DYSF and hyperinsulinemic hypoglycemia, familial, 4: To further determine if mitochondrial dysfunction may contribute to the observed metabolic deficiency in LGMD2B myobundles, we measured mitochondrial membrane potential (MMP) with JC‐10 dye (Figure 4H) and found that LGMD2B but not HLT myobundle mitochondria lost their MMP as evident from the loss of red JC‐10 aggregates which only accumulate in healthy respiring mitochondria.