Prevalence of Anxiety Disorders among Children with Phenylketonuria

In conclusion, doctors, mental health professionals, and dietary professionals who treat individuals with PKU should do everything in their power to prevent above recommended levels of blood phenyla-lanine and significant blood variations in those who are diagnosed since an early age as well as late diagnosed individuals. Good quality metabolic regulation in children and ongoing assistance for PKU communities could contribute to improved quality of life, decreased anxiety, and perhaps even improved engagement among impacted teenagers during their teenage years of an uprising.

Limitation:

One center study and the cross-sectional nature of the study are the main limitations. Small sample size is another limitation of our study as it is a rare metabolic disease. Using parent rated anxiety scale carry bias because anxiety is an internalizing disorder.

Recommendation:

• Strict adherence to metabolic control can prevent the development of anxiety disorders in children with classic PKU.
• Screening for anxiety disorders in those with high levels of over 1 year mean of phenylalanine.

Abbereviations:

PKU: phenylketouria

Phe: phenylalanine

Declarations

Author's Contributions

ISA, GMB, AMK, SIS and MIA conceived the study. ISA, GMB, AMK designed the research, AMK, SIS and ISA prepared the socio-demographic and anxiety scales. ISA collected the data. SIS performed statistical analysis. ISA analyzed the data and wrote the manuscript. All authors contributed to drafting the manuscript and approved the final version of the manuscript. ISA shall act as the corresponding author of the paper.

Acknowledgements: Not applicable.

Consent for publication: Written informed consent obtained from parents/legal guardian.

Competing interests: The authors declare that there was no competing interest.

Introduction

One of the most prevalent inborn metabolic errors, phenylketonuria, is now a well-known example of a rare but treatable illness. To prevent severe brain damage and intellect-tual incapacity in impacted children, a therapeutic diet low in phenylalanine (Phe) should be introduced as soon as possible, preferably during the initial fourteen days of life ⁽¹⁾.

The food plan must be followed by the patients for the rest of their lives. Regretfully, PKU treatment adherence declines over time, just like it does in other chronic conditions. High

blood Phe concentration bouts occur frequently as a result, and brain dysfunction that manifests as behavioral abnormalities and neuropsy-chological deficiencies may result ^(2,3).

The incidence of less obvious psychiatric consequences, including anxiety and sadness, which could compromise the therapeutic objectives, is little recognized despite the fact that significant cognitive deficits were commonly observed, particularly in adoles-cents who stopped receiving nutritional treatment ^(4,5).

Clinical findings in adult patients have frequently served as the basis for prior reports ^(6,7), but the situation with children is less certain. In Egypt the national newborn screening program has been started since 2015, and it involves screening for 19 genetic diseases including PKU ^(8,9).

In this study we aimed to evaluate the presence of anxiety disorders in children with classic phenylketonuria (early diagnosed through national screening program and late diagnosed) in comparison with healthy children, and to correlate this psychiatric comorbidity to the dynamics of blood phenylalanine level which reflect dietary control.

Patients and methods

Research design and participants:

This is a cross sectional, case-control study, including 50 PKU children recruited from the inborn errors of metabolism clinic in Minia university hospital, EL-Minya governorate, Egypt, from the period October 2023 to April 2024. The PKU children were subdivided according to the onset of diagnosis in to; early diagnosed cases, who were diagnosed through national newborn screening program within 6 weeks after delivery (NO= 22), and late diagnosed cases (NO= 28) who were diagnosed and treated after 6 weeks of life ⁽⁸⁾. The cases were age and sex matched with 26 healthy control children.

The study entry criteria included: 1) children with classic PKU 2) from both sexes 3) aged from 7 to 17 years. Exclusion criteria included: 1) being diagnosed with other types of PKU like hyperphenylalanenemia and tetrahydro-biopetrin deficiency 2) being diagnosed with other neurological complication like moderate to severe intellectual disability, epilepsy, autism and attention deficit hyperactivity disorders 3) refusal to complete the study.

Ethical consideration:

The study was approved by the Institutional Review Board of Minia University with NO: 698/3/2023. Before the start of the study, the purpose, the study aims, and design were explained to the children and their caregivers. Written consent was obtained from the caregivers, and verbal consent was obtained from the children themselves.

Methods

During a routine follow-up visit, every caregiver was asked to fulfill the demographic data including age, sex, residence, mother education, and family history of PKU, consanguinity, family size, number of affected siblings, birth order and age of diagnosis. The children were assessed through an interview with a pediatrician who performed thorough mental and physical assessment to exclude patients with associated neurological comor-bidity.

Anxiety disorders were scanned via specified anxiety questionnaire (Spence Children’s Anxiety Scale) after application of IQ test to exclude children with moderate and severe mental retardation especially from the late diagnosed cases.

Tools:

1. Anxiety scale and subscales:

We used the Spence Children Anxiety Scale parent-rated form (SCAS-P), which is completed by the parents. The scale consisted of 38 questions asking about the frequency of anxiety symptoms, and the answer will be chosen from 4 answers on a 4-points Likert scale graded from 0 to 3 as follows: 0) never, 1) sometimes, 2) often, and 3) always, with one open-ended question added if the parent wanted to add any additional symptoms, and the question is not scored. The scale is a well-validated tool for the diagnosis of anxiety disorders in children ^{(10, 11)}.

Each set of the 38 items will form a subscale, making the SCAS-P scale subdivided into 6 subscales, namely: obsessive-compulsive diso-rder (OCD), social phobia, panic agora-phobia, separation anxiety, physical injury fears, and generalized anxiety disorder.

The total SCAS scores, together with subscale scores, are transformed into t-scores. A t-score greater than 40 indicates a high anxiety level that requires additional clinical assessment and intervention, while t-score below 40 indicates no presence of anxiety symptoms. The Arabic version validity and reliability was approved by Milano et al., 2025 ^(12).

1. Intelligence quotient testing:

It is performed by an expert psychologist using Stanford bient 5^th edition.

Procedures:

Phenylalanine measurement:

The PKU children phenylalanine level was measured during the routine follow-up visit in the inborn errors of metabolism clinic at the time of questionnaire application and this reading will be referred as (recent pheny-lalanine), while the values of the previous readings over the last year were recorded and the mean was calculated for each child which will be used as a referral for the long-term control of the phenylalanine level (remote control).

Statistical analysis of the data

IBM SPSS software package version 26 (Armonk, NY: IBM Corp.) was used to analyze the data that was supplied into the computer's memory. Numbers and percentages were used to express qualitative findings. The statistical pattern of distribution was confirmed using the Shapiro-Wilk and Kolmogorov-Smirnov tests. For numerical data, we used mean, standard deviation and the range to describe the data which were normally distributed, while median and interquartile range were used for the data which is not normally distributed, At the 5% level, the results' significance was assessed.

For non-numerical data we used chi-square test and fisher exact test, to compare between different groups. For quantitative variables that were regularly distributed, ANOVA test was used to compare between more than 2 sets of normally distributed quantitative variables, to compare between more than two studied groups followed by post hoc analysis.  Although the Kruskal Wallis test is employed for quantitative data that is not regularly distributed. To compare two groups under study, we employed the independent t-test for numerical variables that are normally distributed. To compare two sets of numerical normally distributed data, we used the Mann Whitney test. For both uniform and irregular items, a Pearson and Spearman correlation analysis was performed respectively, and Roc curve analysis was done for prediction of elevated SCAS total score.

Results

Regarding demographic data of our children, we found significant difference between cases and control regarding residence that 96.5% of late diagnosed PKU children, and 68.2 % of early diagnosed children were from rural areas. Significant difference was found between cases and the control regarding mother literacy, with near half of the mothers of late diagnosed children were illiterate and, near one third of the mothers of early diagnosed children were illiterates, while only 11.5 % of mothers of the control group were illiterates. Parents of late diagnosed PKU children had 89.2% positive consanguinity and this was significantly differed from families of the control, also 77.2% of early diagnosis children had positive consanguinity while healthy children's parents had no history of consanguineous marriage (Table 1).

There is significant difference between IQ of the cases and the control children, with both early diagnosed and late diagnosed PKU children had significantly lower IQ levels than healthy children, and early diagnosed children had significantly higher IQ levels than late diagnosed ones as shown in (Table 1).

Regarding level of phe that was tested at the interview time (Recent phenylalanine) and mean of 1-year recording Phe levels (Remote phenylalanine), both were higher than the normal values however with no significant difference between recent and remote levels as shown in (Table 2).

In comparing levels of anxiety disorders, there were significant differences between cases and control. Late diagnosed, children showed significantly higher levels in all anxiety disorders than healthy control. Early diagnosed children behave like normal children with significant differences with late diagnosed children regarding obsessive compulsive disorder (OCD), panic agoraphobia and total SCAS score. However, early diagnosed children still show significantly higher levels regarding social phobias, separation anxiety and physical injury fears than healthy control as shown in (Table 3).

On trying to find out if there was association between phenylalanine levels (recent and

remote) and levels of anxiety disorders, we performed Pearson correlation and we found significant positive correlation between the recent phenylalanine levels with OCD, social phobia, separation anxiety, physical injury fears and total SCAS score, while remote pheny-lalanine correlated positively and significantly with all anxiety disorders and total SCAS score. The remote phenylalanine levels correlated significantly negatively with the IQ level. Mother education also correlated negatively with the phenylalanine levels as shown in (Table 4).

regression analysis was done to detect factors associated with elevated total anxiety SCAS, we found that the child age at test application, mother education, Consanguinity, number of siblings in the same family, onset of diagnosis and remote phenylalanine levels were significantly associated with development of high scores of total anxiety scale. However, on performing multivariate analysis, only remote phenylalanine levels and onset of diagnosis were associated with development of high total anxiety scale as shown in (Table 5).

On performing ROC Curve analysis for remote phenylalanine levels prediction of elevated SCA total scores, we found that values of the remote phenylalanine above 440.5 µmol/L, will significantly associated with elevated total SCAS score as shown in (Figure 1) and (Table 6), with sensitivity 94%, specificity 86.7%, Positive predictive value 65.2% and negative predictive value 98.1% with 88.1% total accuracy.

Discussion

Anxiety disorders are linked to impaired educational, interpersonal, and familial performance. Juvenile anxiety problems that are neglected often lead to persistent, unrelenting patterns that last throughout life ⁽¹³⁾. Youngsters who suffer from anxiety problems also have a higher chance of developing anxiety-related illnesses, depressive symptoms, drug use, and lower scholastic progression as they grow older ⁽¹⁴⁾. 

In this study, we aimed to investigate the prevalence of anxiety disorders in PKU children either early diagnosed and treated (within the 1^st 6 weeks of life) through national neonatal screening program or late diagnosed who born before the neonatal screening program, in comparison with normal healthy children.

Our study found that there were significant differences between late diagnosed PKU children and healthy controls regarding total anxiety scale score and all subscales' scores namely OCD, social phobia, panic agora-phobia, separation anxiety, physical injury fears and generalized anxiety disorder, with higher scores in late diagnosed PKU children.

Early treated PKU children behave like normal children with significant differences with late diagnosed children regarding total scale and subscales except for social phobia, separation anxiety and physical injury fears. These three anxiety disorders showed significantly higher differences in comparison with healthy controls.

These findings were in accordance with previous research which confirmed the presence of psychological comorbidities in PKU patients; Mainka et al., found that late diagnosed PKU patients have higher prevalence of anxiety disorders than normal population ⁽¹⁵⁾. Also, regarding early-treated PKU children, many studies showed that those children had an insufficient degree of independence from society and fears ⁽¹⁶⁾. According to some authors, PKU in children ⁽¹⁷⁾ and young teens ^{(18, 19)} can cause feelings of loneliness, anxious-sness, somatic problems, and depression.

In our study, at the test time phenylalanine level (recent phenylalanine) and the over 1 year mean Phenylalanine levels (remote phenylalanine) for early treated PKU children were (478.3±212 µmol/L and 451.5±194.3 µmol/L) respectively, and that for late diagnosed PKU children were (486±265 µmol/L and 582.3±362 µmol/L) respectively. Both levels for both groups were greater than the referenced blood Phe values (120 to 360 µmol/L) for children with classic phenylketonuria below 12 years old ⁽²⁰⁾.

These high levels of recent and remote phenylalanine correlated positively with the scores of anxiety disorders with more significant positive association observed between remote phenylalanine levels and all levels of anxiety disorders and total SCAS score.

On performing ROC curve analysis for prediction of elevated SCAS score using remote Phenylalanine level; we found that a cut-off value greater than 440.5 µmol/L was significantly associated with elevated total anxiety SCAS score. This is in accordance with some research which suggests that regulating blood phenylalanine levels in the range of (120 to 360 µmol/L) for the entire life is necessary for appropriate metabolic management ^(21,22).

It was found that sustained increase of phenylalanine can lead to affected myelination⁽²³⁾ and a reduction in the synthesis of brain protein ⁽²⁴⁾, with ultimately irrever-sible, severe damage to the brain ^(25,26). This is in agree with our finding that remote phenylalanine is significantly linked to the development of anxiety disorders, indicating that PKU children's propensity to experience stress and anxiety may be a chronic and nearly irreversible condition if phenylalanine levels not kept below the referenced values not only for 12 years but may be for life.

A shortage of serotonin in the central nervous system may be linked to several anxiety disorders, notably generalized anxiety disorder, obsessional compulsive disorder, special phobias, and panic attack disorder ⁽²⁷⁾. 

Many changes in serotonin arrangement include variations in the serotonin transporter gene, which have been linked to anxiety ⁽²⁸⁾ and the same for the gene of tryptophan hydroxy-lase specified for the mental processing⁽²⁹⁾. Unsurprisingly, then, increased phenylalanine levels in individuals with phenyl-ketonuria and the resulting decrease in levels of serotonin in the central nervous system have been linked to a higher incidence of developing anxiety symptoms ⁽³⁰⁾.

Besides high levels of phenylalanine that was detected in our PKU children, our study found a significant role of maternal education, family size and onset of diagnosis in the development of anxiety disorders in those children.

It is widely acknowledged that youngs-ters, along with their parents, experience emotional strain due to the demands of rigorous monitoring and diet restriction ⁽³⁰⁾; but

according to most of the other research, increased phenylalanine is linked to serious anxiety ⁽³¹⁾.

This is in accordance with our results as on performing multiple regression analysis only high phenylalanine levels and delayed diagnosis are associated with higher levels of total anxiety score.

It was found that anxiety symptoms were shown to be significantly attenuated when phenylalanine values were reduced as when using antidepressant drugs, especially selective serotonin reuptake inhibitors, it proves beneficial for a particular category of patients, especially individuals who have failed to achieve a satisfactory drop in phenyla-lanine levels ^(31).