Phenylketonuria: nutritional advances and challenges

Targeting specific nutrient deficiencies in protein-restricted diets: some practical facts in PKU dietary management

Among aminoacidopathies, phenylketonuria (PKU) is the most prevalent one. Early diagnosis in the neonatal period with a prompt nutritional therapy (low natural-protein and phenylalanine diet, supplemented with phenylalanine-free amino acid mixtures and special low-protein foods) remains the mainstay of the treatment. Data considering nutrient contents of cooked dishes is lacking. In this study, fourteen dishes specifically prepared for PKU individuals were analysed, regarding the lipid profile and iron and zinc contents. These dishes are poor sources of essential nutrients like Fe, Zn or n-3 fatty acids, reinforcing the need for adequate supplementation to cover individual patients' needs. This study can contribute to a more accurate adjustment of PKU diets and supplementation in order to prevent eventual nutritional deficiencies. This study contributes to a better understanding of nutrient intake from PKU patients' meals, showing the need for dietary supplementation.

Bone health in phenylketonuria: a systematic review and meta-analysis

Patients with Phenylketonuria (PKU) reportedly have decreased bone mineral density (BMD). The primary aim of this study was to perform a systematic review and meta-analysis to determine the extent and significance of low BMD in early treated patients with PKU. Secondary aims were to assess other bone status indicators including bone turnover markers (BTM) and to define areas for future research. Two research teams (Amsterdam, Netherlands and Atlanta, USA) performed literature searches for articles reporting data on BMD, osteopenia and osteoporosis, BTM or other bone indicators in patients with PKU. Included articles were compared between research teams and assessed for quality and risk of bias. A total of 13 unique articles were included; 11/13 articles reported BMD including a total of 360 patients. Ten out of 11 articles found BMD was significantly lower in patients with PKU. Meta-analyses for total BMD (TBMD; 3 studies; n = 133), lumbar spine BMD (LBMD; 7 studies; n = 247), and femoral neck BMD (FBMD; 2 studies; n = 78) Z-scores were performed. Overall effect sizes were: TBMD -0.45 (95% CI -0.61, -0.28); LBMD -0.70 (95% CI -0.82, -0.57); FBMD -0.96 (95% CI -1.42, -0.49). Definitions of osteopenia and osteoporosis were highly heterogeneous between studies and did not align with World Health Organization standards and the International Society for Clinical Densitometry positions on BMD measurement. Despite individual study findings of low BMD indicating higher risk of osteoporosis, pooled available data suggest reduction in BMD is not clinically important when using standard definitions of low BMD. Results from studies evaluating BTM are inconclusive. Phenylalanine concentration, vitamin D, PTH, and nutrient intake do not correlate with BMD or BTM. We recommend forthcoming studies use standard definitions of low BMD to determine clinical implications of BMD Z-scores below 0, explore cause of low BMD in the subset of patients with low BMD for chronological age (Z-score < -2) and assess fracture risk in patients with PKU.

Liver transplantation for pediatric metabolic disease

Liver transplantation (LTx) was initially developed as a therapy for liver diseases known to be associated with a high risk of near-term mortality but is based upon a different set of paradigms for inborn metabolic diseases. As overall outcomes for the procedure have improved, LTx has evolved into an attractive approach for a growing number of metabolic diseases in a variety of clinical situations. No longer simply life-saving, the procedure can lead to a better quality of life even if not all symptoms of the primary disorder are eliminated. Juggling the risk-benefit ratio thus has become more complicated as the list of potential disorders amenable to treatment with LTx has increased. This review summarizes presentations from a recent conference on metabolic liver transplantation held at the Children's Hospital of Pittsburgh of UPMC on the role of liver or hepatocyte transplantation in the treatment of metabolic liver disease.

Preservation of high phenylalanine ammonia lyase activities in roots of Japanese Striped corn: a potential oral therapeutic to treat phenylketonuria

Phenylketonuria (PKU) is an inherited metabolic disorder caused by deficient phenylalanine hydroxylase (PAH) activity, the enzyme responsible for the disposal of excess amounts of the essential amino acid phenylalanine (Phe). Phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) has potential to serve as an enzyme substitution therapy for this human genetic disease. Using 7-day-old Japanese Striped corn seedlings (Japonica Striped maize, Zea mays L. cv. japonica) that contain high activities of PAL, we investigated a number of methods to preserve the roots as an intact food and for long-term storage. The cryoprotectant effects of maple syrup and other edible sugars (mono- and oligosaccharides) were evaluated. Following thawing, the preserved roots were then examined to determine whether the rigid plant cell walls could protect the PAL enzyme from proteolysis during simulated (in vitro) digestion comprised of gastric and intestinal phases. While several treatments led to retention of PAL activity during freezing, upon thawing and in vitro digestion, root tissues that had been previously frozen in the presence of maple syrup exhibited the highest residual PAL activities (∼50% of the initial enzyme activity), in marked contrast to all of the treatments using other edible sugars. The structural integrity of the root cells, and the stability of the functional PAL tetramer were also preserved with the maple syrup protocol. These results have significance for the formulation of oral enzyme/protein therapeutics. When plant tissues are adequately preserved, the rigid cell walls constitute a protective barrier even under harsh (e.g. gastrointestinal-like) conditions.

People with intellectual disability: what do we know about adulthood and life expectancy?

Increases in the life expectancy of people with Intellectual Disability have followed similar trends to those found in the general population. With the exception of people with severe and multiple disabilities or Down syndrome, the life expectancy of this group now closely approximates with that of the general population. Middle and old age, which until 30 years ago were not recognized in this population, are now important parts of the life course of these individuals. Older adults with Intellectual Disabilities form a small, but significant and growing proportion of older people in the community. How these persons grow older and how symptoms and complications of the underlying cause of the Intellectual Disability will influence their life expectancy is of the utmost importance.

Requirements for a minimum standard of care for phenylketonuria: the patients' perspective

Phenylketonuria (PKU, ORPHA716) is an inherited disorder that affects about one in every 10,000 children born in Europe. Early and continuous application of a modified diet is largely successful in preventing the devastating brain damage associated with untreated PKU. The management of PKU is inconsistent: there are few national guidelines, and these tend to be incomplete and implemented sporadically. In this article, the first-ever pan- European patient/carer perspective on optimal PKU care, the European Society for Phenylketonuria and Allied Disorders (E.S.PKU) proposes recommendations for a minimum standard of care for PKU, to underpin the development of new pan-European guideline for the management of PKU. New standards of best practice should guarantee equal access to screening, treatment and monitoring throughout Europe. Screening protocols and interpretation of screening results should be standardised. Experienced Centres of Expertise are required, in line with current European Union policy, to guarantee a defined standard of multidisciplinary treatment and care for all medical and social aspects of PKU. Women of childbearing age require especially intensive management, due to the risk of severe risks to the foetus conferred by uncontrolled PKU. All aspects of treatment should be reimbursed to ensure uniform access across Europe to guideline-driven, evidence-based care. The E.S.PKU urges PKU healthcare professionals caring for people with PKU to take the lead in developing evidence based guidelines on PKU, while continuing to play an active role in serving as the voice of patients and their families, whose lives are affected by the condition.

[Phenylketonuria: new treatments]

Low phenylalanine diet has been the key treatment of phenylketonuria for more than 50years, allowing efficient management of thousands of PKU patients to date. However, non-compliance exists, mainly after adolescence. A medication for PKU received approval in Europe in 2009 (sapropterine dihydrochloride or Kuvan(®)) and can benefit to patients responsive to this drug. Other treatment options are available in some countries (glycomacropeptides, large neutral amino acids) or are currently under investigation (phenylalanine ammonia lyase, chaperones molecules, gene therapy).

Tetrahydrobiopterin therapy vs phenylalanine-restricted diet: impact on growth in PKU

BACKGROUND

Treatment of phenylketonuria based upon strict vegetarian diets, with very low phenylalanine intake and supplemented by phenylalanine-free formula, has proven to be effective in preventing the development of long-term neurological sequelae due to phenylalanine accumulation. On the other hand, such diets have occasionally been reported to hinder normal development, some individuals presenting with growth retardation. Tetrahydrobiopterin therapy has opened up new treatment options for a significant proportion of phenylketonuric patients, enabling them to eat normal diets and be freed from the need to take synthetic supplements. However, little is known about how this therapy affects their physical development.

METHODS

We conducted a retrospective longitudinal study examining anthropometric characteristics (height, weight, body mass index and growth speed Z-scores) in a cohort of phenylketonuric patients on tetrahydrobiopterin therapy (38 subjects) comparing their characteristics with those of a group of phenylketonuric patients on phenylalanine-restricted diets (76 subjects). Nutritional issues were also considered, to further explore the possibility of higher natural protein intake being associated with better physical development. Data were collected every six months over two different periods of time (two or five years).

RESULTS

No improvement was observed in the aforementioned anthropometric variables in the cohort on tetrahydrobiopterin therapy, from prior to starting treatment to when they had been taking the drug for two or five years. Rather, in almost all cases there was a fall in the mean Z-score for the variables during these periods, although the changes were not significant in any case. Further, we found no statistically differences between the two groups at any considered time point. Growth impairment was also noted in the phenylketonuric patients on low-phenylalanine diets. Individuals on tetrahydrobiopterin therapy increased their natural protein intake and, in some instances, this treatment enabled individuals to eat normal diets, with protein intake meeting RDAs. No association was found, however, between higher protein intake and growth.

CONCLUSION

Our study identified growth impairment in patients with phenylketonuria on tetrahydrobiopterin, despite higher intakes of natural proteins. In fact, individuals undergoing long-term tetrahydrobiopterin treatment seemed to achieve similar developmental outcomes to those attained by individuals on more restricted diets.

Molecular nutrition research: the modern way of performing nutritional science

In spite of amazing progress in food supply and nutritional science, and a striking increase in life expectancy of approximately 2.5 months per year in many countries during the previous 150 years, modern nutritional research has a great potential of still contributing to improved health for future generations, granted that the revolutions in molecular and systems technologies are applied to nutritional questions. Descriptive and mechanistic studies using state of the art epidemiology, food intake registration, genomics with single nucleotide polymorphisms (SNPs) and epigenomics, transcriptomics, proteomics, metabolomics, advanced biostatistics, imaging, calorimetry, cell biology, challenge tests (meals, exercise, etc.), and integration of all data by systems biology, will provide insight on a much higher level than today in a field we may name molecular nutrition research. To take advantage of all the new technologies scientists should develop international collaboration and gather data in large open access databases like the suggested Nutritional Phenotype database (dbNP). This collaboration will promote standardization of procedures (SOP), and provide a possibility to use collected data in future research projects. The ultimate goals of future nutritional research are to understand the detailed mechanisms of action for how nutrients/foods interact with the body and thereby enhance health and treat diet-related diseases.

A Systematic Review of BH4 (Sapropterin) for the Adjuvant Treatment of Phenylketonuria

CONTEXT

Dietary management is the mainstay of effective treatment in PKU, but dietary restriction is difficult and additional treatment options are needed.

OBJECTIVE

To systematically review evidence regarding sapropterin (BH4) use as an adjunct to dietary restriction in individuals with PKU.

DATA SOURCES

Five databases including MEDLINE up to August 2011.

STUDY SELECTION

Two reviewers independently assessed studies against predetermined inclusion/exclusion criteria.

DATA EXTRACTION

Two reviewers independently extracted data regarding participant and intervention characteristics and outcomes and assigned overall quality and strength of evidence ratings based on predetermined criteria.

RESULTS

BH4 research includes two randomized controlled trials (RCTs) and three uncontrolled open-label trials. Phenylalanine (Phe) levels were reduced by at least 30 % in up to half of treated participants (32-50 %). In one RCT comparing placebo on likelihood of a 30 % reduction in Phe, 9 % of those on placebo achieved this effect, compared with 44 % of the treated group after 6 weeks. Phe tolerance and variability were improved in treated participants in studies assessing those outcomes. No comparative studies assessed long-term outcomes including cognitive effects, nutritional status, or quality of life.

CONCLUSIONS

Adjuvant pharmacologic therapy has the potential to support individuals in achieving optimal Phe levels. BH4 has been shown to reduce Phe levels in some individuals, with significantly greater reductions seen in treated versus placebo groups. The strength of the evidence is moderate for short-term effects on reducing Phe in a subset of initially BH4-responsive individuals, moderate for a lack of significant harms, low for longer-term effects on cognition, and insufficient for all other outcomes.