EPAS1 and cholesteryl ester measurement: Causes of CE include pathogenic variants in the Epo receptor gene (EPOR), components of the oxygen-sensing pathway such as the alpha subunit of the hypoxia-inducible transcription factor (EPAS1, also known as HIF2A), prolyl hydroxylase Egl nine homolog 1 (EGLN1, also known as PHD2), and the von Hippel-Lindau disease tumor supressor (VHL).