Recent studies have demonstrated that DRD is caused by autosomal dominant mutations in the coding region of the GCH1 gene, which encodes for GTPCH (12), but only in 40-50% of cases (13).
PTPS and DHPR activities can be measured in liver biopsies (19, 20), erythrocytes (21, 22), and fibroblasts (23, 24), whereas GTPCH is measurable in liver biopsies (25).
Of these, three patients (two males, one female) had an autosomal recessive GTPCH deficiency (McKusick 233910), seven (five males, two females) had a PTPS deficiency (McKusick 261640), and three (all males) had a DHPR deficiency (McKusick 261630).
Dihydroneopterin triphosphate was prepared enzymatically as described previously (30), but using recombinant GTPCH (Thony B, Blau N.
To induce the expression of GTPCH, confluent cell monolayers in 78-[cm.sup.2] plates were stimulated with recombinant human IFN-[gamma] and TNF-[alpha] at concentrations of 250 and 100 kilounits/L, respectively, in fresh medium.
One unit of GTPCH produces 1 [micro]mol of neopterin per minute at 37[degrees]C.
Statistical differences between multiple groups (neopterin and biopterin concentrations in controls and patients with different disorders; GTPCH activity in controls and patients with DRD and GTPCH deficiency) were tested using a one-way ANOVA with pairwise comparison according to Tukey.
REFERENCE VALUES FOR NEOPTERIN AND BIOPTERIN PRODUCTION AND GTPCH ACTIVITY IN STIMULATED CELLS
GTPCH activity was very low in amniocytes but increased in fibroblasts collected after birth (P <0.01).
In both diseases, GTPCH activity was lower than in controls (P <0.001).