These studies all confirmed the importance of HLA-encoded susceptibility to type 1 diabetes (designated also as IDDM1); and also excluded the possibility of a locus with an effect equivalent to HLA. The individual impact of other susceptibility genes is, therefore, much smaller than that of HLA. Nevertheless, statistically significant and suggestive evidence of linkage of type 1 diabetes to at least ten chromosome regions has been published, although association studies at INS [27] and CTLA4 have been required to confirm with fine map loci. Here, CTLA4 is linked to type 1 diabetes mellitus.