SDHD and polycythemia: The syndromic presentation of HNPGLs is associated with mutations in SDHD (paraganglioma syndrome type 1, PGL1), SDHAF2 (PGL2), SDHC (PGL3), SDHB (PGL4), SDHA (PGL5), VHL (von Hippel–Lindau syndrome), HIF-2α (paraganglioma–somatostatinoma–polycythemia), and NF1 (neurofibromatosis type 1 syndrome) [29].