- Correspondence to Dr J T Merrill, Oklahoma Medical Research Foundation, University of Oklahoma Health Sciences Center, 825 NE 13th St., Oklahoma City, OK 73104 USA;
- Received March 25, 2015
- Revised June 18, 2015
- Accepted August 1, 2015
- First published August 20, 2015.
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- Data supplement 1 - Online supplement
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