ABSTRACT
Many disorders of amino acid metabolism are characterized by raised plasma concentrations of one or more amino acids, with overflow amino aciduria. The tyrosinase involved in catecholamine synthesis is a different isoenzyme, controlled by a different gene; consequently, adrenaline metabolism is normal. Histidinaemia is associated with deficiency of histidinase, an enzyme needed for normal histidine metabolism, and is probably inherited as an autosomal recessive trait. Between the two extremes there are many variations that produce functional abnormalities or inborn errors of metabolism (IEM). An inborn error of metabolism should be suspected on the death of a baby or when a child presents with failure to thrive, particularly if the parents are consanguineous, for example cousins. The clinical effects of some IEM may be modified by, or depend entirely on, physiological or environmental factors. There are many other IEMs, including congenital adrenal hyperplasia, adenosine deaminase deficiency, electron transport chain defects and sulphite oxidase deficiency.
