Aquaporin channel proteins are found in the plasma membrane of various cell types. Scientists studied the production of aquaporins in the keratinocytes (skin cells) of healthy individuals and found that these proteins play a role in hydration of the skin. Some individuals have a skin disorder that causes the absorption of excess water by the skin of their hands and feet when they are soaked in water. Scientists determined that the keratinocytes of these individuals are characterized by the presence of abnormal aquaporins. Scientists studied a family in which some individuals have this skin disorder and constructed a pedigree (Figure 1).