Porphyria cutanea tarda (PCT) is the most common subtype of porphyria

Porphyria

Porphyrias are a group of inherited or acquired disorders of certain enzymes in the heme bio-synthetic pathway . They are broadly classified as acute porphyrias and cutaneous porphyrias, based on the site of the overproduction and accumulation of the porphyrins...

. The disorder results from low levels of the enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 responsible for the fifth step

Uroporphyrinogen III decarboxylase

Uroporphyrinogen decarboxylase, also known as UROD, is an enzyme that in humans is encoded by the UROD gene.- Function :This gene encodes the fifth enzyme of the heme biosynthetic pathway...

 in heme

Heme

A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as their prosthetic group; these are...

 production. Heme is a vital molecule for all of the body's organs. It is a component of hemoglobin

Hemoglobin

Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...

, the molecule that carries oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 in the blood.

Hepatoerythropoietic porphyria

Hepatoerythropoietic porphyria

Hepatoerythropoietic porphyria is a very rare form of hepatic porphyria caused by a disorder in both genes which code Uroporphyrinogen III decarboxylase .It has a similar presentation to porphyria cutanea tarda , but with earlier onset...

 has been described as a homozygous form of porphyria cutanea tarda, although it can also be caused if two different mutations occur at the same locus.
Porphyria cutanea tarda (commonly referred to as PCT) is recognized as the most prevalent subtype of porphyritic diseases.

The disease is characterized by onycholysis

Onycholysis

Onycholysis refers to the detachment of the nail from the nail bed, starting at its distal and/or lateral attachment. It is said to occur particularly on the ring finger but can occur on any of the fingernails. The most common cause of onycholysis is psoriasis. It can also occur in thyrotoxicosis...

 and blistering of the skin in areas that receive higher levels of exposure to sunlight.