Wiedemann–Steiner Syndrome (WSS) is an autosomal dominant disorder characterized by hypertrichosis, short stature, intellectual disability, developmental delay, and facial dysmorphism. Since the original reports by Wiedemann and co-workers, and Steiner and Marques, only a few cases have been described. Recently, the clinical variability of the disorder has more precisely been characterized by Jones and co-workers, who also identified heterozygousKMT2Amutations as the molecular defect underlying this condition. Here, we report on a boy with a complex phenotype overlapping WSS but exhibiting epilepsy, feeding difficulties, microcephaly, and congenital immunodeficiency with low levels of immunoglobulins as additional features. Whole exome sequencing allowed identifying a previously unreported de novoKMT2Amissense mutation affecting the DNA binding domain of the methyltransferase. This finding expands the clinical phenotype associated withKMT2Amutations to include immunodeficiency and epilepsy as clinically relevant features for this disorder. © 2016 Wiley Periodicals, Inc.