Serum CHI3L1 levels were measured from 105 patients including diseased controls (no PH; as defined by a cutoff of a mean PAP < 20 mmHg) (3, 4) and World Symposium on Pulmonary Hypertension (WSPH) groups 1 through 5. This evidence concerns the gene CHI3L1 and pulmonary arterial hypertension.