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.
Congenital. 1  The most common inherited sideroblastic anaemia is X-linked sideroblastic anaemia (XLSA) caused by mutations of the erythroid-specific delta-aminolevulinic acid synthase 2 gene (ALAS2). 2  Congenital causes of sideroblastic anaemia also include Wolfram's syndrome. There are two types, each caused by a genetic error on a different chromasome. Wolfram's syndrome 1 is characterised by DIDMOAD (= Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy and Deafness).