The mean ± SD decrease from baseline in blood phenylalanine levels at the end of the 6 week study period was 235.9 ± 257.0 μ mol/ l for the sapropterin treated group (n=47) as compared to an increase of 2.9 ± 239.5 μ mol/ l for the placebo group (n=41) (p < 0.001).