SDHD and metastatic neoplasm: In a study of 32 pediatric PPGL patients who developed metastatic disease, the three patients with a primary HNPGL were all identified to have a SDHD mutation (49), however in three other studies of pediatric PPGL patients, 17 of 177 patients, 5 of 88 patients, and 2 of 25 patients were found to have SDHD mutations, and only 2 of 17 later developed metastatic disease (4, 5, 7).