors). Altered signalling via nuclear receptors is likely to impact a wide range of genes implicated in development, homeostasis and metabolism leading to the BILU syndrome. In this proposal, we develop a strategy to characterize the impact of the newly discovered mutation on nuclear receptor signalling. We will use analysis of patients’ primary fibroblasts, induced pluripotent stem (iPS) cells and CRISPR-Cas9 edited cell lines to investigate how the mutation impacts transcriptional responses after hormonal stimulations. This project will give insights in the function of the newly identified protein that is involved in the BILU syndrome and will help to understand its broader role in regulation of gene transcription.