Historically routes of transmission have included corneal transplantation and neurosurgical instruments, but the largest numbers of cases of iCJD worldwide have been through the use of cadaveric pituitary-derived hormones and human growth hormone-associated CJD (hGH-iCJD) in France, the UK and the USA and dura mater grafting (largely, but not exclusively in Japan) (reviewed by Ref. [8] and summarized in Table 2). This evidence concerns the gene GH1 and Creutzfeldt Jacob disease.