Regulation and crystallization of phosphorylated and dephosphorylated forms of truncated dimeric phenylalanine hydroxylase

Phenylalanine hydroxylase is regulated in a complex manner, including activation by phosphorylation. It is normally found as an equilibrium of dimeric and tetrameric species, with the tetramer thought to be the active form. We converted the protein to the dimeric form by deleting the C-terminal 24 residues and show that the truncated protein remains active and regulated by phosphorylation. This indicates that changes in the tetrameric quaternary structure of phenylalanine hydroxylase are not required for enzyme activation. Truncation also facilitates crystallization of both phosphorylated and dephosphorylated forms of the enzyme.

[Atypical form of phenylketonuria caused by lack of dihydrobiopterin synthetase activity]

A case of non-typical phenylketonuria produced by the inactivity of dihydrobiopterin synthetases is presented. Dihydrobiopterin synthetases are enzymes converting neopterin to biopterin. Presented case indicates a possibility of erroneous classification of hyperphenylalaninemia due to BH4 deficit, if the complete differential diagnosis is not performed. A complete differential diagnosis is necessary in all cases of hyperphenylalaninemia distinguished in neonates during screening tests.

A synopsis of the unconjugated acidic transamination metabolites of phenylalanine in phenylketonuria

We present blood and urine levels of unconjugated o-hydroxyphenylacetic, phenyllactic and phenylpyruvic acids in 61 children (2 years of age and above) and juveniles with phenylketonuria on or partially off diet. The samples were obtained during 185 scheduled outpatient visits and have been analysed with gas chromatographic methods. The compiled data define reference ranges of phenylalanine transamination capacity and of renal transport of metabolites which may be of value in further studies on the pathogenesis of phenylketonuria.

Aberrant splicing of phenylalanine hydroxylase mRNA: the major cause for phenylketonuria in parts of southern Europe

We report a mutation within the phenylalanine hydroxylase (PAH) gene that causes aberrant splicing of the mRNA and that is in tight association with chromosomal haplotypes 6, 10, and 36. Because of the high frequency of these particular haplotypes in Bulgaria, Italy, and Turkey, it appears to be one of the more frequent defects in the PAH gene causing classical phenylketonuria in this part of Europe. The mutation is a G to A transition at position 546 in intron 10 of the PAH gene, 11 bp upstream from the intron 10/exon 11 boundary. It activates a cryptic splice site and results in an in-frame insertion of 9 nucleotides between exon 10 and exon 11 of the processed mRNA. Normal amounts of liver PAH protein are present in homozygous patients, but no catalytic activity can be detected. This loss of enzyme activity is probably caused by conformational changes resulting from the insertion of three additional amino acids (Gly-Leu-Gln) between the normal sequences encoded by exon 10 and exon 11.

[Follow up protocol of patients with hyperphenylalaninemia]

The protocol of treatment and follow-up of diagnosed as hyperphenylalaninemia (4 mg/dl) by neonatal screening patients, is presented. When admission to the Reference Center for Cataluña in relation to their concentration of phenylalanin in plasma. The only infants who receive restricted in this aminoacid diet, are those with plasma concentrations greater than 10 mg/dl.

Birth weight and pathogenesis in phenylketonuria

The birthweights of an ethnically homogeneous sample of infants with phenylketonuria, their unaffected siblings, and control infants were compared after adjusting for the effects of: mother's age, mother's date of birth, mother's height and obstetric history, the length of gestation, the infant's sex, the place and date of birth. There were no significant differences between the infants with phenylketonuria and their unaffected siblings either in adjusted or unadjusted birthweights. Control infants had slightly, but statistically significant, greater adjusted and unadjusted birthweights than the combined phenylketonuria and unaffected sibling groups. This effect of the phenylketonuria gene is a previously unreported finding but unlikely to be related to the pathogenesis of phenylketonuria. Our results do not provide support for the "justification" hypothesis that the mental and neurological defects in phenylketonuria result from prenatal tyrosine deprivation which would be reflected in lower birthweights.

Protein metabolism in phenylketonuria and Lesch-Nyhan syndrome

Animal and in vitro studies have implicated decreased protein synthesis in the pathogenesis of tissue damage in phenylketonuria (PKU) and of growth failure in Lesch-Nyhan syndrome. Protein turnover was measured in vivo in ten young adult subjects with classical PKU, two subjects with hyperphenylalaninemia, and three children with Lesch-Nyhan syndrome using techniques based on continuous infusions of [13C]leucine and, in Lesch-Nyhan subjects, [2H5]phenylalanine. The PKU subjects had various degrees of dietary phenylalanine restriction and plasma phenylalanine levels at the time of study ranged from 450-1540 mumol/L (mean 1106). Plasma phenylalanine in the two hyperphenylalaninemic subjects was 533 and 402 mumol/L. Rates of protein synthesis in all PKU subjects (mean 3.71 g/kg/24 h, range 2.68-5.10, [13C]leucine as tracer) were in a range similar to or above control values (mean 2.97, range 2.78-3.22, n = 6), as were rates of protein catabolism (PKU mean 4.23 g/kg/24 h, range 3.15-5.45; controls 3.64, 3.50-3.91). Protein turnover values in hyperphenylalaninemia were also similar to those in controls. With [13C]leucine as tracer, both mean protein synthesis and catabolism values in Lesch-Nyhan subjects (mean 4.80 and 5.64 g/kg/24 h, respectively) were higher than values in control children matched for protein intake (synthesis 4.32 +/- 0.74 (SD) and catabolism 4.85 +/- 0.57 (g/kg/24 h, n = 5). Similar results were obtained in Lesch-Nyhan subjects using [2H5]phenylalanine as tracer. These results suggest that protein turnover is not decreased in either PKU or Lesch-Nyhan syndrome. This conclusion is inconsistent with the hypothesis that tissue damage in PKU results from impaired protein synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

[Nutrition and metabolic diseases with a mass incidence]

Metabolic diseases with a mass incidence (simple obesity, arterial hypertension, hyperlipoproteinaemia, type II diabetes and gout) are the main risk factors for the manifestation of cardiovascular diseases which can be influenced, as has been reliably proved. They are at present the cause of 56% of all deaths in Czechoslovakia. It is important to emphasize that we are living and dying in an epidemic of cardiovascular diseases. The founder of morbid anatomy, Rudolf Virchow, stated more than 100 years ago: "If the prevalence of a certain disease in a population becomes epidemic, it reflects always a disorder of human culture". It is a fact that a great proportion of the population in Czechoslovakia has adopted during the past decades and still practices an unsound dietary regime and there are other negative lifestyle factors (obesity, smoking, little exercise, high alcohol consumption) for which we pay at present by a declining life expectancy, unnecessary human suffering and the nation as a whole by immense economic losses. The question arises: who and what prevents us from starting in Czechoslovakia as rapidly as possible expedient, comprehensively conceived prevention on a wide front, making use of all findings and advances of world science in this field?

Malignant phenylketonuria due to defective synthesis of dihydrobiopterin

A defect in the synthesis of dihydrobiopterin was detected in an Arab girl, ascertained through high blood phenylalanine level on neonatal screening. An oral loading test with tetrahydrobiopterin (BH4) caused a significant fall in her blood phenylalanine and a rise in tyrosine concentrations. Her blood biopterin levels were low. In urine and cerebrospinal fluid (CSF) very high neopterin and low biopterin levels were observed. A deficiency of metabolites of neurotransmitters, serotonin and dopamine, was observed in CSF and urine. The patient was given replacement therapy of BH4, 5-hydroxytryptophan, and L-dopa with carbidopa starting from the age of 16 to 18 weeks. On this treatment the blood phenylalanine levels dropped to the desired range, while in urine and CSF a satisfactory rise of neurotransmitter metabolites was observed. In spite of this biochemical control, the patient developed neurological symptoms with myoclonic jerks and changes in muscle tone and presented severe cerebral damage with mental retardation. She died suddenly at the age of 38 weeks.

Hyperphenylalaninaemia caused by defects in biopterin metabolism

The hepatic phenylalanine hydroxylating system consists of three essential components, phenylalanine hydroxylase, dihydropteridine reductase and the non-protein coenzyme, tetrahydrobiopterin. The reductase and the pterin coenzyme are also essential components of the tyrosine and tryptophan hydroxylating systems. Recent studies have shown that there are three distinct forms of phenylketonuria or hyperphenylalaninaemia, each caused by the lack of one of these essential components. The variant forms of the disease that are caused by the lack of dihydropteridine reductase or tetrahydrobiopterin are characterized by severe neurological deterioration, impaired functioning of tyrosine and tryptophan hydroxylases and the resultant deficiency of tyrosine- and tryptophan-derived monoamine neurotransmitters in brain.

[Malignant phenylketonuria caused by biopterin synthetase deficiency. Study of neuromediator catabolites in the cerebrospinal fluid during treatment]

In a child presenting with malignant phenylketonuria due to dihydrobiopterin synthetase deficiency, the authors studied the cerebrospinal fluid (CSF) homovanillic acid and 5 hydroxyindole acetic acid levels under different circumstances: without treatment; under a treatment with tetrahydrobiopterin used alone at various doses; under a treatment associating BH4, L-dopa, 5 hydroxytryptophan and carbidopa, with increasing doses and varying administration schedules. This biological study compared with clinical evolution, shows clearly the inefficacy, regardless of the doses, of BH4 on the CSF levels of neuromediators and on the neurological status, and the excellent efficacy of neuromediator precursors provided high doses are given, divided in the nyctohemeral period.

Inhibition by L-phenylalanine of tryptophan transport by synaptosomal plasma membrane vesicles: implications in the pathogenesis of phenylketonuria

Phenylalanine is accumulated in the genetically linked deficiency phenylketonuria. The effect of L-phenylalanine on the transport of tryptophan was studied using membrane vesicles from rat-brain synaptosomes. Phenylalanine at similar concentrations to those found in phenylketonuric patients competitively inhibits tryptophan uptake, with a Ki of the same order as the Km for tryptophan. This inhibition could be responsible for the depletion of serotonin found in phenylketonuria.

Atypical phenylketonuria due to biopterin deficiency. Early treatment with tetrahydrobiopterin and neurotransmitter precursors, trials of monotherapy

This report presents the first case where an infant with tetrahydrobiopterin deficiency has been identified by screening of newborns with hyperphenylalaninemia for tetrahydrobiopterin deficiency. Therapy with L-Dopa, 5-hydroxytryptophan, Carbidopa and tetrahydrobiopterin was started at the age of seven weeks while the child received a normal diet. At that time already muscular hypotonia was observed. The girl, now 2 1/2 years old, shows slight muscular hypotonia and hypomotility, short periods of hypertonic extension of the limbs, and retardation of sensomotor and mental development of about 6-8 months. Monotherapy with tetrahydrobiopterin dihydrochloride, 20-40 mg/kg b.w., diminished the muscular hypotonia. The effect lasted however for only about 1 day. While urinary serotonin and phenylalanine remained normal for at least 3 days and neopterin was only slightly elevated, urinary free dopamine however remained low. Similar results were obtained after 1',2'-diacetyl tetrahydrobiopterin dihydrochloride administration, 20 mg/kg b.w.