The report of the use of a DNA genotyping test by Healy et al. (1995), citing a personal communication from G.S. Johnson at the University of Missouri, implied that the molecular basis of this disorder within the gene for ferrochelatase had been determined by Dr Johnson. Jenkins et al. (1998) appear to have been the first to publicly report the molecular basis of this disorder. They did so by cloning and sequencing a very likely comparative candidate gene (based on the homologous human disorder), and reported a base substitution in the stop codon of the bovine ferrochelatase gene, that destroys that codon, resulting in an additional 27 amino acids in the peptide. To FN's knowledge, this is the first reported case in non-laboratory animals of the obliteration of a stop codon by a base substitution: a stop-loss or extension mutation.
