Long-term follow-up and outcome of phenylketonuria patients on sapropterin: a retrospective study.

OBJECTIVE: Sapropterin dihydrochloride, the synthetic form of 6R-tetrahydrobiopterin (BH4), is an approved drug for the treatment of patients with BH4-responsive phenylketonuria (PKU). The purpose of this study was to assess genotypes and data on the long-term effects of BH4/sapropterin on metabolic control and patient-related outcomes in 6 large European countries. METHODS: A questionnaire was developed to assess phenotype, genotype, blood phenylalanine (Phe) levels, Phe tolerance, quality of life, mood changes, and adherence to diet in PKU patients from 16 medical centers. RESULTS: One hundred forty-seven patients, of whom 41.9% had mild hyperphenylalaninemia, 50.7% mild PKU, and 7.4% classic PKU, were followed up over ≤12 years. A total of 85 different genotypes were reported. With the exception of two splice variants, all of the most common mutations were reported to be associated with substantial residual Phe hydroxylase activity. Median Phe tolerance increased 3.9 times with BH4/sapropterin therapy, compared with dietary treatment, and median Phe blood concentrations were within the therapeutic range in all patients. Compared with diet alone, improvement in quality of life was reported in 49.6% of patients, improvement in adherence to diet was reported in 47% of patients, and improvement in adherence to treatment was reported in 63.3% of patients. No severe adverse events were reported. CONCLUSIONS: Our data document a long-term beneficial effect of orally administered BH4/sapropterin in responsive PKU patients by improving the metabolic control, increasing daily tolerance for dietary Phe intake, and for some, by improving dietary adherence and quality of life. Patient genotypes help in predicting BH4 responsiveness.

The monitoring of trace elements in blood samples from patients with inborn errors of metabolism.

Patients having inborn errors of intermediary metabolism (IEMs) may have element deficiencies related to dietary treatment. Our objective was to study several elements [cobalt (Co), copper (Cu), zinc (Zn), selenium (Se), manganese (Mn), molybdenum (Mo) and magnesium (Mg)] in patients with IEMs with and without dietary treatment and to compare these results with those established in a healthy paediatric population. We studied 72 patients with IEMs (age range 2 months-44 years; median 10.5 years), with and without protein-restricted dietary treatment. Control values were established in 92 subjects (age range 1 day-42 years; median 6.5 years). Dietary treatment consisted of a natural protein-restricted diet supplemented with a special formula, depending on the specific metabolic defect. Samples were analysed with an Agilent 7500ce-ICP mass spectrometer. Significant differences were observed when we compared patients under dietary treatment and control values for Se and Co (P < 0.0001). No differences were observed for the other elements when the different groups were compared, except for Co (IEM patients without dietary treatment vs control group; P = 0.003). For Se and cobalamin, the daily intake of our patients (Se 48 ± 16 µg/day; cobalamin 3.5 µg/day) was slightly higher than the recommended daily averages (RDAs) (40 µg/day and 1.8 µg/day, respectively). We concluded that IEM patients under dietary treatment showed significantly lower selenium values in spite of correct supplementation, reinforcing the idea that these patients should be regularly monitored, at least for this element. Further investigations seem advisable about Se and Co availability in special diets.

Long-chain polyunsaturated fatty acid status in phenylketonuric patients treated with tetrahydrobiopterin.

OBJECTIVES: To evaluate LCPUFA composition in PKU patients treated with BH(4). DESIGN AND METHODS: Cross-sectional study of plasma and erythrocyte LCPUFA composition of 13 PKU patients treated with BH(4) compared with data from 48 PKU patients on protein-restricted diet, and 17 mild HPA patients on free diet. PUFA were analysed by gas chromatography. RESULTS: Plasma and erythrocyte docosahexaenoic acid (DHA), and LCPUFA deficiency markers did not show significant differences in PKU patients on BH(4) compared with those with mild HPA and our reference values, but they did in comparison with PKU on protein-restricted diet (p<0.0001). Essential fatty acids and arachidonic acid composition were not significantly different in any of the studied groups. DHA values correlate with the index of dietary control only in PKU patients on protein-restricted diet (p=0.002). CONCLUSION: LCPUFA status is within the reference values in PKU patients treated with BH(4). This translates to a further advantage of BH(4) therapy.

Is deoxypyridinoline a good resorption marker to detect osteopenia in phenylketonuria?

OBJECTIVES: To evaluate deoxypyridinoline as a resorption marker in phenylketonuria (PKU) and to search for a relationship between deoxypyridinoline, calcium/creatinine index (Ca/Cr I), osteocalcin and bone alkaline phosphatase (BAP). METHODS: This was a transversal analytical study of 46 PKU patients [17.5 (4-38) years]. Deoxypyridinoline and osteocalcin were measured with a chemiluminescent assay and BAP was measured with an immunoradiometric assay. RESULTS: Deoxypyridinoline was significantly increased in patients aged 7-14 and >18 years old, being associated with age (r=-0.724, P<0.001). Adult patients showed significantly higher Ca/Cr I, which correlates with Phe values for the year prior to the study (P=0.014). Serum BAP was significantly increased in pediatric patients (9-13 years), while it was decreased in adult patients (P=0.003). Decreased osteocalcin levels were found in patients>15 years (P=0.028). Altered deoxypyridinoline and BAP values were related (P=0.042). CONCLUSION: PKU patients excreted increased D-Pyr, suggesting high bone resorption. Bone formation seems active in childhood but deteriorates in adult PKU patients. Periodic measurement of D-Pyr and BAP may be useful in the prevention of osteopenia in PKU patients.

Clinical and nutritional evaluation of phenylketonuric patients on tetrahydrobiopterin monotherapy.

The clinical, nutritional, and neuropsychological data of 11 mild/moderate PKU patients after one year of treatment with BH4 are evaluated. BH4 monotherapy was introduced at 5 mg/kg/day in 14 PKU patients. In 11/14 patients, Phe tolerance increased significantly from 356+/-172 to 1546+/-192 mg/day (p=0.004), and special PKU formula was gradually reduced until complete removal. In them, mean plasma Phe concentrations remained below 360 micromol/L at 5 mg BH4/kg/day (7 mg/kg/day in one patient). BH4 therapy was stopped in three patients (V388M/P362T and R243Q/IVS10-11G>A genotypes) because it was not possible to improve Phe tolerance and to remove formula intake. Serum micronutrients were not significantly different at the start of treatment and at one year follow-up, except for selenium, which increased significantly after one year of therapy (p=0.017). Anthropometric, and nutritional measurements were within the age- and sex-specific percentiles for a healthy population after one year therapy. Neuropsychological follow-up indicated that intelligence scores persisted within normal limits. In terms of patients' genotype, we confirmed that the P275S mutation combined with R408W was associated with long-term BH4 responsiveness, while the combination of P362T/V388M, and R243Q/IVS10-11G>A resulted in poor metabolic control in long-term BH4 therapy. In summary, our data confirm that BH4 is a safe, and effective therapy in a selected group of mild, and moderate PKU patients who respond to the BH4 loading test. Low doses of BH4 in monotherapy permit withdrawal of the special formula and guarantee a good clinical and nutritional outcome with no adverse side effects in PKU patients.

Tetrahydrobiopterin responsiveness in patients with phenylketonuria.

OBJECTIVES: To investigate the BH4 response in a group of patients with phenylketonuria (PKU) in order to offer this alternative treatment to the responsive patients. DESIGN AND METHODS: The 24-h-long Phe/BH4 loading test was performed on 64 PKU patients requiring dietary treatment. RESULTS: All patients with mild-PKU and 75% of patients with moderate-PKU were BH4 responsive, while only 11% of classic-PKU patients showed good/partial response (P < 0.0001). The percentages of Phe decrease after the BH4 loading test were significantly different in the three PKU phenotypes (mild PKU: 67.9 +/- 18.7; moderate PKU: 37.4 +/- 16.8; and classical PKU: 21.9 +/- 13.7; ANOVA with Bonferroni correction: P < 0.0001). We report four mutations (P147S, D222G, P275S, and P362T) not previously associated with BH4 responsiveness, all of them combined with mutations with zero predicted residual activity. CONCLUSION: Both the percentage of Phe decrease and the Phe value achieved 24 h after BH4 loading are valuable data in predicting a response. We report four mutations not previously associated with BH4 responsiveness.

A longitudinal study of antioxidant status in phenylketonuric patients.

OBJECTIVES: To investigate the implications of the three main factors of the antioxidant system reported in relation to oxidative damage in phenylketonuric patients: selenium, ubiquinone-10 (Q10) and antioxidant enzymes over 3 years of metabolic follow-up. DESIGN AND METHODS: Longitudinal study of 46 phenylketonuric patients (age range: 6 months-34 years). Antioxidants were measured by atomic absorption spectrophotometric, chromatographic and spectrophotometric procedures. RESULTS: Plasma selenium concentrations in phenylketonuria (PKU) were not different from those of a healthy population. Decreased plasma Q10 concentrations were mainly related to the dietary control and the age of patients. Erythrocyte catalase activity was significantly decreased in PKU while the other enzyme activities were not different from those of a healthy population. CONCLUSION: Selenium status is not impaired in phenylketonuric patients under dietary treatment. Q10 values tend to decrease with increased patient age. Catalase activity was negatively associated with plasma phenylalanine values.

Lipophilic antioxidants in patients with phenylketonuria.

BACKGROUND: Low serum ubiquinone-10 concentrations have been described in phenylketonuric patients fed natural-protein-restricted diets. Such low concentrations may be related to increased free radical damage. OBJECTIVE: We evaluated the relation between low serum ubiquinone-10 concentrations and other lipophilic antioxidants (tocopherol and retinol), selenium, glutathione peroxidase activity, and malondialdehyde concentrations as a marker of lipid peroxidation. DESIGN: This was a cross-sectional study of 58 patients with phenylketonuria (aged 2-36 y; median: 13 y) under dietary treatment, 58 age-matched control subjects, and 30 children with moderate hyperphenylalaninemia fed unrestricted diets (aged 3-17 y; median: 7.5 y). Serum ubiquinone-10 concentrations were analyzed by HPLC with electrochemical detection. Serum retinol, serum tocopherol, and plasma malondialdehyde were analyzed by HPLC with ultraviolet detection. RESULTS: A significant positive correlation was observed between ubiquinone-10 and tocopherol (r = 0.510, P < 0.001) in the patients with phenylketonuria. After the patients were stratified into 2 groups according to ubiquinone-10 values, significantly lower concentrations of tocopherol were observed in group 1 (low ubiquinone values) than in group 2 (normal ubiquinone values), the hyperphenylalaninemic children, and the control group. Plasma malondialdehyde concentrations were significantly higher in group 1 than in the other groups. No significant differences between groups 1 and 2 were observed in daily intakes of selenium, ascorbate, tocopherol, or retinol. CONCLUSIONS: Plasma lipid peroxidation seems to be increased in phenylketonuria. Low concentrations of ubiquinone-10 could be associated with either excessive tocopherol consumption or high malondialdehyde concentrations in patients with phenylketonuria.

Ubiquinone-10 content in lymphocytes of phenylketonuric patients.

OBJECTIVES: To investigate the ubiquinone-10 content in lymphocytes from phenylketonuric patients. DESIGN AND METHODS: We compared 23 patients with 25 age-matched controls. Ubiquinone-10 was analyzed by HPLC with electrochemical detection. RESULTS: Ubiquinone-10 concentrations were significantly lower in patients (77-270 nmol/g of protein) compared with controls (190-550) (p < 0.001). Significantly negative correlation was observed between ubiquinone-10 and phenylalanine (r = -0.441; p < 0.05). CONCLUSIONS: Ubiquinone-10 concentrations are decreased in lymphocytes from phenylketonuric patients. This deficiency is associated with high plasma phenylalanine concentrations.