Sepiapterin reductase deficiency (SRD) is a dopa-sensitive neurotransmitter disorder, caused by mutation of the SPR gene located on chromosome 2p14-p12.1 To date, 31 patients with 14 mutations have been diagnosed (BIODEF database, update November 2010, www.biopku.org).
While classic tetrahydrobiopterin deficiencies present with hyperphenylalaninemia and deficiency of monoamine neurotransmitters, SRD is typically associated with normal phenylalanine levels in blood and pterins in urine2 and not detectable by neonatal screening for phenylketonuria. This implies how important it is to diagnose this condition clinically, in order to provide timely and proper treatment. A summary of the pathophysiology and biochemical pathway is provided by Bonafé et al.
With the following case report and review of 21 published cases, we elucidate the clinical features of SRD as well as the diagnostic strategy and therapeutic approach.