Executive strategic processing during verbal fluency performance in children with phenylketonuria

Verbal Fluency in Prelingually Deaf, Early Implanted Children and Adolescents With Cochlear Implants

PURPOSE

Verbal fluency tasks assess the ability to quickly and efficiently retrieve words from the mental lexicon by requiring subjects to rapidly generate words within a phonological or semantic category. This study investigated differences between cochlear implant users and normal-hearing peers in the clustering and time course of word retrieval during phonological and semantic verbal fluency tasks.

METHOD

Twenty-eight children and adolescents (aged 9-17 years) with cochlear implants and 33 normal-hearing peers completed measures of verbal fluency, nonverbal intelligence, speech perception, and verbal short-term/working memory. Phonological and semantic verbal fluency tests were scored for total words generated, words generated in each 10-s interval of the 1-min task, latency to first word generated, number of word clusters, average cluster size, and number of word/cluster switches.

RESULTS

Children and adolescents with cochlear implants generated fewer words than normal-hearing peers throughout the entire 60-s time interval of the phonological and semantic fluency tasks. Cochlear implant users also had slower start latency times and produced fewer clusters and switches than normal-hearing peers during the phonological fluency task. Speech perception and verbal working memory scores were more strongly associated with verbal fluency scores in children and adolescents with cochlear implants than in normal-hearing peers.

CONCLUSIONS

Cochlear implant users show poorer phonological and semantic verbal fluency than normal-hearing peers, and their verbal fluency is significantly associated with speech perception and verbal working memory. These findings suggest deficits in fluent retrieval of phonological and semantic information from long-term lexical memory in cochlear implant users.

Association between executive functions and gross motor skills in overweight/obese and eutrophic preschoolers: cross-sectional study

BACKGROUND

Preschool age (3-5 years old) is a crucial period for children to acquire gross motor skills and develop executive functions (EFs). However, the association between the qualitative gross motor skills and EFs remains unknown in preschoolers, especially among overweight and obese children.

METHODS

This was a cross-sectional, exploratory, and quantitative study carried out on 49 preschool children, divided into two subgroups according to their body mass index (overweight/obese: 24; eutrophic [normal weight]: 25). The mean age was 4.59 years. More than half of the sample were boys (55%) and most of the mothers had completed high school (67%) and were class C socioeconomic level (63%). Gross motor skills were assessed using the Test of Gross Motor Development-2, while EFs were evaluated using Semantic verbal fluency (SVF), Tower of Hanoi (TH), Day/Night Stroop, and Delayed Gratification tests. Multiple linear regression models adjusted for sex, age, maternal education, socioeconomic status, quality of the home environment, and quality of the school environment using the stepwise method were executed, considering the cognitive tasks as independent variables and gross motor skills as dependent variable.

RESULTS

The overweight/obese preschoolers showed worse locomotor skills than their eutrophic peers and below average gross motor quotient (GMQ). Overweight/obese girls performed worse in OC skills than boys with excess weight. SVF (number of errors) and TH (rule breaks) explained 57.8% of the variance in object control (OC) skills and 40.5% of the variance in GMQ (p < .05) in the overweight/obese children. Surprisingly, there was no significant association between any of the EF tasks and gross motor skills in the eutrophic children.

CONCLUSION

A relationship between EF tasks (number of errors in SVF and rule breaks in TH) and gross motor skills (OC and GMQ) was demonstrated in the overweight/obese preschoolers, indicating that worse cognitive flexibility, working memory, planning, and problem solving are associated with worse gross motor skills in this population when compared to eutrophic children.

Beneficial Effects of Slow-Release Large Neutral Amino Acids after a Phenylalanine Oral Load in Patients with Phenylketonuria

The mainstay of phenylketonuria treatment is a low protein diet, supplemented with phenylalanine (Phe)-free protein substitutes and micronutrients. Adhering to this diet is challenging, and even patients with good metabolic control who follow the dietary prescriptions in everyday life ignore the recommendations occasionally. The present study explores the ability of slow-release large neutral amino acids (srLNAAs) to prevent Phe increase following a Phe dietary load. Fourteen phenylketonuric patients aged ≥13 years were enrolled in a 6-week protocol. Oral acute Phe loads of 250 and 500 mg were added to the evening meal together with srLNAAs (0.5 gr/kg). Phe and tyrosine were dosed before dinner, 2h-after dinner, and after the overnight fast. After oral Phe loads, mean plasma Phe remained stable and below 600 µmol/L. No Phe peaks were registered. Tyrosine levels significantly increased, and Phe/Tyrosine ratio decreased. No adverse events were registered. In conclusion, a single oral administration of srLNAAs at the dose of 0.5 gr/kg is effective in maintaining stable plasma Phe during acute oral loads with Phe-containing food and may be added to the dietetic scheme in situations in which patients with generally good adherence to diet foresee a higher than prescribed Phe intake due to their commitments.

Large Neutral Amino Acids (LNAAs) Supplementation Improves Neuropsychological Performances in Adult Patients with Phenylketonuria

Phenylketonuria is an inborn error of phenylalanine (Phe) metabolism diagnosed by newborn screening and treated early with diet. Although diet prevents intellectual disability, patients often show impairment of executive functions, working memory, sustained attention, and cognitive flexibility. Large neutral amino acids (LNAAs) have been proposed as a dietary supplement for PKU adults. Few studies show that LNAAs may help in improving metabolic control as well as cognitive functions. In this study, 10 adult PKU patients with poor metabolic control were treated for 12 months with LNAAs (MovisCom, 0.8–1 g/kg/day) and underwent Phe and Tyrosine (Tyr) monitoring monthly. Neuropsychological assessment was performed at T0, T+3, and T+12 months by using the American Psychological General Well-Being Index, the Wisconsin Card Sorting Test, the Test of Attentional Performance, and the 9-Hole Peg Test. No change in plasma Phe levels was observed during LNAAs supplementation, while Tyr levels significantly improved during LNAAs supplementation (p = 0.03). Psychometric tests showed an improvement of distress and well-being rates, of executive functions, attention, and vigilance, whereas no difference was noted regarding hand dexterity. This study adds evidence of the advantage of LNAAs supplementation in improving cognitive functions and well-being in patients with PKU with poor metabolic control.

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.

Neuropsychological Profile of Children with Early and Continuously Treated Phenylketonuria: Systematic Review and Future Approaches

OBJECTIVE

To provide a comprehensive systematic review of the literature by examining studies published on all cognitive aspects of children with early and continuously treated phenylketonuria (ECT-PKU) included in the databases Medline, PsycINFO, and PsycARTICLE.

METHOD

In addition to a classical approach, we summarized methodology and results of each study in order to discuss current theoretical and methodological issues. We also examined recent advances in biochemical markers and treatments of PKU, with implications for future research on metabolic control and its role as a determinant of neuropsychological outcome.

RESULTS

Consistent with previous reviews, the hypothesis of a specific and central executive impairment in children with ECT-PKU was suggested. However, findings are inconclusive regarding the nature of executive impairments as well as their specificity, impact on everyday life, persistence over time, and etiology.

CONCLUSION

Given the current state of the science, we suggest future directions for research that utilizes a developmental and integrative approach to examine the effects of recent advances in biochemical markers and treatment of PKU. (JINS, 2019, 25, 624-643).

Changes in semantic fluency across childhood: Normative data from Australian-English speakers

PURPOSE

Verbal fluency tests are often used as part of an assessment battery to investigate children's lexical knowledge as well as executive function skills. To date, however, issues surrounding consistency of measurement cloud comparisons across studies, with the developmental performance of Australian-English speaking children also currently lacking. This study tracked verbal fluency development as measured by two semantic fluency tasks that included coding of fluency, clustering and switching type responses.

METHOD

Participants included 355 typically developing Australian-English speaking children (4-10 years) and 46 young adults. Total fluency was determined by the number of words produced for each category (Animals or Food), minus repetitions and rule violations. Semantic clusters (words generated within a subcategory) were coded while switches between single words or subcategories were differentiated and coded as either hard or cluster switches.

RESULT

Fluency showed consistent improvement over age. Cluster Switches and Hard Switches showed some evidence of a plateau in performance relative to fluency, but in opposite direction. Other measures showed no strong trends over age. Results were similar for both semantic categories.

CONCLUSION

Our results highlight the rich information available within a semantic fluency task and the importance of differentiating hard and cluster switches in paediatric samples.

Developmental Trajectories of Executive and Verbal Processes in Children with Phenylketonuria

Phenylketonuria (PKU) is a hereditary disorder characterized by disrupted phenylalanine metabolism and cognitive impairment. However, the precise nature and developmental trajectory of this cognitive impairment remains unclear. The present study used a verbal fluency task to dissociate executive and verbal processes in children with PKU (n = 23; 7-18 years) and controls (n = 44; 7-19 years). Data were collected at three longitudinal timepoints over a three-year period, and the contributions of age, group, and their interaction to fluency performance were evaluated. Results indicated impairments in executive processes in children with PKU, which were exacerbated by declining metabolic control.

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

Speed of processing and executive functions in adults with phenylketonuria: Quick in finding the word, but not the ladybird

A reduction in processing speed is widely reported in phenylketonuria (PKU), possibly due to white matter pathology. We investigated possible deficits and their relationships with executive functions in a sample of 37 early-treated adults with PKU (AwPKUs). AwPKUs were not characterized by a generalized speed deficit, but instead their performance could be explained by two more specific impairments: (a) a deficit in the allocation of visuo-spatial attention that reduced speed in visual search tasks, in some reading conditions and visuo-motor coordination tasks; and (b) a more conservative decision mechanism that slowed down returning an answer across domains. These results suggest that the impairments in executive functions seen in AwPKUs are not the consequence of a generalized speed deficit. They also suggest that processing speed is linked to the efficiency of a particular cognitive component and cannot be considered a general function spanning domains. Similarities with patterns in ageing are discussed.

Brazilian Normative Data on Letter and Category Fluency Tasks: Effects of Gender, Age, and Geopolitical Region

Verbal fluency is a basic function of language that refers to the ability to produce fluent speech. Despite being an essentially linguistic function, its measurements are also used to evaluate executive aspects of verbal behavior. Performance in verbal fluency (VF) tasks varies according to age, education, and cognitive development. Neurodevelopmental disorders that affect the functioning of frontal areas tend to cause lower performance in VF tasks. Despite the relative consensus that has been reached in terms of the use of VF tasks for the diagnosis of dyslexia and attention-deficit/hyperactivity disorder, few studies have considered regional variations in Brazil. The present study sought to provide normative data on VF tasks in children by considering gender, age, education, and geopolitical region of origin with auxiliary purposes in neuropsychological diagnosis of disorders that occur with executive changes The study included 298 participants, 7–10 years of age of both genders, who performed three letter fluency tasks and three category fluency tasks. The data were subjected to correlational and variance analyses, with age and gender as factors. No effect of gender on the children's performance was found. However, significant differences between age groups were observed, with better performance in letter tasks in older children and better performance in letter tasks compared with category tasks. Significant regional differences in performance on the letter VF task were observed. These results reinforce the importance of regional normative data in countries with high regional cultural variations, such as Brazil.

Word Retrieval Ability on Phonemic Fluency in Typically Developing Children

Verbal fluency tasks are simple behavioral measures useful in assessing word retrieval abilities. Among the verbal fluency tasks, the utility of the Phonemic Fluency Task in children has received less attention. As the task is dependent on phonemic characteristics of each language, there is a great need for understanding its developmental trend. The present study, therefore, aims to delineate the performance on phonemic fluency in typically developing Malayalam-speaking children. Verbal fluency performance on 2 tasks of phonemic fluency was tested using a cross-sectional study design among 1,015 school-going Malayalam-speaking typically developing children aged 5 to 15 years old. Performance with respect to word productivity and clustering-switching measures was analyzed. The effect of age, gender, and tasks on the outcome measures were investigated in the present study. Study findings revealed a positive influence of age with no statistically significant gender effects. Children employed both task-discrepant and task-consistent organizational strategies during tasks of phonemic fluency, dependent purely on the Malayalam language. Future research focusing on developmental trends across different languages is vital for enhancing the task's clinical sensitivity and specificity among childhood disorders.

The effects of tetrahydrobiopterin (BH4) treatment on brain function in individuals with phenylketonuria

Phenylketonuria (PKU) is a rare genetic condition characterized by an absence or mutation of the PAH enzyme, which is necessary for the metabolism of the amino acid phenylalanine into tyrosine. Recently, sapropterin dihydrochloride, a synthetic form of tetrahydrobiopterin (BH₄), has been introduced as a supplemental treatment to dietary phe control for PKU. Very little is known regarding BH₄ treatment and its effect on brain and cognition. The present study represents the first examination of potential changes in neural activation in patients with PKU during BH₄ treatment. To this end, we utilized an n-back working memory task in conjunction with functional magnetic resonance imaging (fMRI) to evaluate functional brain integrity in a sample of individuals with PKU at three timepoints: Just prior to BH₄ treatment, after 4 weeks of treatment, and after 6 months of treatment. Neural activation patterns observed for the PKU treatment group were compared with those of a demographically-matched sample of healthy non-PKU individuals who were assessed at identical time intervals. Consistent with past research, baseline evaluation revealed impaired working memory and atypical brain activation in the PKU group as compared to the non-PKU group. Most importantly, BH₄ treatment was associated with improvements in both working memory and brain activation, with neural changes evident earlier (4-week timepoint) than changes in working memory performance (6-month timepoint).

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We examine working memory and neural activation in patients with PKU at baseline.

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We track behavioral and neural changes related to BH4 treatment in the patients.

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BH4 treatment associated with improvement in neural activity at 4-week timepoint.

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BH4 treatment associated with improvement in working memory at 6-month timepoint.

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.

Processing speed and executive abilities in children with phenylketonuria

OBJECTIVE

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

METHOD

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

RESULTS

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

CONCLUSIONS

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