In a similar scenario, ‘autoimmunizing positive selection’ (complemented by defective negative selection) might be operative in thymomas (see below), and in patients with ZAP70 mutations: while inactivating mutations of ZAP70 cause severe immunodeficiency, hypomorphic mutations lead to positive selection of autoreactive thymocytes [142]. The gene discussed is ZAP70; the disease is Immunodeficiency.