Scenario A 3-year-old girl presents in clinic with mild to moderate general delay in all areas. There is no other relevant history, no family history and clinical examination is normal. The paediatric registrar decides to order some investigations, including the biotinidase activity level, to identify the possible aetiology of the global developmental delay (GDD). Structured clinical question In preschool children with global developmental delay [patients], is the prevalence of biotinidase deficiency [outcome] higher than in the general population? Search strategy and outcome Medline (1950–August 2010) was searched using different combinations of MeSH terms including ‘global developmental delay’, ‘severe learning disabilities’, ‘moderate learning disabil...<div id="medworm"><p><b><i>MedWorm Sponsor Message:</i></b> Please support the <a href="http://www.doctorsinchains.org/">DoctorsInChains.org</a> campaign for the health workers in Bahrain. #FreeDoctors</p></div>