The focus of his research is the molecular definition of primary immunodeficiency diseases (PIDD) and the investigation of new techniques to confirm the diagnosis. He and his collaborators contributed significantly to the identification of a number of genes associated with PIDD located on the X chromosome (CD40L, Wiskott-Aldrich syndrome protein [WASP], FOXP3, gp91phox) or on autosomes (uracil-DNA glycosulase; Rag1, Rag2 hypomorphic mutations as the cause of Omenn syndrome, STAT3 responsible for AD-HIES).