1. Department of Paediatric Surgery, University Medical Center Hamburg-Eppendorf (UKE), Hamburg, Germany
2. Department of Paediatric Surgery, Altona Children's Hospital, Hamburg, Germany
3. Department of Child and Adolescent Psychiatry and Psychotherapy, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
4. Institute of Medical Biometry and Epidemiology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
5. Institute of Biometry and Clinical Epidemiology, Charité – Universitaetsmedizin Berlin, Berlin, Germany
6. Department of General Paediatrics, Altona Children's Hospital, Hamburg, Germany
7. Laboratory Dr. Fenner and colleagues, Hamburg, Germany