A diagnosis of sarcoidosis-like is suspected when a chest CT scan is compatible (micronodular pulmonary disease, ground-glass infiltrates with subpleural or perihilar distribution, and/or enlarged hilar–mediastinal lymph nodes), and a suggestive bronchoalveolar lavage (lymphocytosis with increased CD4/CD8 ratio), and is confirmed by compatible histology (non-necrotising granulomas) after ruling out other causes. The gene discussed is CD4; the disease is sarcoidosis.