[Changes of erythrocyte and lymphocyte membrane fluidity after plasma extraction in children with type II homozygous hypercholesterolemia].

Two young girls with type IIa homozygotic familial hypercholesterolemia were treated by plasma exchange to reduce circulating cholesterol levels, values prior to treatment being abnormally elevated (greater than 10 mmol/l). Simultaneous determination of membrane fluidity (by fluorescence polarization) of erythrocytes and lymphocytes showed marked decreases due principally to an increase in the intramembrane cholesterol/phospholipid ratio. Values after treatment showed a tendency to return to physiologic levels without, however, attaining normal values. In vitro studies of cholesterol incorporation in these membranes demonstrated the primordial role of cholesterol in these processes of membrane rigidity, and their reversibility. It is suggested that certain physical membranal properties could provide a useful index to assess need for more or less frequent plasma exchanges.