Recently, the HIF2α D539N mutation has been reported in patients with both PPGL and polycythemia (i.e. Class 1 phenotype) and patients with only polycythemia (i.e. Class 2 phenotype), suggesting that this mutation can cause either Class 1 and 2 HIF2-driven disease in different individuals (Oliveira et al., 2018; Pacak et al., 2014; Pang et al., 2019). The gene discussed is EPAS1; the disease is polycythemia.