Benefits of normalizing plasma phenylalanine: impact on behaviour and health. A case report

The impact of metabolic control on cognition, neurophysiology, and well-being in PKU: A systematic review and meta-analysis of the within-participant literature

Phenylketonuria (PKU) is a metabolic disease where Phenylalanine (Phe) rises much above normal levels. Cross-sectional and correlational studies provide valuable information on the importance of maintaining low blood-Phe to achieve good outcomes, but they may be confounded, at least partially, by differences in participant demographics. Moreover, the effect of Phe at older ages is difficult to ascertain because of strong associations between Phe levels across ages. Within-participant studies avoid confounding issues. We have reviewed these studies. We followed PRISMA guidelines to search the literature for studies reporting the impact of Phe changes within participants. Phe was either increased or decreased through diet relaxation/resumption or through pharmacological interventions. Forty-six separate articles reported, singly or in combination, results on cognition (N = 37), well-being (N = 22) and neurophysiological health (N = 14). For all studies, we established, in a binary way, whether a benefit of lower Phe was or was not demonstrated and compared numbers showing benefit versus a null or negative outcome. We then analyzed whether critical parameters (e.g., length of the study/condition for the change, size of Phe change achieved) influenced presence or absence of benefit. For a subset of studies that reported quantitative cognitive outcomes, we carried out a meta-analysis to estimate the size of change in cognitive performance associated with a change in Phe and its significance. There were significantly more studies with benefits than no benefits, both for cognitive and well-being outcomes, and a trend in this direction for neurophysiological outcomes. The meta-analysis showed a highly significant effect size both overall (0.55) and when studies with adults/adolescents were considered separately (0.57). There was some indication that benefits were easier to demonstrate when differences in Phe were larger and achieved across a longer period, but these effects were not always consistent. These results reinforce results from the literature by demonstrating the importance of lower Phe in children as well as in adolescents and adults, even when confounding factors in group composition are eliminated. The field would benefit from further studies where Phe levels are contrasted within-participants to ascertain how much Phe needs to be changed and for how long to see a difference and which measures demonstrate a difference (e.g., which cognitive tasks).

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.

Pilot study to evaluate the effects of tetrahydrobiopterin on adult individuals with phenylketonuria with measurable maladaptive behaviors

OBJECTIVES

To evaluate the effects of tetrahydrobiopterin (BH4) on maladaptive behavior in patients with phenylketonuria (PKU).

METHODS

In an effort to determine if BH4 has any effects on the central nervous system, we studied 10 individuals with PKU and measurable maladaptive behaviors for 1 year. Behavioral assessments using the Vineland Adaptive Behavior Scales-Second Edition and a PKU Behavior Checklist were obtained at baseline, 6 months, and at the end of the study. Biochemical measures including plasma amino acids were obtained quarterly, and phenylalanine (Phe) and tyrosine (Tyr) were obtained monthly.

RESULTS

Out of the 10 subjects, 2 were responders to BH4, as determined by a blood Phe reduction >30%. While blood Phe in the 8 nonresponders did not change significantly throughout the study, their Tyr levels were significantly higher at 6 months (p=0.012), but not at 12 months (p=0.23). By the end of the study, 8 subjects exhibited fewer maladaptive behaviors on the components of the Vineland Maladaptive Behavior Index, and all 10 had lower total scores on the PKU Behavior Checklist.

CONCLUSION

These findings suggest that there may be direct effects of BH4 on the central nervous system, independent of lowering blood Phe.

Phenylalanine hydroxylase deficiency

Phenylalanine hydroxylase deficiency is an autosomal recessive disorder that results in intolerance to the dietary intake of the essential amino acid phenylalanine. It occurs in approximately 1:15,000 individuals. Deficiency of this enzyme produces a spectrum of disorders including classic phenylketonuria, mild phenylketonuria, and mild hyperphenylalaninemia. Classic phenylketonuria is caused by a complete or near-complete deficiency of phenylalanine hydroxylase activity and without dietary restriction of phenylalanine most children will develop profound and irreversible intellectual disability. Mild phenylketonuria and mild hyperphenylalaninemia are associated with lower risk of impaired cognitive development in the absence of treatment. Phenylalanine hydroxylase deficiency can be diagnosed by newborn screening based on detection of the presence of hyperphenylalaninemia using the Guthrie microbial inhibition assay or other assays on a blood spot obtained from a heel prick. Since the introduction of newborn screening, the major neurologic consequences of hyperphenylalaninemia have been largely eradicated. Affected individuals can lead normal lives. However, recent data suggest that homeostasis is not fully restored with current therapy. Treated individuals have a higher incidence of neuropsychological problems. The mainstay of treatment for hyperphenylalaninemia involves a low-protein diet and use of a phenylalanine-free medical formula. This treatment must commence as soon as possible after birth and should continue for life. Regular monitoring of plasma phenylalanine and tyrosine concentrations is necessary. Targets of plasma phenylalanine of 120-360 μmol/L (2-6 mg/dL) in the first decade of life are essential for optimal outcome. Phenylalanine targets in adolescence and adulthood are less clear. A significant proportion of patients with phenylketonuria may benefit from adjuvant therapy with 6R-tetrahydrobiopterin stereoisomer. Special consideration must be given to adult women with hyperphenylalaninemia because of the teratogenic effects of phenylalanine. Women with phenylalanine hydroxylase deficiency considering pregnancy should follow special guidelines and assure adequate energy intake with the proper proportion of protein, fat, and carbohydrates to minimize risks to the developing fetus. Molecular genetic testing of the phenylalanine hydroxylase gene is available for genetic counseling purposes to determine carrier status of at-risk relatives and for prenatal testing.

Psychiatric features in children with genetic syndromes: toward functional phenotypes

Neurodevelopmental disorders with identified genetic etiologies present a unique opportunity to study gene-brain-behavior connections in child psychiatry. Parsing complex human behavior into dissociable components is facilitated by examining a relatively homogenous genetic population. As children with developmental delay carry a greater burden of mental illness than the general population, familiarity with the most common genetic disorders will serve practitioners seeing a general child population. In this article, basic genetic testing and 11 of the most common genetic disorders are reviewed, including the evidence base for treatment. Based on their training in child development, family systems, and multimodal treatment, child psychiatrists are well positioned to integrate cognitive, behavioral, social, psychiatric, and physical phenotypes, with a focus on functional impairment.

Challenges and pitfalls in the management of phenylketonuria

Despite recent advances in the management of phenylketonuria and hyperphenylalaninemia, important questions on the management of this disorder remain unanswered. Consensus exists on the need for neonatal screening and early treatment, yet disagreement persists over threshold levels of blood phenylalanine for starting treatment, target blood phenylalanine levels, and the management of older patient groups. The mainstay of treatment is a phenylalanine-restricted diet, but its application varies between and within countries. Beyond diet treatment, there is a lack of consensus on the use of newer treatments such as tetrahydrobiopterin. Although neonatal screening and early treatment has meant that most well-treated children grow up with near-normal IQ scores, the effect of relaxing metabolic control on cognitive and executive function later in life is still not fully understood. Although it is clear from the available literature that the active control of blood phenylalanine levels is of vital importance, there are other treatment-related factors that affect outcome. A uniform and firmly evidence-based approach to the management of phenylketonuria is required.

Psychiatric features in children with genetic syndromes: toward functional phenotypes

Neurodevelopmental disorders with identified genetic etiologies present a unique opportunity to study gene-brain-behavior connections in child psychiatry. Parsing complex human behavior into dissociable components is facilitated by examining a relatively homogenous genetic population. As children with developmental delay carry a greater burden of mental illness than the general population, familiarity with the most common genetic disorders will serve practitioners seeing a general child population. In this article basic genetic testing and 11 of the most common genetic disorders are reviewed, including the evidence base for treatment. Based on their training in child development, family systems, and multimodal treatment, child psychiatrists are well positioned to integrate cognitive, behavioral, social, psychiatric, and physical phenotypes, with a focus on functional impairment.

Characterization of tremor in phenylketonuric patients

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

Treatment of Phenylketonuria-associated Tremor with Deep Brain Stimulation: Case Report

OBJECTIVE AND IMPORTANCE:

Phenylketonuria (PKU) is an inborn error of metabolism that causes severe neurological impairment, despite dietary treatment. We present a case of PKU-induced cerebellar tremor treated with deep brain stimulation. There have been no previously reported cases of a patient with a PKU tremor treated with deep brain stimulation.

CLINICAL PRESENTATION:

A 36-year-old male patient with PKU presented with signs of cerebellar disease including dysmetria, resting tremor, and intention tremor in the left upper extremity.

INTERVENTION:

A deep brain stimulation electrode was placed in the ventral intermediate nucleus of the right thalamus.

CONCLUSION:

Immediately after surgery, the patient had nearly complete resolution of intention tremor in the left arm. His resting tremor in the left hand was also greatly improved. The 30-month follow-up examination revealed maintenance of the immediate postoperative improvement.

Phenylalanine-restricted diet should be life long. A case report on long-term follow-up of an adolescent with untreated phenylketonuria

The aim of this brief report is to stimulate a debate and to advocate life-long treatment with phenylalanine restricted diet to persons with phenylketonuria. We present a case of an adolescent male who today is a 65 year old with moderate mental retardation. He was previously observed as having severe challenging and self-injurious behaviour, sleeping disorder, hyperactivity, and masturbation. In the last year before reassessment he displayed loss of weight, muscle weakness resulting in wheelchair placement, upper respiratory infections, and fungal skin infections. After reassessment in 1998 the patient was started on treatment with a phenylalanine-restricted diet supplemented with vitamin B12, iron, and folic acid. At follow-up one year later the patient had regained his weight and was walking around freely. The challenging and self-injurious behaviour, and the masturbation, had ceased, and he was participating in social activities which he had previously not been able to participate in. At follow-up four years later he was still at this level of accomplishment. In general, this patient's quality of life had increased. We therefore recommend life-long treatment with phenylalanine restricted diet for persons with previously treated, and also for those with untreated, phenylketonuria.