DHPR activity decrease in dried blood spots stored at 4 degrees C.

Dihydropteridine reductase (DHPR) activity has been measured in dried blood spots by the Arai method in 286 subjects divided into 4 groups: 45 newborns aged between 4 and 7 days; 40 subjects with hyperphenylalainaemia; 199 apparently normal subjects, and 2 patients with DHPR deficiency. Furthermore, a study of the persistence of enzymatic activity on the spots stored at 4 degrees C revealed that after 1 year it decreased to one third of the original value, corresponding to the mean value of controls minus 2 SD.