PDC and hyperinsulinemic hypoglycemia, familial, 4: Pyruvate dehydrogenase E1 subunit deficiency showed normal activity in three out of four patients; however, PDC-E1 deficiency was confirmed in muscle samples of all cases, indicating that enzyme measurements in fibroblasts are not always the appropriate method for the diagnosis of PDC deficiency in females due to the possibility of a skewed XCI [66].