Phenylketonuria due to phenylalanine hydroxylase deficiency: an unfolding story. Medical Research Council Working Party on Phenylketonuria

Protein Substitutes in PKU; Their Historical Evolution

Protein substitutes developed for phenylketonuria (PKU) are a synthetic source of protein commonly based on L-amino acids. They are essential in the treatment of phenylketonuria (PKU) and other amino acid disorders, allowing the antagonistic amino acid to be removed but with the safe provision of all other amino acids necessary for maintaining normal physiological function. They were first formulated by a chemist and used experimentally on a 2-year-old girl with PKU and their nutritional formulations and design have improved over time. Since 2008, a bioactive macropeptide has been used as a base for protein substitutes in PKU, with potential benefits of improved bone and gut health, nitrogen retention, and blood phenylalanine control. In 2018, animal studies showed that physiomimic technology coating the amino acids with a polymer allows a slow release of amino acids with an improved physiological profile. History has shown that in PKU, the protein substitute's efficacy is determined by its nutritional profile, amino acid composition, dose, timing, distribution, and an adequate energy intake. Protein substitutes are often given little importance, yet their pharmacological actions and clinical benefit are pivotal when managing PKU.

Tyrosine supplementation for phenylketonuria

BACKGROUND

Phenylketonuria is an inherited disease for which the main treatment is the dietary restriction of the amino acid phenylalanine. The diet has to be initiated in the neonatal period to prevent or reduce mental handicap. However, the diet is very restrictive and unpalatable and can be difficult to follow. A deficiency of the amino acid tyrosine has been suggested as a cause of some of the neuropsychological problems exhibited in phenylketonuria. Therefore, this review aims to assess the efficacy of tyrosine supplementation for phenylketonuria. This is an update of previously published versions of this review.

OBJECTIVES

To assess the effects of tyrosine supplementation alongside or instead of a phenylalanine-restricted diet for people with phenylketonuria, who commenced on diet at diagnosis and either continued on the diet or relaxed the diet later in life. To assess the evidence that tyrosine supplementation alongside, or instead of a phenylalanine-restricted diet improves intelligence, neuropsychological performance, growth and nutritional status, mortality rate and quality of life.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Trials Register which is comprised of references identified from comprehensive electronic database searches, handsearches of relevant journals and abstract books of conference proceedings. Additional studies were identified from handsearches of the Journal of Inherited Metabolic Disease (from inception in 1978 to 1998). The manufacturers of prescribable dietary products used in the treatment of phenylketonuria were also contacted for further references. Date of the most recent search of the Group's Inborn Errors of Metabolism Trials Register: 07 December 2020.

SELECTION CRITERIA

All randomised or quasi-randomised trials investigating the use of tyrosine supplementation versus placebo in people with phenylketonuria in addition to, or instead of, a phenylalanine-restricted diet. People treated for maternal phenylketonuria were excluded.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed the trial eligibility, methodological quality and extracted the data.

MAIN RESULTS

Six trials were found, of which three trials reporting the results of a total of 56 participants, were suitable for inclusion in the review. The blood tyrosine concentrations were significantly higher in the participants receiving tyrosine supplements than those in the placebo group, mean difference 23.46 (95% confidence interval 12.87 to 34.05). No significant differences were found between any of the other outcomes measured. The trials were assessed as having a low to moderate risk of bias across several domains.

AUTHORS' CONCLUSIONS

From the available evidence no recommendations can be made about whether tyrosine supplementation should be introduced into routine clinical practice. Further randomised controlled studies are required to provide more evidence. However, given this is not an active area of research, we have no plans to update this review in the future.

Dietary interventions for phenylketonuria

BACKGROUND

Phenylketonuria is an inherited disease treated with dietary restriction of the amino acid phenylalanine. The diet is initiated in the neonatal period to prevent learning disability; however, it is restrictive and can be difficult to follow. Whether the diet can be relaxed or discontinued during adolescence or should be continued for life remains a controversial issue, which we aim to address in this review. This is an updated version of a previously published review.

OBJECTIVES

To assess the effects of a low-phenylalanine diet commenced early in life for people with phenylketonuria. To assess the possible effects of relaxation or termination of the diet on intelligence, neuropsychological outcomes and mortality, growth, nutritional status, eating behaviour and quality of life.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group Trials Register comprising references identified from comprehensive electronic database searches, handsearches of relevant journals and abstract books of conference proceedings. Most recent search of the Inborn Errors of Metabolism Trials Register: 30 April 2020.

SELECTION CRITERIA

All randomised or quasi-randomised controlled trials comparing a low-phenylalanine diet to relaxation or termination of dietary restrictions in people with phenylketonuria.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed study eligibility and methodological quality, and subsequently extracted the data.

MAIN RESULTS

We included four studies in this review (251 participants), and found few significant differences between treatment and comparison groups for the outcomes of interest. Blood phenylalanine levels were significantly lower in participants with phenylketonuria following a low-phenylalanine diet compared to those on a less restricted diet, mean difference (MD) at three months -698.67 (95% confidence interval (CI) -869.44 to -527.89). Intelligence quotient was significantly higher in participants who continued the diet than in those who stopped the diet, MD after 12 months 5.00 (95% CI 0.40 to 9.60). However, these results came from a single study.

AUTHORS' CONCLUSIONS

The results of non-randomised studies have concluded that a low-phenylalanine diet is effective in reducing blood phenylalanine levels and improving intelligence quotient and neuropsychological outcomes. We were unable to find any randomised controlled studies that have assessed the effect of a low-phenylalanine diet versus no diet from diagnosis. In view of evidence from non-randomised studies, such a study would be unethical and it is recommended that low-phenylalanine diet should be commenced at the time of diagnosis. There is uncertainty about the precise level of phenylalanine restriction and when, if ever, the diet should be relaxed. This should be addressed by randomised controlled studies; however, no new studies are expected in this area so we do not plan to update this review.

Maternal PKU: Defining phenylalanine tolerance and its variation during pregnancy, according to genetic background

BACKGROUND AND AIMS

Phenylketonuria (PKU)-affected women may become pregnant, and dietary phenylalanine (Phe) intake must be adjusted according to Phe tolerance. We report our experience with maternal PKU in relation to genotype PKU heterogeneity.

METHODS AND RESULTS

A total of 10 pregnancies in 7 PKU women (7 different genotypes) were followed up as part of personalized care. Phe tolerance during preconception and pregnancy was assessed by strict dietary control and weekly Phe measurement (blood spots) in relation to genotype. Most women had stopped PKU diet during childhood or adolescence and six pregnancies were unplanned; a phenylalanine-restricted diet was reinstituted soon after conception. Women were classified according to their Phe levels at birth screening and genotype. Phe tolerance increased systematically in the course of pregnancy in all cases, but the increase was different in subjects with classic PKU (cPKU) when compared with cases with mild hyperphenylalaninemia (mHPA), both on average (+297 mg/day in cPKU vs. 597 in mHPA; P = 0.017) and as percentage (+107% in cPKU vs. +17% in mHPA). Notably, Phe tolerance also varied in the same women in the course of different pregnancies, when body weight gain was also different. Two newborns from the same cPKU mother (unplanned pregnancies on free diet) were affected by congenital alterations.

CONCLUSIONS

Several factors influence metabolic phenotype in maternal PKU, to an unpredictable extent even in the same woman. The number of maternal PKU cases is growing in dedicated Nutrition Units, and the burden associated with careful management of this condition for the health care system should be adequately considered.

Treating Phenylketonuria: A Single Centre Experience

Hyperphenylalaninaemia (HPA) is an inherited disorder that results in raised plasma phenylalanine levels with a range of severities, including phenylketonuria (PKU). Since the first attempts at treatment using a low-phenylalanine diet and after more than 50 years of research, considerable progress has been made so we are now at a stage where mental retardation caused by high plasma phenylalanine can be prevented. We must, however, be aware of the new challenges we face in managing PKU. These include: maintaining optimal growth by providing enough phenylalanine without jeopardizing the child's psychomotor development; providing an optimal nutritional status that ensures other essential nutrients, such as long chain polyunsaturated fatty acids, are not excluded from the diet; ensuring optimal compliance to the dietary intervention; and considering patients' quality of life. New strategies, such as tetrahydrobiopterin (BH4) supplementation, need to be evaluated with regard to safety, efficacy and expected outcomes in specific types of HPA.

[What should the paediatrician know about hyperphenylalaninaemia?]

Hyperphenylalaninaemias are defined by a blood phenylalanine over 2mg/dl. The main cause is due to a mutation in the gene that codes the phenylalanine hydroxylase that catalyses the reaction that converts phenylalanine into tyrosine. The hyperphenylalaninaemias are classified into benign or mild hyperphenylalaninaemias, or mild, moderate or classic phenylketonurias. Due to its delayed detection outside the neonatal period it causes severe mental retardation. Its detection along with congenital hypothyroidism has been part of the National Neonatal Screening Program since 1992 in Chile. This article aims to answer the most common questions asked by the paediatrician when faced with a patient with hyperphenylalaninaemias.

Sapropterin dihydrochloride for phenylketonuria

BACKGROUND

Phenylketonuria results from a deficiency of the enzyme phenylalanine hydroxylase. Dietary restriction of phenylalanine keeps blood phenylalanine concentration low. Most natural foods are excluded from diet and supplements are used to supply other nutrients. Recent publications report a decrease in blood phenylalanine concentration in some patients treated with sapropterin dihydrochloride. We examined the evidence for the use of sapropterin dihydrochloride to treat phenylketonuria. This is an update of a previously published Cochrane Review. 

OBJECTIVES

To assess the safety and efficacy of sapropterin dihydrochloride in lowering blood phenylalanine concentration in people with phenylketonuria.

SEARCH METHODS

We identified relevant trials from the Group's Inborn Errors of Metabolism Trials Register. Date of last search: 11 August 2014.We also searched ClinicalTrials.gov and Current controlled trials. Last search: 4 September 2014We contacted the manufacturers of the drug (BioMarin Pharmaceutical Inc.) for information regarding any unpublished trials.

SELECTION CRITERIA

Randomized controlled trials comparing sapropterin with no supplementation or placebo in people with phenylketonuria due to phenylalanine hydroxylase deficiency.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trials and extracted outcome data.

MAIN RESULTS

Two placebo-controlled trials were included. One trial administered 10 mg/kg/day sapropterin in 89 children and adults with phenylketonuria whose diets were not restricted and who had previously responded to saproterin.This trial measured change in blood phenylalanine concentration. The second trial screened 90 children (4 to 12 years) with phenylketonuria whose diet was restricted, for responsiveness to sapropterin. Forty-six responders entered the placebo-controlled part of the trial and received 20 mg/kg/day sapropterin. This trial measured change in both phenylalanine concentration and protein tolerance. Both trials reported adverse events. The trials showed an overall low risk of bias; but both are Biomarin-sponsored. One trial showed a significant lowering in blood phenylalanine concentration in the sapropterin group (10 mg/kg/day), mean difference -238.80 μmol/L (95% confidence interval -343.09 to -134.51); a second trial (20 mg/kg/day sapropterin) showed a non-significant difference, mean difference -51.90 μmol/L (95% confidence interval -197.27 to 93.47). The second trial also reported a significant increase in phenylalanine tolerance, mean difference18.00 mg/kg/day (95% confidence interval 12.28 to 23.72) in the 20 mg/kg/day sapropterin group.

AUTHORS' CONCLUSIONS

There is evidence of short-term benefit from using sapropterin in some people with sapropterin-responsive forms of phenylketonuria; blood phenylalanine concentration is lowered and protein tolerance increased. There are no serious adverse events associated with using sapropterin in the short term.There is no evidence on the long-term effects of sapropterin and no clear evidence of effectiveness in severe phenylketonuria.

Phenylketonuria Scientific Review Conference: state of the science and future research needs

New developments in the treatment and management of phenylketonuria (PKU) as well as advances in molecular testing have emerged since the National Institutes of Health 2000 PKU Consensus Statement was released. An NIH State-of-the-Science Conference was convened in 2012 to address new findings, particularly the use of the medication sapropterin to treat some individuals with PKU, and to develop a research agenda. Prior to the 2012 conference, five working groups of experts and public members met over a 1-year period. The working groups addressed the following: long-term outcomes and management across the lifespan; PKU and pregnancy; diet control and management; pharmacologic interventions; and molecular testing, new technologies, and epidemiologic considerations. In a parallel and independent activity, an Evidence-based Practice Center supported by the Agency for Healthcare Research and Quality conducted a systematic review of adjuvant treatments for PKU; its conclusions were presented at the conference. The conference included the findings of the working groups, panel discussions from industry and international perspectives, and presentations on topics such as emerging treatments for PKU, transitioning to adult care, and the U.S. Food and Drug Administration regulatory perspective. Over 85 experts participated in the conference through information gathering and/or as presenters during the conference, and they reached several important conclusions. The most serious neurological impairments in PKU are preventable with current dietary treatment approaches. However, a variety of more subtle physical, cognitive, and behavioral consequences of even well-controlled PKU are now recognized. The best outcomes in maternal PKU occur when blood phenylalanine (Phe) concentrations are maintained between 120 and 360 μmol/L before and during pregnancy. The dietary management treatment goal for individuals with PKU is a blood Phe concentration between 120 and 360 μmol/L. The use of genotype information in the newborn period may yield valuable insights about the severity of the condition for infants diagnosed before maximal Phe levels are achieved. While emerging and established genotype-phenotype correlations may transform our understanding of PKU, establishing correlations with intellectual outcomes is more challenging. Regarding the use of sapropterin in PKU, there are significant gaps in predicting response to treatment; at least half of those with PKU will have either minimal or no response. A coordinated approach to PKU treatment improves long-term outcomes for those with PKU and facilitates the conduct of research to improve diagnosis and treatment. New drugs that are safe, efficacious, and impact a larger proportion of individuals with PKU are needed. However, it is imperative that treatment guidelines and the decision processes for determining access to treatments be tied to a solid evidence base with rigorous standards for robust and consistent data collection. The process that preceded the PKU State-of-the-Science Conference, the conference itself, and the identification of a research agenda have facilitated the development of clinical practice guidelines by professional organizations and serve as a model for other inborn errors of metabolism.

Current situation and prospects of newborn screening and treatment for Phenylketonuria in China - compared with the current situation in the United States, UK and Japan

Phenylketonuria (PKU) is a treat-able and prevent-able inborn error of metabolism which leads to severe mental retardation and neurobehavioral abnormalities. A screening program, especially for early detection, combined with a Phe-restricted therapeutic diet can help to control the process of PKU of most patients. The China government has put more emphasis on newborn screening and treatment against PKU, yet by comparing the situation of newborn screening and treatment against PKU in China and the relatively developed countries - United States, United Kingdom and Japan, the newborn screening and treatment against PKU in China is relatively weak and many deficiencies are found. More studies concerning multi-stage target blood Phe concentration criteria, a policy that requires newborn screening has to be taken, better financial support for newborn screening, publicity for newborn screening, and national guidelines for treatment of PKU may be prospects in China and may provide some support for better development of newborn screening and treatment against PKU in China.

Tyrosine supplementation for phenylketonuria

BACKGROUND

Phenylketonuria is an inherited disease for which the main treatment is the dietary restriction of the amino acid phenylalanine. The diet has to be initiated in the neonatal period to prevent or reduce mental handicap. However, the diet is very restrictive and unpalatable and can be difficult to follow. A deficiency of the amino acid tyrosine has been suggested as a cause of some of the neuropsychological problems exhibited in phenylketonuria. Therefore, this review aims to assess the efficacy of tyrosine supplementation for phenylketonuria.

OBJECTIVES

To assess the effects of tyrosine supplementation alongside or instead of a phenylalanine-restricted diet for people with phenylketonuria, who commenced on diet at diagnosis and either continued on the diet or relaxed the diet later in life. To assess the evidence that tyrosine supplementation alongside, or instead of a phenylalanine-restricted diet improves intelligence, neuropsychological performance, growth and nutritional status, mortality rate and quality of life.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Trials Register which is comprised of references identified from comprehensive electronic database searches, handsearches of relevant journals and abstract books of conference proceedings. Additional studies were identified from handsearches of the Journal of Inherited Metabolic Disease (from inception in 1978 to 1998). The manufacturers of prescribable dietary products used in the treatment of phenylketonuria were also contacted for further references.Date of the most recent search of the Group's Inborn Errors of Metabolism Trials Register: 28 June 2012.

SELECTION CRITERIA

All randomised or quasi-randomised trials investigating the use of tyrosine supplementation versus placebo in people with phenylketonuria in addition to, or instead of, a phenylalanine-restricted diet. People treated for maternal phenylketonuria were excluded.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed the trial eligibility, methodological quality and extracted the data.

MAIN RESULTS

Six trials were found, of which three trials reporting the results of a total of 56 participants, were suitable for inclusion in the review. The blood tyrosine concentrations were significantly higher in the participants receiving tyrosine supplements than those in the placebo group, mean difference 23.46 (95% confidence interval 12.87 to 34.05). No significant differences were found between any of the other outcomes measured.

AUTHORS' CONCLUSIONS

From the available evidence no recommendations can be made about whether tyrosine supplementation should be introduced into routine clinical practice. Further randomised controlled studies are required to provide more evidence.

Costs and outcomes over 36 years of patients with phenylketonuria who do and do not remain on a phenylalanine-restricted diet

BACKGROUND

To quantify the costs and consequences of managing phenylketonuria (PKU) in the UK and to estimate the potential implications to the UK's National Health Service (NHS) of keeping patients on a phenylalanine-restricted diet for life.

METHOD

A computer-based model was constructed depicting the management of PKU patients over the first 36 years of their life, derived from patients suffering from this metabolic disorder in The Health Improvement Network database (a nationally representative database of patients registered with general practitioners in the UK). The model was used to estimate the incidence of co-morbidities and the levels of healthcare resource use and corresponding costs over the 36 years.

RESULTS

Patients who remained on a phenylalanine-restricted diet accounted for 38% of the cohort. Forty-seven per cent of patients discontinued their phenylalanine-restricted diet between 15 and 25 years of age. Of these, 73% remained off diet and 27% restarted a restricted diet at a mean 30 years of age. Fifteen per cent of the cohort had untreated PKU. Eleven per cent of patients who remained on a phenylalanine-restricted diet for 36 years received the optimum amount of prescribed amino acid supplements. Patients had a mean 12 general practitioner visits per year and one hospital outpatient visit annually, but phenylalanine levels were only measured once every 18 to 24 months. The mean NHS cost (at 2007/08 prices) of managing a PKU sufferer over the first 36 years of their life was estimated to range between £21 000 and £149 000, depending on the amount of prescribed nutrition they received.

CONCLUSION

The findings suggest that the majority of patients with PKU were under-treated. The NHS cost of patient management should not be an obstacle to encouraging patients to remain on a restricted diet until further information becomes available about the long-term clinical impact of stopping such a diet. Nevertheless, patients require counselling and managed follow up regardless of the choices they make about their diet.

Adaptation of phenylalanine and tyrosine catabolic pathway to hibernation in bats

Some mammals hibernate in response to harsh environments. Although hibernating mammals may metabolize proteins, the nitrogen metabolic pathways commonly activated during hibernation are not fully characterized. In contrast to the hypothesis of amino acid preservation, we found evidence of amino acid metabolism as three of five key enzymes, including phenylalanine hydroxylase (PAH), homogentisate 1,2-dioxygenase (HGD), fumarylacetoacetase (FAH), involved in phenylalanine and tyrosine catabolism were co-upregulated during hibernation in two distantly related species of bats, Myotis ricketti and Rhinolophus ferrumequinum. In addition, the levels of phenylalanine in the livers of these bats were significantly decreased during hibernation. Because phenylalanine and tyrosine are both glucogenic and ketogenic, these results indicate the role of this catabolic pathway in energy supply. Since any deficiency in the catabolism of these two amino acids can cause accumulations of toxic metabolites, these results also suggest the detoxification role of these enzymes during hibernation. A higher selective constraint on PAH, HPD, and HGD in hibernators than in non-hibernators was observed, and hibernators had more conserved amino acid residues in each of these enzymes than non-hibernators. These conserved amino acid residues are mostly located in positions critical for the structure and activity of the enzymes. Taken together, results of this work provide novel insights in nitrogen metabolism and removal of harmful metabolites during bat hibernation.

Sapropterin dihydrochloride for phenylketonuria

BACKGROUND

Phenylketonuria results from a deficiency of the enzyme phenylalanine hydroxylase. Dietary restriction of phenylalanine keeps blood phenylalanine concentration low. Most natural foods are excluded from diet and supplements are used to supply other nutrients. Recent publications report a decrease in blood phenylalanine concentration in some patients treated with sapropterin dihydrochloride. We examined the evidence for the use of sapropterin dihydrochloride to treat phenylketonuria.  

OBJECTIVES

To assess the safety and efficacy of sapropterin dihydrochloride in lowering blood phenylalanine concentration in people with phenylketonuria.

SEARCH METHODS

We identified relevant trials from the Group's Inborn Errors of Metabolism Trials Register. Date of last search: 29 June 2012.We also searched ClinicalTrials.gov and Current controlled trials. Last search: 23 July 2012.We contacted the manufacturers of the drug (BioMarin Pharmaceutical Inc.) for information regarding any unpublished trials.

SELECTION CRITERIA

Randomized controlled trials comparing sapropterin with no supplementation or placebo in people with phenylketonuria due to phenylalanine hydroxylase deficiency.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trials and extracted outcome data.

MAIN RESULTS

Two placebo-controlled trials were included. One trial administered 10 mg/kg/day sapropterin in 89 children and adults with phenylketonuria whose diets were not restricted and who had previously responded to saproterin.This trial measured change in blood phenylalanine concentration. The second trial screened 90 children (4 to 12 years) with phenylketonuria whose diet was restricted, for responsiveness to sapropterin. Forty-six responders entered the placebo-controlled part of the trial and received 20 mg/kg/day sapropterin. This trial measured change in both phenylalanine concentration and protein tolerance. Both trials reported adverse events. The trials showed an overall low risk of bias; but both are Biomarin-sponsored. One trial showed a significant lowering in blood phenylalanine concentration in the sapropterin group (10 mg/kg/day), mean difference -238.80 μmol/L (95% confidence interval -343.09 to -134.51); a second trial (20 mg/kg/day sapropterin) showed a non-significant difference, mean difference -51.90 μmol/L (95% confidence interval -197.27 to 93.47). The second trial also reported a significant increase in phenylalanine tolerance, mean difference18.00 mg/kg/day (95% confidence interval 12.28 to 23.72) in the 20 mg/kg/day sapropterin group.

AUTHORS' CONCLUSIONS

There is evidence of short-term benefit from using sapropterin in some patients with sapropterin-responsive forms of phenylketonuria; blood phenylalanine concentration is lowered and protein tolerance increased. There are no serious adverse events associated with using sapropterin in the short term.There is no evidence on the long-term effects of sapropterin and no clear evidence of effectiveness in severe phenylketonuria.

Commentary: What degree of hyperphenylalaninaemia requires treatment?

Despite some 50 years' experience in the treatment of phenylketonuria and numerous scientific publications on the subject there is no clear consensus as to what degree of hyperphenylalaninaemia will result in intellectual impairment. Studies of three main types, on untreated cases of moderate hyperphenylalaninaemia, on treated cases of phenylketonuria, and on the effects of current blood phenylalanine concentration on executive function, have lead to different conclusions. Overall, there appears to be a fairly strong case for limiting dietary treatment to individuals whose blood phenylalanine levels would otherwise exceed 600 μmol/L. This is now policy in some European countries but a formal large-scale study of long-term outcomes to validate the approach is urgently required.

Chaperone-like therapy with tetrahydrobiopterin in clinical trials for phenylketonuria: is genotype a predictor of response?

Prospectively enrolled phenylketonuria patients (n=485) participated in an international Phase II clinical trial to identify the prevalence of a therapeutic response to daily doses of sapropterin dihydrochloride (sapropterin, KUVAN(®)). Responsive patients were then enrolled in two subsequent Phase III clinical trials to examine safety, ability to reduce blood Phenylalanine levels, dosage (5-20 mg/kg/day) and response, and bioavailability of sapropterin. We combined phenotypic findings in the Phase II and III clinical trials to classify study-related responsiveness associated with specific alleles and genotypes identified in the patients. We found that 17% of patients showed a response to sapropterin. The patients harbored 245 different genotypes derived from 122 different alleles, among which ten alleles were newly discovered. Only 16.3% of the genotypes clearly conferred a sapropterin-responsive phenotype. Among the different PAH alleles, only 5% conferred a responsive phenotype. The responsive alleles were largely but not solely missense mutations known to or likely to cause misfolding of the PAH subunit. However, the metabolic response was not robustly predictable from the PAH genotypes, based on the study design adopted for these clinical trials, and accordingly it seems prudent to test each person for this phenotype with a standardized protocol.

Non-PKU mild hyperphenylalaninemia (MHP)--the dilemma

Recent reviews have suggested that some patients with "non-PKU mild hyperphenylalaninemia" (MHP) might display neuropsychological executive function deficits and should be considered for treatment with tetrahydrobipterin (BH4) and/or phenylalanine (Phe) restricted diet. Patients with phenylketonuria (PKU)--Classical and Mild/Atypical variants--appear to need "mean lifetime phenylalanine (Phe) levels" of 120-360 μmol/L for optimal results. MHP patients, on the other hand, have natural Phe levels of 200-600 μmol/L. Until recently this was thought to be a benign condition. The available literature has been reviewed in detail and no good evidence, to date, has been uncovered to support treatment of MHP. It is suggested that more MHP subjects be tested to confirm this. A plea is made to formulate a consistent world-wide classification of the PKU phenotypes.

Tyrosine supplementation for phenylketonuria

BACKGROUND

Phenylketonuria is an inherited disease for which the main treatment is the dietary restriction of the amino acid phenylalanine. The diet has to be initiated in the neonatal period to prevent or reduce mental handicap. However, the diet is very restrictive and unpalatable and can be difficult to follow. A deficiency of the amino acid tyrosine has been suggested as a cause of some of the neuropsychological problems exhibited in phenylketonuria. Therefore, this review aims to assess the efficacy of tyrosine supplementation for phenylketonuria.

OBJECTIVES

To assess the effects of tyrosine supplementation alongside or instead of a phenylalanine-restricted diet for people with phenylketonuria, who commenced on diet at diagnosis and either continued on the diet or relaxed the diet later in life. To assess the evidence that tyrosine supplementation alongside, or instead of a phenylalanine-restricted diet improves intelligence, neuropsychological performance, growth and nutritional status, mortality rate and quality of life.

SEARCH STRATEGY

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Trials Register which is comprised of references identified from comprehensive electronic database searches, handsearches of relevant journals and abstract books of conference proceedings. Additional studies were identified from handsearches of the Journal of Inherited Metabolic Disease (from inception in 1978 to 1998). The manufacturers of prescribable dietary products used in the treatment of phenylketonuria were also contacted for further references.Date of the most recent search of the Group's Inborn Errors of Metabolism Trials Register: 09 June 2010.

SELECTION CRITERIA

All randomised or quasi-randomised trials investigating the use of tyrosine supplementation versus placebo in people with phenylketonuria in addition to, or instead of, a phenylalanine-restricted diet. People treated for maternal phenylketonuria were excluded.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed the trial eligibility, methodological quality and extracted the data.

MAIN RESULTS

Six trials were found, of which three trials reporting the results of a total of 56 participants, were suitable for inclusion in the review. The blood tyrosine concentrations were significantly higher in the participants receiving tyrosine supplements than those in the placebo group, mean difference 23.46 (95% confidence interval 12.87 to 34.05). No significant differences were found between any of the other outcomes measured.

AUTHORS' CONCLUSIONS

From the available evidence no recommendations can be made about whether tyrosine supplementation should be introduced into routine clinical practice. Further randomised controlled studies are required to provide more evidence.

Sapropterin dihydrochloride for phenylketonuria

BACKGROUND

Phenylketonuria results from a deficiency of the enzyme phenylalanine hydroxylase. Dietary restriction of phenylalanine keeps blood phenylalanine concentration low. Most natural foods are excluded from diet and supplements are used to supply other nutrients. Recent publications report a decrease in blood phenylalanine concentration in some patients treated with sapropterin dihydrochloride. We examined the evidence for the use of sapropterin dihydrochloride to treat phenylketonuria.

OBJECTIVES

To assess the safety and efficacy of sapropterin dihydrochloride in lowering blood phenylalanine concentration in people with phenylketonuria.

SEARCH STRATEGY

We identified relevant trials from the Group's Inborn Errors of Metabolism Trials Register. Last search:07 May 2010.We also searched ClinicalTrials.gov and Current controlled trials. Last search: 01 September 2009.We contacted the manufacturers of the drug (BioMarin Pharmaceutical Inc.) for information regarding any unpublished trials.

SELECTION CRITERIA

Randomized controlled trials comparing sapropterin with no supplementation or placebo in people with phenylketonuria due to phenylalanine hydroxylase deficiency.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trials and extracted outcome data.

MAIN RESULTS

Two placebo-controlled trials were included. One trial administered 10 mg/kg/day sapropterin in 89 children and adults with phenylketonuria whose diets were not restricted and who had previously responded to saproterin.This trial measured change in blood phenylalanine concentration. The second trial screened 90 children (4 to 12 years) with phenylketonuria whose diet was restricted, for responsiveness to sapropterin. Forty-six responders entered the placebo-controlled part of the trial and received 20 mg/kg/day sapropterin. This trial measured change in both phenylalanine concentration and protein tolerance. Both trials reported adverse events. The trials showed an overall low risk of bias; but both are Biomarin-sponsored. One trial showed a significant lowering in blood phenylalanine concentration in the sapropterin group (10 mg/kg/day), mean difference -238.80 mumol/L (95% confidence interval -343.09 to -134.51); a second trial (20 mg/kg/day sapropterin) showed a non-significant difference, mean difference -51.90 mumol/L (95% confidence interval -197.27 to 93.47). The second trial also reported a significant increase in phenylalanine tolerance, mean difference18.00 mg/kg/day (95% confidence interval 12.28 to 23.72) in the 20 mg/kg/day sapropterin group.

AUTHORS' CONCLUSIONS

There is evidence of short-term benefit from using sapropterin in some patients with sapropterin-responsive forms of phenylketonuria; blood phenylalanine concentration is lowered and protein tolerance increased. There are no serious adverse events associated with using sapropterin in the short term.There is no evidence on the long-term effects of sapropterin and no clear evidence of effectiveness in severe phenylketonuria.

Dietary interventions for phenylketonuria

BACKGROUND

Phenylketonuria is an inherited disease treated with dietary restriction of the amino acid phenylalanine. The diet is initiated in the neonatal period to prevent mental handicap; however, it is restrictive and can be difficult to follow. Whether the diet can be relaxed or discontinued during adolescence or should be continued for life remains a controversial issue, which we aim to address in this review.

OBJECTIVES

To assess the effects of a low-phenylalanine diet commenced early in life for people with phenylketonuria. To assess the possible effects of relaxation or termination of the diet on intelligence, neuropsychological outcomes and mortality, growth, nutritional status, eating behaviour and quality of life.

SEARCH STRATEGY

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group Trials Register comprising references identified from comprehensive electronic database searches, handsearches of relevant journals and abstract books of conference proceedings.Most recent search of the Inborn Errors of Metabolism Trials Register: 05 March 2009.

SELECTION CRITERIA

All randomised or quasi-randomised controlled trials comparing a low-phenylalanine diet to relaxation or termination of dietary restrictions in people with phenylketonuria.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed study eligibility and methodological quality, and subsequently extracted the data.

MAIN RESULTS

We included four studies in this review (251 participants), and found few significant differences between treatment and comparison groups for the outcomes of interest. Blood phenylalanine levels were significantly lower in participants with phenylketonuria following a low-phenylalanine diet compared to those on a less restricted diet, mean difference (MD) at three months -698.67 (95% confidence interval (CI) -869.44 to -527.89). Intelligence quotient was significantly higher in participants who continued the diet than in those who stopped the diet, MD after 12 months 5.00 (95% CI 0.40 to 9.60). However, these results came from a single study.

AUTHORS' CONCLUSIONS

The results of non-randomised studies have concluded that a low-phenylalanine diet is effective in reducing blood phenylalanine levels and improving intelligence quotient and neuropsychological outcomes. We were unable to find any randomised controlled studies that have assessed the effect of a low-phenylalanine diet versus no diet from diagnosis. In view of evidence from non-randomised studies, such a study would be unethical and it is recommended that low-phenylalanine diet should be commenced at the time of diagnosis. There is uncertainty about the precise level of phenylalanine restriction and when, if ever, the diet should be relaxed. This should be addressed by randomised controlled studies.

Cost effectiveness of establishing a neonatal screening programme for phenylketonuria in Libya

BACKGROUND

Inborn errors of metabolism (IEM) are a significant cause of morbidity and mortality in North Africa and the Middle East. With the evident success of neighbouring countries in initiating neonatal screening for IEM, the Libyan Authorities are now considering introducing neonatal screening for phenylketonuria (PKU) in Libya in the first instance, with the prospect of expanding the programme to cover other IEM in the future.

OBJECTIVE

To estimate the cost effectiveness of neonatal screening for PKU compared with no neonatal screening in Libya.

METHODS

A decision model was constructed to estimate the cost effectiveness of neonatal screening for PKU, from the perspective of Libyan society. Healthcare resource use and other input parameters were based on expert opinion.

RESULTS

The expected discounted cost to Libyan society of screening over 15 years and managing ∼374 patients with detected PKU over their lifetime was estimated to be $US213.6 (95% CI 211.9, 214.3) million (year 2007-8 values). The current expected discounted cost of managing these same PKU patients over their lifetime as a result of not screening was estimated to be $US321.2 (95% CI 318.0, 322.7) million. Hence, screening would save Libyan society $US107.6 (95% CI 105.5, 109.1) million over the lifetime of PKU patients and lead to an additional 6947 life-years (95% CI 6837, 7056). The expected cost per undiscounted life-year gained was estimated to be -$US15,500 (95% CI -16,600, 1100). There would be a 90% return on investment in the screening programme since society would gain $US1.9 for every $US1 invested. Probabilistic sensitivity analysis demonstrated that the screening programme has a 0.95 probability of being cost effective even at a willingness-to-pay threshold of $US4000 per life-year gained.

CONCLUSIONS

Within the model's limitations, neonatal screening for PKU appears to offer Libyan society a strategy that is cost effective compared with no neonatal screening.

What we know that could influence future treatment of phenylketonuria

Phenylketonuria (PKU), a Mendelian autosomal recessive phenotype (OMIM 261600), is an inborn error of metabolism that can result in impaired postnatal cognitive development. The phenotypic outcome is multifactorial in origin, based both in nature, the mutations in the gene encoding the L-phenylalanine hydroxylase enzyme, and nurture, the nutritional experience introducing L-phenylalanine into the diet. The PKU story contains many messages including a framework to appreciate the complexity of this disease where phenotype reflects both locus-specific and genomic components. This knowledge is now being applied in the development of patient-specific therapies.

PKU-what is daily practice in various centres in Europe? Data from a questionnaire by the scientific advisory committee of the European Society of Phenylketonuria and Allied Disorders

BACKGROUND

Since the start of the European Society of Phenylketonuria and Allied Disorders Treated as Phenylketonuria (ESPKU) in 1987, an increasing number of parental organizations of member countries have joined. Treatment varies widely within Europe. A survey among professionals was done to determine goals and practice.

METHOD

In 2005, a questionnaire was sent to professionals of member countries, addressing diagnostic and treatment procedures, numbers of patients necessary for a PKU centre, guidelines followed, numbers of patients treated and professionals involved in care, target phenylalanine concentrations, amount of protein prescribed, frequency of monitoring and clinical visits, need for follow-up of various clinical and biochemical data, the importance of various abnormalities, and definition of (non)compliance.

RESULTS

Seventeen centres of 12 countries answered. Professionals of 13 countries could not be reached or did not respond. Differences in care were observed in many issues of care including target phenylalanine concentrations. Only few issues had general consensus.

CONCLUSION

Not all countries were really active at ESPKU level. In the active countries, a professional could not always be contacted. Responses show that PKU care varies largely between European countries. Notwithstanding the large diversity on many issues of day-to-day care and therapeutic targets, results showed increasing consensus on some issues. The most important outcome of this questionnaire might be that the Scientific Advisory Committee of the ESPKU initiated meetings for professionals of different backgrounds taking care of PKU patients besides the already existing programme for parents, patients and delegates. Discussion among these professionals may improve quality of care.

The truth of treating patients with phenylketonuria after childhood: the need for a new guideline

In recent years, an increasing number of national guidelines on the treatment of phenylketonuria (PKU) have emerged. Most of these guidelines are dedicated to the care of children, while less attention is paid to the care of adults, although all guidelines underline the importance of diet for life. This review aims to summarize issues that need to be addressed within a guideline on the treatment of PKU, especially when care for patients beyond childhood is concerned. In this respect, it is of importance that adult patients, both willing and unwilling to be treated, need a guideline for care and follow-up. In PKU there is certainly a need for an improved unified guideline, especially after childhood, although many of the considerations in this article also apply to recommendations for treatment of children. Such a guideline will be a tool to improve treatment in PKU patients but should also include recommendations for collecting data for clinical and research purposes. Guideline development should also focus on nutritional, neuropsychological and psychosocial issues and not only on target plasma phenylalanine concentrations. In addition, guidelines must address not only what has to be done but also how it can be done, thereby improving concordance with the recommendations for treatment and management.

The PAH gene, phenylketonuria, and a paradigm shift

"Inborn errors of metabolism," first recognized 100 years ago by Garrod, were seen as transforming evidence for chemical and biological individuality. Phenylketonuria (PKU), a Mendelian autosomal recessive phenotype, was identified in 1934 by Asbjörn Fölling. It is a disease with impaired postnatal cognitive development resulting from a neurotoxic effect of hyperphenylalaninemia (HPA). Its metabolic phenotype is accountable to multifactorial origins both in nurture, where the normal nutritional experience introduces L-phenylalanine, and in nature, where mutations (>500 alleles) occur in the phenylalanine hydroxylase gene (PAH) on chromosome 12q23.2 encoding the L-phenylalanine hydroxylase enzyme (EC 1.14.16.1). The PAH enzyme converts phenylalanine to tyrosine in the presence of molecular oxygen and catalytic amounts of tetrahydrobiopterin (BH4), its nonprotein cofactor. PKU is among the first of the human genetic diseases to enter, through newborn screening, the domain of public health, and to show a treatment effect. This effect caused a paradigm shift in attitudes about genetic disease. The PKU story contains many messages, including: a framework on which to appreciate the complexity of PKU in which phenotype reflects both locus-specific and genomic components; what the human PAH gene tells us about human population genetics and evolution of modern humans; and how our interest in PKU is served by a locus-specific mutation database (http://www.pahdb.mcgill.ca; last accessed 20 March 2007). The individual Mendelian PKU phenotype has no "simple" or single explanation; every patient has her/his own complex PKU phenotype and will be treated accordingly. Knowledge about PKU reveals genomic components of both disease and health.

Efficacy of sapropterin dihydrochloride (tetrahydrobiopterin, 6R-BH4) for reduction of phenylalanine concentration in patients with phenylketonuria: a phase III randomised placebo-controlled study

BACKGROUND

Early and strict dietary management of phenylketonuria is the only option to prevent mental retardation. We aimed to test the efficacy of sapropterin, a synthetic form of tetrahydrobiopterin (BH4), for reduction of blood phenylalanine concentration.

METHODS

We enrolled 89 patients with phenylketonuria in a Phase III, multicentre, randomised, double-blind, placebo-controlled trial. We randomly assigned 42 patients to receive oral doses of sapropterin (10 mg/kg) and 47 patients to receive placebo, once daily for 6 weeks. The primary endpoint was mean change from baseline in concentration of phenylalanine in blood after 6 weeks. Analysis was on an intention-to-treat basis. The study is registered with ClinicalTrials.gov, number NCT00104247.

FINDINGS

88 of 89 enrolled patients received at least one dose of study drug, and 87 attended the week 6 visit. Mean age was 20 (SD 9.7) years. At baseline, mean concentration of phenylalanine in blood was 843 (300) micromol/L in patients assigned to receive sapropterin, and 888 (323) micromol/L in controls. After 6 weeks of treatment, patients given sapropterin had a decrease in mean blood phenylalanine of 236 (257) micromol/L, compared with a 3 (240) micromol/L increase in the placebo group (p<0.0001). After 6 weeks, 18/41 (44%) patients (95% CI 28-60) in the sapropterin group and 4/47 (9%) controls (95% CI 2-20) had a reduction in blood phenylalanine concentration of 30% or greater from baseline. Blood phenylalanine concentrations fell by about 200 micromol/L after 1 week in the sapropterin group and this reduction persisted for the remaining 5 weeks of the study (p<0.0001). 11/47 (23%) patients in the sapropterin group and 8/41 (20%) in the placebo group experienced adverse events that might have been drug-related (p=0.80). Upper respiratory tract infections were the most common disorder.

INTERPRETATION

In some patients with phenylketonuria who are responsive to BH4, sapropterin treatment to reduce blood phenylalanine could be used as an adjunct to a restrictive low-phenylalanine diet, and might even replace the diet in some instances.

Phenylketonuria: dietary and therapeutic challenges

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

Peak bone mass in patients with phenylketonuria

OBJECTIVE

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

PATIENTS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Muckle-Wells syndrome: report of six cases with hyperpigmented sclerodermoid skin lesions

Muckle-Wells syndrome (MWS) is a rare syndrome, characterized by chronic recurrent urticaria, often combined with fever, chills, rigors, malaise, and arthralgia. Progressive sensorineural deafness, and, in approximately one third of the patients, amyloidosis of the kidneys as well as of other organs may occur. It was first described in 1962 by Muckle and Wells. Herein we describe six cases of MWS showing, in addition to the classic features of MWS, unique skin lesions that to the best of our knowledge have not been described before in association with MWS.

Executive functioning and speed of processing in phenylketonuria

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

Phenylalanine ammonia lyase, enzyme substitution therapy for phenylketonuria, where are we now?

Phenylketonuria (PKU) is an autosomal recessive genetic disorder in which mutations in the phenylalanine-4-hydroxylase (PAH) gene result in an inactive enzyme (PAH, EC 1.14.16.1). The effect is an inability to metabolize phenylalanine (Phe), translating into elevated levels of Phe in the bloodstream (hyperphenylalaninemia). If therapy is not implemented at birth, mental retardation can occur. PKU patients respond to treatment with a low-phenylalanine diet, but compliance with the diet is difficult, therefore the development of alternative treatments is desirable. Enzyme substitution therapy with a recombinant phenylalanine ammonia lyase (PAL) is currently being explored. This enzyme converts Phe to the harmless metabolites, trans-cinnamic acid and trace ammonia. Taken orally and when non-absorbable and protected, PAL lowers plasma Phe in mutant hyperphenylalaninemic mouse models. Subcutaneous administration of PAL results in more substantial lowering of plasma and significant reduction in brain Phe levels, however the metabolic effect is not sustained following repeated injections due to an immune response. We have chemically modified PAL by pegylation to produce a protected form of PAL that possesses better specific activity, prolonged half-life, and reduced immunogenicity in vivo. Subcutaneous administration of pegylated molecules to PKU mice has the desired metabolic response (prolonged reduction in blood Phe levels) with greatly attenuated immunogenicity.

Development of pegylated forms of recombinant Rhodosporidium toruloides phenylalanine ammonia-lyase for the treatment of classical phenylketonuria

Phenylketonuria (PKU) is a metabolic disorder due primarily to mutations in the PAH gene that impair both phenylalanine hydroxylase activity and disposal of l-phenylalanine from the normal diet. Excess phenylalanine is toxic to cognitive development and a low-phenylalanine diet prevents mental retardation, but it is a difficult therapeutic option. Previous studies with recombinant phenylalanine ammonia-lyase, PAL, demonstrated pharmacologic and physiologic proofs of principle for PAL as an alternative therapy for PKU but its immunogenicity was problematic. From a series of formulations of linear and branched polyethylene glycols chemically conjugated to PAL, we have created a parenteral therapeutic agent for PKU treatment. All the pegylated molecules were fully characterized in vitro and the most promising formulations were then tested in vivo in the PKU mouse model. The linear 20-kDa PEG-PAL combination abolished in vivo immunogenicity after repeated challenge while retaining full catabolic activity against phenylalanine, suggesting potential as a novel PKU therapeutic.

Living with phenylketonuria: perspectives of patients and their families

This study surveyed PKU patients and their primary caretakers to assess their current management practices, the barriers to effective management, and the potential utility of a home monitor in managing PKU. A survey instrument was mailed to caretakers of all 50 patients with PKU in Utah between the ages of 2 and 18 years in 1997 (response rate 64%). It included separate components for caretakers and patients aged 10 to 18 years. Although there was uneven compliance with recommended practices, caretakers universally recognized the negative consequences of not adhering to the low-protein diet. There was, however, disagreement regarding such consequences among the older children surveyed. The primary obstacles cited to better adherence were time constraints and stress associated with food preparation and record-keeping, and the restrictions imposed on social life. Phenylalanine test results were regarded as the principal signal for the need for dietary adjustment. Despite the facts that obstacles to dietary adherence are multifaceted and that no single intervention would therefore serve as a panacea, a large majority of respondents believed a home monitor would facilitate better management of PKU through more regular and timely feedback.

Infusionstherapie und Ernährung von Risikogruppen

Besondere Situationen erfordern ein besonderes Vorgehen. Während bisher das »Standardvorgehen« bezüglich der Ernährung von pädiatrischen Patienten dargestellt wurde, beschäftigt sich das vorliegende Kapitel mit »Sondersituationen« der pädiatrischen Infusionstherapie und Ernährung. Behandlungssituationen, die ein besonderes Vorgehen bei der Therapie oder spezielle Aufmerksamkeit bei der Anpassung der Ernährung erfordern, entstehen in der Regel durch 4 mögliche Situationen:

spezifische Physiologie von Patientengruppen (z. B. Früh- oder Neugeborene),

Auswirkungen von therapeutischen Maßnahmen (z. B. Operationen),

Pathophysiologie von Erkrankungen (z. B. angeborene Stoffwechselerkrankungen, Erkrankungen des onkologischen, rheumatischen oder atopischen Formenkreises, Anorexia nervosa, Bulimie oder Adipositas) oder

besondere körperliche Belastungen [z. B. (Leistungs-)Sport].

Bekannte Strategien werden systematisch und prägnant dargestellt und diskutiert.

Die Beschäftigung mit der Ernährung von »Risikogruppen« übt das Erkennen und den Umgang von potenziellen Gefahrensituationen bei der Verordnung von bilanzierter Ernährung. So sollte auch derjenige von dem Kapitel profitieren, der sich mit den behandelten Patientengruppen, Situationen, Erkrankungen üblicherweise nicht beschäftigen muss.

Adult phenylketonuria

Newborn screening for phenylketonuria began 35 to 40 years ago in most industrialized countries. Because of this initiative, which resulted in early institution of phenylalanine-restricted diets, there are now many young adults with this disease who have normal or near-normal intellectual function. In North America alone, 200 patients with phenylketonuria enter adulthood every year. Most expert panels recommend following a phenylalanine-restricted "diet for life." However, there are few adult physicians dedicated to continuing care of this group, with the possible exception of maternal phenylketonuria. Up to 10% of adults with classic phenylketonuria, and possibly 50% of those with milder variants, may not need treatment; after adolescence, intelligence does not appear to deteriorate, at least into early adulthood, even if diet therapy is discontinued or not in good control. However, neuropsychological and psychosocial problems develop frequently, needing focused and intensive support by health care providers. New investigative methods and treatment options are on the horizon. There is an urgent need for physicians who will orchestrate the care of adults with phenylketonuria.

Optimal management of phenylketonuria: a centralized expert team is more successful than a decentralized model of care

OBJECTIVE

To compare phenylketonuria (PKU) management by a centralized, expert team in the Province of Nova Scotia (NS) with the decentralized approach in New Brunswick (NB).

STUDY DESIGN

Retrospective chart review documented frequency of outpatient visits, phenylalanine (Phe) concentration, and medical formula use. Structured telephone interviews with the 8 regional NB dietitians (NB-D) documented their knowledge and support in PKU management. Patients with PKU (n=108; age, birth to 42 years) reside in NB (n=69) and NS (n=39). More were lost to contact in NB than in NS (9/69 vs 1/39) and more were completely off diet in NB than in NS (24/60 vs 1/38, P=.05). All 15 children <2 years old followed by a PKU team in either NS or Saint John, NB had optimal Phe levels. Children 2 to 12 years of age in NS had better Phe control and more medical visits than in NB (P <.01). Older patients had more episodes of elevated Phe levels (P=.01). Formula was dispensed in appropriate yearly amounts to 52% in NB and >95% in NS. Mental handicap or borderline intelligence was common in both NB (44%) and NS (42%). All NB-D wished additional specialized medical, nursing, or social work assistance.

CONCLUSIONS

PKU management appears to be more effective with an expert, coordinated team approach.

Modifier effects in autism at the MAO-A and DBH loci

Autism is one of a group of pervasive developmental disorders (PDD) characterized by qualitative impairments in reciprocal social communication and by a preference for repetitive, stereotyped activities, interests, and behaviors. The disorder is caused in large part by genetic mechanisms, though no disease genes have yet been identified. The objective of this study was to investigate three markers, two in the DBH gene and one in the MAO-A gene, for maternal or fetal modifier effects on level of functioning (IQ). At the same time, the possibility of maternal or fetal susceptibility effects was also examined. We assembled 67 affected sibpairs and 45 singletons and determined allele frequencies at the three markers among the affected children and first degree relatives. Sizeable and significant modifier effects were found at the MAO locus and, to a lesser extent, at the DBH locus. Susceptibility effects were also found but not without qualification. We conclude that maternal genotypes at the MAO-A locus, and possibly at the DBH one, may modify IQ in children with autism through the intrauterine environment.

Motor function under lower and higher controlled processing demands in early and continuously treated phenylketonuria

This study examined motor control in 61 early and continuously treated patients with phenylketonuria (PKU) and 69 control participants, aged 7 to 14 years. The pursuit task demanded concurrent planning and execution of unpredictable movements, whereas the tracking task required a highly automated circular movement that could be planned in advance. PKU patients showed significantly poorer motor control in both tasks compared with control participants. Deficits were particularly observed for younger patients (age < 11 years). Differences between control participants and PKU patients were significantly greater in the pursuit task compared with the tracking task, indicating more serious deficits when a higher level of controlled processing is required. Correlations with historical phenylalanine levels indicated a later maturation of the level of control required by the pursuit task compared with the tracking task.

Assessment of adult phenylketonuria

Phenylketonuria (PKU) has been detected on the newborn screening programme since the 1960s. Although it is recognised that dietary treatment is successful in avoiding the severe mental retardation associated with untreated PKU, the long-term outcome for adults remains unclear. The Medical Research Council recommends that the diet be followed for life. This paper discusses the relevance of the findings of neurological deterioration, neuropsychological problems and brain imaging in adults with PKU. It suggests an approach to follow-up for adults with PKU including neurological assessments, awareness of nutritional deficiencies, educational requirements and the risks of maternal PKU.

Evaluation of possible reasons for the low phenylalanine ammonia lyase activity in cellulose nitrate membrane microcapsules

Microencapsulated phenylalanine ammonia lyase (PAL) exhibits a marked reduction in activity compared to the activity of the free enzyme in pH 8.5 Tris buffer. The purpose of this investigation was to evaluate the contribution of incomplete entrapment, the internal environment of cellulose nitrate membrane microcapsules, the diffusional barrier of the membrane and the microcapsulation process to the low activity of encapsulated PAL. A solution of PAL and 10% w/v hemoglobin was incorporated into cellulose nitrate membrane microcapsules. Hemoglobin incorporation was used as a surrogate marker of PAL entrapment. Using 14C hemoglobin, the encapsulation efficiency was determined to be 70% and suggested that incomplete entrapment might partially account for the low activity of encapsulated PAL. The effect of the internal environment of the microcapsule (10% hemoglobin solution) on PAL activity was evaluated by comparing enzyme activity in 10% w/v hemoglobin solution and pH 8.5 Tris buffer. Similar K(M) and V(max) values of PAL in the two media indicated that the internal environment of the microcapsule did not contribute to the reduction in activity of the encapsulated enzyme. The contribution of a membrane diffusional barrier was determined by breaking the putative barrier and measuring PAL activity in intact and broken microcapsules. Similar activity of PAL in these two conditions is evidence for the lack of a diffusional barrier. The effect of the microencapsulation process on PAL activity was evaluated by comparing K(M) and V(max) of free and encapsulated PAL. Similar K(M) values in these two media suggested that the process did not affect the conformation of PAL. However, encapsulated PAL had a 50% lower V(max) value compared to free PAL, which showed that the microencapsulation process deactivated a substantial proportion of the enzyme.

Biochemical effects of supplemented long-chain polyunsaturated fatty acids in hyperphenylalaninemia

Hyperphenylalaninemic (HPA) children display low levels of long-chain polyunsaturated fatty acids (LCPUFA), particularly docosahexaenoic acid (DHA), in circulating lipids and erythrocytes. We have investigated the effects on the blood fatty acid status and lipid picture of a balanced supplementation with LCPUFA in HPA children through a double-blind, placebo-controlled trial. A total of 20 well-controlled HPA, school-age children were randomized to receive through a 12-month trial fat capsules supplying either 26% fatty acid as LCPUFA (including 4.6%gamma -linolenic acid, 7.4% arachidonic acid, AA, 5.5% eicosapentaenoic acid and 8% DHA) or placebo (olive oil). The study supplementation was administered in order to provide 0.3-0.5% of the individual daily energy requirements as LCPUFA. Reference data were obtained from healthy children of comparable age. Among HPA children (whose DHA status was poor at baseline), those supplemented with LCPUFA showed an increase of around 100% in the baseline DHA levels in plasma phospholipids and erythrocytes. No changes of AA levels were observed. Blood lipid levels did not significantly change. A balanced supplementation with LCPUFA in treated HPA children may improve the DHA status without adversely affecting the AA status.

Effects of long-chain polyunsaturated fatty acid supplementation on fatty acid status and visual function in treated children with hyperphenylalaninemia

BACKGROUND

Children with phenylalanine-hydroxylase deficiency (type-I hyperphenylalaninemia, HPA) follow a low-phenylalanine diet, severely restricted in animal foods and long-chain polyunsaturated fatty acids (LCPUFA). Consequently, they have a poor LCPUFA status, particularly for docosahexaenoic acid (DHA). DHA is relevant to visual and neural development.

OBJECTIVE

To investigate the effects of a 12-month supplementation with LCPUFA in a double-blind, placebo-controlled trial in treated children with HPA.

STUDY DESIGN

Twenty children with well-controlled HPA were randomly allocated to receive either a fat supplement (supplying 26% as fatty acids including DHA, 8%) or a placebo. The fatty acid composition of erythrocyte lipids and the visual evoked potentials were measured at baseline and after 12 months of supplementation. Reference data were obtained from healthy children of comparable age.

RESULTS

At baseline children with HPA had a poorer DHA status and prolonged P100 wave latencies than the reference group. At the end of the trial the LCPUFA group showed a significant increase in DHA levels of erythrocyte lipids. In the LCPUFA group P100 wave latency decreased and was negatively associated with the DHA changes.

CONCLUSIONS

A balanced dietary supplementation with LCPUFA in children with HPA is associated with an increase of the DHA pool and improved visual function.

Increased risk of vitamin B12 deficiency in patients with phenylketonuria on an unrestricted or relaxed diet

OBJECTIVE

To investigate whether dietary relaxation or cessation in patients with phenylketonuria (PKU) predisposes to vitamin B12 deficiency.

STUDY DESIGN

Patients with PKU aged 11 to 38 years underwent a neurologic examination and dietetic assessment and were divided according to their diet into 1 of 3 groups: Strict - those on a strict low phenylalanine (phe) diet with amino acid, mineral, and vitamin supplements; Relaxed - those on a total protein intake of approximately 1 g/kg/d with 50% of this from natural protein and 50% from amino acid, mineral, and vitamin supplements; Unrestricted - those on no formal protein restriction and not taking amino acid supplements. Assays of blood samples were taken for vitamin B12 and folate levels by standard assays. Results were analyzed with Student t test.

RESULTS

Vitamin B12 levels were significantly lower in the PKU groups on relaxed or unrestricted diets compared with the normal population (P <.0001 [unrestricted] and.0034 [relaxed]). Folate levels were significantly elevated in all PKU groups (<.0001).

CONCLUSION

Patients with PKU who are no longer under strict dietary control may be at risk from vitamin B12 deficiency. We recommend that all patients should remain under medical and dietetic supervision and in particular have their vitamin B12 status monitored.

Tyrosine requirements in children with classical PKU determined by indicator amino acid oxidation

Tyrosine (Tyr) is an essential amino acid in phenylketonuria (PKU) because of the limited hydroxylation of phenylalanine (Phe) to Tyr. The recommended intakes for Tyr in PKU are at least five times the recommended phenylalanine intakes. This suggests that Phe and Tyr contribute approximately 20 and 80%, respectively, of the aromatic amino acid (AAA) requirement (REQ). In animals and normal humans, dietary Tyr was shown to spare 40-50% of the Phe requirement, proportions that reflect dietary and tissue protein composition. We tested the hypothesis that the Tyr REQ in PKU would account for 45% of the total AAA REQ by indicator amino acid oxidation (IAAO). Tyr REQ was determined in five children with PKU by examining the effect of varying dietary Tyr intake on lysine oxidation and the appearance of (13)CO(2) in breath (F(13)CO(2)) under dietary conditions of adequate energy, protein (1.5 g x kg(-1) x day(-1)), and phenylalanine (25 mg x kg(-1) x day(-1)). Lysine oxidation and F(13)CO(2) were determined using a primed 4-h oral equal-dose infusion of L-[1-(13)C]lysine. Lysine oxidation and F(13)CO(2) decreased linearly as Tyr intake increased, to a break point that was interpreted as the mean dietary Tyr requirement (16.3 and 19.2 mg x kg(-1) x day(-1), respectively). At Tyr intakes of >16.3 and 19.2 mg x kg(-1) x day(-1), lysine oxidation and F(13)CO(2), respectively, were low and constant. This represents 40.4 and 44.4%, respectively, of the total AAA intake. The current recommendations for Tyr intake in PKU patients appear to be overestimated by a factor of approximately 5. This study is the first application of the IAAO technique in a pediatric population and in humans with an inborn error of metabolism.

Dietary interventions for phenylketonuria

BACKGROUND

Phenylketonuria is an inherited disease for which the main treatment is the dietary restriction of the amino acid phenylalanine. The diet has to be initiated in the neonatal period to prevent or reduce mental handicap however the diet is very restrictive and unpalatable and can be difficult to follow. Whether the diet can be relaxed or discontinued during adolescence or should be continued for life remains a contraversial issue which we aim to address in this review.

OBJECTIVES

To assess the effects of a phenylalanine restricted diet commenced early in life for patients with phenylketonuria. To assess the possible adverse effects of relaxation or termination of the diet on intelligence, neuropsychological outcomes and mortality, and to assess the effect on growth, nutritional status and eating behaviour and quality of life.

SEARCH STRATEGY

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Trials Register which is a specialist trials register which comprises references identified from comprehensive electronic database searches, handsearching relevant journals and handsearching abstract books of conference proceedings. Additional studies were identified from handsearching the Journal of Inherited Metabolic Disease (from inception, 1978 to 1998). The manufacturers of dietary products for phenylketonuria were also contacted. Date of the most recent search of the Group's specialised register: November 1999.

SELECTION CRITERIA

All randomised or pseudorandomised controlled trials comparing a phenylalanine restricted diet to either relaxation or termination of dietary restrictions in patients with phenylketonuria.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed the trial eligibility, methodological quality and extracted the data.

MAIN RESULTS

Four studies were included in this review including a total of 251 patients. Few statistically significant differences were found between treatment and comparison groups for any of the outcomes apart from for blood phenylalanine level and intelligence quotient. Blood phenylalanine levels were significantly lower in those subjects with phenylketonuria following a phenylalanine restricted diet compared to those on a less restricted or relaxed diet (weighted mean difference at three months -672.203, 95% Confidence interval (CI) -813.799 to - 530.608). Intelligence quotient was significantly higher in subjects who continued on the phenylalanine restricted diet compared to those who terminated the diet (weighted mean difference after 12 months -5.00, 95% CI -9.595 to -0.405). However this is based on the results of only one study.

REVIEWER'S CONCLUSIONS

The results of non-randomised studies have concluded that a phenylalanine restricted diet is effective in reducing blood phenylalanine levels and improving intelligence quotient and neuropsychological outcome. No randomised controlled trials have assessed the effect of a phenylalanine restricted diet versus no dietary restrictions from diagnosis. In view of evidence from non-randomised studies, such a trial would now be unethical and it is recommended that phenylalanine restricted diet should be commenced at the time of diagnosis. There is uncertainty about the precise level of phenylalanine restriction and when, if ever, the diet should be relaxed. These questions should be addressed by randomised controlled trials with careful consideration given to which patients to include.

Tyrosine supplementation for phenylketonuria

BACKGROUND

Phenylketonuria is an inherited disease for which the main treatment is the dietary restriction of the amino acid phenylalanine. The diet has to be initiated in the neonatal period to prevent or reduce mental handicap however the diet is very restrictive and unpalatable and can be difficult to follow. A deficiency of the amino acid tyrosine has been suggested as a cause of some of the neuropsychological problems exhibited in PKU. Therefore, this review aims to assess the efficasy of tyrosine supplementation for phenylketonuria.

OBJECTIVES

To assess the effects of tyrosine supplementation alongside or instead of phenylalanine restricted diet for patients with phenylketonuria who commenced on diet at diagnosis and either continued on the diet or relaxed the diet later in life. To assess the evidence that tyrosine supplementation alongside, or instead of phenylalanine restricted diet improves intelligence, neuropsychological performance, growth and nutritional status, mortality rate and quality of life.

SEARCH STRATEGY

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Trials Register which is a specialist trials register which comprises references identified from comprehensive electronic database searches, handsearching relevant journals and handsearching abstract books of conference proceedings. Additional studies were identified from handsearching the Journal of Inherited Metabolic Disease (from inception, 1978, to 1998). The manufacturers of prescribable dietary products used in the treatment of phenylketonuria were also contacted for further references. Date of the most recent search of the Group's specialised register: November 1999.

SELECTION CRITERIA

All randomised or pseudo-randomised trials investigating the use of tyrosine supplementation versus placebo in patients with phenylketonuria in addition to, or instead of, a phenylalanine restricted diet. Patients treated for maternal phenylketonuria were excluded.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed the trial eligibility, methodological quality and extracted the data.

MAIN RESULTS

Two trials were included with a total of 47 patients. The blood tyrosine concentrations were significantly higher in the patients receiving tyrosine supplements than those in the placebo group (weighted mean difference 22.526, 95% Confidence interval (CI) 12.182 - 32.870). No significant differences were found between any of the other outcomes measured.

REVIEWER'S CONCLUSIONS

From the available evidence no recommendations can be made about whether tyrosine supplementation should be introduced into routine clinical practice. Further randomised controlled studies are required to provide further evidence.