Micronutrient status in phenylketonuria

Patients with phenylketonuria (PKU) encompass an 'at risk' group for micronutrient imbalances. Optimal nutrient status is challenging particularly when a substantial proportion of nutrient intake is from non-natural sources. In PKU patients following dietary treatment, supplementation with micronutrients is a necessity and vitamins and minerals should either be added to supplement phenylalanine-free l-amino acids or given separately. In this literature review of papers published since 1990, the prevalence of vitamin and mineral deficiency is described, with reference to age of treatment commencement, type of treatment, dietary compliance, and dietary practices. Biological micronutrient inadequacies have been mainly reported for zinc, selenium, iron, vitamin B12 and folate. The aetiology of these results and possible clinical and biological implications are discussed. In PKU there is not a simple relationship between the dietary intake and nutritional status, and there are many independent and interrelated complex factors that should be considered other than quantitative nutritional intake.

Early dietary treated patients with phenylketonuria can achieve normal growth and body composition

BACKGROUND

In the past, overtreatment may have resulted in growth impairment in patients with phenylketonuria.

OBJECTIVE

The paper aims to investigate height and body composition in early treated patients with phenylketonuria who were diagnosed between 1981 and 2008.

DESIGN

A cross-sectional study of 89 patients with phenylketonuria and 78 controls aged (mean ± SD, in years) 14.4 ± 6.6 and 15.9 ± 7.1, respectively, was undertaken, including anthropometric and body composition evaluation using bioelectrical impedance. Median Phe concentrations in the last year before study enrollment were used as a measure of metabolic control. Natural protein and amino acid mixture intakes were recorded in patients.

RESULTS

No statistically significant differences were found on height z-scores between patients and controls aged less than 19 years (p=0.301), although all patients with classical phenylketonuria revealed negative height z-scores, resulting in a mean ± SD of -0.65 ± 0.41. Among participants aged 19 years or more, median (p25-p75) of height was significantly higher in controls [168.0 cm (159.2-174.8)] than in patients [160.5 cm (151.9-167.5)] (p=0.017). No significant differences were found between patients and controls regarding fat mass, fat free mass, muscular mass, body cell mass index and phase angle.

CONCLUSION

Our results suggest that early and continuously treated patients with phenylketonuria born after 1992 can achieve normal growth and body composition, although the negative height z-score in patients with classical phenylketonuria strengthens the continuous need to optimize the quality of their protein intake.

Visual functions in phenylketonuria-evaluating the dopamine and long-chain polyunsaturated fatty acids depletion hypotheses

BACKGROUND

In phenylketonuria presymptomatic treatment following newborn screening prevents severe mental and physical impairment. The reasons for subtle impairments of cerebral functions despite early treatment remain unclear. We assessed a broad spectrum of visual functions in early-treated patients with phenylketonuria and evaluated two hypotheses-the dopamine and the long-chain polyunsaturated fatty acids (LCPUFAs) depletion hypotheses.

METHODS

Contrast sensitivity, colour vision, electroretinography, frequency doubling technology campimetry (FDT), and their relation with blood phenylalanine and docosahexaenoic acid levels were assessed in 36 patients with phenylketonuria and 18 age-matched healthy controls.

RESULTS

Contrast sensitivity was significantly lower and total error scores in colour vision significantly higher in patients than controls. Electroretinography results differed significantly between patients and controls. We found a trend for the effect of phenylalanine-levels on contrast sensitivity and a significant effect on colour vision/FDT results. Docosahexaenoic acid levels in erythrocytes were not associated with visual functions.

CONCLUSION

This is the first evaluation of visual functions in phenylketonuria using a comprehensive ophthalmological test battery. We found no evidence supporting the long-chain polyunsaturated fatty acids depletion hypothesis. However, the effect of phenylalanine-levels on visual functions suggests that imbalance between phenylalanine and tyrosine may affect retinal dopamine levels in phenylketonuria. This is supported by the similar patterns of visual functions in patients with phenylketonuria observed in our study and patients with Parkinson's disease.

GTP cyclohydrolase regulation: implications for brain development and function

Tetrahydrobiopterin (BH4) is essential for the biosynthesis of dopamine, noradrenaline, and serotonin, which serve as cofactors for tyrosine hydroxylase (TH) and tryptophan hydroxylase. GTP cyclohydrolase (GCH) is the first and rate-limiting enzyme for BH4 biosynthesis. Genetic defects in an allele of the GCH gene can result in dopa-responsive dystonia due to partial BH4 deficiency. To explore the transcriptional control of the GCH gene, we analyzed the signaling pathway. Bacterial lipopolysaccharide (LPS) greatly enhanced the expression of GCH in RAW264 cells, and the induction of GCH by LPS was suppressed by treatment with either a MEK1/2 inhibitor or an inhibitor for the NF-κB pathway. Next, we analyzed two types of biopterin-deficient transgenic mice. We found that both mice exhibited motor disorders with slight differences. Dopamine and TH protein levels were markedly and concurrently increased from birth (P0) to P21 in wild-type mice, and these increases were abolished in both types of biopterin-deficient mice. Our results suggest that the developmental manifestation of psychomotor symptoms in BH4 deficiency might be attributable at least partially to the high dependence of dopaminergic development on the availability of BH4.

Processing speed and executive abilities in children with phenylketonuria

OBJECTIVE

Phenylketonuria (PKU) is a hereditary metabolic disorder that often results in neuropsychological impairment, even in individuals treated early and continuously. This study was conducted to examine processing speed, variability in processing speed, and the relationship between processing speed variables and executive abilities in children with early and continuously treated PKU.

METHOD

Participants were 42 children with PKU and 81 typically developing children from 7 to 18 years of age. Children completed 3 computerized reaction time (RT) tasks (simple RT, go/no-go, stimulus-response compatibility) and 7 tasks assessing executive abilities (working memory, inhibitory control, strategic processing).

RESULTS

Performance of children with PKU was significantly slower and more variable than that of controls across the 3 tasks administered. When age was considered, it was shown that processing speed improved with age to a comparable degree for both groups. Variability in processing speed, however, decreased more with age for the PKU than control group, reflecting the fact that variability in younger, but not older, children with PKU was greater than that of controls. With regard to executive abilities, processing speed and variability contributed to performance on most, but not all, executive tasks; and after controlling for processing speed and variability, executive impairments were still identified in working memory and inhibitory control (not strategic processing).

CONCLUSIONS

These findings indicate that information processing is slower and less efficient in children with PKU. In addition, processing speed and variability contribute to some, but not all, of the impairments in executive abilities observed in children with PKU.

Decreased functional brain connectivity in individuals with early-treated phenylketonuria: evidence from resting state fMRI

Previous histological and neuroimaging studies have documented structural abnormalities in the white matter of the brain in individuals with early-treated phenylketonuria (ETPKU). It remains unclear, however, the extent to which the function of the brain's interconnections are impacted by this condition. Presently, we utilized functional magnetic resonance imaging (fMRI) to evaluate the synchronization of neural signals (i.e., functional connectivity) among brain regions comprising the default mode network (DMN) in a sample of 11 individuals with ETPKU and 11 age- and gender-matched neurologically intact controls. The DMN is a group of interconnected brain regions that are known to be generally more active during rest than during task performance. Data analysis revealed decreased functional connectivity among DMN regions for the ETPKU group compared with the control group. Within the PKU group, we also found a significant relationship between blood phenylalanine (phe) levels and the functional connectivity between select regions of the DMN. In conjunction with findings from another recent fMRI study (Christ, Moffitt et al. 2010), the present results suggest that ETPKU-related deficiencies in functional connectivity are pervasive. The current findings also provide initial evidence that the extent of such impairment may be moderated in part by blood phe levels.

Bone development in children and adolescents with PKU

INTRODUCTION

Individuals with phenylketonuria (PKU, OMIM 261600) have shown bone disease from childhood. Factors such as non-adherence to treatment, nutritional inadequacy, and high phenylalanine levels are associated with bone disease in several studies. This research aimed to describe the impact of dietary factors (consumption of energy, protein, calcium, phosphorus, and phenylalanine), and the control of plasma phenylalanine levels on bone age (BA) and bone mineral density (BMD).

METHODOLOGY

Thirteen patients of both genders, from 8 to 16 years old participated in this study. Control data were collected of phenylalanine levels, food frequency and record, hand and fist X-rays, and spinal bone densitometry.

RESULTS

In children group (CG), individuals non-adherent to diet (NAD) consumed lower amounts of calcium (472 ± 100 mg/day) and energy (1743 ± 486 Kcal); they had higher rates of phenylalanine (564 ± 94 μmol/L) in blood, intake phenylalanine (701 ± 334 mg/g), and higher protein intake from free foods (14 ± 6.67 g/day); bone age (BA) values higher than the chronological age (CA) and less BMD values (-0.7 ± 1.6 SD) also were verified. In adolescent group (AG, N = 8) of NAD, values were lower for energy intake (1379 ± 258 Kcal), calcium (801 ± 152 mg/day), phosphorus (657 ± 102 mg/day), food protein (25 ± 7.6 g/day), and intake phenylalanine (1067 ± 382 mg/day) than recommended. Higher levels of plasma phenylalanine (851 ± 244 μmol/L), bone age greater than chronological age and lower BMD values (-2.4 ± -2.5 SD) were observed.

CONCLUSION

The results suggest effects on BA and on BMD, in both children and adolescent groups. The bone development is expressed differently in children and adolescents. The non-adherence to the diet verified in both groups and the consequent imbalance in the nutrients intake involved in bone metabolism suggest that these factors influence the failure to thrive in children and reduced bone mineralization in adolescents.

Relationships between lumbar bone mineral density and biochemical parameters in phenylketonuria patients

BACKGROUND

The etiology of reduced bone mineral density (BMD) in phenylketonuria (PKU) is unknown. Reduced BMD may be inherent to PKU and/or secondary to its dietary treatment.

MATERIALS AND METHODS

Lumbar BMD was measured by dual-energy X-ray absorptiometry in 53 early and continuously treated PKU patients (median age 16, range 2-35 years). First, Z-scores of BMD were correlated to age group, clinical severity of PKU, mean phenylalanine (Phe) concentration and Phe variation in the year prior to DXA scanning, as well as to blood vitamin, mineral, and alkaline phosphatase concentrations. Second, parameters were compared between subjects with reduced BMD (Z-score<-2 SD) and subjects with normal BMD.

RESULTS

BMD was significantly reduced in our cohort (p=0.000). Z-scores of BMD were neither significantly correlated to age group, nor clinical severity of PKU. Both mean Phe concentration and Phe variation in the year prior to DXA scanning did not significantly correlate with Z-scores of BMD. Higher blood calcium concentrations were significantly associated with lower BMD (r(2)=-0.485, p=0.004). Other biochemical parameters, including vitamin B12 availability markers, did not show significant correlations with Z-score of BMD. Subjects with reduced BMD had significantly higher blood phosphorus concentrations than subjects with normal BMD (p=0.009). No other significant differences were found between both BMD groups.

CONCLUSION

Reduced BMD in PKU is present from early age onward and does not progress with age. Therefore, BMD deserves attention from early age onward in PKU patients. Our findings are consistent with increased bone turnover in PKU. It remains unclear whether reduced BMD is inherent to PKU and/or secondary to its dietary treatment.

Physical development in patients with phenylketonuria on dietary treatment: a retrospective study

OBJECTIVES

To evaluate the growth and physical development in patients with phenylalanine hydroxylase deficiency who follow exclusively dietary treatment.

METHODS

Anthropometric measurements of 160 patients with hyperphenylalaninemia who were followed at our center over a 25 year period were obtained. Only patients treated exclusively with a protein-restrictive diet supplemented with amino acid mixtures were included. Height, weight and body mass index were measured at birth, at diagnosis, at 6 and 12 months of age, and annually until 18 years of age in patients with phenylketonuria or until 9 years of age in patients with mild hyperphenylalaninemia and compared to official national reference values. The final height of PKU patients was also compared to their expected family height.

RESULTS

The analysis of z scores suggested no significant differences in physical development between PKU patients and the healthy population during the study period. The final height of PKU patients revealed that they were 2 to 4 cm taller than expected when compared to the mean family height (p<0.001). The mean weight and BMI at puberty suggested that many patients with severe PKU, but not other phenotypes, were overweight during this period.

CONCLUSION

Physical development can be optimal in PKU patients regardless of their phenotype and the severity of the diet. A tendency to excessive weight gain is seen in adolescence in the most severe phenotypes.

Disorders of BH4 metabolism and the treatment of patients with 6-pyruvoyl-tetrahydropterin synthase deficiency in Taiwan

6-Pyruvoyl-tetrahydropterin synthase (PTPS) deficiency is the most frequent form of tetrahydrobiopterin (BH4) deficiency related to hyperphenylalaninemia (HPA). PTPS deficiency may not only cause a typical phenylketonuric phenotype, but is also accompanied by various neurological signs and symptoms due to impaired synthesis of catecholamines and serotonin. The treatment of PTPS deficiency is aimed at normalizing phenylalanine levels and brain neurotransmitters. The BH4 can be administered to normalize phenylalanine (PHE) levels easily, but, owing to severe side effects, the neurotransmitters, L-DOPA and 5-hydroxytryptophan, should be administered for these patients very carefully. However, optimal dosage of the neurotransmitters for PTPS deficiency patients is difficult to be determined. Several reports have described unsatisfied outcomes in a large percentage of patients with PTPS deficiency, despite early detection and treatment. Between 1988 and 2000, 12 newborns with PTPS deficiency identified by newborn screening were referred and received early treatment at our hospital. The mean IQ score of these 12 patients was 96.7 (±9.7; range: 86-119), which is considerably higher than previous reports of other populations of PTPS-deficient patients. In this report, we reviewed the disorders of BH4 briefly and then described treatments of our PTPS-deficient patients.

Experimental evidence that phenylalanine is strongly associated to oxidative stress in adolescents and adults with phenylketonuria

Few studies have looked at optimal or acceptable serum phenylalanine levels in later life in patients with phenylketonuria (PKU). This study examined the oxidative stress status of adolescents and adults with PKU. Forty PKU patients aged over fifteen years were enrolled, and were compared with thirty age-matched controls. Oxidative stress markers, anti-oxidant enzyme activities in erythrocytes, and blood anti-oxidant levels were examined. Nitric oxide (NO) production was also examined as a measure of oxidative stress. Plasma thiobarbituric acid reactive species and serum malondialdehyde-modified LDL levels were significantly higher in PKU patients than control subjects, and correlated significantly with serum phenylalanine level (P<0.01). Plasma total anti-oxidant reactivity levels were significantly lower in the patient group, and correlated negatively with phenylalanine level (P<0.001). Erythrocyte superoxide dismutase and catalase activities were higher and correlated significantly with phenylalanine level (P<0.01). Glutathione peroxidase activity was lower and correlated negatively with phenylalanine level (P<0.001). The oxidative stress score calculated from these six parameters was significantly higher in patients with serum phenylalanine of 700-800 μmol/l. Plasma anti-oxidant substances, beta-carotene, and coenzyme Q(10) were also lower (P<0.001), although the decreases did not correlate significantly with the phenylalanine level. Serum nitrite/nitrate levels, as stable NO products, were higher together with low serum asymmetric dimethylarginine, as an endogenous NO inhibitor. Oxidative stress status is closely linked with serum phenylalanine levels. Phenylalanine level in should be maintained PKU below 700-800 μmol/l even in adult patients.

Tackling frontal lobe-related functions in PKU through functional brain imaging: a Stroop task in adult patients

BACKGROUND

Profound mental retardation in phenylketonuria (PKU) can be prevented by a low phenylalanine (Phe) diet. However, even patients treated early have inconsistently shown deficits in several frontal lobe-related neuropsychological tasks such as the widely accepted Stroop task. The goal of this study was to investigate whether adult patients exhibit altered brain activation in Stroop-related locations in comparison to healthy controls and if an acute increase in blood Phe levels in patients has an effect on activation patterns.

METHODS

Seventeen male, early-treated patients with classic PKU (mean ± SD age: 31.0 ± 5.2 years) and 15 male healthy controls (32.1 ± 6.4 years) were compared using a color-word matching Stroop task in a functional magnetic resonance imaging (fMRI) study at 3T. Participants were scanned twice, and an oral Phe load (100 mg/kg body weight) was administered to patients prior to one of the fMRI sessions (placebo-controlled). Activity in brain regions that are known to be involved in Stroop tasks was assessed.

RESULTS

PKU patients exhibited poorer accuracy in incongruent trials. Reaction times were not significantly different. There were no consistent differences in BOLD activations in Stroop-associated brain regions. The oral Phe administration had no significant effect on brain activity.

CONCLUSIONS

Neither a generally slower task performance nor distinctively altered functioning of brain networks involved in a task representing a subset of dopamine-dependent executive functions could be proven. Decreased accuracy and inconsistent findings in posterior areas necessitate further study of frontal-lobe functioning in PKU patients in larger study samples.

Serum vitamin B12 concentrations within reference values do not exclude functional vitamin B12 deficiency in PKU patients of various ages

Homocysteine (Hcy) and in particular methylmalonic acid (MMA) are considered reliable parameters for vitamin B(12) status in healthy individuals. Phenylketonuria (PKU) patients are at risk for functional vitamin B(12) deficiency based on their diet.

OBJECTIVE

The aim of this study was to investigate the prevalence of functional vitamin B(12) deficiency in continuously treated PKU patients and the association of parameters of vitamin B(12) and metabolic control.

METHODS

In 75 continuously treated PKU patients of 1-37 years of age, serum vitamin B(12) concentrations, plasma Hcy, MMA, and phenylalanine concentrations were studied.

RESULTS

Eight patients had vitamin B(12) concentrations below normal. Out of these eight patients, two had elevated MMA and/or Hcy concentrations. Ten other patients with normal vitamin B(12) concentrations had elevated concentrations of MMA and/or Hcy.

CONCLUSIONS

A vitamin B(12) concentration within the reference range does not automatically imply a sufficient vitamin B(12) status. We recommend measuring serum MMA, or alternatively plasma Hcy, yearly in all PKU patients to diagnose functional vitamin B(12) deficiency.

Does a lower carbohydrate protein substitute impact on blood phenylalanine control, growth and appetite in children with PKU?

BACKGROUND

In children with phenylketonuria (PKU), it is possible that high carbohydrate protein substitutes may adversely affect blood phenylalanine control. We evaluated if a low carbohydrate, 'ready-to-drink' protein substitute would impact on short term blood phenylalanine control, weight and appetite in children with PKU aged 3-10 years.

METHODS

This was a 3-part, 5-week randomised, controlled, crossover study in which two different carbohydrate/protein-equivalent ratios in protein substitute [control protein substitute (CPS) median 1:1; trial protein substitute (TPS) 0.5:1] were compared. The effects on feeding behaviour, weight change and phenylalanine concentrations were studied. Fourteen children (12 boys; median age 6.3 y, range 3 to 9.7 y) with PKU on diet were recruited from 2 treatment centres.

RESULTS

Phenylalanine control did not deteriorate with TPS and remained unchanged between pre-study and CPS (p = 0.783). No statistical differences were noted in energy intake between the two study parts. Any changes in weight were similar between the two groups and there was limited change in feeding behaviour.

CONCLUSION

This study suggests that the carbohydrate/protein-equivalent ratio of protein substitutes can be reduced to 0.5:1 with no loss of blood phenylalanine control or adverse effect on weight gain in children with PKU.

Diurnal variations in blood phenylalanine of PKU infants under different feeding regimes

In phenylketonuria (PKU) patients, diurnal fluctuations of blood phenylalanine (Phe) are different from healthy individuals. Until now this pattern has been studied in PKU patients over one year of age.

OBJECTIVE

The aim of this observational study was to investigate diurnal patterns in PKU infants under one year of age receiving both the natural protein and Phe-free formula at the same time or in an alternating feeding scheme.

METHODS

In 7 PKU infants (aged 3-8 months), diurnal variations in blood Phe concentrations were recorded: on day A they received natural protein and Phe-free formula combined in each feeding; on day B they received these in an alternating feeding scheme. The number of feedings, total protein, and energy intake was similar on both study days. Blood samples were taken before each feeding.

RESULTS

The means (± SD) of the difference between the individual minimum and maximum blood Phe concentrations were 81(± 50) μmol/L and 104(± 26) μmol/L on days A and B, respectively (n.s.). Fifty and 30% of the samples were below target range for age (120 μmol/L), while only 3% and 6% were above target range (360 μmol/L) on days A and B respectively (n.s.).

CONCLUSION

Both feeding regimes, i.e. the natural protein and Phe-free formula combined in each feeding or alternating, resulted in comparable diurnal fluctuations of blood Phe concentrations.

Nutrition in phenylketonuria

The same basic principles are used to deliver dietary treatment in PKU that was developed sixty years ago. Dietary treatment is undoubtedly very successful, but it has gradually evolved and been guided commonly by individual experience and expert opinion only. There is little international consensus about dietary practice with improvements in specialist dietary products concentrating on taste and presentation rather than nutritional composition. Many areas of dietary treatment have not been rigorously examined. In particular, the amino acid and micronutrient profile of Phenylalanine-free (phe-free) amino acids requires further study. In different formulations of phe-free amino acids, there are variations in the amino acid patterns as well the amount of essential and non essential amino acids per 100g/amino acids. The amount of added tyrosine and branch chain amino varies substantially, and in PKU specifically, there is little data about their relative absorption rates and bioavailability. In phe-free amino acids, there is evidence suggesting that some of the added micronutrients may be excessive and so the source and amount of each micronutrient should be scrutinized, with a need for the development of international nutritional composition standards exclusively for these products. There is a dearth of data about the life-long phenylalanine tolerance of patients or the nutritional state of adult patients treated with diet. There is a growing need to measure body composition routinely in children with PKU and with the rise in childhood obesity, it is important to measure body fatness and identify those who are at greatest risk of 'co-morbidities' of obesity. There is necessity for international collaboration to ensure robust data is collected on many basic aspects of nutritional care to guarantee that diet therapy is delivered to the highest standard.

Cognitive, neurophysiological, neurological and psychosocial outcomes in early-treated PKU-patients: a start toward standardized outcome measurement across development

The aim of this paper is to provide a concise summary of findings from outcome studies in early-treated phenylketonuria (PKU). The paper should not be considered as an extensive review of the many different outcome measures that have been used in PKU-research, but as an attempt to integrate such findings so that they will be of additional value for day to day monitoring of PKU-patients and may direct future research to fill the present gaps of knowledge. Neurological, neuropsychological, neurophysiological, neuroimaging, quality of life, and psychosocial findings will be discussed in the context of their potential contributions to lifelong follow-up and treatment of PKU-patients being summarized in statements.

Whole body composition analysis by the BodPod air-displacement plethysmography method in children with phenylketonuria shows a higher body fat percentage

BACKGROUND

Phenylketonuria (PKU) causes irreversible central nervous system damage unless a phenylalanine (PHE) restricted diet with amino acid supplementation is maintained. To prevent growth retardation, a protein/amino acid intake beyond the recommended dietary protein allowance is mandatory. However, data regarding disease and/or diet related changes in body composition are inconclusive and retarded growth and/or adiposity is still reported. The BodPod whole body air-displacement plethysmography method is a fast, safe and accurate technique to measure body composition.

AIM

To gain more insight into the body composition of children with PKU.

METHODS

Patients diagnosed with PKU born between 1991 and 2001 were included. Patients were identified by neonatal screening and treated in our centre. Body composition was measured using the BodPod system (Life Measurement Incorporation©). Blood PHE values determined every 1-3 months in the year preceding BodPod analysis were collected. Patients were matched for gender and age with data of healthy control subjects. Independent samples t tests, Mann-Whitney and linear regression were used for statistical analysis.

RESULTS

The mean body fat percentage in patients with PKU (n = 20) was significantly higher compared to healthy controls (n = 20) (25.2% vs 18.4%; p = 0.002), especially in girls above 11 years of age (30.1% vs 21.5%; p = 0.027). Body fat percentage increased with rising body weight in patients with PKU only (R = 0.693, p = 0.001), but did not correlate with mean blood PHE level (R = 0.079, p = 0.740).

CONCLUSION

Our data show a higher body fat percentage in patients with PKU, especially in girls above 11 years of age.

Fatty acid profile in patients with phenylketonuria and its relationship with bone mineral density

BACKGROUND

Patients with phenylketonuria (PKU) undergo a restrictive vegan-like diet, with almost total absence of n-3 fatty acids, which have been proposed as potential contributors to bone formation in the healthy population. The PKU diet might lead these patients to bone mass loss and, consequently, to the development of osteopenia/osteoporosis. Therefore, we proposed to analyze their plasma fatty acid profile status and its relationship with bone health.

METHODS

We recruited 47 PKU patients for this cross-sectional study and divided the cohort into three age groups (6-10 years, 11-18 years, 19-42 years). We measured their plasma fatty acid profile and bone mineral density (BMD) (both at the femoral neck and the lumbar spine). Seventy-seven healthy controls also participated as reference values of plasma fatty acids.

RESULTS

Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) and total n-3 fatty acids were significantly diminished in PKU patients compared with healthy controls. DHA, EPA, and total n-3 fatty acids were also positively associated with bone mineral density (r = 0.83, p = 0.010; r = 0.57, p = 0.006; r = 0.73, p = 0.040, respectively). There was no association between phenylalanine (Phe), Index of Dietary Control (IDC), calcium, 25-hydroxivitamin D concentrations, daily calcium intake, and BMD.

CONCLUSION

Our results suggest a possible influence of essential fatty acids over BMD in PKU patients. The lack of essential n-3 fatty acids intake in the PKU diet might affect bone mineralization. Further clinical trials are needed to confirm the effect of the n-3 essential fatty acids on bone accrual in a cohort of PKU patients.

BH(4) therapy impacts the nutrition status and intake in children with phenylketonuria: 2-year follow-up

The impact of tetrahydrobiopterin (BH(4)) treatment on phenylalanine tolerance, medical-food consumption, and nutrition status in patients with phenylketonuria (PKU) was investigated. Six children (5-12 years) with well-controlled PKU, responding to a BH(4) dose of 20 mg/kg per day, were assessed for 24 months. Mean dietary phenylalanine tolerance increased from 421 ± 128 to 1470 ± 455 mg/day. Height Z scores significantly improved from 0.25 ± 0.99 at baseline to 0.53 ± 1.16 at 24 months (p for trend < 0.001). Patients tolerated more phenylalanine and more intact protein and required less medical food (protein supplement). Improved linear growth and nutrition status was seen over the course of the 24-month follow-up. Due to the variation in phenylalanine tolerance, dietary recommendations should be tailored to the patient's individual requirements.

Oligodendrocyte development and myelinogenesis are not impaired by high concentrations of phenylalanine or its metabolites

Phenylketonuria (PKU) is a metabolic genetic disease characterized by deficient phenylalanine hydroxylase (PAH) enzymatic activity. Brain hypomyelination has been reported in untreated patients, but its mechanism remains unclear. We therefore investigated the influence of phenylalanine (Phe), phenylpyruvate (PP), and phenylacetate (PA) on oligodendrocytes. We first showed in a mouse model of PKU that the number of oligodendrocytes is not different in corpus callosum sections from adult mutants or from control brains. Then, using enriched oligodendroglial cultures, we detected no cytotoxic effect of high concentrations of Phe, PP, or PA. Finally, we analyzed the impact of Phe, PP, and PA on the myelination process in myelinating cocultures using both an in vitro index of myelination, based on activation of the myelin basic protein (MBP) promoter, and the direct quantification of myelin sheaths by both optical measurement and a bioinformatics method. None of these parameters was affected by the increased levels of Phe or its derivatives. Taken together, our data demonstrate that high levels of Phe, such as in PKU, are unlikely to directly induce brain hypomyelination, suggesting involvement of alternative mechanisms in this myelination defect.

Animal models of brain dysfunction in phenylketonuria

Phenylketonuria (PKU) is a metabolic disorder that results in significant brain dysfunction if untreated. Although phenylalanine restricted diets instituted at birth have clearly improved PKU outcomes, neuropsychological deficits and neurological changes still represent substantial problems. The specific mechanisms by which Phe affects the brains of individuals with PKU are yet fully determined. The use of animal models in PKU research significantly broadens the possibilities for investigating these mechanisms. This report presents an overview of findings from animal studies on the mechanisms of Phe action in the PKU brain, discussing the importance of changes in protein synthesis, transport of large neutral amino acids across the blood-brain barrier, synthesis of monoamine neurotransmitters, activity of glutamate receptors, animal behavior, and translation of animal behavioral data to patients with PKU. This report shows that great progress has been made in past years and demonstrates the importance of further animal research to understand the neuropathological mechanisms underlying brain dysfunction in PKU. A better understanding of these mechanisms will guide the development of optimal treatment strategies for PKU.

Disruption of prefrontal function and connectivity in individuals with phenylketonuria

Phenylketonuria (PKU) is a genetic disorder associated with disruption of prefrontal cortex (PFC) development and executive dysfunction. To date, however, there is little evidence directly linking these two sequelae of PKU. We utilized functional magnetic resonance imaging (fMRI) to evaluate prefrontal functioning in six individuals with early-treated PKU (ETPKU) during performance of an n-back working memory task and compared results with those of six age- and gender-matched neurologically intact individuals. In addition, we evaluated the possible presence of PKU-related disruptions in functional connectivity, as might be hypothesized based on prior reports of white matter injury in individuals with ETPKU. A number of brain regions, nearly half of which were located in the PFC, were found to show atypical neural activity in individuals with ETPKU during working memory performance. We also found decreased connectivity both within the PFC as well as between the PFC and other brain regions in individuals with ETPKU compared with controls. Results from this preliminary study suggest that both prefrontal dysfunction and disruptions in functional connectivity may contribute to PKU-related executive impairment. In addition to advancing our understanding of PKU, the current findings have a broader impact in that PKU is regularly used as a model of early prefrontal dysfunction in the study of other neurodevelopmental disorders (e.g., autism).