The PCr/ATP ratio has been described as a marker for the energetic state of a tissue [9], the PCr/Pi ratio for the oxidative capacity [10,11,12], the Pi/ATP ratio for ATP turnover [13,14], and the PME/PDE ratio as a surrogate for membrane turnover [15,16,17,18], and ratios between the membrane-related and the energy-related ratios have been described as a reflection of tumor growth [19]. The gene discussed is ALDH7A1; the disease is neoplasm.