HMGCR and X-linked adrenoleukodystrophy: To elucidate how increased amounts of cholesterol esters impact cholesterol homeostasis in X-ALD, we first investigated the expression of key genes involved in cholesterol homeostasis (Figure 2A): 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR), sterol-O-acyltransferase 1 (SOAT1), neutral cholesterol ester hydrolase 1 (NCEH1) and ATP-binding cassette transporter A1 (ABCA1) by RT-qPCR.