Hair root versus red cell individual phenotype in Sardinian heterozygotes for G6PD deficiency (Mediterranean type).

G6PD activity was assayed in 20 Sardinian heterozygotes for G6PD deficiency and related to that of LDH and MDH. One of these heterozygotes showed a deficient phenotype in all her follicles, while the remaining 19 had different proportions of deficient, intermediate, and normal follicles. This is in accordance with a previous estimate. Because of the broad fiducial limits at the 5% level and because of some developmental considerations, this value cannot be interpreted as indicative of the number of primordial cells for scalp epidermis at the time of X-chromosome inactivation, as previously stated. The assay of single hair follicles is, however, a very valuable tool for establishing the role of cell selection in the same or in a different tissue, like peripheral blood.