Does hyperphenylalaninemia induce brain glucose hypometabolism? Cerebral spinal fluid findings in treated adult phenylketonuric patients

Despite numerous studies in human patients and animal models for phenylketonuria (PKU; OMIM#261600), the pathophysiology of PKU and the underlying causes of brain dysfunction and cognitive problems in PKU patients are not well understood. In this study, lumbar cerebral spinal fluid (CSF) was obtained immediately after blood sampling from early-treated adult PKU patients who had fasted overnight. Metabolite and amino acid concentrations in the CSF of PKU patients were compared with those of non-PKU controls. The CSF concentrations and CSF/plasma ratios for glucose and lactate were found to be below normal, similar to what has been reported for glucose transporter1 (GLUT1) deficiency patients who exhibit many of the same clinical symptoms as untreated PKU patients. CSF glucose and lactate levels were negatively correlated with CSF phenylalanine (Phe), while CSF glutamine and glutamate levels were positively correlated with CSF Phe levels. Plasma glucose levels were negatively correlated with plasma Phe concentrations in PKU subjects, which partly explains the reduced CSF glucose concentrations. Although brain glucose concentrations are unlikely to be low enough to impair brain glucose utilization, it is possible that the metabolism of Phe in the brain to produce phenyllactate, which can be transported across the blood-brain barrier to the blood, may consume glucose and/or lactate to generate the carbon backbone for glutamate. This glutamate is then converted to glutamine and carries the Phe-derived ammonia from the brain to the blood. While this mechanism remains to be tested, it may explain the correlations of CSF glutamine, glucose, and lactate concentrations with CSF Phe.

Phenylketonuria (PKU) Urinary Metabolomic Phenotype Is Defined by Genotype and Metabolite Imbalance: Results in 51 Early Treated Patients Using Ex Vivo 1H-NMR Analysis

Phenylketonuria (PKU) is a rare metabolic disorder caused by mutations in the phenylalanine hydroxylase gene. Depending on the severity of the genetic mutation, medical treatment, and patient dietary management, elevated phenylalanine (Phe) may occur in blood and brain tissues. Research has recently shown that high Phe not only impacts the central nervous system, but also other organ systems (e.g., heart and microbiome). This study used ex vivo proton nuclear magnetic resonance (¹H-NMR) analysis of urine samples from PKU patients (mean 14.9 ± 9.2 years, n = 51) to identify the impact of elevated blood Phe and PKU treatment on metabolic profiles. Our results found that 24 out of 98 urinary metabolites showed a significant difference (p < 0.05) for PKU patients compared to age-matched healthy controls (n = 51) based on an analysis of urinary metabolome. These altered urinary metabolites were related to Phe metabolism, dysbiosis, creatine synthesis or intake, the tricarboxylic acid (TCA) cycle, end products of nicotinamide-adenine dinucleotide degradation, and metabolites associated with a low Phe diet. There was an excellent correlation between the metabolome and genotype of PKU patients and healthy controls of 96.7% in a confusion matrix model. Metabolomic investigations may contribute to a better understanding of PKU pathophysiology.

Ex vivo proton spectroscopy (1 H-NMR) analysis of inborn errors of metabolism: Automatic and computer-assisted analyses

There are about 1500 genetic metabolic diseases. A small number of treatable diseases are diagnosed by newborn screening programs, which are continually being developed. However, most diseases can only be diagnosed based on clinical symptoms or metabolic findings. The main biological fluids used are urine, plasma and, in special situations, cerebrospinal fluid. In contrast to commonly used methods such as gas chromatography and high performance liquid chromatography mass spectrometry, ex vivo proton spectroscopy (¹ H-NMR) is not yet used in routine clinical practice, although it has been recommended for more than 30 years. Automatic analysis and improved NMR technology have also expanded the applications used for the diagnosis of inborn errors of metabolism. We provide a mini-overview of typical applications, especially in urine but also in plasma, used to diagnose common but also rare genetic metabolic diseases with ¹ H-NMR. The use of computer-assisted diagnostic suggestions can facilitate interpretation of the profiles. In a proof of principle, to date, 182 reports of 59 different diseases and 500 reports of healthy children are stored. The percentage of correct automatic diagnoses was 74%. Using the same ¹ H-NMR profile-targeted analysis, it is possible to apply an untargeted approach that distinguishes profile differences from healthy individuals. Thus, additional conditions such as lysosomal storage diseases or drug interferences are detectable. Furthermore, because ¹ H-NMR is highly reproducible and can detect a variety of different substance categories, the metabolomic approach is suitable for monitoring patient treatment and revealing additional factors such as nutrition and microbiome metabolism. Besides the progress in analytical techniques, a multiomics approach is most effective to combine metabolomics with, for example, whole exome sequencing, to also diagnose patients with nondetectable metabolic abnormalities in biological fluids. In this mini review we also provide our own data to demonstrate the role of NMR in a multiomics platform in the field of inborn errors of metabolism.

Undiagnosed Phenylketonuria Can Exist Everywhere: Results From an International Survey

Many countries do not have a newborn screening (NBS) program, and immigrants from such countries are at risk for late diagnosis of phenylketonuria (PKU). In this international survey, 52 of 259 patients (20%) with late diagnosed PKU were immigrants, and 145 of the 259 (55%) were born before NBS or in a location without NBS.

Health economic burden of patients with phenylketonuria (PKU) - A retrospective study of German health insurance claims data

This retrospective matched-cohort analysis compared health-economic burdens of adults (≥18 years; n = 377) with phenylketonuria (PKU) and age/gender-matched non-PKU controls (n = 3770) in Germany. Healthcare costs and resource-utilization were analyzed for the year 2015. Differences between groups were tested using 95% CI of mean differences (MD). PKU patients had significantly higher mean costs in total (MD €3307, 95% CI €1736–€4879), for pharmaceuticals (MD €1912, 95% CI €1195–€2629) [including dietary amino-acid supplements (MD €1268, 95% CI €864–€1672)], and outpatient costs (MD €395, 95% CI €115–€675). Inpatient costs (MD €904, 95% CI -€293 to €2100) and costs for aids and remedies (MD €97, 95% CI -€10 to €203) were also higher in PKU patients. PKU patients had more outpatient visits and stayed longer in hospital. Adult PKU patients incur higher total healthcare costs than non-PKU controls, especially regarding pharmaceuticals and outpatient costs, and more frequent resource-utilization, resulting in higher health-economic burden for the statutory healthcare system.

Patient's thoughts and expectations about centres of expertise for PKU

BACKGROUND

In the Netherlands (NL) the government assigned 2 hospitals as centres of expertise (CE) for Phenylketonuria (PKU), while in the United Kingdom (UK) and Germany no centres are assigned specifically as PKU CE's.

METHODS

To identify expectations of patients/caregivers with PKU of CEs, a web-based survey was distributed through the national Phenylketonuria societies of Germany, NL and UK.

RESULTS

In total, 105 responded (43 patients, 56 parents, 4 grandparents, 2 other) of whom 59 were from NL, 33 from UK and 13 from Germany. All participants (n = 105) agreed that patients and/or practitioners would benefit from CEs. The frequency patients would want to visit a CE, when not treated in a CE (n = 83) varied: every hospital visit (24%, n = 20), annual or bi-annual (45%, n = 37), at defined patient ages (6%, n = 5), one visit only (22%, n = 18), or never (4%, n = 3). Distance was reported as a major barrier (42%, n = 35). 78% (n = 65) expected CE physicians and dieticians to have a higher level of knowledge than in non-CE centres. For participants already treated in a CE (n = 68), 66% requested a more extensive annual or bi-annual review. In general, psychology review and neuropsychologist assessment were identified as necessary by approximately half of the 105 participants. In addition, 66% (n = 68) expected a strong collaboration with patient associations.

CONCLUSION

In this small study, most participants expected that assigning CEs will change the structure of and delivery of Phenylketonuria care.

Phenylalanine Effects on Brain Function in Adult Phenylketonuria

OBJECTIVE

To evaluate the relationship between circulating phenylalanine and brain function as well as neuropsychiatric symptoms in adults with phenylketonuria.

METHODS

In this prospective cross-sectional study, early-treated patients with phenylketonuria older than 30 years and age- and sex-matched controls were included. Extensive neurologic evaluation, neuropsychological and behavioral testing, sensory and motor evoked potentials, and MRI were performed. CSF concentrations of neurodegenerative markers were evaluated in addition in a subset of 10 patients.

RESULTS

Nineteen patients with phenylketonuria (median age 41 years) with different phenylalanine levels (median 873 μmol/L) entered the study. They showed higher prevalence of neurologic symptoms, cognitive and behavioral abnormalities, autonomic dysfunction, alterations in neurophysiologic measures, and atrophy in putamen and right thalamus compared to controls. In CSF, patients with phenylketonuria exhibited higher β-amyloid 1-42 (p = 0.003), total tau (p < 0.001), and phosphorylated tau (p = 0.032) levels compared to controls. Plasma phenylalanine levels highly correlated with the number of failed neuropsychological tests (r = 0.64, p = 0.003), neuropsychiatric symptoms (r = 0.73, p < 001), motor evoked potential latency (r = 0.48, p = 0.030), and parietal lobe atrophy.

CONCLUSIONS

Our study provides strong evidence for a correlation between phenylalanine levels and clinical, neuropsychological, neurophysiologic, biochemical, and imaging alterations in adult patients with phenylketonuria.

PKU dietary handbook to accompany PKU guidelines

Background

Phenylketonuria (PKU) is an autosomal recessive inborn error of phenylalanine metabolism caused by deficiency in the enzyme phenylalanine hydroxylase that converts phenylalanine into tyrosine.

Main body

In 2017 the first European PKU Guidelines were published. These guidelines contained evidence based and/or expert opinion recommendations regarding diagnosis, treatment and care for patients with PKU of all ages. This manuscript is a supplement containing the practical application of the dietary treatment.

Conclusion

This handbook can support dietitians, nutritionists and physicians in starting, adjusting and maintaining dietary treatment.

Lower plasma cholesterol, LDL-cholesterol and LDL-lipoprotein subclasses in adult phenylketonuria (PKU) patients compared to healthy controls: results of NMR metabolomics investigation

Background

Phenylketonuria (PKU; OMIM#261600) is a rare metabolic disorder caused by mutations in the phenylalanine hydroxylase (PAH) gene resulting in high phenylalanine (Phe) in blood and brain. If not treated early this results in intellectual disability, behavioral and psychiatric problems, microcephaly, motor deficits, eczematous rash, autism, seizures, and developmental problems. There is a controversial discussion of whether patients with PKU have an additional risk for atherosclerosis due to interference of Phe with cholesterol synthesis and LDL-cholesterol regulation. Since cholesterol also plays a role in membrane structure and myelination, better insight into the clinical significance of the impact of Phe on lipoprotein metabolism is desirable. In 22 treated PKU patients (mean age 38.7 years) and 14 healthy controls (mean age 35.2 years), we investigated plasma with NMR spectroscopy and quantified 105 lipoprotein parameters (including lipoprotein subclasses) and 24 low molecular weight parameters. Analysis was performed on a 600 MHz Bruker AVANCE IVDr spectrometer as previously described.

Results

Concurrent plasma Phe in PKU patients showed a wide range with a mean of 899 μmol/L (50–1318 μmol/L). Total cholesterol and LDL-cholesterol were significantly lower in PKU patients versus controls: 179.4 versus 200.9 mg/dL (p < 0.02) and 79.5 versus 104.1 mg/dL (p < 0.0038), respectively. PKU patients also had lower levels of 22 LDL subclasses with the greatest differences in LDL2 Apo-B, LDL2 Particle Number, LDL2-phospholipids, and LDL2-cholesterol (p < 0.0001). There was a slight negative correlation of total cholesterol and LDL-cholesterol with concurrent Phe level. VLDL5-free cholesterol, VLDL5-cholesterol, VLDL5-phospholipids, and VLDL4-free cholesterol showed a significant (p < 0.05) negative correlation with concurrent Phe level. There was no difference in HDL and their subclasses between PKU patients and controls. Tyrosine, glutamine, and creatinine were significantly lower in PKU patients compared to controls, while citric and glutamic acids were significantly higher.

Conclusions

Using NMR spectroscopy, a unique lipoprotein profile in PKU patients can be demonstrated which mimics a non-atherogenic profile as seen in patients treated by statins.

Cerebrospinal fluid biogenic amines depletion and brain atrophy in adult patients with phenylketonuria

Biogenic amines synthesis in phenylketonuria (PKU) patients with high phenylalanine (Phe) concentration is thought to be impaired due to inhibition of tyrosine and tryptophan hydroxylases and competition with amino acids at the blood-brain barrier. Dopamine and serotonin deficits might explain brain damage and progressive neuropsychiatric impairment in adult PKU patients. Ten early treated adult PKU patients (mean age 38.2 years) and 15 age-matched controls entered the study. Plasma and cerebrospinal fluid (CSF) Phe, 5-hydroxyindoleacetic acid (5-HIAA), 5-hydroxytryptophan (5-HTP), 3,4-dihydroxy-l-phenylalanine (l-DOPA) and homovanillic acid (HVA) were analyzed. Voxel-based morphometry statistical nonparametric mapping was used to test the age-corrected correlation between gray matter atrophy and CSF biogenic amines levels. 5-HIAA and 5-HTP were significantly reduced in PKU patients compared to controls. Significant negative correlations were found between CSF 5-HIAA, HVA, and 5-HTP and Phe levels. A decrease in 5-HIAA and 5-HTP concentrations correlated with precuneus and frontal atrophy, respectively. Lower HVA levels correlated with occipital atrophy. Biogenic amines deficits correlate with specific brain atrophy patterns in adult PKU patients, in line with serotonin and dopamine projections. These findings may support a more rigorous Phe control in adult PKU to prevent neurotransmitter depletion and accelerated brain damage due to aging.

The complete European guidelines on phenylketonuria: diagnosis and treatment

Phenylketonuria (PKU) is an autosomal recessive inborn error of phenylalanine metabolism caused by deficiency in the enzyme phenylalanine hydroxylase that converts phenylalanine into tyrosine. If left untreated, PKU results in increased phenylalanine concentrations in blood and brain, which cause severe intellectual disability, epilepsy and behavioural problems. PKU management differs widely across Europe and therefore these guidelines have been developed aiming to optimize and standardize PKU care. Professionals from 10 different European countries developed the guidelines according to the AGREE (Appraisal of Guidelines for Research and Evaluation) method. Literature search, critical appraisal and evidence grading were conducted according to the SIGN (Scottish Intercollegiate Guidelines Network) method. The Delphi-method was used when there was no or little evidence available. External consultants reviewed the guidelines. Using these methods 70 statements were formulated based on the highest quality evidence available. The level of evidence of most recommendations is C or D. Although study designs and patient numbers are sub-optimal, many statements are convincing, important and relevant. In addition, knowledge gaps are identified which require further research in order to direct better care for the future.

Clinical pattern, mutations and in vitro residual activity in 33 patients with severe 5, 10 methylenetetrahydrofolate reductase (MTHFR) deficiency

BACKGROUND

Severe methylenetetrahydrofolate reductase (MTHFR) deficiency is a rare inborn defect disturbing the remethylation of homocysteine to methionine (<200 reported cases). This retrospective study evaluates clinical, biochemical genetic and in vitro enzymatic data in a cohort of 33 patients.

METHODS

Clinical, biochemical and treatment data was obtained from physicians by using a questionnaire. MTHFR activity was measured in primary fibroblasts; genomic DNA was extracted from cultured fibroblasts.

RESULTS

Thirty-three patients (mean age at follow-up 11.4 years; four deceased; median age at first presentation 5 weeks; 17 females) were included. Patients with very low (<1.5%) mean control values of enzyme activity (n = 14) presented earlier and with a pattern of feeding problems, encephalopathy, muscular hypotonia, neurocognitive impairment, apnoea, hydrocephalus, microcephaly and epilepsy. Patients with higher (>1.7-34.8%) residual enzyme activity had mainly psychiatric symptoms, mental retardation, myelopathy, ataxia and spasticity. Treatment with various combinations of betaine, methionine, folate and cobalamin improved the biochemical and clinical phenotype. During the disease course, patients with very low enzyme activity showed a progression of feeding problems, neurological symptoms, mental retardation, and psychiatric disease while in patients with higher residual enzyme activity, myelopathy, ataxia and spasticity increased. All other symptoms remained stable or improved in both groups upon treatment as did brain imaging in some cases. No clear genotype-phenotype correlation was obvious.

DISCUSSION

MTHFR deficiency is a severe disease primarily affecting the central nervous system. Age at presentation and clinical pattern are correlated with residual enzyme activity. Treatment alleviates biochemical abnormalities and clinical symptoms partially.

Tetrahydrobiopterin (BH4) responsiveness in neonates with hyperphenylalaninemia: a semi-mechanistically-based, nonlinear mixed-effect modeling

Neonatal loading studies with tetrahydrobiopterin (BH4) are used to detect hyperphenylalaninemia due to BH4 deficiency by evaluating decreases in blood phenylalanine (Phe) concentrations post BH4 load. BH4 responsiveness in phenylalanine hydroxylase (PAH)-deficient patients introduced a new diagnostic aspect for this test. In older children, a broad spectrum of different levels of responsiveness has been described. The primary objective of this study was to develop a pharmacodynamic model to improve the description of individual sensitivity to BH4 in the neonatal period. Secondary objectives were to evaluate BH4 responsiveness in a large number of PAH-deficient patients from a neonatal screening program and in patients with various confirmed BH4 deficiencies from the BIODEF database. Descriptive statistics in patients with PAH deficiency with 0-24-h data available showed that 129 of 340 patients (37.9%) had a >30% decrease in Phe levels post load. Patients with dihydropteridine reductase deficiency (n = 53) could not be differentiated from BH4-responsive patients with PAH deficiency. The pharmacologic turnover model, "stimulation of loss" of Phe following BH4 load, fitted the data best. Using the model, 193 of 194 (99.5%) patients with a proven BH4 synthesis deficiency or recycling defect were classified as BH4 sensitive. Among patients with PAH deficiency, 216 of 375 (57.6%) patients showed sensitivity to BH4, albeit with a pronounced variability; PAH-deficient patients with blood Phe <1200 μmol/L at time 0 showed higher sensitivity than patients with blood Phe levels >1200 μmol/L. External validation showed good correlation between the present approach, using 0-24-h blood Phe data, and the published 48-h prognostic test. Pharmacodynamic modeling of Phe levels following a BH4 loading test is sufficiently powerful to detect a wide range of responsiveness, interpretable as a measure of sensitivity to BH4. However, the clinical relevance of small responses needs to be evaluated by further studies of their relationship to long-term response to BH4 treatment.

Clinical presentation and outcome in a series of 88 patients with the cblC defect

The cblC defect is the most common inborn error of vitamin B12 metabolism. Despite therapeutic measures, the long-term outcome is often unsatisfactory. This retrospective multicentre study evaluates clinical, biochemical and genetic findings in 88 cblC patients. The questionnaire designed for the study evaluates clinical and biochemical features at both initial presentation and during follow up. Also the development of severity scores allows investigation of individual disease load, statistical evaluation of parameters between the different age of presentation groups, as well as a search for correlations between clinical endpoints and potential modifying factors.

RESULTS

No major differences were found between neonatal and early onset patients so that these groups were combined as an infantile-onset group representing 88 % of all cases. Hypotonia, lethargy, feeding problems and developmental delay were predominant in this group, while late-onset patients frequently presented with psychiatric/behaviour problems and myelopathy. Plasma total homocysteine was higher and methionine lower in infantile-onset patients. Plasma methionine levels correlated with "overall impression" as judged by treating physicians. Physician's impression of patient's well-being correlated with assessed disease load. We confirmed the association between homozygosity for the c.271dupA mutation and infantile-onset but not between homozygosity for c.394C>T and late-onset. Patients were treated with parenteral hydroxocobalamin, betaine, folate/folinic acid and carnitine resulting in improvement of biochemical abnormalities, non-neurological signs and mortality. However the long-term neurological and ophthalmological outcome is not significantly influenced. In summary the survey points to the need for prospective studies in a large cohort using agreed treatment modalities and monitoring criteria.

Fluctuations in phenylalanine concentrations in phenylketonuria: a review of possible relationships with outcomes

Fluctuations in blood phenylalanine concentrations may be an important determinant of intellectual outcome in patients with early and continuously treated phenylketonuria (PKU). This review evaluates the studies on phenylalanine fluctuations, factors affecting fluctuations, and if stabilizing phenylalanine concentrations affects outcomes, particularly neurocognitive outcome. Electronic literature searches of Embase and PubMed were performed for English-language publications, and the bibliographies of identified publications were also searched. In patients with PKU, phenylalanine concentrations are highest in the morning. Factors that can affect phenylalanine fluctuations include age, diet, timing and dosing of protein substitute and energy intake, dietary adherence, phenylalanine hydroxylase genotype, changes in dietary phenylalanine intake and protein metabolism, illness, and growth rate. Even distribution of phenylalanine-free protein substitute intake throughout 24h may reduce blood phenylalanine fluctuations. Patients responsive to and treated with 6R-tetrahydrobiopterin seem to have less fluctuation in their blood phenylalanine concentrations than controls. An increase in blood phenylalanine concentration may result in increased brain and cerebrospinal fluid phenylalanine concentrations within hours. Although some evidence suggests that stabilization of blood phenylalanine concentrations may have benefits in patients with PKU, more studies are needed to distinguish the effects of blood phenylalanine fluctuations from those of poor metabolic control.

Is overweight an issue in phenylketonuria?

Dietary treatment may be associated with an increased risk of obesity in phenylketonuria (PKU). The earliest studies describe a tendency for overweight in PKU, but not all recent publications confirm this, although there are an increasing number of studies describing increased obesity in female patients with PKU. There is little data describing the metabolic consequences of obesity in PKU. It is difficult to interpret and compare published results due to variable patient age, differing dietary treatment approaches, poor treatment adherence, inconsistencies in metabolic control achieved, variable criteria used to classify overweight. There is also a lack of comparison with normal population data which is widely variable between countries. Generally in PKU it is unknown if obesity etiology is a result of the underlying condition, a treatment consequence, or an outcome of inadequate metabolic control. Differences in treatment strategies, target ranges for blood phenylalanine concentrations and severity of PKU can alter nutritional intakes and dietary experiences which ultimately modulate the course of overweight development. It is clear further investigation is required. Treating overweight and obesity in the general population is difficult and no studies have described the impact of obesity treatment strategies in PKU. However, the PKU management team has an important role in monitoring nutritional status and preventing overweight and obesity. It is important that PKU treatment attends to the general aspects of nutrition, feeding behavior and exercise in order to prevent the development of overweight in these individuals.

Safety of extended treatment with sapropterin dihydrochloride in patients with phenylketonuria: results of a phase 3b study

BACKGROUND

Phenylketonuria (PKU) results from impaired breakdown of phenylalanine (Phe) due to deficient phenylalanine hydroxylase (PAH) activity. Sapropterin dihydrochloride (sapropterin, Kuvan®) is the only US- and EU-approved pharmaceutical version of naturally occurring 6R-BH(4), the cofactor required for PAH activity. Sapropterin enhances residual PAH activity in sapropterin-responsive PKU patients and, in conjunction with dietary management, helps reduce blood Phe concentrations for optimal control. Approval was based on the positive safety and efficacy results of four international clinical studies, the longest of which was 22 weeks in duration.

OBJECTIVE

To evaluate the safety of long-term treatment with sapropterin in PKU subjects who participated in previous Phase 3 sapropterin trials.

METHODS

PKU-008 was designed as a Phase 3b, multicenter, multinational, open-label, 3-year extension trial to evaluate the long-term safety of sapropterin in patients with PKU who were classified as sapropterin responders and participated in prior Phase 3 sapropterin studies: 111 subjects aged 4-50 years completed prior studies and were subsequently enrolled in study PKU-008. Routine safety monitoring was performed at 3-month intervals and included adverse event reporting, blood Phe monitoring, clinical laboratory evaluations, physical examinations and vital sign measurements.

RESULTS

Average exposure during PKU-008 was 658.7±221.3 days (range, 56-953; median, 595). The average total duration of participation in multiple studies (PKU-001, PKU-003, PKU-004, and PKU-008; or PKU-006 and PKU-008) was 799.0±237.5 days (range, 135-1151). The mean sapropterin dose was 16.2±4.7 mg/kg/day. Most adverse events were considered unrelated to treatment, were mild or moderate in severity, and were consistent with prior studies of sapropterin. No age-specific differences were observed in adverse event reporting. Three subjects discontinued treatment due to adverse events that were considered possibly or probably related to study treatment (one each of difficulty concentrating, decreased platelet count, and intermittent diarrhea). No deaths were reported. Of seven reported serious adverse events, one was considered possibly related to study treatment (gastroesophageal reflux). There were no laboratory or physical examination abnormalities requiring medical interventions. For most subjects, blood Phe concentrations were consistently within target range, confirming the durability of response in subjects undergoing extended treatment with sapropterin.

CONCLUSION

Sapropterin treatment was found to be safe and well tolerated at doses of 5 to 20mg/kg/day for an average exposure of 659 days. This study supports the safety and tolerability of sapropterin as long-term treatment for patients with PKU.

Adult phenylketonuria outcome and management

The problem to evaluate treatment outcome in adult PKU (phenylketonuric) patients lies in the heterogeneity of the adult PKU population. This heterogeneity is not only based on the different treatment history of every individual patient but also on the different severity of the underlying defect of the enzyme phenylalanine hydroxylase. Recent, partly double blind studies in adult PKU patients further support recommendation for lifelong treatment. However, it has become evident that dietary treatment is suboptimal and continuation to adulthood often not accepted. Late detected PKU patients (up to 4-6 years of age) benefit from strict dietary treatment and are able to catch up in intellectual performance. Untreated, severely retarded patients with behavioral changes may benefit from introduction of dietary treatment. However, individual decision is necessary and based on the personal situation of the patient. In early and well treated patients a number of studies have demonstrated that cognitive and neurosychologic tests are different from controls. In addition there is evidence that patients with higher blood phenylalanine (phe) levels demonstrate more often psychiatric symptoms like depression and anxiety. Medical problems are more often observed: there are certain risks as impaired growth, decreased bone mineral density and nutrional deficits probably caused by dietary treatment with an artificial protein substitute and/or missing compliance with an unpleasant diet. The long term risk of a strict dietary treatment must be balanced with the risk of higher blood phe (mean blood phenylalanine >600-900 μmol/L) on cognitive and neuropsychological functions and psychiatric symptoms. Further studies should consider the role of blood phe exposure for brain development in childhood and for brain function in all ages. Besides mean blood phe, fluctuation of blood phe over time is important. Fluctuation of blood phe is decreased by sapropterin treatment in responsive patients which would on the long term may have positive effects on cognitive outcome. Further studies also should include adult PKU patients.

RAMEDIS: a comprehensive information system for variations and corresponding phenotypes of rare metabolic diseases

RAMEDIS is a manually curated resource of human variations and corresponding phenotypes for rare metabolic diseases. The system is based on separate case reports that comprehensively describe various aspects of anonymous case study, e.g. molecular genetics, symptoms, lab findings, treatments, etc. Scientists are able to make use of the database by a simple and intuitive web-based user interface with a common web browser. A registration or login is not necessary for a full reading access to the system content. Furthermore, a mutation analysis table summarizes the submitted variations per diagnosis and enables direct access to detailed information of corresponding case reports. Interested scientists may open an account to submit their case reports in order to share valuable genotype-phenotype information efficiently with the scientific community. Currently, 794 case reports have been submitted, describing 92 different genetic metabolic diseases. To enhance the comprehensive coverage of available knowledge in the field of rare metabolic diseases, all case reports are linked to integrated information from public molecular biology databases like KEGG, OMIM and ENZYME. This information upgrades the case reports by related data of the corresponding diseases as well as involved enzymes, genes and metabolic pathways. Academic users may freely use the RAMEDIS system at http://www.ramedis.de.

Psychosocial issues and outcomes in maternal PKU

Elevated phenylalanine (Phe) levels in pregnant women with PKU are teratogenic. Fetal damage due to elevated maternal Phe levels during pregnancy is known as maternal phenylketonuria (MPKU). The risk of birth defects in MPKU, including global developmental delays, microcephaly, congenital heart disease, and low birth weight, can be dramatically reduced by controlling Phe levels during pregnancy (metabolic control). Phe levels should be maintained in the range of 120-360 micromol/L, ideally starting before pregnancy begins (i.e., when planning a pregnancy). If control is not achieved before pregnancy (e.g., if the pregnancy was unplanned), good outcomes are still possible if metabolic control is established by 8 weeks of pregnancy. Unfortunately, metabolic control before and during pregnancy can be poor. As well, many mothers stop treatment after pregnancy, which can decrease the mother's ability to focus on her child and increase her risk of behavioral and psychological problems. This can have a negative effect on the home environment. Many factors affect adherence to the strict diet used to control Phe levels, including poor access to medical care, lack of reimbursement for medical foods (in some regions, such as parts of the United States), practical difficulties with implementing the diet, financial constraints, demographics, and psychosocial issues. A comprehensive treatment approach that begins prior to pregnancy and continues after the infant is born may help to improve the management of MPKU. This approach should include education of girls about MPKU at an early age, interventions to prevent unplanned pregnancies, psychosocial support, improved treatment access and reimbursement for medical foods, and treatment guidelines. Treatments such as sapropterin may also have a role in improving metabolic control during pregnancy.

Mapping of a new locus for congenital anomalies of the kidney and urinary tract on chromosome 8q24

BACKGROUND

Congenital anomalies of the kidney and urinary tract (CAKUT) account for the majority of end-stage renal disease in children (50%). Previous studies have mapped autosomal dominant loci for CAKUT. We here report a genome-wide search for linkage in a large pedigree of Somalian descent containing eight affected individuals with a non-syndromic form of CAKUT.

METHODS

Clinical data and blood samples were obtained from a Somalian family with eight individuals with CAKUT including high-grade vesicoureteral reflux and unilateral renal agenesis. Total genome search for linkage was performed using a 50K SNP Affymetric DNA microarray. As neither parent is affected, the results of the SNP array were analysed under recessive models of inheritance, with and without the assumption of consanguinity.

RESULTS

Using the non-consanguineous recessive model, a new gene locus (CAKUT1) for CAKUT was mapped to chromosome 8q24 with a significant maximum parametric Logarithm of the ODDs (LOD) score (LOD(max)) of 4.2. Recombinations were observed in two patients defining a critical genetic interval of 2.5 Mb physical distance flanked by markers SNP_A-1740062 and SNP_A-1653225.

CONCLUSION

We have thus identified a new non-syndromic recessive gene locus for CAKUT (CAKUT1) on chromosome 8q24. The identification of the disease-causing gene will provide further insights into the pathogenesis of urinary tract malformations and mechanisms of renal development.

RAMEDIS: the rare metabolic diseases database

The RAMEDIS system is a platform-independent, web-based information system for rare diseases based on individual case reports. It was developed in close cooperation with clinical partners and collects information on rare metabolic diseases in extensive detail (e.g. symptoms, laboratory findings, therapy and genetic data). This combination of clinical and genetic data enables the analysis of genotype-phenotype correlations. By using largely standardised medical terms and conditions, the contents of the database are easy to compare and analyse. In addition, a convenient graphical user interface is provided by every common web browser. RAMEDIS supports an extendable number of different genetic diseases and enables cooperative studies. Furthermore, use of RAMEDIS should lead to advances in epidemiology, integration of molecular and clinical data, and generation of rules for therapeutic intervention and identification of new diseases.

AVAILABILITY

RAMEDIS is available from http://www.ramedis.de

CONTACT

Thoralf Töpel (thoralf.toepel@uni-bielefeld.de).

Maternal Phenylketonuria Collaborative Study (MPKUCS)--the 'outliers'

Analysis of outcome data from 305 of the 414 offspring from the Maternal Phenylketonuria Collaborative Study (MPKUCS), plus 70 control offspring, revealed significant deficits in the IQ (intelligence quotient), as measured by the Wechsler Intelligence Scale for Children--Revised (WISC-R), when maternal metabolic control during pregnancy was delayed and/or inadequate. There were, however, 23 'outliers' (7.5% of the 305) in which the offspring's intellectual IQ was worse (n =10) or better (n =13) than expected. The aim of this study was to determine whether collection parameters were incomplete or whether these subjects were true biological variants influenced by other undetected factors or, perhaps, by modifier genes. Among the 10 offspring whose intellectual functioning was worse than expected, additional complications were uncovered that could explain the poor outcome. Four of the 13 offspring with higher than expected IQ had mothers with mild variants of PKU in which the insult to the fetus would not be expected to be as profound. For the other nine offspring whose intellectual performance was better than expected, there was no explanation, based on the parameters studied. We hypothesize that modifier genes will, at times, protect the fetus despite high maternal concentrations of phenylalanine. Not all offspring from the same (untreated) PKU mother may be similarly affected. Finding the source of these modifiers might effect the treatment of MPKU.

Impact of the phenylalanine hydroxylase gene on maternal phenylketonuria outcome

OBJECTIVE

The aim of the present study was to examine to what extent maternal and offspring phenylalanine hydroxylase (PAH) genotypes in conjunction with maternal IQ and dietary control during pregnancy are related to cognitive development in offspring of women with phenylketonuria (PKU).

METHODS

PAH gene mutations were determined in 196 maternal PKU subjects and their offspring. The women were grouped according to PAH genotype, which predicts the metabolic phenotype (severe PKU, mild PKU, and mild hyperphenylalaninemia [MHP]). IQ was determined in both the mothers (Wechsler Adult Intelligence Scale-Revised at >18 years) and their children (Wechsler Intelligence Scale for Children-Revised at > or = 6-7 years of age).

RESULTS

According to PAH genotypes, 62% of the women exhibited severe PKU, 19% exhibited mild PKU, and 19% exhibited MHP. Maternal IQ increased, and the assigned phenylalanine (Phe) levels decreased with decreasing severity of PAH genotype. In offspring of mild maternal PKU, multiple regression analysis showed offspring IQ to be significantly related to maternal IQ but not to Phe exposure during pregnancy, which was <750 micromol/L in all cases of mild PKU. In offspring of mothers with severe PKU and average Phe exposure during pregnancy of 360 to 750 micromol/L, multiple regression analysis revealed both maternal IQ and Phe exposure to be significant predictors of offspring IQ. When average Phe exposure was <360 micromol/L, cognitive development was normal (mean IQ: 105), whereas an average Phe exposure of >750 micromol/L severely depressed offspring IQ (mean IQ: 56) in this group regardless of maternal IQ. It could not be documented that the offspring PAH genotype affects cognitive development.

CONCLUSION

Female individuals with severe PKU should be offered a diet for a lifetime. If good metabolic control is established, then women with PKU will have children with IQ scores that are not influenced by their disease.

Research design, organization, and sample characteristics of the Maternal PKU Collaborative Study

OBJECTIVE

The Maternal PKU Collaborative Study (MPKUCS) was initiated in 1984 by the National Institute of Child Health and Human Development (NICHD). The purpose was to assess the efficacy of dietary restriction of phenylalanine in reducing morbidity in offspring of women with hyperphenylalaninemia (HPA). A contract was awarded to Childrens Hospital Los Angeles as the Coordinating Center to provide implementation of the research protocol, data collection, and analysis.

METHODS

The Study included four regional contributing centers: Childrens Hospital Los Angeles (Western Region), Boston Children's Hospital (Northeast Region), University of Illinois (Midwest Region), and University of Texas Medical Branch, Galveston (Southeast Region). Within each region, many participating clinics were responsible for obstetric care, treatment, and monitoring protocols. In 1985, Canada joined the MPKUCS, and in 1992, Germany entered. They were selected because they provided dietary supplies and strong professional services. Acquisition began in 1984 and ended in October 1995. The study included 574 pregnancies in women with HPA and 100 control subjects matched on age, race, parity, and weeks of gestation. The sample included women with blood phenylalanine values >240 micromol/L, 66% of whom had classical PKU, 22% had atypical PKU, and 12% had mild HPA. Informed consents were obtained on all participants. The women ranged in age from 15 to 36 years of age, with a mean age at conception of 23 years. Teenage pregnancies accounted for 19%. Seventy-five percent graduated from high school. Offspring included 416 newborns, 317 of whom were evaluated at 4 years of age and 289 at 6 to 7 years. Follow-up involved medical, nutritional, psychosocial, and psychological assessments.

CONCLUSION

Women with PKU treated before conception and in control of their blood phenylalanine levels between 120 and 360 micromol/L (2-6 mg) exhibited normal pregnancies and neonatal outcome. Surprisingly, women who achieved control in the recommended range by 8 weeks of pregnancy also had a normal fetal outcome.

Supporting genotype-phenotype correlation with the rare metabolic diseases database Ramedis

To gain further knowledge about rare genetic diseases, a world wide method for data collection via the Internet has been established. This new approach will improve collecting valuable data from single case reports. Ramedis saves standardised patient data which will be usable for statistics, longitudinal examinations and cooperative studies in future time. Embedded in the scene of the German Human Genome Project, Ramedis directly will enable phenotype-genotype correlations. Beside the better characterisation of clinical heterogeneity of rare metabolic diseases, there may be a great benefit for the treatment of these patients in whom prospective studies are otherwise expensive and difficult to perform. This contribution presents the motivation for this system, introduces features, current state and the future of the project. Additionally, first experiences of using Ramedis by health professionals are explained.

Septo-optic dysplasia associated with a new mitochondrial cytochrome b mutation

We report on a 25-year-old patient with isolated mitochondrial complex III deficiency and a new heteroplasmic mutation (T14849C) in the cytochrome b gene. He suffered from septo-optic dysplasia, retinitis pigmentosa, exercise intolerance, hypertrophic cardiomyopathy, and rhabdomyolysis. A HESX1 mutation was excluded as a cause of his septo-optic dysplasia. Low alpha-tocopherol concentrations in his muscles and an elevated urinary leukotriene E(4) excretion indicate increased production of reactive oxygen species.

RAMEDIS- rare metabolic diseases publishing tool for genotype-phenotype correlation

To gain further knowledge about rare genetic diseases, a world wide method for data collection via the Internet has been established. This new approach will improve collecting valuable data from single case reports. RAMEDIS saves standardised patient data which will be usable for statistics, longitudinal examinations and co-operative studies in future time. Embedded in the scene of the German Human Genome Project, RAMEDIS directly will enable phenotype-genotype correlation's. Technically RAMEDIS is based on the Oracle database management system with some additional tools. Since November 2000 first case reports are committed online. Beside the better characterisation of clinical heterogeneity of rare diseases, there may be a great benefit for the treatment of these patients in whom prospective studies are otherwise expensive and difficult to perform. Quality of clinical diagnostic process and therapy will increase.

Congenital heart disease in maternal phenylketonuria: report from the Maternal PKU Collaborative Study

The frequency and types of congenital heart disease in offspring from pregnancies in women with hyperphenylalaninemia were examined in the international prospective Maternal Phenylketonuria Collaborative Study. Relationships of congenital heart disease in offspring to the basal blood phenylalanine level in the mother, metabolic control through diet during pregnancy, and phenylalanine hydroxylase mutations in mother and offspring were determined. The 416 offspring from 412 maternal phenylketonuria pregnancies that produced live births and 100 offspring from the 99 control pregnancies were included in this examination. Thirty-four of the 235 offspring (14%; 95% CI, 10.2 to 19.6%) from pregnancies in phenylketonuric women with a basal phenylalanine level > or = 900 microM (15 mg/dL) [normal blood phenylalanine < 120 microM (2 mg/dL)] and not in metabolic control [phenylalanine level < or = 600 microM (10 mg/dL)] by the eighth gestational week had congenital heart disease compared with one control offspring (1%) with congenital heart disease. One offspring among the 50 (2%) from mothers with non-phenylketonuria mild hyperphenylalaninemia also had congenital heart disease. Coarctation of the aorta and hypoplastic left heart syndrome were overrepresented compared with expected percentages among those with congenital heart disease in the general population. A basal maternal phenylalanine level > 1800 microM (30 mg/dL) significantly increased the risk for bearing a child with congenital heart disease (p = 0.003). Phenylalanine hydroxylase mutations in the mothers and offspring did not have an independent relationship to congenital heart disease but were related through the basal maternal phenylalanine levels. The data in this study indicate that a basal maternal phenylalanine level of 900 microM may be a threshold for congenital heart disease, that women with the most severe degree of phenylketonuria are at highest risk for bearing such a child, and that prevention of the congenital heart disease requires initiation of the low phenylalanine diet before conception or early in pregnancy with metabolic control no later than the eighth gestational week.

The International Collaborative Study of Maternal Phenylketonuria: status report 1998

The Maternal Phenylketonuria Study began in 1984 and during the intervening years, 572 pregnancies in hyperphenylalaninemic women and 99 controls and their outcomes have been evaluated. Among hyperphenylalaninemic women who delivered a live infant, only 15.9% were treated and in metabolic control preconceptually, however, another 18.4% were in control by 10 weeks. Compared to the results reported by Lenke and Levy in 1980, there is a marked improvement in outcome with treatment. Microcephaly was unusual in preconceptually treated pregnancies with well controlled phenylalanine restricted diets. Even in pregnancies that established control after conception but before the 8th week, congenital heart disease did not occur in the offspring, however, it did occur in 12% of pregnancies not achieving control until after 10 weeks of pregnancy.

CONCLUSION

The recommended level of blood phenylalanine during pregnancy is 120-360 mumol/l. Best results were obtained by close cooperation between the attending obstetrician and a metabolic team experienced in the care of persons with phenylketonuria.

Maternal phenylketonuria: an international study

Maternal phenylketonuria (PKU) syndrome results in multiple congenital anomalies in the offspring, usually consisting of microcephaly, intrauterine growth retardation, dysmorphology, and congenital heart disease. Pregnancies treated preconceptionally with a phenylalanine-restricted diet and control of maternal blood phenylalanine levels within the recommended range result in normal offspring. However, in this 15-year study, several significant factors resulted in microcephaly in 27% of the offspring, and 7% exhibited serious congenital heart disease. These results occurred chiefly in women with mean IQ scores of 83 associated with low socioeconomic status and decreased educational achievement. Another important factor associated with suboptimal control of blood phenylalanine levels during pregnancy was the fact that most pregnancies were not carefully planned and occurred in women off dietary treatment with phenylalanine-restricted products. These results indicate that greater effort must be developed to assist women with PKU in remaining on diet during their reproductive years. It appears that continued adherence to the diet, resulting in normal maternal intelligence, is an important contribution to improved fetal development.

Outcome at age 4 years in offspring of women with maternal phenylketonuria: the Maternal PKU Collaborative Study

CONTEXT

Untreated maternal phenylketonuria (PKU) increases risk for developmental problems in offspring. The extent to which this risk is reduced by maternal dietary therapy at various stages of pregnancy is not known.

OBJECTIVE

To determine whether dietary treatment during pregnancy of women with PKU affects developmental outcomes of offspring.

DESIGN

The Maternal PKU Collaborative Study, an ongoing, longitudinal prospective study begun in 1984.

SETTING

A total of 78 metabolic clinics and obstetrical offices in the United States, Canada, and Germany.

PARTICIPANTS

A total of 253 children of women with PKU (n = 149), with untreated mild hyperphenylalaninemia (n = 33), or without known metabolic problems (comparison group; n = 71) were followed up to age 4 years.

INTERVENTION

Women with PKU were offered a low-phenylalanine diet prior to or during pregnancy with the aim of maintaining metabolic control (plasma phenylalanine < or =10 mg/dL [< or =605 micromol/L]). Women with mild hyperphenylalaninemia, who had plasma phenylalanine levels of no more than 10 mg/dL (605 micromol/L) on a normal diet, were not treated.

MAIN OUTCOME MEASURES

Children's scores on cognitive and behavioral assessments (McCarthy Scales of Children's Abilities, Test of Language Development, Achenbach Child Behavior Checklist, Vineland Adaptive Behavior Scales, and Home Observation for Measurement of the Environment), compared by maternal metabolic status at 0 to 10 weeks', 10 to 20 weeks', and after 20 weeks' gestation.

RESULTS

Scores on the McCarthy General Cognitive Index decreased as weeks to metabolic control increased (r = -0.58; P<.001). Offspring of women who had metabolic control prior to pregnancy had a mean (SD) score of 99 (13). Forty-seven percent of offspring whose mothers did not have metabolic control by 20 weeks' gestation had a General Cognitive Index score 2 SDs below the norm. Overall, 30% of children born to mothers with PKU had social and behavioral problems.

CONCLUSIONS

Our data suggest that delayed development in offspring of women with PKU is associated with lack of maternal metabolic control prior to or early in pregnancy. Treatment at any time during pregnancy may reduce the severity of delay.

The international study of pregnancy outcome in women with maternal phenylketonuria: report of a 12-year study

OBJECTIVE

The purpose of this report was to update the results of the Maternal Phenylketonuria Collaborative Study, which was established to assess the efficacy of a phenylalanine-restricted diet in preventing morbidity among the offspring of women with hyperphenylalaninemia.

STUDY DESIGN

During a 12-year period 576 women with hyperphenylalaninemia were enrolled in this study. Outcome measures were stratified according to classification of maternal hyperphenylalaninemia and the time at which dietary control of phenylalanine level was achieved.

RESULTS

Optimal physical and cognitive fetal outcomes occurred when maternal blood phenylalanine level <600 micromol/L was achieved by 8 to 10 weeks' gestation and maintained throughout pregnancy (trimester average, </=600 micromol/L).

CONCLUSIONS

The achievement of blood phenylalanine level control through a phenylalanine-restricted diet significantly diminished the occurrence of congenital abnormalities among offspring of women with hyperphenylalaninemia and improved early intellectual progress of these offspring.

Maternal phenylketonuria syndrome: congenital heart defects, microcephaly, and developmental outcomes

OBJECTIVE

A cohort of women with phenylketonuria (PKU) were selected to explore the impact of phenylalanine (Phe) levels and other factors on congenital heart defects (CHDs), microcephaly, and development of their offspring.

STUDY DESIGN

Three hundred fifty-four women with PKU were followed up weekly with diet records, blood Phe levels, and sonograms obtained at 18 to 20 and 32 weeks' gestation. At birth, 413 offspring were examined and followed up at 6 months and annually by means of Bayley Mental Developmental Index and Psychomotor Developmental Index tests at 1 and 2 years. The women had Wechsler Adult Intelligence Scales and DNA testing.

RESULTS

Thirty-one offspring had CHDs; of these, 17 also had microcephaly. Mean Phe levels at 4 to 8 weeks' gestation predicted CHDs (P <.0001). An infant with a CHD had a 3-fold risk of having microcephaly when the mother had higher Phe levels (P =.02). The Bayley Mental Developmental Index and Psychomotor Developmental Index scores correlated with both CHDs (P =.037 and.0015, respectively) and microcephaly (P =.0001 for both). No direct relationship to the PKU mutation was found.

CONCLUSION

None of the women whose offspring had CHDs had blood Phe levels in control during the first 8 weeks of gestation. Women with PKU need to be well controlled on a low-phenylalanine diet before conception and throughout pregnancy.

Relationship among genotype, biochemical phenotype, and cognitive performance in females with phenylalanine hydroxylase deficiency: report from the Maternal Phenylketonuria Collaborative Study

OBJECTIVE

To examine the relationship of phenylalanine hydroxylase (PAH) genotypes to biochemical phenotype and cognitive development in maternal phenylketonuria (PKU).

METHODOLOGY

PAH gene mutations were examined in 222 hyperphenylalaninemic females enrolled in the Maternal PKU Collaborative Study (MPKUCS). A total of 84 different mutations were detected, and complete genotype was obtained in 199 individuals. Based on previous knowledge about mutation-phenotype associations, 78 of the mutations could be assigned to one of four classes of severity (severe PKU, moderate PKU, mild PKU, and mild hyperphenylalaninemia [MHP]). Then, 189 MPKUCS subjects were grouped according to the various combinations of mutation classifications. The sample sizes were large enough for statistical testing in four groups with at least one mutation that completely abolishes enzyme activity. These patients are considered functionally hemizygous.

RESULTS

The biochemical phenotype predicted from the genotype in functionally hemizygous patients was related significantly to the assigned phenylalanine level. Cognitive performance (IQ) was also significantly related to genotype. The IQ of PAH-deficient mothers with a severe PKU mutation in combination with a MHP mutation or a mild PKU mutation was 99 and 96, respectively, whereas the IQ of PKU mothers with two severe PKU mutations or with one severe and one moderate PKU mutation was 83 and 84, respectively. Of the patients with PKU, 92% had been treated during childhood. Those who were untreated or treated late had lower than average IQ scores for their group of mutation combinations. Females with moderate or mild PKU who were treated early and treated for >6 years showed IQ scores 10 points above average for their group.

CONCLUSIONS

The reproductive outcome in maternal phenylketonuria is dependent on prenatal metabolic control and postnatal environmental circumstances. Both factors depend on the intellectual resources of the mother with PKU. The significant relationship among genotype, biochemical phenotype, and cognitive performance observed in the present study is of importance for the development of an optimal strategy for future treatment of females with PKU who plan pregnancy.

Maternal Phenylketonuria Collaborative Study (MPKUCS) offspring: facial anomalies, malformations, and early neurological sequelae

Maternal phenylketonuria (PKU) in untreated women has resulted in offspring with microcephaly, mental retardation, congenital heart disease (CHD), and intrauterine growth retardation. The Maternal Phenylketonuria Collaborative Study (MPKUCS) was designed to determine the effect of dietary control of blood phenylalanine (Phe) during pregnancy in preventing damage to the fetus associated with untreated Maternal PKU. A cohort of offspring from MPKUS pregnancies was ascertained and examined to evaluate malformations, including CHD, craniofacial abnormalities, microcephaly, intrauterine and postnatal growth retardation, other major and minor defects, and early abnormal neurological signs. For analysis, the women were grouped according to their mean Phe levels in mumol/liter, < or = 360, 361-600, 601-900, or > 900, during critical gestational weeks of 0-8 (N = 203) and 8-12 (N = 190), and average for Phe exposure throughout pregnancy (N = 183). Frequencies of congenital abnormalities increased with increasing maternal Phe levels. Significant relationships included average Phe 0-8 weeks and CHD (P = 0.001); average Phe 8-12 weeks and brain, fetal, and postnatal growth retardation (P < 0.0005 for all), wide nasal bridge (P < 0.0005), and anteverted nares (P = 0.001); and average Phe exposure during the entire pregnancy and neurological signs (P < 0.0005). Although 14% of infants had CHD, none of the CHD occurred at 120-360 mumol/liter and only one (3%) at 361-600 mumol/liter. At levels of 120-360 mumol/liter, there were three infants (6%) with microcephaly, two (4%) with postnatal growth, and none with intrauterine growth retardation, in contrast to 85%, 51%, and 26%, respectively, with Phe above 900 mumol/liter. These data support the concept that women with PKU should begin a low-phenylalanine diet to achieve Phe levels of < 360 mumol/liter prior to conception and should maintain this throughout pregnancy.

Phenylalanine hydroxylase gene mutations in the United States: report from the Maternal PKU Collaborative Study

The major cause of hyperphenylalaninemia is mutations in the gene encoding phenylalanine hydroxylase (PAH). The known mutations have been identified primarily in European patients. The purpose of this study was to determine the spectrum of mutations responsible for PAH deficiency in the United States. One hundred forty-nine patients enrolled in the Maternal PKU Collaborative Study were subjects for clinical and molecular investigations. PAH gene mutations associated with phenylketonuria (PKU) or mild hyperphenylalaninemia (MHP) were identified on 279 of 294 independent mutant chromosomes, a diagnostic efficiency of 95%. The spectrum is composed of 71 different mutations, including 47 missense mutations, 11 splice mutations, 5 nonsense mutations, and 8 microdeletions. Sixteen previously unreported mutations were identified. Among the novel mutations, five were found in patients with MHP, and the remainder were found in patients with PKU. The most common mutations were R408W, IVS12nt1g-->a, and Y414C, accounting for 18.7%, 7.8%, and 5.4% of the mutant chromosomes, respectively. Thirteen mutations had relative frequencies of 1%-5%, and 55 mutations each had frequencies < or = 1%. The mutational spectrum corresponded to that observed for the European ancestry of the U.S. population. To evaluate the extent of allelic variation at the PAH locus within the United States in comparison with other populations, we used allele frequencies to calculate the homozygosity for 11 populations where >90% ascertainment of mutations has been obtained. The United States was shown to contain one of the most heterogeneous populations, with homozygosity values similar to Sicily and ethnically mixed sample populations in Europe. The extent of allelic heterogeneity must be a major determining factor in the choice of mutation-detection methodology for molecular diagnosis in PAH deficiency.

The International Collaborative Study on maternal phenylketonuria: organization, study design and description of the sample

The International Maternal Phenylketonuria (PKU) Collaborative Study commenced in 1984 to evaluate the efficacy of the low-phenylalanine diet in reducing the morbidity associated with maternal PKU syndrome. Four hundred and sixty eight (468) pregnancies resulted in 331 live births, 3 stillbirths, 61 spontaneous abortions, 2 ectopic pregnancies and 71 elective terminations. Since its inception, the study has steadily progressed toward its goal of diet initiation preconception or early in pregnancy. By 1994, 51% of the sample began the diet preconceptionally, with an additional 41% doing so by 8 weeks gestation. The number of adolescent pregnancies has decreased from 31% to 9%, college attendance has increased from 5% to 16%, number of women in the lowest socioeconomic classes has decreased from 95% to 59% and average IQ has increased from 78 to 88. The organization of the network of 130 referral centers and clinics within the U.S.A., Canada and Germany and the objectives of the scientific research investigation have served to provide a derived benefit of outreach, education, reproductive counseling and early diet intervention in a large cohort of PKU women.

Outcome implications of the International Maternal Phenylketonuria Collaborative Study (MPKUCS): 1994

It is well established that women with phenylketonuria who remain untreated during pregnancy face serious problems in offspring outcome. Surveys have documented that maternal phenylalanine (Phe) blood concentrations above 1200 mumol/l are associated with microcephaly, congenital heart disease and intrauterine growth retardation among their offspring. To investigate the efficacy of the Phe restricted diet, the National Institute of Child Health and Human Development in Bethesda Maryland developed an international study to evaluate fetal outcome in pregnancies treated with the Phe restricted diet. The study involves over 100 metabolic clinics in the United States, Canada and Germany, and is now in its 10th year. The results included in this report are still preliminary in nature and the actual risk for such pregnancies remains to be determined.

The international collaborative study of maternal phenylketonuria: status report 1994

Neonatal screening for phenylketonuria (PKU) has created a problem as females with PKU are reaching child-bearing age. Surveys have revealed that maternal phenylalanine blood concentrations greater than 1200 mumol/l are associated with fetal microcephaly, congenital heart defects and intrauterine growth retardation. It is estimated that as many as 3000 hyperphenylalaninemic females may be at risk of producing these fetal abnormalities. To examine this problem, the international maternal PKU collaborative study was developed to evaluate the efficacy of a phenylalanine-restricted diet in reducing fetal morbidity. Preliminary findings have indicated that phenylalanine restriction should begin before conception for females with PKU planning a pregnancy. Dietary control should maintain maternal blood phenylalanine levels between 120 and 360 mumol/l and should provide adequate energy, protein, vitamin and mineral intake. Pregnant hyperphenylalaninemic females who achieved metabolic control after conception or by the 10th week of pregnancy had a better offspring outcome than anticipated. The results of 402 pregnancies are reviewed.

Neuropsychological and biochemical investigations in heterozygotes for phenylketonuria during ingestion of high dose aspartame (a sweetener containing phenylalanine)

Aspartame, a high intensity sweetener, is used extensively worldwide in over 5,000 products. Upon ingestion, aspartame is completely metabolized to two amino acids and methanol (approximately 50% phenylalanine, 40% aspartic acid, and 10% methanol). The effects of aspartame on cognitive function, electroencephalograms (EEGs) and biochemical parameters were evaluated in 48 adult (21 men, 27 women) heterozygotes for phenylketonuria (PKUH), PKUH subjects whose carrier status had been proven by DNA analysis ingested aspartame (either 15 or 45 mg/kg/day) and placebo for 12 weeks on each treatment using a randomized, double-blind, placebo-controlled, crossover study. A computerized battery of neuropsychological tests was administered at baseline weeks -2 and -1, and during treatment at weeks 6, 12, 18, and 24. Samples for plasma amino acids and urinary organic acids were also collected during these visits. EEGs were evaluated by conventional and spectral analysis at baseline week -1 and treatment weeks 12 and 24. The results of the neuropsychological tests demonstrated that aspartame had no effect on cognitive function. Plasma phenylalanine significantly increased, within the normal range for PKUH, at 1 and 3 h following the morning dose of aspartame in the group receiving the 45 mg/kg per day dose only. There were no significant differences in the conventional or spectral EEG analyses, urinary organic acid concentrations, and adverse experiences when aspartame was compared with placebo. This study reaffirms the safety of aspartame in PKUH and refutes the speculation that aspartame affects cognitive performance, EEGs, and urinary organic acids.

Idiopathic de Toni-Debré-Fanconi syndrome with absence of proximal tubular brush border

In a girl with idiopathic de Toni-Debré-Fanconi syndrome associated with psychomotor retardation, severe renal tubular dysfunction was observed from the first day of life. At the age of 21/2 and 4 years the glomerular filtration rate (GFR) was only 60 ml/min/1.73 m2. No tubular transport of glucose, phosphate, paraaminohippurate and amino acids could be demonstrated. The tubular handling of uric acid, potassium and calcium, was also disturbed. Renal net acid excretion was zero at a plasma bicarbonate level of 14 mmol/l. Urinary osmolality ranged between 88 and 680 mosmol/kg. During hypotonic saline diuresis GFR decreased further; a GFR of 19 ml/min/1.73 m2 was accompanied by a fractional distal sodium delivery of 96.5% and a fractional free water clearance of 73%. In a renal biopsy specimen the proximal tubular cells showed variations in height with dedifferentiation and a widespread absence of brush border on electron microscopy. This formerly undescribed tubulopathy offers a unique chance to investigate glomerulo-tubular balance, adaptive mechanisms of distal tubular transport and renal metabolism under conditions where an apparently unchanged ultrafiltrate is offered by the proximal tubule to the loop of Henle and to a primarily intact distal tubule.

Compound heterozygotes in hyperphenylalaninaemia

Three children with hyperphenylalaninaemia and hyperphenylalaninaemic mothers are presented. At least one of the affected children was a compound heterozygote for hyperphenylalaninaemia and phenylketonuria. The families were examined by an L-phenylalanine loading test, by direct determination of phenylalanine hydroxylase and/or a loading test with hepta-deuterophenylalanine. We conclude that most of the patients with moderately elevated serum phenylalanine should have the genotype hyperphenylalaninaemia/phenylketonuria, i.e. they are compound heterozygotes.