EDN1 and glycogen storage disease VI: Left and right ventricular myocardialbiopsy specimens from patients with CSFP have demonstrated the presence of coronarymicrovascular disease.6 Small vessel disease, cell edema, capillary damage, subclinicalatherosclerosis, inflammation, fibromuscular hypertrophy, and degeneration ofendothelial cells with resultant microvascular luminal narrowing have been reportedas existing in association with CSFP.6,16, -18 On the molecular level,endothelin-1 and neuropeptide Y (another reason for the label “syndrome Y”) havebeen implicated as possible mediators of the microvascular constriction response.6