NINA A. J. CARSON and DW NEILL From the Royal Belfast Hospital for Sick Children and the Royal Victoria Hospital, Belfast (RECEIVED FOR PUBLICATION JUNE 8, 1962) In 1908, Sir Archibald Garrod in his Croonian lectures coined the name'inborn errors of metabolism'to describe a group of raremetabolic disorders which appeared to be genetically determined. In 1923, he described six such conditions in a monograph-alcaptonuria, pentosuria, cystinuria, albinism, pancreatic steatorrhoea and porphyria. He predicted that a biochemical reason would be found for these disorders and that they probably resulted from a block at some point in metabolism due to thecongenital deficiency of a specific enzyme. The development of chromatographic and enzymatic techniques over the past 15 years has led to the elucidation of many metabolic pathways and provided the scientific proof of his brilliant induction. Garrod thought that in alcaptonuria, the accumulation of homogentisic acid was evidence that this substance was a normal metabolite in the breakdown of tyrosine and that its increase was due to a failure of oxidation of homogentisic acid. Now, a half century later, Garrod's hypothesis has been proved by demonstration of the absence of homogentisic acid oxidase activity in the liver of a patient with alcaptonuria (La Du, Zannoni, Laster and Seegmiller, 1958).

In the past decade many abnormalities in the excretion of aminQ acids have been noted in asso-ciation with hereditary biochemical disorders and mental retardation. Among these may be noted maple syrup urine disease (Dancis, Levitz, Miller and Westall, 1959), in which there is a metabolic block in the degradative pathway of the branched chain amino acids isoleucine, leucine and valine; this is associated with mental retardation, muscular hypertonicity and a maple syrup odour to the urine. Hartnup disease was first described by Baron, Dent, Harris, Hart and Jepson in 1956; this is character-ized by a pellagra-like, light-sensitive skin rash, cerebellar ataxia and emotional instability. A constant feature of the disease is a generalized aminoaciduria related to an intermittent upset in