QDPR and pterin-4 alpha-carbinolamine dehydratase 1 deficiency: With the exception of DHPR deficiency, which can be detected by determination of DHPR activity in dried blood spots (DBS), all other forms of BH4 deficiency (GTPCH, PTPS, and PCD deficiency) can be detected by specific pterin patterns in urine or DBS [19, 23, 24].