ORIGINAL ARTICLE The response of patients with phenylketonuria and elevated serum phenylalanine to treatment with oral sapropterin dihydrochloride (6R-tetrahydrobiopterin): a phase II, multicentre, open-label, screening study B. K. Burton & D. K. Grange & A. Milanowski & G. Vockley & F. Feillet & E. A. Crombez & V. Abadie & C. O. Harding & S. Cederbaum & D. Dobbelaere & A. Smith & A. Dorenbaum Received: 2 March 2007 / Submitted in revised form: 30 May 2007 / Accepted: 12 June 2007 / Published online: 12 September 2007 # SSIEM and Springer 2007 Summary This study aimed to evaluate the response to and safety of an 8-day course of sapropterin dihydrochloride (6R-tetrahydrobiopterin or 6R-BH 4 ) 10 mg/kg per day in patients with phenylketonuria (PKU), who have elevated blood phenylalanine (Phe) levels, and to identify a suitable cohort of patients who would respond to sapropterin dihydrochloride treat- ment with a reduction in blood Phe level. Eligible patients were aged Q8 years, had blood Phe levels Q450 mmol/L and were not adhering to a Phe-restricted diet. Suitable patients were identified by a Q30% reduction in blood Phe level from baseline to day 8 following sapropterin dihydrochloride treatment. The proportion of patients who met these criteria was calculated for the overall population and by baseline J Inherit Metab Dis (2007) 30:700–707 DOI 10.1007/s10545-007-0605-z Communicating editor: Nenad Blau Competing interests: None declared References to electronic databases: Phenylketonuria (PKU): OMIM 261600. B. K. Burton Children_s Memorial Hospital, Northwestern University Feinberg School of Medicine, Chicago, IL, USA D. K. Grange St. Louis Children_s Hospital, Washington School of Medicine, St. Louis, MO, USA A. Milanowski Instytut Matki i Dziecka, Warszawa, Poland G. Vockley Children_s Hospital of Pittsburgh, Pittsburgh, PA, USA F. Feillet Department of Pediatrics, Ho ˆ pital d_Enfants, Vandoeuvre les Nancy, France E. A. Crombez David Geffen School of Medicine at UCLA, Los Angeles, CA, USA V. Abadie Ho ˆ pital Necker – Enfants Malades Pediatrie Generale, Paris, France C. O. Harding Oregon Health & Science University, Portland, OR, USA S. Cederbaum UCLA Medical Center, Los Angeles, CA, USA D. Dobbelaere CHRU de Lille – Ho ˆ pital Jeanne de Flandres, Lille, France A. Smith Pacific Data Designs, San Francisco, CA, USA A. Dorenbaum BioMarin Pharmaceutical Inc., Novato, CA, USA B. K. Burton (*) Children_s Memorial Hospital, Division of Genetics, Box 59, 2300 Children_s Plaza, Chicago, IL 60614, USA e-mail: bburton@childrensmemorial.org