PDP1 and hyperinsulinemic hypoglycemia, familial, 4: Typical hallmarks of PDH deficiency (such as elevated lactate levels or low lactate/pyruvate ratio in serum and CSF) or MRI abnormalities (such as bilateral pallidal hyperintensities or agenesis of the corpus callosum) may suggest the diagnosis, but their absence does not rule out PDH deficiency [59].