Instability of mutant G6PD. Western blot analysis was performed on red blood cells, leukocytes, and ex vivo–cultured proerythroblasts¹⁰  from 2 controls (C1 and C2) and the athlete, using a polyclonal antibody against G6PD (kindly provided by Robin van Bruggen, Sanquin Research, Amsterdam, The Netherlands). In contrast to leukocytes and ex vivo–cultured proerythroblasts, mutant G6PD was not detectable in the athlete's erythrocytes.