In other species: sheep

Possibly relevant human trait(s) and/or gene(s) (MIM number): 176100

Mendelian trait/disorder: unknown

Considered a defect: yes

Cross-species summary: Porphyrins are a class of organic compounds characterised by four pyrrole nuclei connected in a ring structure. When combined with iron, porphyrins form haem, which is a component of haemoglobin, cytochromes, catalases and peroxidases. Thus, porphyrins are constituents of many compounds that play a vital role in biological systems. The biosynthesis of porphyrins involves a six-step process, starting with aminolaevulinic acid (ALA) and ending with protoporphyrin. Each step is catalysed by an enzyme. A deficiency of any one of these enzymes results in a buildup of intermediates prior to the step for which the enzyme is lacking, and a deficiency of intermediates after that step. In much of the literature, these intermediates are loosely called porphyrins. Porphyria cutanea tarda results from a deficiency of the fourth enzyme, uroporphyrinogen decarboxylase, and a consequent buildup of intermediates (i.e. a buildup of porphyrins) that have been synthesised in the three previous steps.