The neonatal tetrahydrobiopterin loading test in phenylketonuria: what is the predictive value?

BACKGROUND: It is unknown whether the neonatal tetrahydrobiopterin (BH4) loading test is adequate to diagnose long-term BH4 responsiveness in PKU. Therefore we compared the predictive value of the neonatal (test I) versus the 48-h BH4 loading test (test II) and long-term BH4 responsiveness. METHODS: Data on test I (>1991, 20 mg/kg) at T = 8 (n = 85) and T = 24 (n = 5) were collected and compared with test II and long-term BH4 responsiveness at later age, with ≥30% Phe decrease used as the cut-off. RESULTS: The median (IQR) age at hospital diagnosis was 9 (7-11) days and the age at test II was 11.8 (6.6-13.7) years. The baseline Phe concentrations at test I were significantly higher compared to test II (1309 (834-1710) versus 514 (402-689) µmol/L, respectively, P = 0.000). 15/85 patients had a positive test I T = 8. All, except one patient who was not tested for long-term BH4 responsiveness, showed long-term BH4 responsiveness. In 20/70 patients with a negative test I T = 8, long-term BH4 responsiveness was confirmed. Of 5 patients with a test I T = 24, 1/5 was positive at both tests and showed long-term BH4 responsiveness, 2/5 had negative results at both tests and 2/5 showed a negative test I T = 24, but a positive test II with 1/2 showing long-term BH4 responsiveness. CONCLUSIONS: Both a positive neonatal 8- and 24-h BH4 loading test are predictive for long-term BH4 responsiveness. However, a negative test does not rule out long-term BH4 responsiveness. Other alternatives to test for BH4 responsiveness at neonatal age should be investigated.

Evaluation of quality of life in PKU before and after introducing tetrahydrobiopterin (BH4); a prospective multi-center cohort study.

BACKGROUND: Phenylketonuria (PKU) is a rare inborn error of metabolism caused by phenylalanine hydroxylase enzyme (PAH) deficiency. Treatment constitutes a strict Phe restricted diet with unpalatable amino acid supplements. Residual PAH activity enhancement with its cofactor tetrahydrobiopterin (BH4) is a novel treatment which increases dietary tolerance in some patients and permits dietary relaxation. Relaxation of diet may improve health related quality of life (HRQoL). This prospective cohort study aims to evaluate HRQoL of patients with PKU and effects of BH4 treatment on HRQoL. METHODS: Patients aged 4years and older, diagnosed through newborn screening and early and continuously treated, were recruited from eight metabolic centers. Patients and mothers completed validated generic and chronic health-conditions HRQoL questionnaires (PedsQL, TAAQOL, and DISABKIDS) twice: before and after testing BH4 responsivity. Baseline results were compared to the general population. Data collected after BH4 testing was used to find differences in HRQoL between BH4 unresponsive patients and BH4 responsive patients after one year of treatment with BH4. Also a within patient comparison was performed to find differences in HRQoL before and after treatment with BH4. RESULTS: 69/81 (85%) patients completed the questionnaires before BH4 responsivity testing, and 45/69 (65%) participated again after testing. Overall PKU patients demonstrated normal HRQoL. However, some significant differences were found when compared to the general population. A significantly higher (thus better) score on the PedsQL was reported by children 8-12 years on physical functioning and by children 13-17 years on total and psychosocial functioning. Furthermore, adult patients reported significantly lower (thus worse) scores in the TAAQOL cognitive domain. 10 patients proved to be responsive to BH4 treatment; however improvement in their HRQoL after relaxation of diet could not be demonstrated.

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

BACKGROUND: How to efficiently diagnose tetrahydrobiopterin (BH4) responsiveness in patients with phenylketonuria remains unclear. This study investigated the positive predictive value (PPV) of the 48-hour BH4 loading test and the additional value of genotype. METHODS: Data of the 48-hour BH4 loading test (20 mg BH4/kg/day) were collected at six Dutch university hospitals. Patients with ≥30% phenylalanine reduction at ≥1 time points during the 48 hours (potential responders) were invited for the BH4 extension phase, designed to establish true-positive BH4 responsiveness. This is defined as long-term ≥30% reduction in mean phenylalanine concentration and/or ≥4 g/day and/or ≥50% increase of natural protein intake. Genotype was collected if available. RESULTS: 177/183 patients successfully completed the 48-hour BH4 loading test. 80/177 were potential responders and 67/80 completed the BH4 extension phase. In 58/67 true-positive BH4 responsiveness was confirmed (PPV 87%). The genotype was available for 120/177 patients. 41/44 patients with ≥1 mutation associated with long-term BH4 responsiveness showed potential BH4 responsiveness in the 48-hour test and 34/41 completed the BH4 extension phase. In 33/34 true-positive BH4 responsiveness was confirmed. 4/40 patients with two known putative null mutations were potential responders; 2/4 performed the BH4 extension phase but showed no true-positive BH4 responsiveness. CONCLUSIONS: The 48-hour BH4 loading test in combination with a classified genotype is a good parameter in predicting true-positive BH4 responsiveness. We propose assessing genotype first, particularly in the neonatal period. Patients with two known putative null mutations can be excluded from BH4 testing.

Necrotizing enterocolitis and respiratory distress syndrome as first clinical presentation of mitochondrial trifunctional protein deficiency.

BACKGROUND: Newborn screening (NBS) for long-chain 3-hydroxy acyl-CoA dehydrogenase (LCHAD) deficiency does not discriminate between isolated LCHAD deficiency, isolated long-chain keto acyl-CoA (LCKAT) deficiency and general mitochondrial trifunctional protein (MTP) deficiency. Therefore, screening for LCHAD deficiency inevitably comprises screening for MTP deficiency, which is much less amenable to treatment. Furthermore, absence of a clear classification system for these disorders is still lacking. MATERIALS AND METHODS: Two newborns screened positive for LCHAD deficiency died at the age of 10 and 31 days, respectively. One due to severe necrotizing enterocolitis (NEC), cardiomyopathy and multiorgan failure and the other due to severe infant respiratory distress syndrome (IRDS) and hypertrophic cardiomyopathy. (Keto)-acylcarnitine concentration and enzymatic analysis of LCHAD and LCKAT suggested MTP deficiency in both patients. Mutation analysis revealed a homozygous HADHB c.357+5delG mutation in one patient and a homozygous splice-site HADHB mutation c.212+1G>C in the other patient.Data on enzymatic and mutation analysis of 40 patients with presumed LCHAD, LCKAT or MTP deficiency were used to design a classification to distinguish between these disorders. DISCUSSION: NEC as presenting symptom in MTP deficiency has not been reported previously. High expression of long-chain fatty acid oxidation enzymes reported in lungs and gut of human foetuses suggests that the severe NEC and IRDS observed in our patients are related to the enzymatic deficiency in these organs during crucial stages of development.Furthermore, as illustrated by the cases we propose a classification system to discriminate LCHAD, LCKAT and MTP deficiency based on enzymatic analysis.

Parenting a child with phenylketonuria or galactosemia: implications for health-related quality of life.

Parents of children with chronic disorders have an impaired health-related quality of life (HRQoL) compared to parents of healthy children. Remarkably, parents of children with a metabolic disorder reported an even lower HRQoL than parents of children with other chronic disorders. Possibly, the uncertainty about the course of the disease and the limited life expectancy in many metabolic disorders are important factors in the low parental HRQoL. Therefore, we performed a cross-sectional study in parents of children with phenylketonuria (PKU, OMIM #261600) and galactosemia (OMIM #230400), metabolic disorders not affecting life expectancy, in order to investigate their HRQoL compared to parents of healthy children and to parents of children with other metabolic disorders. A total of 185 parents of children with PKU and galactosemia aged 1-19 years completed two questionnaires. Parents of children with PKU or galactosemia reported a HRQoL comparable to parents of healthy children and a significantly better HRQoL than parents of children with other metabolic disorders. Important predictors for parental mental HRQoL were the psychosocial factors emotional support and loss of friendship. As parental mental functioning influences the health, development and adjustment of their children, it is important that treating physicians also pay attention to the wellbeing of the parents. The insight that emotional support and loss of friendship influence the HRQoL of the parents enables treating physicians to provide better support for these parents.