G6PD and G6PD deficiency: Gartler explained that he became interested in G6PD deficiency not because of an interest in X chromosome inactivation per se but rather as a potential marker for clonality in studies of tissue cell development.61 In the case of the Sephardic family being studied by Fairbanks and Beutler, Gartler was using skin biopsies to develop a technique to clone skin fibroblasts; he hoped to validate the presence of a clone by assaying the level of G6PD activity.