SDHD and multiple endocrine neoplasia type 2: The most common underlying genetic causes of pediatric PPGL are von Hippel-Lindau syndrome (VHL, 27-51%), mutations in succinate dehydrogenase subunit genes (collectively referred to as SDHx, 13-39% in SDHB and 8-10% in SDHD), multiple endocrine neoplasia type 2 (MEN-2, 0.6-10%), and neurofibromatosis type 1 (NF-1, 1-3%) (2, 4, 5, 7–11).