[Bone mineral turnover and bone densitometry in patients with a high-risk diet: hyperphenylalaninemia and galactosemia]

INTRODUCTION

Patients with any type of congenital metabolism error are at risk for developing osteoporosis. To gain further insight into the physiopathology of this disease, we studied bone mineral turnover in 10 children with hyperphenylalaninemia, seven with phenylketonuria and six with galactosemia. Oral intake was strictly controlled and the children followed recommendations for physical exercise.

MATERIAL AND METHOD

Markers of bone resorption (hydroxyproline and pyridinoline in urine samples) and markers of bone formation (levels of osteocalcin and C-terminal procollagen peptide type I) were analyzed. Bone mineral density was analyzed by ultrasound densitometry.

RESULTS

A non-significant reduction in bone densitometry with respect to the normal population was observed. Bone mineral turnover was slightly diminished in patients with phenylketonuria but was within the normal range in patients with hyperphenylalaninemia and galactosemia.

CONCLUSION

Adequate control of dietary intake of both proteins and minerals, as well as a healthy lifestyle, can prevent the development of significant alterations in bone mineralization.

Impaired glutamatergic synaptic transmission in the PKU brain

This paper reviews recent results of our investigation of the mechanisms whereby hyperphenylalaninemia may cause brain dysfunction in classical phenylketonuria (PKU). Acute applications of L-Phe in rat and mouse hippocampal and cerebrocortical cultured neurons, at a range of concentrations found in PKU brain, significantly and reversibly depressed glutamatergic synaptic transmission by a combination of pre- and postsynaptic actions: (1) competition for the glycine-binding site of the N-methyl-D-aspartate (NMDA) receptors; (2) attenuation of neurotransmitter release; (3) competition for the glutamate-binding site of (RS)-amino-3-hydroxy-5-methyl-4-isoxazolepropioinic acid and kainate (AMPA/kainate) receptors. Unlike L-Phe, its non-tyrosine metabolites, phenylacetic acid, phenylpyruvic acid, and phenyllactic acid, did not produce antiglutamatergic effects. L-Phe did not affect inhibitory gamma-aminobutyric (GABA)-ergic transmission. Consistent with this specific pattern of effects caused by L-Phe in neuronal cultures, the expression of NMDA receptor NR2A and AMPA receptor Glu1 and Glu2/3 subunits in brain of hyperphenylalaninemic PKU mice (Pah(enu2) strain) was significantly increased, whereas expression of the NMDA receptor NR2B subunit was decreased. There was no change in GABA alpha1 subunit expression. Considering the important role of glutamatergic synaptic transmission in normal brain development and function, these L-Phe-induced changes in glutamatergic synaptic transmission in PKU brain may be a critical element of the neurological symptoms of PKU.

Use of handheld computers for assessment of prefrontal cortex function in patients with phenylketonuria

Assessment of prefrontal brain cortex function can be helpful in treatment monitoring in patients with phenylketonuria. We aimed to assess the usefulness of computerized neuropsychological tests developed for handheld computers for this purpose. We observed worse test performance among persons with blood phenylalanine concentrations exceeding the recommended range. Use of handheld computers was assessed by patients and by doctors as interesting, not time-consuming and convenient. This method can be helpful during routine follow-up visits.

Genetically rescued tetrahydrobiopterin-depleted mice survive with hyperphenylalaninemia and region-specific monoaminergic abnormalities

One of the possibly mutated genes in DOPA-responsive dystonia (DRD, Segawa's disease) is the gene encoding GTP cyclohydrolase I, which is the rate-limiting enzyme for tetrahydrobiopterin (BH4) biosynthesis. Based on our findings on 6-pyruvoyltetrahydropterin synthase (PTS) gene-disrupted (Pts(-/-)) mice, we suggested that the amount of tyrosine hydroxylase (TH) protein in dopaminergic nerve terminals is regulated by the intracellular concentration of BH4. In this present work, we rescued Pts(-/-) mice by transgenic introduction of human PTS cDNA under the control of the dopamine beta-hydroxylase promoter to examine regional differences in the sensitivity of dopaminergic neurons to BH4-insufficiency. The DPS-rescued (Pts(-/-), DPS) mice showed severe hyperphenylalaninemia. Human PTS was efficiently expressed in noradrenergic regions but only in a small number of dopaminergic neurons. Biopterin and dopamine contents, and TH activity in the striatum were poorly restored compared with those in the midbrain. TH-immunoreactivity in the lateral region of the striatum was far weaker than that in the medial region or in the nucleus accumbens. We concluded that dopaminergic nerve terminals projecting to the lateral region of the striatum are the most sensitive to BH4-insufficiency. Biochemical and pathological changes in DPS-rescued mice were similar to those in human malignant hyperphenylalaninemia and DRD.

MR imaging-based volumetry in patients with early-treated phenylketonuria

BACKGROUND AND PURPOSE

Our purpose was to specify the most severely affected brain structures in early treated phenylketonuria regarding volume loss and establish possible correlations between volume loss and plasma levels of phenylalanine (Phe).

METHODS

In 31 patients with early treated phenylketonuria and in 27 healthy volunteers, we acquired volumetric MR imaging data. Serum Phe concentrations at different times were measured as well. Semiautomatic volumetric postprocessing of the cerebellum, cerebrum (supratentorial brain tissue), hippocampus, intracranial volume, lateral ventricles, nucleus caudatus, nucleus lentiformis, pons, and thalamus, as well as the two-dimensional extension of the corpus callosum, was performed using the software BRAINS2. For each separate brain structure, the relative differences between the normal and the phenylketonuria group (delta(rel)) were calculated.

RESULTS

The cerebrum, corpus callosum, hippocampus, intracranial volume, and pons were significantly smaller in patients with phenylketonuria than in healthy patients. The volume of the lateral ventricles was significantly larger in patients with phenylketonuria than in healthy ones. The most severely affected structures were the pons (delta(rel) = 16%), hippocampus (delta(rel) = 14.5%), cerebrum (delta(rel) = 13%), and corpus callosum (delta(rel) = 10%). No significant differences were found for the basal ganglia, cerebellum, and thalamus. There were no significant correlations found between the volume of any of the different brain structures and the metabolic parameters.

CONCLUSION

The most severely affected brain structures in early-treated patients with phenylketonuria regarding volume loss are the cerebrum, corpus callosum, hippocampus, and pons.

Characterization of tremor in phenylketonuric patients

Tremor of unknown origin is detected in 10-30% of early-treated and in more than 30% late-treated phenylketonuric patients. With the aim of characterizing tremor in phenylketonuria, we carried out a systematic study in 54 patients aged 6 to 37 years. Tremor examination was done by applying the WHIGET Tremor Rating Scale and by accelerometer recording (BYOPAC System MP100WSW). Age at diet onset, IQ test results, concomitant plasma phenylalanine levels and index of dietary control were also studied. Tremor was not observed at rest in any case, but was apparent in 22 patients (40.7%) when carrying out a kinetic task. In 15 patients tremor was also evident during maintenance of a postural task at a frequency ranging between 7.5 and 12.7 Hz. Frequency of tremor was not significantly modified by loading the arms or by increasing muscle contraction. Patients with tremor had a later age at onset of phenylalanine restricted diet (p < 0.001). Other treatment-related variables did not differ between patients with and without tremor. Our results of the neurophysiological examination suggest that tremor in phenylketonuric patients is dependent on a dysfunction of central nervous system networks and may be an index of cerebral damage.

Altered expression of myocilin in the brain of a mouse model for phenylketonuria (PKU)

Phenylketonuria (PKU) is an inborn error of amino acid metabolism. Phenylalanine hydroxylase (PAH) mutations resulting reduced enzyme levels lead to accumulation of phenylalanine (Phe) in brain, if Phe diet is not restricted. Patients with PKU show neurophysiological abnormalities including demyelination and cognitive defect. How PAH defect causes events seen in PKU is not obvious. Therefore, expression analysis was performed in the brain of a mouse model for PKU. Microarray expression profile of the brain showed lower expression of myocilin (Myoc) in the PKU mouse. Reduced expression of Myoc was further confirmed by one-step real-time RT-PCR. Western blotting analysis of the brain using equal quantities of protein showed a thin band in PKU compared to a prominent band in the wild type brain. In addition, expression of genes associated with transcription was found to be altered in the PKU mouse brain as observed by microarray analysis. These data suggest that PAH defect alters other genes expression likely to contribute neurophysiological abnormalities seen in the mouse, if documented also in patients with PKU.

Cognitive functions in classic phenylketonuria and mild hyperphenylalaninaemia: experience in a paediatric population

A study of 37 individuals with phenylketonuria (PKU; 17 females and 20 males, mean age 9y 9mo (standard deviation [SD] 5y 3mo), range 2y 8mo to 19y 4mo; and 35 individuals with hyperphenylalaninaemia (HPA; 20 females, 15 males, mean age 7y 10mo [SD 3y 2mo], range 2y 8mo to 17y 3mo) compared with 29 healthy controls (14 females and 15 males, mean age 9y 8mo [SD 4y 9mo], range 2y 6mo to 18y 10mo) was performed. The aim was to assess cognitive function in persons with HPA and to investigate the relation between cognitive function in PKU and the metabolic control of patients. A wide variety of neuropsychological tests was employed. Those with PKU showed lower values in intelligence and in visuo-spatial, fine motor, executive, and attention functions when compared with a control population. Plasma phenylalanine values from the first 6 years of life were negatively associated with intelligence and other cognitive functions. Executive function scores were significantly lower when comparing HPA patients with the control group. It was concluded that individuals with PKU under dietary treatment may present slightly decreased cognitive function scores when compared with control individuals, while those with HPA have scores mostly similar to those of controls, except for executive function tests. Good metabolic control of PKU seems necessary to prevent cognitive function impairments, especially during the first 6 years of life.

Executive functioning, memory, and learning in phenylketonuria

The executive deficit hypothesis of treated phenylketonuria (PKU) suggests that dopaminergic depletion in the lateral prefrontal cortex leads to selective executive impairment. This was examined by comparing adults with PKU on a lifelong diet with a matched healthy control group. Those with PKU were impaired on selective and sustained attention, working memory (Self-Ordered Pointing), and letter fluency. However, they failed to show differential sensitivity to increased cognitive load on the attentional and working memory tasks, and they did not differ significantly on the remaining executive tasks (rule finding, inhibition, and multitasking). Nor did they differ significantly on recall or recognition memory. Overall, the findings provided little support for the executive deficit hypothesis. A possible explanation in terms of slowed information processing speed is explored.

Long-term changes in glutamatergic synaptic transmission in phenylketonuria

The cellular mechanisms that underlie impaired brain function during phenylketonuria (PKU), the most common biochemical cause of mental retardation in humans, remain unclear. Acute application of L-Phe at concentrations observed in the PKU brain depresses glutamatergic synaptic transmission but does not affect GABA receptor activity in cultured neurons. If these depressant effects of L-Phe take place in the PKU brain, then chronic impairment of the glutamate system, which may contribute to impaired brain function, could be detected as changes in postsynaptic glutamate receptors. This hypothesis was tested by using a combination of liquid chromatography-mass spectrometry, patch-clamp, radioligand binding and western blot approaches in forebrain tissue from heterozygous and homozygous (PKU) Pah(enu2) mice. Brain concentrations of L-Phe were nearly six-fold greater in PKU mice (863.12 +/- 17.96 micromol/kg) than in their heterozygous counterparts (149.32 +/- 10.23 micromol/kg). This concentration is significantly higher than the K(B) of 573 microM for L-Phe to compete for N-methyl-D-aspartate (NMDA) receptors. Receptor binding experiments with [3H]MK-801 showed significant up-regulation of NMDA receptor density in PKU mice. Consistent with the depressant effects of L-Phe, expression of NMDA receptor NR2A and (RS)-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor Glu1 and Glu2/3 subunits was significantly increased, whereas expression of the NR2B subunit was decreased. There was no change in GABA alpha1 subunit expression. Given the role of the glutamatergic system in brain development and function, these changes may, at least in part, explain the brain disorders associated with PKU.

Frontal lobe-dependent functions in treated phenylketonuria: blood phenylalanine concentrations and long-term deficits in adolescents and young adults

Even early-treated phenylketonurics may suffer from phenylalanine-related deficits. Elevated phenylalanine concentrations can interfere with the development and function of the CNS. Outcome beyond childhood has not been extensively investigated. This long-term study was performed to determine whether adolescents and young adults with PKU show frontal lobe-dependent deficits when compared to diabetic patients. The comparative study covered 35 PKU patients, 13-21 years of age (mean 17.8 years), and 35 diabetic patients matched for sex, age and socioeconomic status. Patients were assessed for IQ (Culture Fair Intelligence Test), information processing (Trail Making Test), and selective and sustained attention (Stroop Task, Test d-2). Assessments were repeated within a 3-year follow-up. PKU patients showed no increase in blood phenylalanine concentrations at follow-up. They had significantly poorer test results than the diabetic patients at both assessment times. Within the tests, however, this was due to reduced performance speed but not to deficits in specific frontal lobe-dependent functions. Elevated phenylalanine concentrations seem to exert a global effect slowing performance speed. This effect is enduring in adolescence and early adulthood.

[Pathogenetic mechanisms in phenylketonuria: disorders affecting the metabolism of neurotransmitters and the antioxidant system]

AIM

To review the clinical and biochemical changes in neurotransmission and antioxidant system in phenylketonuric patients under dietary treatment.

DEVELOPMENT

Phenylketonuria (PKU) is an inborn error of metabolism caused by decreased activity of the enzyme L-phenylalanine-4-mono-oxigenase that synthesizes tyrosine from phenylalanine. According to analytical data from PKU patients and to experimental studies in animal models, high phenylalanine values in plasma and tissues seem to be related with defective biosynthesis of neurotransmitter (mainly serotonin and dopamine) and impairment of antioxidant system. Despite dietary treatment, PKU patients usually present moderate hyperphenylalaninemia over the evolution of the disease that might cause clinical and biochemical abnormalities.

CONCLUSIONS

Increased plasma phenylalanine concentrations and dietary treatment might be related with neurotransmitter and antioxidant system abnormalities in human phenylketonuria. These biochemical alterations might be involved in the physiopathology of PKU.

A preliminary report on dopamine system reactivity in PKU: acute effects of haloperidol on neuropsychological, physiological, and neuroendocrine functions

BACKGROUND

Classic phenylketonuria (PKU) is due to an inborn error of metabolism resulting in an inability to metabolize the amino acid phenylalanine. To avoid mental retardation, affected individuals observe a phenylalanine-restricted diet. When dietary control is poor, deficits in prefrontally mediated cognitive functions have been observed. It has been suggested that these deficits are due to disruptions in the mesocortical dopamine system that projects to the prefrontal cortex.

METHODS

In this study, dopamine system reactivity was examined in individuals with PKU, relative to age-matched controls, using the non-specific DA antagonist haloperidol, in a repeated measures placebo-controlled design. Outcome variables included neuroendocrine, physiological, and cognitive measures.

RESULTS

Regardless of drug condition, PKU participants differed from control participants in their blood phenylalanine and tyrosine levels, and in their times to complete measures of attention and working memory. Also, relative to placebo, haloperidol influenced several variables irrespective of group status, including serum prolactin secretion, times to complete attention and working memory tasks, and accuracy of working memory performance. An interaction between group and drug condition was observed for the digit span task, where PKU participants exhibited greater relative impairments on haloperidol. When composite indices of impairment were derived, PKU participants demonstrated selective disruption in executive function on haloperidol relative to control subjects.

CONCLUSIONS

Findings are consistent with the presence of frontostriatal dysfunction in PKU but are less consistent with the notion that PFC dopamine function is specifically affected.

Funções executivas em crianças fenilcetonúricas: variações em relação ao nível de fenilalanina

Este estudo investiga a hipótese de um déficit específico das funções executivas em crianças com fenilcetonúria (PKU) cujo nível de fenilalanina encontra-se entre 360 e 600 mmol/l. Participaram do estudo 21 crianças fenilcetonúricas de nove meses de idade, tratadas precoce e continuamente, e 18 crianças normais de mesma idade. As crianças com PKU foram divididas em dois grupos em função do nível médio de fenilalanina antes do estudo: o grupo de crianças cujo nível encontrava-se entre 120 e 360 mmol/l e o grupo de crianças cujo nível encontrava-se entre 360 e 600 mmol/l. Embora os três grupos de crianças tenham apresentado desempenho semelhante em um teste que avalia o desenvolvimento mental global, as crianças com alto nível de fenilalanina apresentaram desempenho significativamente pior do que as demais crianças em um teste que avalia as funções executivas.

Neuropsychological functioning in children with early-treated phenylketonuria: impact of white matter abnormalities

Impact of white matter abnormalities (WMAs) on neuropsychological functioning in children with early-treated phenylketonuria (ETPKU) was examined. Children with ETPKU (20 males, 12 females, mean age 11 years 2 months, SD 3 years 6 months) and controls (20 males, 14 females, mean age 10 years 4 months, SD 3 years 1 month) aged 7 to 18 years were assessed using tests of attention, processing speed, memory and learning, executive function, and academic achievement. Those with ETPKU, exhibiting WMAs extending into subcortical/frontal regions (n=14), displayed significant impairments in a number of domains. Children with ETPKU but no WMAs (n=6), or pathology restricted to the posterior periventricular region (n=12), displayed only mild deficits. Concurrent phenylalanine levels correlated weakly with cognitive parameters, whereas lifetime phenylalanine levels were associated with deficits in several cognitive domains. Impairments in children with extensive WMAs are consistent with compromised neural transmission, which is characterized by dysmyelination. However, children with no detectable, or mild WMAs, also displayed cognitive problems, indicating that neuropsychological functioning in children with ETPKU is determined by a complex interaction of biological and environmental factors.

Executive function impairment in early-treated PKU subjects with normal mental development

Executive functions were studied in 14 early and continuously treated PKU subjects (age 10.8 years, range 8-13) in comparison with controls matched for IQ, sex, age and socioeconomic status. Brain MRI examination was normal in all PKU patients. Neuropsychological evaluation included Wisconsin Card Sorting Test, Rey-Osterreith Complex Figure Test, Elithorn's Perceptual Maze Test, Weigl's Sorting Test, Tower of London, Visual Search and Motor Motor Learning Test. Whatever the IQ, PKU subjects performed worse than controls in tests exploring executive functions. Subgrouping the PKU subjects according to the quality of dietary control for the entire follow-up period (using 400 micromol/L as cut-off value for blood phenylalanine (Phe) concentration) showed that patients with worse dietary control performed more poorly than both the PKU group with the best dietary control and the control group. However, a mild impairment of executive functions was still found in PKU patients with a good dietary control (Phe <400 micromol/L) compared to controls. Concerning the PKU group as a whole, no linear correlation was found between neuropsychological performance and historical and concurrent biochemical parameters. We conclude that (a) PKU patients, even when treated early, rigorously and continuously, show an impairment of frontal lobe functions; (b) a protracted exposure to moderately high levels of Phe can affect frontal lobe functions independently of the possible effect of the same exposure on IQ; (c) in order to reduce the risk of frontal lobe dysfunction, the target of dietary therapy should be to maintain blood Phe concentration below 400 micromol/L.

High levels of orexin A in the brain of the mouse model for phenylketonuria: possible role of orexin A in hyperactivity seen in children with PKU

Phenylketonuria (PKU) is a metabolic disorder caused by phenylalanine hydroxylase deficiency leading to increased levels of phenylalanine in the brain. Hyperactivity is reportedly induced by a high level of orexin A, and therefore orexin A content was studied in the PKU mice. Hypothalamus and brain stem had higher levels of orexin A compared to cerebrum and cerebellum both in wild type and PKU mice brains as observed by radioimmunoassay method. Interestingly, all these regions of the brain in PKU mouse showed a higher level of orexin A compared to the wild type. Heart and plasma also had higher levels of orexin A in PKU compared to the wild type. Immunohistochemical analysis revealed an increased number of orexin A-stained cells in the brain and heart of PKU mouse compared to the wild type. This is the first report of increased level of orexin in the PKU mouse brain. Hyperactivity is commonly observed in children with PKU; thus these findings suggest that orexin A is a contributing factor for the hyperactivity.

Nutrient intakes and physical growth of children with phenylketonuria undergoing nutrition therapy

OBJECTIVE

To evaluate nutrient intakes, plasma phenylalanine (PHE) and tyrosine (TYR) concentrations, and physical growth of children with phenylketonuria undergoing nutrition management.

DESIGN

Children were fed three different medical foods during a one-year study. Subjects/setting Children were evaluated at baseline and every three months in metabolic clinics. Children's diets were managed at home. Statistical analyses Intakes of medical foods and nutrients, number of diaries with nutrients <67% and <100% of Recommended Dietary Intakes (RDI), and mean plasma PHE and TYR concentrations were compared among groups using two-way ANOVA. chi-squared test compared the percentage of plasma PHE and TYR concentrations in each group in specific categories. Height and body mass index were plotted against National Center for Health Statistics reference data; means were compared among groups. Tukey's test compared groups with significant treatment effects.

RESULTS

Mean intakes of nutrients, except energy by all groups and vitamin B-12 by the Periflex-fed group, met or exceeded RDIs. The oldest children tended to have the highest PHE intakes and plasma PHE concentrations. Mean length or height z score indicated normal linear growth. Mean body mass index z scores at study end suggested many children were overweight.

APPLICATIONS

Dietitians should prescribe adequate medical food and encourage children with phenylketonuria to ingest all prescribed daily. Linear growth of children, where mean protein equivalent intakes ranged from 113% to 129% of RDI, was normal, demonstrating the need for a protein intake greater than RDIs when an elemental diet is the primary protein source. Dietitians should prescribe and carefully monitor energy intake, physical activity, and weight.

Timing is everything: executive functions in children exposed to elevated levels of phenylalanine

This study addresses how the timing of a known biological insult affects the developmental progression of executive functions. The sample consisted of children exposed to elevated levels of phenylalanine, either postnatally, as in phenylketonuria (PKU; n = 46), or prenatally, as in maternal PKU (n = 15). Nonhyperphenylanemic siblings of children with PKU (n = 18) served as controls. Results indicated that elevated levels of phenylalanine are toxic to the neurological systems that manage executive functions and cognitive tempo. This toxicity is dose dependent, with higher levels of phenylalanine being more detrimental. Executive function difficulties noted in PKU are consistent with attention deficit hyperactivity disorder (ADHD)-inattentive type, whereas maternal PKU offspring had executive function difficulties consistent with ADHD-combined type.

Long term effects of long chain polyunsaturated fats in hyperphenylalaninemic children

Blood fatty acid status and visual function of 20 treated hyperphenylalaninemic (HPA) children, randomly allocated into two groups to receive supplementation of either long chain polyunsaturated fatty acids (LCPUFA), including docosahexaenoic acid (DHA), or placebo for 12 months, have been investigated three years after the end of the treatment. Although in the LCPUFA group blood DHA levels and P100 wave latency improved at the end of supplementation, they had returned to baseline after three years.

Glucose-lowering effect of beta-phenylpyruvate in neonatal mice: a possible mechanism for phenylketonuria-related neurodegenerative changes

Following beta-phenylpyruvate injection, mice developed hypoglycemia clinically manifested as tachypnea, tremor, convulsions and death. To further investigate, neonatal mice were injected with beta-phenylpyruvate and their blood glucose determined and brain histology assessed. beta-Phenylpyruvate-injected mice exhibited higher mortality and neurophysiological changes as compared with controls, although without evidence of neural cell death. Accordingly, we hypothesize that the central neural damage in phenylketonuria might be caused by these recurrent beta-phenylpyruvate-induced hypoglycemic events.

[Markers of bone formation and resorption in prepubertal children with phenylketonuria]

Biochemical bone markers are a valuable noninvasive tool useful in the management of metabolic bone diseases. Phenylketonuria (PKU) is a disorder in which dietary phenylalanine restriction is the only known therapy for the prevention of mental impairment in patients. This kind of diet may influence the bone metabolism, especially in childhood and adolescence, when growth and bone turnover are most intensive. Some authors have described in patients with phenylketonuria reduced mineralization and other abnormalities of bone tissue. We measured osteocalcin and bone alkaline phosphatase (formation markers) and collagen type I crosslinked C-telopeptide (resorption marker) in 33 prepubertal children with PKU and in 65 prepubertal healthy children. Significantly lower serum osteocalcin concentration (83.9 +/- 32.9 ng/mL) in PKU patients than in control group (103.2 +/- 17.0 ng/mL) (p<0.01) was observed. Activity of serum bone alkaline phosphatase was similar in both studied groups. Serum concentration of collagen type I crosslinked C-telopeptide was significantly lower in PKU patients than in healthy children and amounted to 12790 +/- 4332 pmol/L and 16190 +/- 2815 pmol/L, respectively (p<0.001). Further studies of the bone mineral density and metabolism in prepubertal children with PKU are needed in order to prevent osteopenia and osteoporosis in adult patients.