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).

Psychosocial issues and outcomes in maternal PKU

Elevated phenylalanine (Phe) levels in pregnant women with PKU are teratogenic. Fetal damage due to elevated maternal Phe levels during pregnancy is known as maternal phenylketonuria (MPKU). The risk of birth defects in MPKU, including global developmental delays, microcephaly, congenital heart disease, and low birth weight, can be dramatically reduced by controlling Phe levels during pregnancy (metabolic control). Phe levels should be maintained in the range of 120-360 micromol/L, ideally starting before pregnancy begins (i.e., when planning a pregnancy). If control is not achieved before pregnancy (e.g., if the pregnancy was unplanned), good outcomes are still possible if metabolic control is established by 8 weeks of pregnancy. Unfortunately, metabolic control before and during pregnancy can be poor. As well, many mothers stop treatment after pregnancy, which can decrease the mother's ability to focus on her child and increase her risk of behavioral and psychological problems. This can have a negative effect on the home environment. Many factors affect adherence to the strict diet used to control Phe levels, including poor access to medical care, lack of reimbursement for medical foods (in some regions, such as parts of the United States), practical difficulties with implementing the diet, financial constraints, demographics, and psychosocial issues. A comprehensive treatment approach that begins prior to pregnancy and continues after the infant is born may help to improve the management of MPKU. This approach should include education of girls about MPKU at an early age, interventions to prevent unplanned pregnancies, psychosocial support, improved treatment access and reimbursement for medical foods, and treatment guidelines. Treatments such as sapropterin may also have a role in improving metabolic control during pregnancy.

Event-related potential correlates of selective processing in early- and continuously-treated children with phenylketonuria: effects of concurrent phenylalanine level and dietary control

This study focused on important characteristics of attentional (selective) processing in children with early-treated phenylketonuria (PKU). Seven to 14-year-old children with PKU were allocated to high phenylalanine (Phe) and low Phe groups and compared with control children on amplitudes and latencies of early and late event-related potential (ERP) components elicited during a selective processing task. These components are thought to measure early sensory processes (stimulus encoding/perception) and later selection processes (target detection). The effects of concurrent Phe level and dietary control on brain activity and behavioural performance were studied. Results showed that children with PKU with high Phe levels were less accurate and made more false alarms than controls and children with PKU with low Phe levels. Both children with PKU and controls displayed the expected early fronto-central selection negativity and a late positive peak over posterior sites associated with sensory aspects of the selective attention task. However, in contrast with controls, children with PKU showed an absence of condition differences for selection positivity over anterior sites associated with target detection. Negative and positive selection potentials over fronto-central sites were dependent on concurrent and historical Phe levels, whereas sensory potentials depended more strongly on historical Phe levels. It is concluded that both sensory and selection aspects of attention are affected by Phe levels. The relative predictive strength of historical Phe levels suggests that high Phe levels during sensitive periods for brain maturation may have long-lasting influences on selective attention.

Beyond executive function: non-executive cognitive abilities in individuals with PKU

Individuals with early-treated phenylketonuria (ETPKU) most often present with impairment in executive function (EF) and average intelligence compared to the general population. The topic of this review, which is less often discussed, is non-EF impairments that may be associated with ETPKU. Studies that have included assessment of non-EF cognitive functions such as information processing speed, fine motor skills, and perception and visual-spatial abilities suggest that individuals with ETPKU are compromised in these areas. Those assessing non-EF cognitive functions of language skills, long-term memory, and learning skills have yielded mixed results, with some suggesting impairment and others suggesting intact abilities. Although more studies are required, research to date suggests that mechanisms for non-EF deficits may include prefrontal cortex dopamine deficiency and/or white matter abnormalities related to elevated blood phenylalanine levels. For individuals with ETPKU to reach their full potential in life, it is vital to address the challenges associated with EF and non-EF deficits by identifying impairments and appropriate treatment strategies.

Reassessment of phenylalanine tolerance in adults with phenylketonuria is needed as body mass changes

Lifelong treatment of phenylketonuria (PKU) includes a phenylalanine (phe) restricted diet that provides sufficient phe for growth and maintenance plus phe-free amino acid formula to meet requirements for protein, energy and micronutrients. Phe tolerance (mg phe/kg body weight/day) is the amount of phe those with PKU can consume and maintain acceptable blood phe levels; it requires individual assessment because of varying phenylalanine hydroxylase activity. The objective was to reassess phe tolerance in eight adults with PKU considering phe requirements, blood phe levels, genotype and phe tolerance at 5 years of age. Subjects had not received a personalized assessment of phe tolerance in several years, and five subjects were overweight, body mass index (BMI) 25-28. With the guidance of a metabolic dietitian, seven subjects increased phe tolerance (by 15-173%) without significantly increasing blood phe concentration. Increased phe tolerance was associated with both improved dietary compliance and inadequate phe intake at the onset of the protocol compared with current requirements. Improved dietary compliance reflected increased consumption of protein equivalents from amino acid formula and increased frequency of formula intake, from 2.2 to 3 times per day. Predictors of higher final phe tolerance following reassessment included being male and having a lower BMI (R(2)=0.588). This suggests that the rising trend of overweight and obesity may affect assessment of phe tolerance in adults. Therefore, interaction with the metabolic dietitian to reassess phe tolerance in relation to body mass is essential throughout adulthood to insure adequate intake of phe to support protein synthesis and prevent catabolism.

Remarkable differences: the course of life of young adults with galactosaemia and PKU

Although the need for insight in factors influencing the quality of life of patients with an inborn error of metabolism is recognized, psychological adjustment of adults with metabolic diseases has not been properly studied. Adult patients with PKU were demonstrated not to differ from healthy controls in terms of their course of life (CoL) and health-related quality of life (HRQoL). However, adults with galactosaemia had a lower HRQoL with significant lower scores on the domains of cognitive and social function. This study investigated the CoL and the social demographical outcomes in these young adults with galactosaemia, and compared them with the general population and with PKU patients. A total of 15 (88%) adult patients with classical galactosaemia participated in this study. Classical galactosaemia patients had a delayed social and psychosexual development compared to their peers from the general population and to PKU patients. Also, they were significantly less frequently married or living together and significantly less frequently employed than the general population. Our study shows a stark contrast between patients with galactosaemia and patients with PKU, although both are diagnosed in the neonatal period and need life-long dietary restrictions. The observed difference is likely due to the long-term somatic complications frequently seen in galactosaemia and thus not due to the burden of a chronic disease necessitating life-long dietary restrictions. We conclude that it is essential that parents and clinicians encourage children with galactosaemia to participate in peer-related activities in order to stimulate social performance, which may result in a more normal CoL.

Mutation analysis of phenylketonuria patients from Morocco: high prevalence of mutation G352fsdelG and detection of a novel mutation p.K85X

OBJECTIVE

The knowledge of the molecular basis of the Phenylketonuria (PKU, MIM# 261600) in different countries provides relevant information for undertaking specific and rational mutation detection strategies in each population and for the implementation of adequate dietary and cofactor treatment. There are no data available in Moroccan population.

DESIGN AND METHODS

In this work we describe the genetic analysis by mutation scanning using denaturing gradient gel electrophoresis (DGGE) and subsequent direct sequencing of 20 different PKU families from Morocco. We have also included the study of 7 Moroccan PKU patients living in Spain detected by the Spanish newborn screening program.

RESULTS

The mutational spectrum in the first sample included eight different changes, one of them, p.K85X, was novel. The most common mutation was the frame shift change p.G352fsdelG identified in 62.5% of the mutant chromosomes studied. Other changes (p.R176X, IVS10nt-11 g>a, p.W120X, p.A165T, p.R243X and p.R243Q) were identified, respectively, in 2 or 3 mutant alleles. All detected mutations were severe according to the classical phenotype of the patients. In the 7 patients living in Spain we have detected 4 severe mutations (p.G352fs, p.R176X, Y198fs and Exon3del) and also milder changes such as p.A403V, p.S196T, p.D145V and p.R408Q detected in 3 mild hyperphenylalaninemia (MHP) patients and a novel p.L258P found in a mild PKU patient.

CONCLUSION

The results provide important information on the distribution of PKU mutations in this Mediterranean area gaining insight into the genetic epidemiology of the disease.

Sapropterin: a new therapeutic agent for phenylketonuria

OBJECTIVE

To summarize the role of pharmacotherapy in the management of phenylketonuria (PKU) and to review the pharmacology, pharmacokinetics, pharmacodynamics, efficacy data, and safety profile of sapropterin for this indication.

DATA SOURCES

A literature search was conducted using MEDLINE (1966-May 2009), International Pharmaceutical Abstracts (1970-May 2009), and Cochrane database (2008) for the following key words: sapropterin, tetrahydrobiopterin, phenylketonurias, and phenylalanine.

STUDY SELECTION AND DATA EXTRACTION

English-language studies involving humans examining the role of tetrahydrobiopterin (BH4) in the management of PKU were reviewed to evaluate the pharmacology, pharmacokinetics, pharmacodynamics, efficacy data, and safety profile for sapropterin. All Phase 2 and 3 randomized controlled trials assessing the safety and efficacy of sapropterin were included in this literature evaluation.

DATA SYNTHESIS

Sapropterin represents the only Food and Drug Administration-approved medication for BH4-responsive PKU, marking an important advance in the treatment of this condition. Among individuals with hyperphenylalaninemia and some residual phenylalanine hydroxylase function, sapropterin can enhance activity of this enzyme to decrease serum phenylalanine concentrations. Sapropterin has been compared with placebo in one Phase 2 and one Phase 3 clinical trial, demonstrating significantly better response rates. Based on available studies, this agent appears to be safe and well tolerated, with adverse event rates similar to those of placebo. However, additional studies are warranted to assess the long-term safety and efficacy of sapropterin therapy.

CONCLUSIONS

Sapropterin offers a promising therapeutic option for select individuals with BH4-responsive PKU, although long-term data are limited evaluating its safety and efficacy in traditional clinical practice settings. When considering sapropterin therapy, clinicians must consider factors such as cost and patient adherence to drug therapy and/or diet.

Does dietary DHA improve neural function in children? Observations in phenylketonuria

Children with phenylketonuria (PKU) have a restricted protein intake and thus low dietary intakes of long-chain polyunsaturated fatty acids (LC-PUFA), which may cause subtle neurological deficits. We measured plasma phospholipid fatty acids and visual evoked potential (VEP) in 36 children with well-controlled PKU (6.3+/-0.6 years, 19 girls), before and after 3 months of supplementing fish oil capsules providing 15 mg docosahexaenoic acid (DHA)/kg daily. The motometric Rostock-Oseretzky Scale (ROS) was performed before and after supplementation in the 24 PKU children aged >4 years. VEP latencies and ROS were also assessed in omnivorous, age-matched controls without fish oil supply at baseline and after 3 months. Fish oil supply increased plasma phospholipid eicosapentaenoic acid (EPA) (0.40+/-0.03 vs 3.31+/-0.19%, p<0.001) and DHA (2.37+/-0.10 vs 7.05+/-0.24%, p<0.001), but decreased arachidonic acid (AA) (9.26+/-0.23 vs 6.76+/-0.16%, p<0.001). Plasma phenylalanine was unchanged. VEP latencies and ROS results significantly improved after fish oil in PKU children, but remained unchanged in controls. The improvements of VEP latencies, fine motor and coordination skills indicate that preformed n-3 LC-PUFA are needed for neural normalcy in PKU children. The optimal type and dose of supply still needs to be determined. Since PKU children are generally healthy and have normal energy and fatty acid metabolism, these data lead us to conclude that childhood populations in general require preformed n-3 LC-PUFA to achieve optimal neurological function.

Brain dysfunction in phenylketonuria: is phenylalanine toxicity the only possible cause?

In phenylketonuria, mental retardation is prevented by a diet that severely restricts natural protein and is supplemented with a phenylalanine-free amino acid mixture. The result is an almost normal outcome, although some neuropsychological disturbances remain. The pathology underlying cognitive dysfunction in phenylketonuria is unknown, although it is clear that the high plasma concentrations of phenylalanine influence the blood-brain barrier transport of large neutral amino acids. The high plasma phenylalanine concentrations increase phenylalanine entry into brain and restrict the entry of other large neutral amino acids. In the literature, emphasis has been on high brain phenylalanine as the pathological substrate that causes mental retardation. Phenylalanine was found to interfere with different cerebral enzyme systems. However, apart from the neurotoxicity of phenylalanine, a deficiency of the other large neutral amino acids in brain may also be an important factor affecting cognitive function in phenylketonuria. Cerebral protein synthesis was found to be disturbed in a mouse model of phenylketonuria and could be caused by shortage of large neutral amino acids instead of high levels of phenylalanine. Therefore, in this review we emphasize the possibility of a different idea about the pathogenesis of mental dysfunction in phenylketonuria patients and the aim of treatment strategies. The aim of treatment in phenylketonuria might be to normalize cerebral concentrations of all large neutral amino acids rather than prevent high cerebral phenylalanine concentrations alone. In-depth studies are necessary to investigate the role of large neutral amino acid deficiencies in brain.

Cognitive functions and the antioxidant system in phenylketonuric patients

The authors studied the relationship between the antioxidant system and cognitive functions in a group of 36 early and continuously treated phenylketonuric (PKU) patients (mean age=9.7 years) and 29 controls. The authors measured antioxidant cofactors and free radical damage markers in plasma (selenium, retinol, tocopherol, coenzyme Q10, malondialdehide) and antioxidant enzymes in red blood cells (glutathione peroxidase, catalase, superoxide dismutase). The authors used neuropsychological tests to screen for several cognitive functions. PKU patients showed significantly lower values of selenium, coenzyme Q10, and catalase, and significantly higher levels of malondialdehide. PKU patients showed a significantly negative correlation between plasma selenium concentrations and several Conner's Continuous Performance Test measures (more omission errors, fluctuating attention and inconsistency of response times, and slowing reaction time as the test progressed). Selenium deficiency was thus associated with a worsened performance on the Conner's Continuous Performance Test among PKU patients. In conclusion, it is important not only to control blood Phe levels in PKU but also other nutritional components such as selenium. Selenium status seems to be associated with attention functions in these PKU patients.

Phalangeal quantitative ultrasound in children with phenylketonuria: a pilot study

Bone alterations in phenylketonuria (PKU) have been detected, especially with increasing age, in several studies by using different radiologic techniques. Quantitative ultrasound (QUS) assesses skeletal status by measuring the amplitude-dependent speed of sound (AD-SoS) and the bone transmission time (BTT), mainly dependent on mineral density and cortical thickness. Bone condition in 30 children and adolescents (mean age 15.1 +/- 6.4 y) affected by PKU was evaluated by phalangeal QUS, considering its relationship with their clinical, biochemical and therapeutic features. Measured AD-SoS Z-Score and BTT Z-Score were 0.27 +/- 1.42 and -0.26 +/- 1.21, respectively. In patients with previous fractures, the two QUS parameters were lower than in patients without history of fracture (p < 0.001 and p = 0.006, respectively). AD-SoS Z-Score and BTT Z-Score were negatively correlated with plasma phenylalanine (Phe) concentration in the year before QUS (p = 0.005 and p < 0.001, respectively) and with age (p < 0.001 for both parameters). These results parallel the previous findings obtained by different radiologic tools and suggest phalangeal QUS as an attractive option for the regular evaluation and longitudinal monitoring of bone condition in children and adolescents affected by PKU.

Sapropterin dihydrochloride (Kuvan/phenoptin), an orally active synthetic form of BH4 for the treatment of phenylketonuria

Phenylketonuria (PKU) and mild hyperphenylalaninemia (HPA) are genetic disorders characterized by a deficiency in phenylalanine hydroxylase (PAH), resulting in intellectual impairment if not treated with dietary restriction of phenylalanine intake. Sapropterin dihydrochloride (Kuvan) is an orally active synthetic form of (6R)-L-erythro-5,6,7,8-tetrahydrobiopterin (BH4; a cofactor for PAH) that has received Orphan Drug status and Fast Track designation for the treatment of PKU. Phase II and III clinical data demonstrated that Kuvan was a safe and effective therapy in selected patients with HPA and mild-to-moderate PKU who responded to a BH4 loading test. Based on the clinical data, BioMarin Pharmaceutical Inc has estimated that Kuvan could be a potential treatment option for 30 to 50% of the estimated 50,000 patients in the developed world who have been diagnosed with PKU. According to Thomson Scientific's Strategic Drugs Database (SDdb), the worldwide consensus forecast values for Kuvan are approximately US $120, 190 and 260 million for 2008, 2009 and 2010, respectively.

Growth and body composition in children with classical phenylketonuria: results in 34 patients and review of the literature

Treatment of phenylketonuria (PKU, OMIM 261600) means a diet restricted in natural protein and supplemented with phenylalanine (Phe)-free L-amino acid mixtures. Growth impairment has been described even in patients with a total protein intake at or above the recommended dietary allowance (RDA). In the present study, growth and body composition (fat-free mass (FFM) and fat) were recorded over 12 months in 34 treated PKU patients (mean age 8.7 years at baseline). Measurements were compared with those of healthy peers and with general population standard (Z-) scores calculated using the LMS method. In 28 PKU patients, data on birth weight and birth length were available and related to measurements at baseline of the study. Mean total protein intake in PKU patients was 124% (range 77-193%) of the RDA (DACH 2000). No significant differences in growth and body composition were present between PKU patients and healthy populations either at birth or during the study period. The significant correlation of FFM (representing muscle mass) with intake of natural protein--rather than total protein--indicates that the enhancement of tolerance to natural protein may be of value in PKU patients.

Regionally selective decreases in cerebral glucose metabolism in a mouse model of phenylketonuria

Impairment of cognitive function is characteristic of untreated phenylketonuria in humans and in the pah(enu2) mouse model of phenylketonuria. We measured regional cerebral metabolic rate for glucose in the adult male pah(enu2) mouse to determine the effect of PKU on functional activity in brain and to discern what, if any, brain areas are affected. Our results demonstrate selective decreases (17-21%) in regions thought to be involved in executive function. Regions most significantly affected include prelimbic, anterior cingulate, orbital frontal and perirhinal cortex. Sensory and motor areas of cortex and hippocampus were remarkably unaffected.

A neuropsychological profile of off-diet adults with phenylketonuria

The metabolic disorder phenylketonuria (PKU) is treated early by a low-phenylalanine diet. While this prevents global cognitive impairment, some patients still experience cognitive and neurophysiological abnormalities. Neuropsychological testing of early treated, currently off-diet, PKU patients attending an adult PKU clinic showed a reduction in the Perceptual Organization Index (POI), Processing Speed Index (PSI) from the Wechsler Adult Intelligence Scale Third Edition (WAIS-III), and Part A of the Trail Making Test for the PKU group relative to controls. Taken together, these results supported a profile of reduced information-processing speed.

Effect of fish oil supplementation on fatty acid status, coordination, and fine motor skills in children with phenylketonuria

OBJECTIVE

To investigate effects of long-chain omega-3 polyunsaturated fatty acids (LC-PUFA) on motor skills in patients with phenylketonuria (PKU).

STUDY DESIGN

Thirty-six patients with PKU (1-11 years of age, good metabolic control: plasma phenylalanine < or = 360 micromol/L for > or = 6 months). We determined plasma phospholipid fatty acids, and in patients > 4 years of age (N = 24) the motometric Rostock-Oseretzky Scale (ROS), before and after supplementation with fish oil for 3 months (15 mg docosahexaenoic acid [DHA]/kg body weight daily). ROS was also assessed in 22 age-matched controls.

RESULTS

Patients had low n-3 LC-PUFA in plasma phospholipids (DHA, 2.37 +/- 0.10%; eicosapentaenoic acid [EPA], 0.4 +/- 0.03%) and poorer ROS performance than controls (motor development index [MQ] 107 +/- 3 vs 117 +/- 3, P = .010). Supplementation increased phospholipid n-3 LC-PUFA (DHA 7.05 +/- 0.24%; EPA 3.31 +/- 0.19%; P < .001), decreased n-6 LC-PUFA (arachidonic acid, 9.26 +/- 0.23% vs 6.76 +/- 0.16%; P < .001) and improved ROS (MQ 115 +/- 3.54, P = .011, paired t test). ROS was unchanged in 11 retested controls (MQ 115 +/- 5.16, P = NS, paired t test multivariate analysis of variance [MANOVA] for time by group, P = .027). Patients tolerated fish oil well. Plasma phenylalanine remained unchanged.

CONCLUSION

In patients with PKU, fish oil supplementation enhances n-3 LC-PUFA levels and improves motor skills.

Phenylketonuria: dietary and therapeutic challenges

PKU subjects need special attention in the definition of optimal supplementation of nutrients, which may be insufficient in relation to the type of diet and may otherwise manifest symptoms of deficit. In particular, it is necessary to pay great attention to the long-chain polyunsaturated fatty acid (LC-PUFA) levels in relation to correct development of the central nervous system. On the basis of numerous beneficial effects currently known, a permanent supplementation with LC-PUFAs, in particular with docosahexaenoic acid, should be considered. Moreover, new formulas, Phe-free peptides, and 'modulated' amino acid preparations might help in preventing nutritional deficiencies and imbalances, with the ultimate aim of improving growth. New strategies--such as supply of tetrahydrobiopterin--need to be optimized in terms of targets, patients and expected outcomes.

Peak bone mass in patients with phenylketonuria

OBJECTIVE

Several studies have suggested a compromised bone mass in phenylketonuria patients but most reported on heterogeneous or small patient groups. Our aim was to evaluate peak bone mass in adult PKU patients and to relate BMD to nutritional parameters.

PATIENTS AND METHODS

BMD was measured by dual-energy x-ray absorptiometry in 31 adult PKU patients (18 female), mean age 25 +/- 5.3 years. Nutritional intake was calculated based on food diaries. Diet adherence was determined based on patients' report.

RESULTS

Mean blood phenylalanine (Phe) concentration was 968 +/- 526 micromol/L (16 +/- 8.7 mg/dl). Eight patients (32.2%) met the recommended blood Phe concentration of <726 micromol/L (<12 mg/dl), and there was no significant difference in Phe concentrations between diet-adherent and non-adherent patients. Osteopenia was detected in 11 patients (38.7%), while osteoporosis was detected in 2 patients (6.5%). No correlation was found between BMD and age, blood minerals, Phe, vitamin D and alkaline phosphatase levels, calcium and protein intake, body mass index, and body fat percentage.

CONCLUSIONS

Peak bone mass is decreased in PKU patients. Possible explanations include long-standing dietary deficiency in protein, calcium, vitamin D or trace elements, or a primary defect in bone turnover inherent to the disease itself. Our data do not favour any of these hypotheses. Further studies are needed to elucidate the cause of low bone density in PKU patients.

Event-related potentials elicited during a visual Go-Nogo task in adults with phenylketonuria

OBJECTIVE

The aim of the present study was to examine the nature of previously reported deficits in sustained attention and response inhibition in adults with the developmental disorder, phenylketonuria (PKU).

METHODS

This study used event-related potentials (ERPs) to examine the performance of PKU adults (n=9) and a matched control group (n=9) on a visual Go-Nogo task.

RESULTS

Comparison of behavioural measures between the PKU and control groups failed to reach statistical significance, yet analysis of the ERPs showed statistically significant amplitude reductions in the P1 and N1 components elicited following presentation of stimuli, and a reduction in the amplitude of the N2 component elicited following presentation of Nogo stimuli.

CONCLUSIONS

These results suggest that adults with PKU, despite being continuously treated from birth, manifest subtle impairments in distinct aspects of information processing including early sensory processing of visually presented information, as well as impairments in inhibitory functions.

SIGNIFICANCE

The results contribute to an understanding of the neurophysiological mechanisms that are implicated in PKU and highlight the sensitivity of ERP techniques for the identification of the loci of information processing deficits in clinical groups.

Phenylalanine reduces synaptic density in mixed cortical cultures from mice

Classical phenylketonuria (PKU) is caused by deficiency of phenylalanine hydroxylase, resulting in an accumulation of its upstream metabolite phenylalanine in brain tissue and cerebrospinal fluid of PKU patients. PKU is neuropathologically characterized by reduced dendritic arborization, loss of synapses, and neurodegeneration. We investigated whether increased concentrations of phenylalanine cause reduced synaptic density and alter dendritic branching. We treated primary cortical neurons differentiated for 21 d in vitro with 5 mM phenylalanine in the presence of all essential amino acids. Immunocytochemical analysis of 12 and 21 d in vitro primary neurons revealed no changes of dendritic morphology or neuronal viability but a significant difference in synaptic density, suggesting that elevated concentrations of extracellular phenylalanine cause an impairment of synaptogenesis. Although impairment of cerebral energy metabolism has been identified as an important pathophysiological principal in many diseases, respiratory chain function has not been extensively studied in PKU before. We investigated whether phenylalanine inhibits respiratory chain complexes I-V. In vitro analysis revealed no inhibitory effect of phenylalanine on complexes I-V, but an inhibition of pyruvate kinase, a key enzyme of glycolysis, catalyzing the formation of pyruvate. Pyruvate kinase is part of the enzyme assay to investigate enzyme activity of mitochondrial complex V and it remains to be elucidated whether this finding is relevant in vivo. In conclusion, elevated concentrations of phenylalanine might be involved in mechanisms underlying impaired synaptogenesis in PKU, supporting the common therapeutic strategy to reduce phenylalanine concentrations in the brain to prevent neurodegeneration.

Phénylcétonurie

Phenylketonuria is a hereditary metabolic disease, characterized by deficiency of phenylalanine hydroxylase, an enzyme necessary for the transformation of phenylalanine into tyrosine. Untreated, phenylketonuria leads to mental retardation, sometimes profound, as well as hypopigmentation. Dietary phenylalanine restriction allows patients to lead almost normal lives. Phenylalanine is toxic to fetal development and severe disorders occur in the children of women whose phenylketonuria is untreated during pregnancy. These women must be informed that they must plan pregnancy and begin dietary restrictions in the preconceptional period. France has set up routine neonatal screening in view of the incidence of this disease (1/17000 in France) and the existence of effective treatment. Since 1970, approximately 1600 infants with phenylketonuria have thus been diagnosed and treated. Strict metabolic control is necessary during the first 10 years of life, after which the diet can be progressively enlarged. Dietary restriction must resume before any pregnancy. Advances in treatment: a study published in 2002 showed that some patients deficient in phenylalanine hydroxylase are sensitive to pharmacological doses of tetrahydrobiopterin (BH4), a cofactor of this 'enzyme essential to the transformation of phenylalanine into tyrosine. Some patients treated by this cofactor have normal levels of phenylalanine intake. While only a few patients have so far received this alternative treatment, intermediate and long-term experiments are currently being evaluated.

Executive functioning and speed of processing in phenylketonuria

Treated phenylketonuria (PKU) has been linked to dopaminergic depletion in the dorsolateral prefrontal cortex, potentially leading to selective executive impairment. White matter abnormalities may lead to generalized slowing of information processing. These 2 hypotheses were evaluated in adults with PKU on a lifelong diet. Those with PKU were significantly slower than the control group regardless of working memory load on an n-back task and marginally slower regardless of trial type (inhibitory or noninhibitory) on a flanker task. There were no significant differences in speed on object alternation learning or perceptual judgment tasks. There were no group differences in accuracy on any task. These findings do not appear consistent with the selective executive hypothesis. A cognitive slowing account may prove more informative in adults with PKU, but more evidence is needed. The findings suggest that continuous dietary management is a fairly successful strategy in terms of cognitive outcome for adults.