In fact, altered signatures of a subset of proteins (PYGL, PFKM, PGAM2, ENO3 and ALDOA) observed in our MS analysis may be diagnostic of human GSD (Beutler et al., 1973; Chang et al., 1998; Comi et al., 2001; Tarui, 1995; Tsujino et al., 1994). The gene discussed is PYGL; the disease is disorder of glycogen metabolism.