The breadth of claims in patents relating to genetic inventions has been controversial for some time. Possible adverse effects of broad claims include inhibiting research and higher costs, restricting patient access to genetic testing. The Australian Law Reform Commission’s Report on Genes and Ingenuity – Gene Patenting and Human Health examined this issue, and concluded that the existing disclosure requirements contained in s 40 of the Patents Act 1990 (Cth) provide adequate mechanisms to control the breadth of claims. However, application of these requirements may be problematicalin practice due to lack of relevant case law to provide guidance to patent examiners. It has been suggested that this deficit in direct judicial guidance can be obviated by developing appropriate analogies with other chemical systems in decided cases. This article focuses on gene-based diagnostic patents for human diseases, such as those held by Myriad Genetics for testing predisposition towards breast and ovarian cancer using the gene BRCA1. By examining the application of disclosure requirement by courts in genetic and non-genetic chemical inventions, it is possible to provide insight into how this might be applied by courts considering the validity of patent claims for diagnostic testing methods based on mutations in a gene such asBRCA1.