ABSTRACT
A purine is any of a group of organic compounds that are found in tissues, the two major purines being adenine and guanine. Adenylosuccinate lyase deficiency is a rare disorder characterised by a deficiency or an absence of the enzyme adenylosuccinate lyase. This enzyme catalyses two separate steps in the pathways of purine nucleotide synthesis. A pyrimidine is any of a group of organic compounds that are found in certain coenzymes and in tissues, the three major pyrimidines being thymine, uracil and cytosine. Both purines and pyrimidines are components of DNA. Acute intermittent porphyria belongs to a group of conditions known as the porphyrias. It does not cause any skin symptoms in sunlight, unlike most of the other porphyrias. Variegate porphyria belongs to a group of conditions known as the porphyrias. In this form of porphyria there is a deficiency of the enzyme protoporphyrinogen oxidase, which slows down the conversion of aminolevulinic acid (ALA) into haem.
