Of 1849 persons who received growth hormone in the UK between 1959 and 1985, 38 were known to have developed CJD by 2000 and the estimated risk of developing iatrogenic CJD was at that time 4.5%, this risk being greatest in those patients who received treatment at ages 8–10 years with a peak incubation period of 20 years (Swerdlow et al., 2003). This evidence concerns the gene GH1 and Creutzfeldt Jacob disease.