Blood Phe Concentrations Research Articles

In vivo proton magnetic resonance spectroscopy in phenylketonuria.

In vivo nuclear magnetic resonance spectroscopy permits the non-invasive examination of metabolic characteristics of the human brain in a clinical environment. Methods to detect elevated phenylalanine (Phe) in patients with phenylketonuria (PKU) using difference spectroscopy and to estimate absolute brain Phe concentrations, [Phe]brain, have been developed. In patients with classical PKU, [Phe]brain typically varied between 0.14 and 0.78 mmol/l depending upon actual blood Phe concentrations, [Phe]blood, between 0.47 and 2.30 mmol/l. Dynamic investigations can be used to extract information about Phe transport at the human blood-brain barrier, which may be described by a symmetric Michaelis-Menten model. Carrier saturation and competitive inhibition of the influx of other large neutral amino acids can be expected at blood levels usually found in PKU patients. In single cases of untreated, normal intelligent patients, abnormally low [Phe]brain < or = 0.15 mmol/l were observed despite high stationary Phe levels ([Phe]blood = 1.15 +/- 0.10 mmol/l). Significant variations in phenylalanine transport parameters in untreated, normal intelligent patients indicated that blood-brain barrier transport or intracerebral phenylalanine consumption are causative factors for the individual vulnerability to phenylketonuria.

Phenylalanine and Tyrosine Quantification by Stable Isotope Dilution Liquid Chromatography–Mass Spectrometry from Filter Paper Blood Spots

Phenylketonuria (PKU) is one of the more common inborn errors of metabolism, affecting 1 in 10 000–15 000 individuals (1). Newborn screening for PKU is performed in all 50 states and started with the development of the bacterial inhibition screening assay by Guthrie and Susi (2). Frequent monitoring of blood Phe concentrations is required to maintain the concentration as close as possible to the reference interval [60–120 μmol/L (1–2 mg/dL)] to prevent damage to the brain from increased Phe concentrations and to prevent a negative nitrogen balance from an overly Phe-restricted diet. Moreover, the high risk of birth defects for the fetus of a PKU mother requires extremely frequent monitoring of blood Phe concentrations and would greatly benefit from a rapid and accurate blood spot method. Phe determination from dried blood spots is feasible by various methods: bacterial (2), fluorometric (3), liquid chromatography (LC) (4), and tandem mass spectrometry (MS) (5). Of these methods, only tandem MS allows use of a stable isotope as internal standard. Although tandem MS is the most rapid method available, the extremely high equipment cost and the need for sample derivatization are disadvantages. We developed a rapid and precise blood-spot method for Phe and Tyr determination using stable isotope dilution reversed-phase LC-MS. The advantages of this method are the very short sample preparation without derivatization, a short chromatographic run, the use of selective detection to eliminate interference, and the use of ideal internal standardization (stable isotope). The method described herein is now used routinely in our PKU clinic. l-Phe ( M r 165.19) and l-Tyr ( M r 181.19) were purchased from Sigma Chemical Co. Stable isotopes [ring-d5]-l-phenylalanine ( M r 170.23) …

Improved model of maternal phenylketonuria in rats by use of lower dietary concentrations of α-methylphenylalanine and L-phenylalanine in a semipurified diet

Dietary concentrations of 0.5% DL-α-methyl phenylalanine (AMPhe), an inhibitor of phenylalanine hydroxylase, plus 3.0% L-phenylalanine (Phe) have been commonly used in a rat model of maternal phenylketonuria (PKU). The treatment causes a marked depression of the food consumption and weight gain of the gestating dam. A study was carried out to determine if lowering the dietary concentrations of AMPhe and Phe would improve the condition of the dam, yet permit the maintenance of the high blood Phe concentrations typical of PKU. Long-Evans rats were fed from day 11 until day 20 of gestation on AIN-76A semi-purified diet the same diet containing 0.25%, 0.42%, and 0.50% AMPhe plus L-Phe, using a AMPhe: Phe ratio of 1:6. All dietary levels of AMPhe + Phe except 0.25% AMPhe + 1.5% Phe resulted in similarly elevated fetal brain, fetal plasma or maternal plasma concentrations of Phe. Food intake and maternal weight gain were improved substantially at the lowest dietary levels of AMPhe + Phe. We conclude that the gestational model of PKU using Long-Evans rats fed AIN-76A diet can be improved by reducing the dietary concentrations of AMPhe and Phe to 0.35% and 2.1%, respectively.

Recommendations for protein and amino acid intake in phenylketonuric patients.

The methods for the determination of protein requirements are reviewed and the difficulties in achieving the recommendations of the dietary management of phenylketonuria proposed by a Medical Research Council Working Party on Phenylketonuria using currently available low phenylalanine (Phe) protein substitutes and low protein foods are examined. These recommendations are that all infants whose blood Phe concentrations exceed 600 mumol/l in the presence of a normal or low plasma tyrosine and an otherwise normal plasma amino acid profile while receiving a normal protein intake (2-3 g/kg/day), should start a low Phe diet immediately. Infants whose blood Phe concentrations remain persistently between 400 and 600 mumol/l for more than a few days should also start treatment. The diet should contain a protein substitute which is Phe free (or at least very low in Phe) and otherwise nutritionally complete with a composition sufficient to provide 100-120 mg/kg per day of tyrosine and a total amino acid intake of at least 3 g/kg per day in children under 2 years of age. In children over 2 years the intake of amino acids should be maintained at a level of 2 g/kg per day. The protein substitute should be spread as evenly as possible through the 24 h. Blood Phe concentrations should be maintained between 120 and 360 mumol/l. In children aged over 10 years it is suggested that the protein substitute should supply the protein reference nutrient intake + 50%. An upper blood Phe limit of 480 mumol/l rather than 360 mumol/l may be acceptable in school age children. Adults and adolescents should continue treatment with the aim to maintain blood Phe concentrations no higher than 700 mumol/l. During the period before conception and during pregnancy women should aim to have plasma Phe concentrations between 60-250 mumol/l.

Magnetic resonance imaging of the brain in phenylketonuria

Summary Abnormalities of magnetic resonance imaging (MRI) of the brain occur in some patients with phenylketonuria but the clinical importance of this finding is not clear. In order to determine the frequency and functional significance of changes on MRI we investigated 77 adolescent and adult patients with phenylketonuria. Patients aged 14-49 years and taking a restricted diet of 1 g/kg protein underwent clinical examination, IQ testing, neurophysiological investigation, and MRI of the brain. Patients aged between 10-14 years taking a low phenylalanine diet with aminoacid supplements had MRI of the brain only. Biochemical control was assessed from: the lifetime blood phenylalanine determined from the mean blood concentration throughout life; the accumulated time for each patient that phenylalanine was <120 μmol/L; the accumulated time for each patient that phenylalanine was >1200 μmol/L); mean blood concentration in the first 4 years of life; and the mean blood phe concentration in the 5 years prior to imaging. MRI changes, compatible with a disturbance in the water content of white matter, were present in all but 1 patient. The severity of abnormality was most strongly associated with the blood phenylalanine concentration at the time of imaging. Clinical and neurophysiological abnormalities were less common and usually mild. 3 patients had prolonged central motor conduction time, 7 had prolonged visual evoked potentials, and 5 had impaired peripheral sensory nerve conduction. There was no significant association between the extent of MRI abnormalities and IQ, and the presence of neurophysiological, or clinical abnormalities. An abnormal brain scan in PKU may reflect present biochemical control rather than indicate significant neurological damage. As yet there is little evidence that in most patients with PKU these MRI changes are of clinical importance.

Intelligence in mild atypical phenylketonuria

In 82 children with mild phenylketonuria (PKU) (blood phenylalanine (Phe) concentrations consistently below 900 mumol/l throughout follow up) the relationship between intelligence at age 4 (IQ by Stanford-Binet) and average blood Phe concentrations from birth to 4 years was examined. Of the 82 children 24 had received no treatment. In the group as a whole, and in the 24 untreated subjects alone, mean IQs were significantly below population norms, with deficits of approximately 4.5 points and 9 points respectively. After allowing for social class IQ fell progressively by approximately 6 points for each 100 mumol/l rise in mean Phe concentrations in both the treated and untreated subjects. This relationship resembled that previously reported in early treated children with more severe forms of PKU, except that the scale of the relationship was even greater. We conclude that all children whose blood Phe concentrations reach 400 mumol/l or above should receive a low Phe diet, at least during the preschool years, and that the aim should be to control blood Phe levels below 400 mumol/l throughout early childhood in all forms of PKU.

187 Maternal Phenylketonuria/PKU/

Social and family status aswell as intellectual level of 34 PKU girls being in reproductive age was analyzed. The analysis included history of 15 pregnancies. There vere 4 abortions, 2 pregnancies not treated ended with birth of malformed offspring, 3 with low phe diet introduced again during first trimester of pregnancy and 3 treated before the conception and finalyzed with birth of normal healthy newborns. The course of treatment of pregnant women was satisfactory, they tolerated the diet well, and had low blood phe concentration. In all of them drop of phe level at the end of pregnancy was observed. Control of biochemical parameters revealed normal levels of plasma proteins, minerals and most of trace elements, urea and creatinine. Therapeutic problem was iron deficiency anemia which needed to be supplemented. Offspring from the gestations treated with low phe diet were born on time with normal Apgar score. Their psychomotorial development does not rise any objections. The oldest child is 5 years now and his IQ is 100.

MODERATE CHANGES IN PLASMA PHENYLALANINE CONCENTRATIONS AFFECT BRAIN ELECTRICAL DISCHARGE

We previously demonstrated that large changes in blood phenylalanine (phe) concentrations (500 - 2000 pM) decreased plasma L-DOPA, slowed brain electrical discharge and prolonged performance (Fed. Res. 20:112, 1986). In this study we ask whether moderately elevated plasma phe affects brain function. Six heterozygotes for phenylketonuria (PKU) and 2 normal controls were studied in a crossover, blinded protocol of 4, 2-week intervals. Volunteers ingested a constant diet of 40-50 mg/kg/day phe supplemented either with 100 mg/kg/day phe or placebo. On the last three days of each period the mean power frequency of three electroencephalograms (MPF) were measured. Plasma phe rose in both heterozygotes and controls on ingesting supplemental phe from a mean placebo phe concentration of 99 ± 20 to 140 ± 166 μM. The range of changes was from −200 to +400 μM. There was an inverse relationship between changes in plasma phe above 50 μM and changes in the MPF. By regression analysis 100 μM change in plasma phe produced an inverse change of 0.12 CPS in MPF. We conclude that plasma phe concentrations are raised by phe ingestion in both PKU heterozygotes and homozygous normal, and that alterations in brain electrical discharge are induced by intermediate changes in blood phe concentrations supporting a linear rather than threshold relationship to altered brain function.