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.
Genetic Causes of Intellectual Disabilities. Many intellectual disabilities (ID, formerly mental retardation) are caused by genetic abnormalities. The two most common genetic causes of intellectual disabilities are Down syndrome and Fragile X syndrome.Down syndrome (or Down's syndrome in the UK). Down syndrome is the most common genetic origin of intellectual disabilities (ID, formerly mental retardation).Down syndrome occurs in 1 out of every 800 births.Down syndrome derives its name from John Langdon Down. He was the one who first pinpointed the disorder.own syndrome (or Down's syndrome in the UK). Down syndrome is the most common genetic origin of intellectual disabilities (ID, formerly mental retardation). Down syndrome occurs in 1 out of every 800 births. Down syndrome derives its name from John Langdon Down.