In addition to a small number of iCJD cases being caused by neurosurgical instrument contamination (four cases), contaminated electroencephalogram (EEG) needles (two cases), corneal grafts (two cases), and gonadotrophic hormone (four cases), the majority of the iCJD cases were caused by administrations of growth hormone (226 cases) and dura mater grafts (228 cases) derived from human cadavers with undiagnosed CJD contaminations (25). This evidence concerns the gene GH1 and Creutzfeldt Jacob disease.