123/131 I-MIBG are both captured by the norepinephrine transporter: 123I MIBG SPECT/CT sensitivity and specificity is extremely high for sporadic PCCs, though it dramatically decreases for PGLs (52–75%), especially for HNPGLs (18–50%) and for SDHx-related tumours [21,31,32,36,39,40] (Figure 2A–C). The gene discussed is SLC6A2; the disease is neoplasm.