A U wave as seen on ECG. An electrocardiogram of an 18-year-old man showing U waves, most evident in lead V3. The U wave is a wave on an electrocardiogram that is not always seen. It is typically small, and, by definition, follows the T wave. U waves are thought to represent repolarization of the papillary muscles or Purkinje fibers.
HCP is caused by mutations in the CPOX gene, which codes for the enzyme coproporphyrinogen oxidase. This enzyme is responsible for the sixth step in the heme biosynthetic pathway, converting coproporphyrinogen III to protoporphyrinogen IX.
Although the majority of Hereditary Paraganglioma-Pheochromocytoma (PGL/PCC) syndrome tumors are sporadic (i.e. non-familial), approximately 13% of all PGL/PCC tumors are caused by germline pathogenic variants in known PGL/PCC syndrome genes (Welander et al. 2011).