Tract-based evaluation of white matter damage in individuals with early-treated phenylketonuria

Cerebral blood flow and white matter alterations in adults with phenylketonuria

BACKGROUND

Phenylketonuria (PKU) represents a congenital metabolic defect that disrupts the process of converting phenylalanine (Phe) into tyrosine. Earlier investigations have revealed diminished cognitive performance and changes in brain structure and function (including the presence of white matter lesions) among individuals affected by PKU. However, there exists limited understanding regarding cerebral blood flow (CBF) and its potential associations with cognition, white matter lesions, and metabolic parameters in patients with PKU, which we therefore aimed to investigate in this study.

METHOD

Arterial spin labeling perfusion MRI was performed to measure CBF in 30 adults with early-treated classical PKU (median age 35.5 years) and 59 healthy controls (median age 30.0 years). For all participants, brain Phe levels were measured with 1H spectroscopy, and white matter lesions were rated by two neuroradiologists on T2 weighted images. White matter integrity was examined with diffusion tensor imaging (DTI). For patients only, concurrent plasma Phe levels were assessed after an overnight fasting period. Furthermore, past Phe levels were collected to estimate historical metabolic control. On the day of the MRI, each participant underwent a cognitive assessment measuring IQ and performance in executive functions, attention, and processing speed.

RESULTS

No significant group difference was observed in global CBF between patients and controls (F (1, 87) = 3.81, p = 0.054). Investigating CBF on the level of cerebral arterial territories, reduced CBF was observed in the left middle and posterior cerebral artery (MCA and PCA), with the most prominent reduction of CBF in the anterior subdivision of the MCA (F (1, 87) = 6.15, p = 0.015, surviving FDR correction). White matter lesions in patients were associated with cerebral blood flow reduction in the affected structure. Particularly, patients with lesions in the occipital lobe showed significant CBF reductions in the left PCA (U = 352, p = 0.013, surviving FDR correction). Additionally, axial diffusivity measured with DTI was positively associated with CBF in the ACA and PCA (surviving FDR correction). Cerebral blood flow did not correlate with cognitive performance or metabolic parameters.

CONCLUSION

The relationship between cerebral blood flow and white matter indicates a complex interplay between vascular health and white matter alterations in patients with PKU. It highlights the importance of considering a multifactorial model when investigating the impact of PKU on the brain.

Neuroimaging in early-treated phenylketonuria patients and clinical outcome: A systematic review

Lacking direct neuropathological data, neuroimaging exploration has become the most powerful tool to give insight into pathophysiological alterations of early-treated PKU (ETPKU) patients. We conducted a systematic review of neuroimaging studies in ETPKU patients to explore 1) the occurrence of consistent neuroimaging alterations; 2) the relationship between them and neurological and cognitive disorders; 3) the contribution of neuroimaging in the insight of neuropathological background of ETPKU subjects; 4) whether brain neuroimaging may provide additional information in the monitoring of the disease course. Thirty-eight studies met the inclusion criteria for the full-text review, including morphological T1/T2 sequences, diffusion brain imaging (DWI/DTI) studies, brain MRI volumetric, functional neuroimaging studies, neurotransmission and brain energetic imaging studies. Non-progressive brain white matter changes were the most frequent and precocious alterations. As confirmed in hundreds of young adults with ETPKU, they affect over 90% of ETPKU patients. Consistent correlations are emerging between microstructural alteration (as detected by DWI/DTI) and metabolic control, which have also been confirmed in a few interventional trials. Volumetric studies detected later and less consistent cortical and subcortical grey matter alterations, which seem to be influenced by the patient's age and metabolic control. The few functional neuroimaging studies so far showed preliminary but interesting data about cortical activation patterns, skill performance, and brain connectivity. Further research is mandatory in these more complex areas. Recurrent methodological limitations include restricted sample sizes concerning the clinical variability of the disease, large age-range, variable measures of metabolic control, and prevalence of cross-sectional rather than longitudinal interventional studies.

Compromised white matter is related to lower cognitive performance in adults with phenylketonuria

Despite increasing knowledge about the effects of phenylketonuria on brain structure and function, it is uncertain whether white matter microstructure is affected and if it is linked to patients' metabolic control or cognitive performance. Thus, we quantitatively assessed white matter characteristics in adults with phenylketonuria and assessed their relationship to concurrent brain and blood phenylalanine levels, historical metabolic control and cognitive performance. Diffusion tensor imaging and ¹H spectroscopy were performed in 30 adults with early-treated classical phenylketonuria (median age 35.5 years) and 54 healthy controls (median age 29.3 years). Fractional anisotropy and mean, axial and radial diffusivity were investigated using tract-based spatial statistics, and white matter lesion load was evaluated. Brain phenylalanine levels were measured with ¹H spectroscopy whereas concurrent plasma phenylalanine levels were assessed after an overnight fast. Retrospective phenylalanine levels were collected to estimate historical metabolic control, and a neuropsychological evaluation assessed the performance in executive functions, attention and processing speed. Widespread reductions in mean diffusivity, axial diffusivity and fractional anisotropy occurred in patients compared to controls. Mean diffusivity and axial diffusivity were decreased in several white matter tracts and were most restricted in the optic radiation (effect size r_rb = 0.66 to 0.78, P < 0.001) and posterior corona radiata (r_rb = 0.83 to 0.90, P < 0.001). Lower fractional anisotropy was found in the optic radiation and posterior corona radiata (r_rb = 0.43 to 0.49, P < 0.001). White matter microstructure in patients was significantly associated with cognition. Specifically, inhibition was related to axial diffusivity in the external capsule (r_s = -0.69, P < 0.001) and the superior (r_s = -0.58, P < 0.001) and inferior longitudinal fasciculi (r_s = -0.60, P < 0.001). Cognitive flexibility was associated with mean diffusivity of the posterior limb of the internal capsule (r_s = -0.62, P < 0.001), and divided attention correlated with fractional anisotropy of the external capsule (r_s = -0.61, P < 0.001). Neither concurrent nor historical metabolic control was significantly associated with white matter microstructure. White matter lesions were present in 29 out of 30 patients (96.7%), most often in the parietal and occipital lobes. However, total white matter lesion load scores were unrelated to patients' cognitive performance and metabolic control. In conclusion, our findings demonstrate that white matter alterations in early-treated phenylketonuria persist into adulthood, are most prominent in the posterior white matter and are likely to be driven by axonal damage. Furthermore, diffusion tensor imaging metrics in adults with phenylketonuria were related to performance in attention and executive functions.

The relationship between metabolic control and basal ganglia morphometry and function in individuals with early-treated phenylketonuria

Abnormalities of the cortical white matter are the most prominent and widely-reported neurological findings in individuals with early-treated phenylketonuria (ETPKU). Much less is known regarding the effects of ETPKU on gray matter structures in the brain such as the basal ganglia. Previous findings on basal ganglia in ETPKU have been mixed. The current study was designed to further elucidate the effects of ETPKU and elevated phe levels on the morphometry of basal ganglia structures (i.e., putamen, caudate nucleus, nucleus accumbens, and globus pallidus). High resolution magnetic resonance imaging (MRI) data was collected from a sample of 37 adults with ETPKU and a demographically-matched comparison group of 33 individuals without PKU. No overall group differences (ETPKU vs. non-PKU) in basal ganglia volumes were observed. However, within the ETPKU group, poorer metabolic control (as reflected by higher blood phenylalanine levels) was associated with larger putamen volume. Vertex-wise shape analysis revealed that the volume increase was accompanied by shape changes in the middle left putamen. Consistent with this area's role in motor control, a significant correlation between left putamen volume and motor performance was also observed. Additional research is needed to fully understand the cellular level processes underlying this effect as well as to better understand the clinical impact of these morphometric changes and their potential relation to treatment response.

Plasma metabolomic profile changes in females with phenylketonuria following a camp intervention

BACKGROUND

There remains a limited understanding of the metabolic perturbations, beyond phenylalanine (Phe) metabolism, that contribute to phenotypic variability in phenylketonuria (PKU).

OBJECTIVES

This study aimed to characterize changes in the PKU plasma metabolome following a 5-d metabolic camp intervention and to compare PKU profiles with those of matched healthy controls.

METHODS

In 28 females (aged 12-57 y), fasting plasma samples were collected on the first (day 1) and final (day 5) days of camp to measure metabolic control and to complete untargeted metabolomic profiling. Three-day dietary records were collected to assess changes in dietary adherence and composition. Univariate (Wilcoxon signed-rank and Mann-Whitney U test) and multivariate (random forest, hierarchical clustering) analyses were performed to identify clinical and metabolic features that were associated with the intervention and disease state.

RESULTS

Relative to healthy controls, Phe catabolites, ketones, and carnitine- and glycine-conjugated fatty acids were elevated in females with PKU at baseline, whereas fatty acylcholine metabolites were substantially lower. After the camp intervention, plasma Phe concentrations decreased [median change: -173 µmol/L (IQR: -325, -28 µmol/L)] and 70% of PKU participants demonstrated improved dietary adherence by decreasing Phe intake and/or increasing medical food consumption. This was accompanied by a shift in abundance for 223 metabolites (q < 0.05). Compounds associated with the metabolism of Phe, fatty acids, and choline contributed most to profile differences between camp days 1 and 5.

CONCLUSIONS

In females with PKU, untargeted metabolomics identified prominent perturbations in amino acid and lipid metabolites associated with bioenergetic impairment and oxidative stress. Choline-conjugated lipids could have fundamental roles in these pathways and they have not been previously evaluated in PKU. A short-term camp intervention was effective for improving or fully normalizing the abundance of the identified discriminatory metabolites.

Optical Coherence Tomography to Assess Neurodegeneration in Phenylalanine Hydroxylase Deficiency

In phenylalanine hydroxylase (PAH) deficiency, an easily feasible method to access the progression of neurodegeneration is warranted to contribute to current discussions on treatment indications and targets. The objective of the present study was to investigate whether optical coherence tomography (OCT) measures as markers of neurodegeneration differ between patients with PAH deficiency and healthy controls (HCs) according to phenotype and metabolic control. In this single-center cross-sectional study, 92 patients with different phenotypes of PAH deficiency [PAH deficiency not requiring treatment, early treated phenylketonuria (ETPKU), and late-diagnosed phenylketonuria (PKU)] compared with 76 HCs were examined using spectral-domain OCT. Indices of phenylalanine elevation and variability were correlated with OCT parameters. Late-diagnosed PKU patients showed reduced peripapillary retinal nerve fiber layer (pRNFL) thickness and combined ganglion cell and inner plexiform layer (GCIPL) volume. Adult ETPKU patients were found to have lower GCIPL volume (p = 0.016), which correlated with the indices of phenylalanine control. In pediatric ETPKU patients with poor metabolic control, pRNFL was significantly reduced (p = 0.004). Patients with PAH deficiency not requiring treatment did not exhibit retinal degeneration. Inner nuclear layer (INL) was significantly increased in the pediatric ETPKU patients, driven by those with current poor metabolic control (p = 0.006). Our data provide evidence of retinal neuroaxonal degeneration and INL swelling, depending on the phenotype, current age, and metabolic control. These findings suggest that OCT is suitable to investigate neurodegeneration in PKU and we propose OCT as a sensitive, reliable, safe, low-burden, and low-cost examination for future multicenter studies.

Inter- and intra-tract analysis of white matter abnormalities in individuals with early-treated phenylketonuria (PKU)

Even with early and continuous treatment, individuals with phenylketonuria (PKU) may exhibit abnormalities of cortical white matter (WM). The present study utilizes a new analysis approach called Automated Fiber-Tract Quantification (AFQ) to advance our understanding of the tract-specific patterns of change in WM abnormalities in individuals with early-treated PKU (ETPKU). Diffusion Tensor Imaging (DTI) data from a sample of 22 individuals with ETPKU and a demographically-matched sample of 21 healthy individuals without PKU was analyzed using AFQ. In addition, a subsample of 8 individuals with ETPKU was reevaluated six months later after demonstrating a significant reduction in blood phe levels following initiation of sapropterin treatment. Within-tract AFQ analyses revealed significant location-by-group interactions for several WM tracts throughout the brain. In most cases, ETPKU-related disruptions in mean diffusivity (MD) were more apparent in posterior (as compared to anterior) aspects of a given tract. Reduction in blood phe levels with the aforementioned ETPKU subsample was associated with a similar pattern of improvement (posterior-to-anterior) within most tracts. Taken together, these findings suggest that there is a systematic pattern of change in WM abnormalities in individuals with ETPKU in a posterior-to-anterior manner along individual WM tracts.

The effects of early-treated phenylketonuria on volumetric measures of the cerebellum

Past murine studies of phenylketonuria (PKU) have documented significant effects on cerebellum at both the gross and cellular levels. The profile of neurocognitive and motor difficulties associated with early-treated PKU (ETPKU) is also consistent with potential cerebellar involvement. Previous neuroanatomical studies of cerebellum in patients with PKU, however, have yielded mixed results. The objective of the present study was to further examine potential differences in cerebellar morphometry between individuals with and without ETPKU. To this end, we analyzed high resolution T1-weighted MR images from a sample of 20 individuals with ETPKU and an age-matched comparison group of 20 healthy individuals without PKU. Measurements of whole brain volume, whole cerebellum volume, cerebellar gray matter volume, and cerebellar white matter volume were collected by means of semiautomatic volumetric analysis. Data analysis revealed no significant group differences in whole brain volume, whole cerebellar volume, or cerebellar white matter volume. A significant reduction in cerebellar gray matter volume, however, was observed for the ETPKU group compared to the non-PKU comparison group. These findings expand on previous animal work suggesting that cerebellar gray matter is impacted by PKU. It is also consistent with the hypothesis that the cognitive difficulties experienced by individuals with ETPKU may be related to disruptions in gray matter. Additional studies are needed to fully elucidate the timing and extent of the impact of ETPKU on cerebellum and the associated neurocognitive consequences.

Plasma amino acid levels in a cohort of patients in Turkey with classical phenylketonuria

Background

In patients with phenylketonuria, the central nervous system is adversely affected by noncompliance with diet. The levels of phenylalanine and many different amino acids (AAs) in the plasma of patients with phenylketonuria can be measured simultaneously.

Objectives

To measure the blood plasma levels of neurotransmitter AAs in a cohort of patients in Sanliurfa province, Turkey, with phenylketonuria for use as a support parameter for the follow-up of patients.

Methods

The phenylketonurics that we followed (n = 100) were divided into 2 groups according to their compliance with their dietary treatment. Plasma AA analysis results of phenylketonurics were compared with those of healthy children in a control group (n = 50).

Results

In the diet incompliant group (n = 56), the mean levels of γ-aminobutyric acid (GABA; 0.96 ± 1.07 μmol/L) and glycine (305.1 ± 105.19 μmol/L) were significantly higher than those in the diet compliant group (n = 44; GABA P = 0.005, glycine P < 0.001) and in the control group (GABA and glycine P < 0.001), whereas the mean levels of glutamic acid (39.01 ± 22.94 μmol/L) and asparagine (39.3 ± 16.89 μmol/L) were lower (P < 0.001) in the diet incompliant group. A positive correlation was observed between the levels of phenylalanine and GABA and glycine. A negative relationship was found between the levels of phenylalanine and glutamic acid and asparagine.

Conclusions

A relationship exists between the levels of plasma phenylalanine in a cohort of phenylketonurics in Sanliurfa province, Turkey, and the levels of some excitatory and inhibitory AAs. Excitatory and inhibitory AA levels in plasma may be used as support parameters in the follow-up of patients with phenylketonuria.

White matter disturbances in phenylketonuria: Possible underlying mechanisms

White matter pathologies, as well as intellectual disability, microcephaly, and other central nervous system injuries, are clinical traits commonly ascribed to classic phenylketonuria (PKU). PKU is an inherited metabolic disease elicited by the deficiency of phenylalanine hydroxylase. Accumulation of l-phenylalanine (Phe) and its metabolites is found in tissues and body fluids in phenylketonuric patients. In order to mitigate the clinical findings, rigorous dietary Phe restriction constitutes the core of therapeutic management in PKU. Myelination is the process whereby the oligodendrocytes wrap myelin sheaths around the axons, supporting the conduction of action potentials. White matter injuries are implicated in the brain damage related to PKU, especially in untreated or poorly treated patients. The present review summarizes evidence toward putative mechanisms driving the white matter pathology in PKU patients.

Novel imaging technologies for genetic diagnoses in the inborn errors of metabolism

Many inborn errors of metabolism and genetic disorders affect the brain. The brain biochemistry may differ from that in the periphery and is not accessible by simple blood and urine sampling. Therefore, neuroimaging has proven to be a valuable tool to not only evaluate the brain structure, but also biochemistry, blood flow and function. Neuroimaging in patients with inborn errors of metabolism can include additional sequences in addition to T1 and T2-weighted imaging because in early stages, there may be no significant findings on the routine sequnces due to the lack of sensitivity or the evolution of abnormalities lags behind the ability of the imaging to detect it. In addition, findings on T1 and T2-weighted imaging of several inborn errors of metabolism may be non-specific and be seen in other non-genetic conditions. Therefore, additional neuroimaging modalities that have been employed including diffusion tensor imaging (DTI), magnetic resonance spectroscopy, functional MRI (fMRI), functional near infrared spectroscopy (fNIRS), or positron emission tomography (PET) imaging may further inform underlying changes in myelination, biochemistry, and functional connectivity. The use of Magnetic Resonance Spectroscopy in certain disorders may add a level of specificity depending upon the metabolite levels that are abnormal, as well as provide information about the process of brain injury (i.e., white matter, gray matter, energy deficiency, toxic buildup or depletion of key metabolites). It is even more challenging to understand how genetic or metabolic disorders contribute to short and/or long term changes in cognition which represent the downstream effects of IEMs. In order to image “cognition” or the downstream effects of a metabolic disorder on domains of brain function, more advanced techniques are required to analyze underlying fiber tracts or alternatively, methods such as fMRI enable generation of brain activation maps after both task based and resting state conditions. DTI can be used to look at changes in white matter tracks. Each imaging modality can explore an important aspect of the anatomy, physiology or biochemisty of the central nervous system. Their properties, pros and cons are discussed in this article. These imaging modalities will be discussed in the context of several inborn errors of metabolism including Galactosemia, Phenylketonruia, Maple syrup urine disease, Methylmalonic acidemia, Niemann-Pick Disease, type C1, Krabbe Disease, Ornithine transcarbamylase deficiency, Sjogren Larsson syndrome, Pelizeaus-Merzbacher disease, Pyruvate dehydrogenase deficiency, Nonketotic Hyperglycinemia and Fabry disease. Space constraints do not allow mention of all the disorders in which one of these modalities has been investigated, or where it would add value to diagnosis or disease progression.

Treatment With Tetrahydrobiopterin Improves White Matter Maturation in a Mouse Model for Prenatal Hypoxia in Congenital Heart Disease

Background Reduced oxygen delivery in congenital heart disease causes delayed brain maturation and white matter abnormalities in utero. No treatment currently exists. Tetrahydrobiopterin (BH4) is a cofactor for neuronal nitric oxide synthase. BH4 availability is reduced upon NOS activation, such as during hypoxic conditions, and leads to toxin production. We hypothesize that BH4 levels are depleted in the hypoxic brain and that BH4 replacement therapy mitigates the toxic effects of hypoxia on white matter. Methods and Results Transgenic mice were used to visualize oligodendrocytes. Hypoxia was introduced during a period of white matter development equivalent to the human third trimester. BH4 was administered during hypoxia. BH4 levels were depleted in the hypoxic brain by direct quantification (n=7-12). The proliferation (n=3-6), apoptosis (n=3-6), and developmental stage (n=5-8) of oligodendrocytes were determined immunohistologically. Total oligodendrocytes increased after hypoxia, consistent with hypoxia-induced proliferation seen previously; however, mature oligodendrocytes were less prevalent in hypoxia, and there was accumulation of immature oligodendrocytes. BH4 treatment improved the mature oligodendrocyte number such that it did not differ from normoxia, and accumulation of immature oligodendrocytes was not observed. These results persisted beyond the initial period of hypoxia (n=3-4). Apoptosis increased with hypoxia but decreased with BH4 treatment to normoxic levels. White matter myelin levels decreased following hypoxia by western blot. BH4 treatment normalized myelination (n=6-10). Hypoxia worsened sensory-motor coordination on balance beam tasks, and BH4 therapy normalized performance (n=5-9). Conclusions Suboptimal BH4 levels influence hypoxic white matter abnormalities. Repurposing BH4 for use during fetal brain development may limit white matter dysmaturation in congenital heart disease.

Effects of LC-PUFA Supplementation in Patients with Phenylketonuria: A Systematic Review of Controlled Trials

Evidence suggests a role of long chain polyunsaturated fatty acids (LC-PUFA), in which animal foods are especially rich, in optimal neural development. The LC-PUFAs docosahexaenoic acid (DHA) and arachidonic acid, found in high concentrations in the brain and retina, have potential beneficial effects on cognition, and motor and visual functions. Phenylketonuria (PKU) is the most common inborn error of amino acid metabolism. The treatment of PKU consists of a phenylalanine-free diet, which limits the intake of natural proteins of high biological value. In this systematic review, we summarize the available evidence supporting a role for LC-PUFA supplementation as an effective means of increasing LC-PUFA levels and improving visual and neurocognitive functions in PKU patients. Data from controlled trials of children and adults (up to 47 years of age) were obtained by searching the MEDLINE and SCOPUS databases following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. For each selected study, the risk of bias was assessed applying the methodology of the Cochrane Collaboration. The findings indicate that DHA supplementation in PKU patients from 2 weeks to 47 years of age improves DHA status and decreases visual evoked potential P100 wave latency in PKU children from 1 to 11 years old. Neurocognitive data are inconclusive.

White and gray matter brain development in children and young adults with phenylketonuria

Phenylketonuria (PKU) is a recessive disorder characterized by disruption in the metabolism of the amino acid phenylalanine (Phe). Prior research indicates that individuals with PKU have substantial white matter (WM) compromise. Much less is known about gray matter (GM) in PKU, but a small body of research suggests volumetric differences compared to controls. To date, developmental trajectories of GM structure in individuals with PKU have not been examined, nor have trajectories of WM and GM been examined within a single study. To address this gap in the literature, we compared longitudinal brain development over a three-year period in individuals with PKU (n = 35; 18 male) and typically-developing controls (n = 71; 35 male) aged 7–21 years. Using diffusion tensor imaging (DTI) and structural magnetic resonance imaging (MRI), we observed whole-brain and regional WM differences between individuals with PKU and controls, which were often exacerbated with increasing age. In marked contrast with trajectories of WM development, trajectories of GM development did not differ between individuals with PKU and controls, indicating that neuropathology in PKU is more prominent in WM than GM. Within individuals with PKU, mediation analyses revealed that whole-brain mean diffusivity (MD) and regional MD in the corpus callosum and centrum semiovale mediated the relationship between dietary treatment compliance (i.e., Phe control) and executive abilities, suggesting a plausible neurobiological mechanism by which Phe control may influence cognitive outcomes. Our findings clarify the specificity, timing, and cognitive consequences of whole-brain and regional WM pathology, with implications for treatment and research in PKU.

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Individuals with PKU exhibited widespread, age-related white matter compromise.

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Developmental trajectories of gray matter were comparable for PKU and controls.

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Within PKU, white matter compromise influenced cognitive outcomes.

Children and adolescents with phenylketonuria display fluctuations in their blood phenylalanine levels

AIM

This study examined the impact of fluctuations in metabolic control on the intelligence quotient (IQ) of children and adolescents with early, continuously treated phenylketonuria (PKU).

METHODS

This was a clinic-based study carried out at University Hospital Munster, Germany, from 2015 to 2017. We investigated 49 patients (28 boys) with early treated PKU, who were aged 6-18 years with a mean age of 11.2 ± 4.1 years. All the patients were on a continuous phenylalanine-restricted diet. Of the 49 patients, 29 (18 boys) had classic PKU and 21 patients (11 girls) had mild PKU. The patients' blood phenylalanine levels were assessed every week for 26 weeks and analysed for fluctuations, indicated by the standard deviation of the individual blood phenylalanine levels. We also assessed the concurrent Full Scale IQ (FSIQ) of the patients.

RESULTS

In patients with classic PKU, FSIQ was negatively correlated with blood phenylalanine levels, but not with level fluctuations. In patients with mild PKU, FSIQ was not correlated with blood phenylalanine levels, but was negatively correlated with level fluctuations.

CONCLUSION

The blood phenylalanine levels of patients with mild PKU showed minor interindividual differences, which may have allowed fluctuations to exert a negative effect on the FSIQ.

White matter microstructural damage in early treated phenylketonuric patients

BACKGROUND

Despite dietary intervention, individuals with early treated phenylketonuria (ETPKU) could present neurocognitive deficits and white matter (WM) abnormalities. The aim of the present study was to evaluate the microstructural integrity of WM pathways across the whole brain in a cohort of paediatric ETPKU patients compared with healthy controls (HCs), by collecting DTI-MRI (diffusion tensor magnetic resonance imaging) data and diffusion values (mean diffusivity (MD), radial diffusivity (RD) and fractional anisotropy (FA)).

METHODS

DTI-MRI data and diffusion values (MD, RD, FA) from WM tracts across the whole brain were analized using Tract Based Spatial Statistics (TBSS), in 15 paediatrics TPKU patients (median age: 12 years) and compared with 11 HCs. Areas showing abnormal values in the patient group were correlated (Pearson) with age, lifetime Phe values, last year median and mean Phe, concurrent Phe values in plasma, urine neurotransmitters status biomarkers, and with a processing speed task.

RESULTS

ETPKU showed bilaterally decreased MD values compared with HCs in the body and splenium of the corpus callosum, superior longitudinal fasciculus, corona radiata and in the posterior limb of the internal capsule. RD values followed a similar pattern, although decreased RD values in PKU patients were also found in the anterior limb of the internal capsule and in the cerebral peduncle. Decreased MD and RD values within the aforementioned regions had significant negative correlations with age, last year median and mean Phe and concurrent Phe values. No correlations were found with monoamines in urine or processing speed task.

CONCLUSIONS

ETPKU patients showed MD and RD values significantly decreased across the whole brain when compared with HCs, and this damage was associated with high Phe values and the age of patients. Despite this microstructural damage, no affectation in processing speed was observed in patients with good metabolic control. DTI-MRI sequences could be used as a technique to quantify WM damage that is difficult to be detect in T1 or T2-weighted images, but also to quantify damage of WM through the follow up of patients with poor metabolic control in prospective studies.

Clinical and neuropsychological outcomes for children with phenylketonuria in Upper Egypt; a single-center study over 5 years

BACKGROUND

Phenylketonuria (PKU) is considered to be a rare inborn error of metabolism but one of the commonest causes of mental retardation if untreated.

OBJECTIVES

The present study was done to characterize the clinical patterns of PKU and analyze various neuropsychiatric outcomes in PKU children in Sohag Province, Egypt.

PATIENTS AND METHODS

A prospective cohort study was conducted on 113 PKU patients, diagnosed during the period from 2012 to 2017, at the Pediatric Neurology Clinic of Sohag University Hospital, Upper Egypt. One hundred and ten cases were diagnosed based on clinical suspicion combined with laboratory confirmation by measuring their plasma phenylalanine levels using amino acid analyzer, while 3 cases were detected during neonatal screening. With the exception of the 3 cases detected during neonatal screening, all patients were clinically diagnosed and treated late. Psychometric evaluations of PKU patients were done using intelligence quotient (IQ, Stanford- Binet V), Childhood Autism Rating Scale, and Children's Attention and Adjustment Survey. Dietetic management was applied. The results of neuroimaging (computed tomography or magnetic resonance imaging of the brain) and electroencephalography were included when available.

RESULTS

The overall results showed that 15.9% had hyperphenylalaninemia, 35.4% had mild to moderate PKU, and classic PKU was diagnosed in 48.7%. Global developmental delay (54.9%) and delayed language (29.2%) were the most frequent presentations. Moderately impaired or delayed overall IQ was present in 77%. While, 83.2% had moderately impaired or delayed verbal IQ, autism was diagnosed in 50.4%. Super average and average probability of attention-deficit hyperactivity disorder was diagnosed in 88.5%. Abnormal neuroimaging (white matter abnormalities and brain atrophy) was the most important significant predictor for poor language and motor developmental outcome (P<0.05).

CONCLUSION

PKU children had variable neuropsychological outcomes, mainly attention-deficit hyperactivity disorder and impaired verbal IQ, both of which were not related to the initial phenylalanine levels or to duration of dietary therapy, but were significantly related to early dietary intervention.

Subclinical executive function impairment in children with asymptomatic, treated phenylketonuria: A comparison with children with immunodeficiency virus

In this study we compared the neuropsychological profile of phenylketonuria (PKU) and human immunodeficiency virus (HIV) to examine the specificity of the executive function (EF) impairment reported in these two patologies. A total of 55 age-matched children and adolescents were assessed, including 11 patients with PKU, 16 patients with HIV and 28 healthy controls, underwent a neuropsychological assessment. Although neither the PKU nor the HIV group scored below the normative ranges, both groups showed lower scores in neuropsychological tests engaging EFs than controls. In addition, compared to patients with PKU the HIV group performed significantly worse in the Trail-Making Test A, Corsi Span and Verbal Fluency. These findings suggest that EF impairments in PKU (a) are limited to EFs (i.e., working memory and attentional shifting), (b) are not simply due to generalized processing speed deficits and

The complete European guidelines on phenylketonuria: diagnosis and treatment

Phenylketonuria (PKU) is an autosomal recessive inborn error of phenylalanine metabolism caused by deficiency in the enzyme phenylalanine hydroxylase that converts phenylalanine into tyrosine. If left untreated, PKU results in increased phenylalanine concentrations in blood and brain, which cause severe intellectual disability, epilepsy and behavioural problems. PKU management differs widely across Europe and therefore these guidelines have been developed aiming to optimize and standardize PKU care. Professionals from 10 different European countries developed the guidelines according to the AGREE (Appraisal of Guidelines for Research and Evaluation) method. Literature search, critical appraisal and evidence grading were conducted according to the SIGN (Scottish Intercollegiate Guidelines Network) method. The Delphi-method was used when there was no or little evidence available. External consultants reviewed the guidelines. Using these methods 70 statements were formulated based on the highest quality evidence available. The level of evidence of most recommendations is C or D. Although study designs and patient numbers are sub-optimal, many statements are convincing, important and relevant. In addition, knowledge gaps are identified which require further research in order to direct better care for the future.

Neuropsychiatric comorbidities in adults with phenylketonuria: A retrospective cohort study

Adults with phenylketonuria (PKU) may experience neurologic and psychiatric disorders, including intellectual disability, anxiety, depression, and neurocognitive dysfunction. Identifying the prevalence and prevalence ratios of these conditions will inform clinical treatment. This nested, case-controlled study used International Classification of Diseases, Ninth Revision (ICD-9) codes from the MarketScan® insurance claims databases from 2006 to 2012 and healthcare claims data for US-based employer and government-sponsored health plans. Prevalence and prevalence ratio calculations of neuropsychiatric comorbidities for adults (≥20years old) with PKU were compared with two groups [diabetes mellitus (DM) and general population (GP)] matched by age, gender, geographic location, and insurance type. Age cohorts (i.e., 20-29, 30-39, 40-49, 50-59, 60-69, and 70+years, and a combined subset of 20-39) were used to stratify data. The PKU cohort experienced significantly higher rates of several comorbid neurologic, psychiatric and developmental conditions. Compared to GP, PKU was associated with significantly higher prevalence for numerous neuropsychiatric conditions, most notably for intellectual disability (PR=7.9, 95% CI: 6.4-9.9), autism spectrum disorder (PR=6.1, 95% CI: 3.6-10.4), Tourette/tic disorders (PR=5.4, 95% CI: 2.1-14.1), and eating disorders (4.0, 95% CI: 3.2-5.0). Rates of fatigue/malaise, epilepsy/convulsions, sleep disturbance, personality disorders, phobias, psychosis, and migraines among those with PKU exceeded rates for the GP but were comparable to those with DM, with significantly lower rates of concomitant disorders occurring in younger, compared to older, adults with PKU. Lifelong monitoring and treatment of co-occurring neuropsychiatric conditions are important for effective PKU management.

Pretreatment cognitive and neural differences between sapropterin dihydrochloride responders and non-responders with phenylketonuria

Sapropterin dihydrochloride (BH₄) reduces phenylalanine (Phe) levels and improves white matter integrity in a subset of individuals with phenylketonuria (PKU) known as “responders.” Although prior research has identified biochemical and genotypic differences between BH₄ responders and non-responders, cognitive and neural differences remain largely unexplored. To this end, we compared intelligence and white matter integrity prior to treatment with BH₄ in 13 subsequent BH₄ responders with PKU, 16 subsequent BH₄ non-responders with PKU, and 12 healthy controls. Results indicated poorer intelligence and white matter integrity in non-responders compared to responders prior to treatment. In addition, poorer white matter integrity was associated with greater variability in Phe across the lifetime in non-responders but not in responders. These results underscore the importance of considering PKU as a multi-faceted, multi-dimensional disorder and point to the need for additional research to delineate characteristics that predict response to treatment with BH_4.

Brain White Matter Integrity Mediates the Relationship Between Phenylalanine Control and Executive Abilities in Children with Phenylketonuria

We tested the hypothesis that brain white matter integrity mediates the relationship between phenylalanine (Phe) control and executive abilities in children with phenylketonuria (PKU; N = 36). To do so, we examined mean diffusivity (MD) from diffusion tensor imaging (DTI) in two white matter brain regions (posterior parietal-occipital, PPO; centrum semiovale, CSO) and lifetime phenylalanine (Phe) exposure; the executive abilities examined included verbal strategic processing, nonverbal strategic processing, and working memory. Mediation modeling showed that MD in the PPO and CSO mediated the relationship between Phe exposure and nonverbal strategic processing, MD in the CSO mediated the relationship between Phe exposure and verbal strategic processing, and MD in the PPO mediated the relationship between Phe exposure and working memory. These exploratory findings demonstrate the importance of using sophisticated modeling procedures to understand the interplay among metabolic control, neural factors, and functional outcomes in individuals with PKU.

Morphometric analysis of gray matter integrity in individuals with early-treated phenylketonuria

The most widely-reported neurologic finding in individuals with early-treated phenylketonuria (PKU) is abnormality in the white matter of the brain. In contrast, much less is known regarding the impact of PKU on cortical gray matter (GM) structures. Presently, we applied advanced morphometric methods to the analysis of high-resolution structural MRI images from a sample of 19 individuals with early-treated PKU and an age- and gender-matched comparison group of 22 healthy individuals without PKU. Data analysis revealed decreased GM volume in parietal cortex for the PKU group compared with the non-PKU group. A similar trend was observed for occipital GM volume. There was no evidence of group-related differences in frontal or temporal GM volume. Within the PKU group, we also found a significant relationship between blood phenylalanine levels and GM volume for select posterior cortical sub-regions. Taken together with previous research on white matter and gray matter abnormalities in PKU, the present findings point to the posterior cortices as the primary site of neurostructural changes related to early-treated PKU.

Relationship between age and white matter integrity in children with phenylketonuria

Diffusion tensor imaging (DTI) has shown poorer microstructural white matter integrity in children with phenylketonuria (PKU), specifically decreases in mean diffusivity (MD), in comparison with healthy children. However, little research has been conducted to investigate the relationship between age and white matter integrity in this population. The present study examined group differences in the relationship between age and MD across a range of brain regions in 31 children with early- and continuously-treated PKU and 51 healthy control children. Relationships among MD, age, and group were explored using hierarchical linear regression and Pearson correlation. Results indicated a stronger age-related decrease in MD for children with PKU in comparison with healthy children in 4 of the 10 brain regions examined, suggesting that the trajectory of white matter development is abnormal in children with PKU. Further research using longitudinal methodology is needed to fully elucidate our understanding of white matter development in children with PKU.

Prolonged exposure to high and variable phenylalanine levels over the lifetime predicts brain white matter integrity in children with phenylketonuria

In this study, we retrospectively examined the microstructural white matter integrity of children with early- and continuously-treated PKU (N=36) in relation to multiple indices of phenylalanine (Phe) control over the lifetime. White matter integrity was assessed using mean diffusivity (MD) from diffusion tensor imaging (DTI). Eight lifetime indices of Phe control were computed to reflect average Phe (mean, index of dietary control), variability in Phe (standard deviation, standard error of estimate, % spikes), change in Phe with age (slope), and prolonged exposure to Phe (mean exposure, standard deviation exposure). Of these indices, mean Phe, mean exposure, and standard deviation exposure were the most powerful predictors of widespread microstructural white matter integrity compromise. Findings from the two previously unexamined exposure indices reflected the accumulative effects of elevations and variability in Phe. Given that prolonged exposure to elevated and variable Phe was particularly detrimental to white matter integrity, Phe should be carefully monitored and controlled throughout childhood, without liberalization of Phe control as children with PKU age.

Linking genotypes database with locus-specific database and genotype-phenotype correlation in phenylketonuria

The wide range of metabolic phenotypes in phenylketonuria is due to a large number of variants causing variable impairment in phenylalanine hydroxylase function. A total of 834 phenylalanine hydroxylase gene variants from the locus-specific database PAHvdb and genotypes of 4181 phenylketonuria patients from the BIOPKU database were characterized using FoldX, SIFT Blink, Polyphen-2 and SNPs3D algorithms. Obtained data was correlated with residual enzyme activity, patients' phenotype and tetrahydrobiopterin responsiveness. A descriptive analysis of both databases was compiled and an interactive viewer in PAHvdb database was implemented for structure visualization of missense variants. We found a quantitative relationship between phenylalanine hydroxylase protein stability and enzyme activity (r(s) = 0.479), between protein stability and allelic phenotype (r(s) = -0.458), as well as between enzyme activity and allelic phenotype (r(s) = 0.799). Enzyme stability algorithms (FoldX and SNPs3D), allelic phenotype and enzyme activity were most powerful to predict patients' phenotype and tetrahydrobiopterin response. Phenotype prediction was most accurate in deleterious genotypes (≈ 100%), followed by homozygous (92.9%), hemizygous (94.8%), and compound heterozygous genotypes (77.9%), while tetrahydrobiopterin response was correctly predicted in 71.0% of all cases. To our knowledge this is the largest study using algorithms for the prediction of patients' phenotype and tetrahydrobiopterin responsiveness in phenylketonuria patients, using data from the locus-specific and genotypes database.

Variability in phenylalanine control predicts IQ and executive abilities in children with phenylketonuria

A number of studies have revealed significant relationships between cognitive performance and average phenylalanine (Phe) levels in children with phenylketonuria (PKU), but only a few studies have been conducted to examine the relationships between cognitive performance and variability (fluctuations) in Phe levels. In the current study, we examined a variety of indices of Phe control to determine which index best predicted IQ and executive abilities in 47 school-age children with early- and continuously-treated PKU. Indices of Phe control were mean Phe, the index of dietary control, change in Phe with age, and several indices of variability in Phe (standard deviation, standard error of estimate, and percentage of spikes). These indices were computed over the lifetime and during 3 developmental epochs (<5, 5.0-9.9, and ≥10 years of age). Results indicated that variability in Phe was generally a stronger predictor of cognitive performance than other indices of Phe control. In addition, executive performance was better predicted by variability in Phe during older than younger developmental epochs. These results indicate that variability in Phe should be carefully controlled to maximize cognitive outcomes and that Phe control should not be liberalized as children with PKU age.

White matter integrity and executive abilities following treatment with tetrahydrobiopterin (BH4) in individuals with phenylketonuria

Tetrahydrobiopterin (BH(4)) lowers blood phenylalanine (Phe) in individuals with PKU who are responders, but its effects on the brain and cognition have not been explored thoroughly. We examined blood Phe, microstructural white matter integrity, and executive abilities in 12 BH(4) responders before (i.e., baseline) and after (i.e., follow-up) six months of treatment with BH(4). Compared with baseline, Phe in these responders decreased by 51% during a 4 week screening period after initiation of treatment and remained lowered by 37% over the 6 month follow-up period. Significant improvements in white matter integrity, evaluated by mean diffusivity from diffusion tensor imaging, were also found following six months of treatment. Improvements in executive abilities were not identified, although six months may have been a period too brief for changes in cognition to follow changes in the brain. To our knowledge, our study is the first to explore relationships among Phe, white matter integrity, executive abilities, and BH(4) treatment within a single study.

White matter integrity and executive abilities in individuals with phenylketonuria

Previous studies have revealed white matter abnormalities in the brains of individuals with phenylketonuria (PKU), but the microstructural nature of these abnormalities and their relationship to phenylalanine (Phe) levels and cognitive outcomes are poorly understood. In the current study, the microstructural integrity of white matter in 29 individuals with early-treated PKU and 12 healthy controls was examined using two complementary diffusion tensor imaging (DTI) approaches: region-of-interest (ROI) based analysis and voxel-wise tract based spatial statistics (TBSS) analysis. Relationships among DTI, executive abilities, and Phe level findings were explored. DTI revealed widespread lowering of mean diffusivity (MD) in the white matter of the PKU group in comparison with the control group. Executive abilities were also poorer for individuals with PKU than controls. Within the PKU group, lower MD was associated with higher Phe level and poorer executive abilities. These findings are the first to demonstrate the interplay among microstructural white matter integrity, executive abilities, and Phe control in individuals with PKU.