The importance of the CD4+ T helper cells subset characterized by the production of IL-17 (Th17 cells) was elucidated via dominant-negative STAT3 deficiency (DN-STAT3, previously called Autosomal-dominant hyper-IgE syndrome (AD-HIES) and originally termed “Job syndrome”), which is characterized by connective tissue anomalies (e.g., distinct facial features, hyperextensible joints, osteoporosis/bone fractures, scoliosis, retained primary teeth, and coronary and cerebral aneurysms), “cold” skin abscesses (boils) due to S. aureus, and CMC. This evidence concerns the gene STAT3 and brain aneurysm.