 Witte also co-discovered the gene for Bruton's tyrosine kinase, a protein essential for normal B-lymphocyte development that, when mutated, causes the onset of X-linked agammaglobulinemia.This finding influenced the development of targeted drugs like Ibrutinib to treat leukemia and lymphoma.Witte’s current research focuses on characterizing the stem cells for epithelial cancers of the prostate and other organs in order to define new and more targeted therapies.