Cholesterol is bound to apolipoprotein B-100 as LDL in interstitial fluid. Cells may acquire cholesterol via an LDL receptor on the cell membrane. Familial LDL receptor deficiency and familial defective apoprotein B-100 are examples of primary defects that can lead to the accumulation of LDL, which corresponds to a type IIa pattern of hyperlipidemia. Plasma cholesterol levels are severely elevated, but plasma triglyceride levels are typically normal. Patients with type IIa have severe atherosclerosis.