Tetrahydrobiopterin responsiveness in phenylketonuria: prediction with the 48-hour loading test and genotype

Table 1 Demographic and clinical details of patients with non-potential BH4 responsiveness and False/True-positives

BH4 loading test:	Non-potential BH4-responsive (n = 97)	Potential responder (n = 80)
BH4 extension phase:		False-positive (n = 9)	True-positive (n = 58)	Other¹(n = 13)
Sex
Male	47 (48.5)	6 (66.7)	24 (41.4)	7 (53.8)
Female	50 (51.5)	3 (33.3)	34 (58.6)	6 (46.2)
Age (years) A*	14.7 (10.3 – 23.0)	8.0 (6.4 – 11.9)	12.3 (7.7 – 17.9)	14.1 (10.4 – 19.4)
<12 years A**	30 (30.9)	7 (77.8)	25 (43.1)	4 (30.8)
≥12 years	67 (69.1)	2 (22.2)	33 (56.9)	9 (69.2)
Baseline Phe (μmol/L)² B*** C*	663 (530 – 915)	620 (528 – 831)	465 (358 – 555)	485 (386 – 590)
Mean Phe^3,4 B* C	494 (364 – 700)	455 (406 – 553)	304 (244 – 401)	267 (239 – 407)
<12 years B* C**	397 (290 – 441)	455 (372 – 539)	282 (227 – 400)	274 (207 – 318)
≥12 years⁴ B***	564 (427 – 773)	440, 759 (n = 2)	332 (255 – 414)	264 (239 – 456)
Phe at diagnosis⁵ B*, C*
<600 μmol/L	3 (3.5)	0 (0.0)	26 (44.8)	4 (30.8)
600–1199 μmol/L	13 (15.3)	2 (22.2)	26 (44.8)	3 (23.1)
>1200 μmol/L	69 (81.2)	7 (77.8)	6 (10.3)	6 (46.2)

Data are n (%) or median (interquartile range). ¹ no BH4 extension phase. ² Phe concentration at T = 0 (with Phe loading when necessary). ³ Mean Phe concentration prior to the BH4 loading test. ⁴ Missing in n = 14 (<30%), n = 10 (True-positives) and n = 1 (Other). ⁵ First Phe concentration in hospital, missing in n = 12 (<30%). A) comparing non-potential BH4-responsive and false-positive, B) comparing non-potential BH4-responsive and true-positive, C) comparing false-positive and true-positive. *P = <0.05, **P = <0.01, ***P = <0.001.

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