Several important studies were performed exploring the cell biology and molecular biology of disaccharidases and monosaccharide absorption. The cloned glucose transporter was shown to be the physiologically important one. Supporting this finding, two sisters who had a missense mutation of the transporter were unable to absorb glucose. Pancreatic proteases (trypsin) were shown to be important in the cleavage of sucrase-α-dextrinase at the surface of the brush border membrane. Lactase insufficiency type 1 was correlated with messenger RNA levels indicating either a translational defect or increased catabolism of lactase messenger RNA. Sucrase-isomaltase activity was shown to correlate vertically along the crypt-villus axis with steady state messenger RNA levels but along the length of the intestine with translated product. In an important study, lipoprotein AIV was shown to produce satiety.