19 Allen Allen RC RC Armitage Armitage RJ RJ Conley Conley ME ME Rosenblatt Rosenblatt H H Jenkins Jenkins NA NA Copeland Copeland NG NG CD40 ligand gene defects responsible for X-linked hyper-IgM syndrome CD40 ligand gene defects responsible for X-linked hyper-IgM syndrome Science. This evidence concerns the gene CD40LG and hyper-IgM syndrome.