Lecithin cholesterol acyltransferase (LCAT), the major enzyme which esterifies cholesterol present in plasma lipoproteins, plays a central role in HDL metabolism. Patients with LCAT deficiency may present with corneal opacities and renal disease as well as reduced plasma HDL-C and apoA-I concentrations and increased triglycerides. To evaluate the role that LCAT plays in reverse cholesterol transport and the development of atherosclerosis we have established a mouse model for human LCAT-deficiency by performing targeted disruption of the LCAT gene in mouse ES cells. Homozygous LCAT-deficient mice were viable and healthy at birth. Plasma LCAT activity in age-matched control siblings (n=38, LCAT act=42+/-5 nmol/h/ml) was decreased to <0.7 nmol/h/ml in homozygotes. Compared to control mice, homozygous LCAT-deficient mice had decreased cholesterol (28%), cholesteryl ester (14%), phospholipids (46%), HDL-cholesterol (3%) and apoA-I (17%). Analysis of plasma lipoproteins in homozygous LCAT-deficient mice by FPLC demonstrated severe reduction in HDL-cholesterol with the presence of smaller sized particles, as well as triglyceride-rich IDL/LDL. In response to a high fat, high cholesterol diet, homozygous LCAT-ko mice (n=9) had (in mg/dl) cholesterol 32+/-13, triglycerides 185+/-129, cholesteryl esters 10+/-9, HDL-C 7+/-6 and apoA-I 27+/-24 (25%, 167%, 15%, 9% and 11%; that of controls;p<0.05). Electron microscopy (EM) demonstrated the presence of nascent discs in HDL (d=1.063-1.25). Analysis of aortic atherosclerosis revealed a trend (ns;p>0.05)in heterozygous and homozygous LCAT-ko compared to controls. Histologic and EM analysis of kidneys revealed mesangial cell proliferation and glomerulosclerosis in all homozygous LCAT-ko mice. No corneal opacities were evident. The availability of a homozygous animal model for human LCAT deficiency will facilitate our understanding of the role that LCAT plays in the development of renal disease and atherosclerosis.