U.S. Patent No. 7,267,820 is directed to diagnosing neurological disorders.  The claims are directed to detecting an epitope of MuSK with a label in bodily fluid including contacting MuSK with bodily fluid, immunoprecipitating MuSK complex, and monitoring for the label where the label indicates disorder (pages 4-5).  Adding conventional steps to a law of nature does not make the claim patent eligible (page 8).  The natural law is the correlation between naturally-occurring MuSK and MuSK disease (pages 9-10).  The acts of the claim other than the law of nature apply conventional techniques (pages 9-12).  The specification even indicates that the steps to detect are known in the art (page 12).  Leaving open other ways to use the law of nature through specificity in the claim does not make the claim patentable as preemption is not necessary (page 13).  Labeling with a man-made substance that is routine does not make the claim patent eligible (page 14). 

Hindsight:  A new treatment using a natural law is patent eligible.  In this case, it may not have helped to refer to the performing acts as known in the art in the specification.  Identifying and characterizing novelty in how the natural law is applied may help.