MT-CO1 and hyperinsulinemic hypoglycemia, familial, 4: This contrasts to previous COX/SDH histochemistry data that demonstrated overt COX-deficiency within the microvasculature.28,68 Our data support increased SDHA protein levels within vessels that is not matched by either COX1 or porin protein expression; the relevance of a selective increase in SDH activity and expression in microvessels is not understood, but does explain the apparent high levels of COX deficiency.