1. Endocrine Section , Beacon Hospital, Dublin, D18 AK68 , Ireland
2. Department of Endocrinology , St Vincent's University Hospital, Dublin, D04 T6F4 , Ireland
3. School of Medicine , University College Dublin, Dublin, D04 C7X2 , Ireland
4. Metabolic Research Laboratories , Wellcome Trust-MRC Institute of Metabolic Science, University of Cambridge, Cambridge CB2 0QQ , UK