HISTIDINAEMIA - A CHILD AND HIS FAMILY

An 18-month-old boy, presenting with convulsions, was shown to have histidinaemia after an increased histidine spot had been found on a urinary amino acid chromatogram. He was small with a delayed bone age and iron-deficient anaemia, but speech and development were within normal limits. The plasma histidine has been consistently raised but, unlike the majority of reported cases, the urinary ferric chloride and 'Phenistix' tests were negative, except transiently after a histidine load. There was no detectable increase in imidazole compounds on a chromatogram, even after the histidine load. The diagnosis was confirmed by the absence of FIGLU in the urine after a histidine load, the absence of skin histidase activity, and the absence of sweat urocanic acid. His response to a low histidine diet is described, there being no significant reduction in plasma histidine levels and, possibly, a slowing down of growth. The place of histidine as an essential amino acid is discussed. Family studies showed that his parents and other members of the family were heterozygous for the abnormal gene, thus confirming that histidinaemia is an example of autosomal recessive inheritance.