I could probably fit all well-structured data elements in existence for all medical patients in the US for a year on a single DVD. (and even the unstructured non-image data is pretty sparse.)
This is not really a problem where "big data" techniques are the right tool- There's too little data. However, I believe we should be experimenting on cell cultures in laboratories at large scales. None of this is happening, I believe... no laboratory is running hundreds of thousands of cultures in parallel with carefully manipulated chemical environments and generating data from them.
A data set generated from such cell culture analysis could be petabytes in size. With that type of data set I believe it would be possible, using big data techniques, to get a lot of rigorous and causative details of chemical cell pathways relevant to disease formation that we currently lack. This is the direction I think we need to be going.
I certainly would love to be wrong and would love to get news that IBM has cracked heart disease with this new project. However, my guess is that this is a very inefficient way to apply big data techniques to cure diseases.