However, in a heterozygous EPAS1 mutant mouse, haploinsufficiency for the oxygen-sensing factor resulted in augmented carotid body sensitivity to hypoxia, including irregular breathing, apneas, hypertension and elevated norephinephrine levels on one mouse strain background, but protection against pulmonary hypertension on a different strain [77], [78]. The gene discussed is EPAS1; the disease is pulmonary arterial hypertension.