Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, chronic disease that results in an abnormal breakdown of red blood cells. When urine is concentrated overnight by the kidneys as a person with PNH sleeps, the morning urine may turn reddish to a darker cola color. This phenomenon led to the designation of the condition as nocturnal.

Signs and symptoms of PNH include

reddish or dark tea- or cola-colored urine (especially in the morning),
significant fatigue or weakness,
bruising or bleeding easily,
shortness of breath,
headache, and
pale skin.

Other associated symptoms and signs can include

abdominal pain,
seizures,
coughing up blood,
impotence in men,
ulcers, or
jaundice (yellowing of the skin and whites of the eyes).

Causes of paroxysmal nocturnal hemoglobinuria (PNH)

PNH arises due to a spontaneous genetic mutation in a gene known as PIGA. This mutation causes red blood cells to become unusually fragile and prone to break down. The genetic mutation that causes PNH is not inherited from the parents but arises spontaneously.