1. Department of Paediatric Endocrinology, Royal Victoria Infirmary, Newcastle Upon Tyne NE1 4LP, UK
2. Department of Paediatrics, James Cook University Hospital, Middlesborough TS4 3BW, UK
3. Department of Clinical Biochemistry, Royal Victoria Infirmary, Newcastle Upon Tyne NE1 4LP, UK
4. Department of Biochemistry, University Hospital of North Durham, Durham DH1 5TW, UK