Variant Of Phenylketonuria Research Articles

Charles Scriver: Epitome of the physician scientist

Charles Scriver is a towering figure in the medical genetics community. At 92 he can look back upon a remarkable career that established the field of biochemical genetics, a subsection of medical genetics that is translating the developments in basic genetics into the diagnoses and treatments of inherited biochemical diseases. This biographical sketch summarizes the key achievements of Dr. Scriver in research and medicine, integrating the different components of medical genetics into comprehensive provincial programs, teaching a generation of physicians and researchers, and developing worldwide collaborations. Charles has been a mighty figure in so many ways. He began his career by bringing amino acid chromatography from London to North America, thereby greatly enlarging the scope of metabolic disorders. Subsequently, his editorship of the classic Metabolic and Molecular Bases of Inherited Disease brought metabolism into genetics and established the field of biochemical genetics. He discovered a number of new diseases and was the first to recognize shared mediated amino acid transporters in the kidney, a medical breakthrough that has become a basic concept of amino acid homeostasis. He led the formation of the Quebec Network of Genetic Medicine, incorporating screening, diagnosis, counseling, treatment and research of genetic diseases, which to this day serves as a model for collaborative and comprehensive medical genetic programs internationally. He initiated the development of sapropterin (Kuvan®), the first non-dietary treatment for phenylketonuria (PKU) and helped identify the mechanism of this cofactor's action on phenylalanine hydroxylase in variants of PKU. His laboratory also led the development of phenylalanine ammonia lyase (Palynziq®), an enzyme substitution therapy that now serves as an alternative to dietary treatment for PKU. The ecosystem that Charles generated at the deBelle laboratory was collegial and highly fruitful. With the input and support of his remarkable wife Zipper, he found a way to integrate the concept of family into his work environment. Bustling with an endless series of evolving activities, he generated an inclusive setting which drew on the talents of brilliant clinical and research staff, as well as the input of patients and their families. In all these efforts, Charles managed to answer his own musings summarized in the following three questions: Who do we serve? How do we serve? Why do we serve? Charles Scriver's life is one well lived. An extraordinary physician scientist whose accomplishments are cause for pause and wonder; generating volumes of contribution which will forever seem impossible for one individual to deliver.

Диференціальна діагностика фенілкетонурії і порушень обміну птеринів у хворих із гіперфенілаланінемією

Актуальність. Гіперфенілаланінемія (HPA), або підвищення концентрації фенілаланіну (Phe) в крові, є наслідком порушення перетворення фенілаланіну в тирозин. Яскравим прикладом цього клінічного стану є класична фенілкетонурія (PKU). У 1970-х роках стало зрозуміло, що в частини хворих із PKU, незважаючи на ефективну дієтотерапію, розвивалися тяжкі неврологічні порушення. Ці випадки верифікували як атипові, або злоякісні, варіанти PKU, що, як було досліджено, спричинялось мутаціями в генах, які регулюють синтез та регенерацію тетрагідробіоптерину (ВН4). Порушення метаболізму тетрагідробіоптерину, або ВН4-дефіцитні синдроми, — гетерогенна група спадкових захворювань ЦНС, спричинених дефіцитом моноамінів-нейротрансмітерів, які в низці випадків супроводжуються гіперфенілаланінемією. ВН4-дефіцитні синдроми, які є рідкісними вродженими порушеннями метаболізму, спричиненими недостатністю нейротрансмітерів, за відсутності своєчасного лікування призводять до прогресуючої, нерідко летальної, енцефалопатії. Упровадження в медичну практику ранньої диференціальної клінічної та лабораторної діагностики гіперфенілаланінемій дозволить запобігти розвитку летальних енцефалопатій та суттєво підвищити ефективність їх лікування. Матеріали та методи. Були обстежені 59 пацієнтів із діагнозом PKU віком від 2 до 16 років. Гіперфенілаланінемія була загальним симптомом і встановлена в усіх обстежених пацієнтів. Усім хворим було проведено молекулярно-генетичне обстеження на панель мутацій у гені РАН (R408W, Y414C (12-й екзон), R158Q (5-й екзон), Ivs10nt546 (5-й інтрон), Ivs12nt1 (12-й інтрон), R252W, R261W, R261Q, R261X, G272X, P281L, S273F (7-й екзон). Усі хворі були обстежені на спектр птеринів (біоптерин та неоптерин) в крові та сечі. У 4 пацієнтів із вираженими неврологічними симптомами додатково визначали активність дигідроптеринредуктази в сухих краплях крові. Двом пацієнтам проводилося вимірювання концентрації гомованілової кислоти та 5-гідроксііндолоцтової кислоти в спинномозковій рідині методом високоефективної рідинної хроматографії. Усі пацієнти лікувались за допомогою дієтотерапії з використанням продуктів спеціалізованого лікувального харчування. Результати. 59 пацієнтів із гіперфенілаланінемією були обстежені на птериновий профіль. У 55 пацієнтів був установлений діагноз PKU, у 4 пацієнтів із прогресуючим ураженням нервової системи та порушенням птеринового профілю було встановлено діагноз ВН4-дефіцитних синдромів: 3 пацієнти — із діагнозом «PTPS-синдром», 1 пацієнт — «DHPR-синдром». Основні клінічні прояви ВН4-дефіцитних синдромів у виявлених пацієнтів були такими: затримка розумового розвитку, судоми, прогресування екстрапірамідних симптомів, порушення тонусу м’язів і пози, ковтання, гіперсалівація. Перші симптоми виникали частіше протягом перших місяців життя дитини. Головним біохімічним маркером на початку захворювання була гіперфенілаланінемія. При застосуванні дієтотерапії рівень Phe швидко досягав рекомендованих безпечних для нервової системи значень, але хвороба прогресувала. Висновки. Гіперфенілаланінемія — основний прояв гетерогенної групи рідкісних нейрометаболічних захворювань, які вимагають подальшої діагностичної верифікації. У новонароджених, у яких під час проведення масового неонатального скринінгу на фенілкетонурію виявлений підвищений рівень фенілаланіну, необхідно застосовувати додатковий діагностичний протокол (визначення птеринового профілю в крові та сечі, обов’язкове дослідження активності дигідроптеринредуктази у сухій краплі крові). Дослідження птеринів необхідне в пацієнтів із раніше встановленим діагнозом «фенілкетонурія» за неефективності дієтотерапії, прогресування когнітивних і неврологічних порушень, зниження тонусу м’язів, виникнення судомного синдрому, наявності екстрапірамідних симптомів. Рання діагностика ВН4-дефіцитних синдромів та своєчасно розпочате лікування дозволяють суттєво покращити стан хворих. Для деяких ВН4-дефіцитних синдромів гіперфенілаланінемія не характерна, що унеможливлює раннє виявлення таких пацієнтів під час неонатального скринінгу. Тому виявлення прогресуючих неврологічних симптомів у пацієнтів віком до 1 року й у ранньому дитинстві, які супроводжуються втратою когнітивних функцій на тлі м’язової гіпотонії, дистонічних порушень і судом, зумовлює необхідність дослідження птеринового профілю в крові й сечі.

Relationship between genotype, phenylalanine hydroxylase expression and in vitro activity and metabolic phenotype in phenylketonuria

Residual phenylalanine hydroxylase (PAH) activity is the main determinant of the metabolic phenotype in phenylketonuria (PKU). The genotypic heterogeneity of PKU, involving >1000 PAH variants and over 2500 different genotypes, makes genotype-based phenotype prediction challenging. While a relationship between PAH variants and the metabolic phenotype is well established, we questioned the importance of PAH expression and residual in vitro activity for the metabolic phenotype.Thirty-four PAH variants (p.F39 L, p.A47V, p.D59Y, p.I65S, p.R68G, p.R68S, p.E76G, p.A104D, p.D143G, p.R155H, p.R176L, p.V190A, p.G218 V, p.R241C, p.R243Q, p.P244L, p.R252W, p.R261Q, p.E280K, p.R297H, p.A300S, p.I306V, p.A309V, p.L311P, p.A313T, p.L348 V, p.V388 M, A403V, p.R408Q, p.R408W, p.R413P, p.D415N, p.Y417H, and p.A434D) were transiently transfected into COS-7 cells, and expression of PAH was investigated. Expression patterns were compared with in vitro PAH activity and allelic phenotype values (APVs).In vitro PAH activity was significantly higher (p < .01) in variants associated with mild hyperphenylalaninemia (PAH activity = 52.1 ± 8.5%; APV = 6.7–10.0) than that in classic PKU variants (PAH activity = 21.1 ± 7.0%; APV = 0–2.7). Mild PKU variants (PAH activity = 40.2 ± 7.6%; APV = 2.8–6.6) were not significantly different from mild hyperphenylalaninemia, but there was a difference (p < .048) compared with classic PKU phenotypes.

Executive functioning of 4 children with hyperphenylalaninemia from childhood to adolescence.

Hyperphenylalaninemia is a variant of phenylketonuria, and debate remains as to what, if any, active management of this condition is required to preserve cognitive function and psychological well-being. This study is the first to examine longitudinally the executive function (EF) in adolescents with hyperphenylalaninemia. Two sibling pairs with mild hyperphenylalaninemia underwent neuropsychological examination in early childhood and again in adolescence using EF tests that were highly sensitive to phenylalanine exposure. By early adolescence, none of the 4 children demonstrated EF impairment. The children demonstrated a typical developmental trajectory of EF from childhood to adolescence, given phenylalanine exposure consistent with their condition.

Positive effect of a simplified diet on blood phenylalanine control in different phenylketonuria variants, characterized by newborn BH4 loading test and PAH analysis

Until today, the mainstay of phenylketonuria (PKU) treatment is a phenylalanine (Phe)-restricted diet. Strict dietary treatment decreases flexibility and autonomy and still has a major impact on patients and their families. Compliance is often poor, particularly in adolescence. The aim of this study was to investigate the effect of the intake of fruits and vegetables containing Phe less than 100mg/100g (‘simplified diet’), as recommended by WHO for all individuals, instead of classical totally restricted diet on the course and treatment control of the disease in a well-characterized PKU cohort (n=80).All individual blood Phe measurements of each patient (1992–2009) were statistically analyzed before and after diet switch. Epidemiological data, age at diagnosis, PAH mutations, BH4 responsiveness, as well as Phe control measurements and detailed diet information were tabulated in a local database.62.5% had BH4 loading test and 40% had PAH analysis; 50/80 switched from classical to simplified diet, including 26 classical PKU, 13 moderate PKU, 7 mild PKU and 4 mild hyperphenylalaninemia (HPA). Median Phe levels on a simplified diet did not differ significantly to the median Phe levels on classical diet in all disease groups. Our results indicate that a simplified diet has no negative effect on blood Phe control in patients with hyperphenylalaninemia, independent of severity of the phenotype or the age at diet switch, over the period of 3years. Thus, a simpler approach to dietary treatment of PKU available to all HPA patients is more likely to be accepted and adhered by patients and might also increase quality of life.

Adverse Medical Outcomes of Early Newborn Screening Programs for Phenylketonuria

Despite the success of current newborn screening programs, some critics have argued that in the 1960s hundreds of children with false-positive results for phenylketonuria suffered death or disability from treatment with restrictive diets. Medically adverse outcomes after false-positive results may be a reason to be cautious when expanding current newborn screening programs. We sought to determine if newborn screening programs for phenylketonuria before 1980 led to adverse medical outcomes in children with false-positive results. We examined the history of newborn screening programs for phenylketonuria in the United States. We reviewed the historical scholarship, conducted a systematic search for medical adverse outcomes, and interviewed key participants in the history of newborn screening programs. We found no population-based studies of early screening programs for phenylketonuria. One author reported 2 infants treated with restrictive diets after false-positive results for phenylketonuria who were developmentally delayed, and there is unpublished evidence of 4 additional cases of inappropriate treatment, although adverse outcomes were not documented. There were also 4 published reports of adverse medical outcomes after treating children with phenylketonuria variants, as screening for phenylketonuria revealed infants with intermediate or transiently high levels of phenylalanine. We found little evidence of death or disability that resulted from the inappropriate treatment of well children who were falsely identified by early newborn screening programs. Because the first decade of newborn screening typically reveals diagnostic and therapeutic complexity, systematic follow-up of screened populations and rapid dissemination of results may reduce morbidity/mortality rates.

Maternal phenylketonuria: a metabolic teratogen.

The maternal phenylketonuria (PKU) syndrome refers to the teratogenic effects of PKU during pregnancy. These effects include mental retardation, microcephaly, congenital heart disease, and intrauterine growth retardation. In untreated pregnancies wherein the mother has classic PKU with a blood phenylalanine level > or = 1,200 microM (20 mg/dl), the frequencies of these abnormalities in offspring are exceedingly high, approaching 75-90% for microcephaly and mental retardation and 15% for congenital heart disease. There is a dose response relationship with progressively lower frequencies of these abnormalities at lower phenylalanine levels, both in the pregnancies of women with variants of PKU and in treated classic PKU pregnancies. The pathogenesis of this syndrome is unknown; it may be related to inhibition by phenylalanine of large neutral amino acid transport across the placenta or to direct toxicity of phenylalanine and/or a phenylalanine metabolite in certain fetal organs. A mouse model for PKU now exists, and studies of maternal PKU in this model are in progress. The treatment of maternal PKU consists of biochemical control through a phenylalanine restricted diet during pregnancy. The best results are obtained with diet initiation before conception or no later than the earliest weeks of pregnancy. Women with PKU and their families require much psychosocial support to meet the strict requirements of a maternal PKU pregnancy, including compliance with a difficult diet. With such compliance, however, it seems that bearing normal or near normal offspring is possible.

Maternal phenylketonuria: A metabolic teratogen

The maternal phenylketonuria (PKU) syndrome refers to the teratogenic effects of PKU during pregnancy. These effects include mental retardation, microcephaly, congenital heart disease, and intrauterine growth retardation. In untreated pregnancies wherein the mother has classic PKU with a blood phenylalanine level ≥1,200 μM (20 mg/dl), the frequencies of these abnormalities in offspring are exceedingly high, approaching 75–90% for microcephaly and mental retardation and 15% for congenital heart disease. There is a dose response relationship with progressively lower frequencies of these abnormalities at lower phenylalanine levels, both in the pregnancies of women with variants of PKU and in treated classic PKU pregnancies. The pathogenesis of this syndrome is unknown; it may be related to inhibition by phenylalanine of large neutral amino acid transport across the placenta or to direct toxicity of phenylalanine and/or a phenylalanine metabolite in certain fetal organs. A mouse model for PKU now exists, and studies of maternal PKU in this model are in progress. The treatment of maternal PKU consists of biochemical control through a phenylalanine restricted diet during pregnancy. The best results are obtained with diet initiation before conception or no later than the earliest weeks of pregnancy. Women with PKU and their families require much psychosocial support to meet the strict requirements of a maternal PKU pregnancy, including compliance with a difficult diet. With such compliance, however, it seems that bearing normal or near normal offspring is possible. © 1996 Wiley-Liss, Inc.

Maternal phenylketonuria syndrome in cousins caused by mild, unrecognized phenylketonuria in their mothers homozygous for the phenylalanine hydroxylase Arg-261-Gln mutation

Intrauterine growth retardation, microcephaly, and developmental delay in two first cousins lead to the recognition of phenylketonuria (PKU) in their mothers, 24- and 23 year-old sisters with blood phenylalanine concentrations of approx. 1.2 mmol/l who had never been treated and had no overt mental retardation. Both mothers were shown to be homozygous for a point mutation leading to an Arg-to-Gln substitution at codon 261 of the phenylalanine hydroxylase gene, a mutation which has been recently identified and tentatively associated with a mild variant of PKU. Our observation suggests that homozygosity for the Arg-261-Gln mutation can indeed result in "mild" PKU with little or perhaps no mental retardation, but also indicates that in such women, who may go unrecognized if not screened for, blood phenylalanine is elevated enough to cause the maternal PKU syndrome in their offspring.

Brain CT and MR Findings in Hyperphenylalaninemia due to Dihydropteridine Reductase Deficiency (Variant of Phenylketonuria)

Two siblings with malignant hyperphenylalaninemia were examined by magnetic resonance (MR) imaging and CT of the brain. Both techniques demonstrated diffuse cerebral atrophy and cystic loss of parenchyma with surrounding white matter changes. T2-weighted MR images demonstrated the white matter changes better than CT. However, MR images gave no definite indication of the presence of calcification, and CT demonstrated the characteristic calcifications in the basal ganglia and subcortical region bilaterally. Both MR and CT are complementary in the evaluation of this disease.

Possible uses of urinary neopterin and biopterin measurement

The measurement of urinary neopterin and biopterin may be an important non-specific diagnostic tool. Urinary biopterin has been found to be decreased in parkinsonian patients, and in hyperphenylalanemia as a variant of phenylketonuria. Urinary neopterin has been found to be elevated in numerous conditions. It has been shown to be significantly higher in AIDS patients than in ARC patients, and significantly higher in ARC patients than in controls. Urinary neopterin has been shown to be prognostically elevated in a wide range of neoplasias, including multiple myeloma, hematologic and gynecologic neoplasias. Neopterin is thought to be an in-vitro indicator of activation of the immune system.

Synthesis, Function, and Degradation of Catecholamine Neurotransmitters

Publisher Summary This chapter discusses some of the recent findings on the function and regulation of neurotransmitters. The chapter focuses on the intracellular synthesis and degradation of biogenic amines. A few specific examples illustrate the growing knowledge of the role of neurotransmitter-synthesizing and -degrading enzymes in disease processes. Neurotransmitter synthesizing and degrading enzymes play crucial roles in neuronal activity and normal physiological function by contributing to regulation of neurotransmitter levels. They also are important determinants in pathological conditions, as exemplified by the deficiency of dihydropteridine reductase (DHPR) in phenylketonuria variants and by the MAO B-catalyzed activation of a neurotoxin that causes Parkinson's disease in humans and primates. DHPR deficiency appears to be a typical genetic disorder, in which a missing enzyme leads to aberrations in the brain metabolism, although the precise nature of these abnormalities has not yet been identified. MAOs contribution to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-toxicity is particularly intriguing because the disease symptoms result from the interaction of an environmentally derived chemical with a genetically controlled amine-degrading enzyme.

Newborn Phenylalanine/Tyrosine Metabolism

Controversy over the sensitivity of newborn screening for phenylketonuria (PKU) has recently led to the specific recommendation that infants discharged within the first 24 hours of life be routinely retested at 1 to 2 weeks of age. To address this controversy, data from cord blood samples, phenylalanine (Phe) tolerance tests at 3 days of age, and sequential plasma Phe determinations in six siblings of known cases of PKU or hyperphenylalaninemia were analyzed, along with data from the literature. These analyses showed that normal and probably heterozygous infants decrease their Phe concentrations with age, while infants with PKU or PKU variants increase their Phe concentrations with age but at varying rates. Predictive equations showed that the sensitivity of the screening test rapidly increases with age, so that the usual critical value of 4 mg/dL is satisfactory for suspecting PKU after 18 hours of age. A critical value of 3 mg/dL would be equally satisfactory at any age, if the Guthrie test were appropriately modified to include a 3-mg/dL standard.

Renal transport of aromatic acids in patients with phenylketonuria.

Renal clearance of phenylpyruvic acid is maximal at a plasma concentration of 40-60 mumol/l. This concentration is obtained with plasma phenylalanine concentrations of 1.0-1.2 mmol/l, the threshold for separating classical phenylketonuria from phenylketonuria variants.

PHENYLALANINE HYDROXYLASE ACTIVITY IN HUMAN TERM PLACENTA

Phenylketonuria (PKU) is an autosomal recessive aminoacidopathy caused by a deficiency of phenylalanine hydroxylase. PKU is the most common aminoaciduria which responds to dietary restriction of phenylalanine. The enzymic studies of PKU have been difficult to approach since phenylalanine hydroxylase activity has been found primarily in liver. Recently some phenylalanine hydroxylase activity has been reported in cultured human fibroblasts, but the activity seems very low. A search for a new source for phenylalanine hydroxylase was attempted using term human placentas. Slices of fresh placentas were washed with cold 0.15M NaCl and then incubated in serum free medium 199 to which repurified L-U14C-phenylalanine was added. The incubation was carried out for 4 h at 37° with constant stiring. The reaction was terminated by boiling then the material was hydrolyzed with 6 N HCl for 20 h and amino acid analysis was carried out. The conversion of phenylalanine to tyrosine was considered as an indication for phenylalanine hydroxylase activity. In repeated experiments 30%-70% of the labeled phenylalanine was recovered as tyrosine indicating presence of phenylalanine hydroxylase in placenta. Two dimensional thin layer chromatography was performed for the identification of radioactive tyrosine and similar ratios of 30%-70% conversion were observed. These data suggest that placental phenylalanine hydroxylase may be studied in pregnancies at risk for PKU, explore the enzymic differences of PKU variants and possibly used for prenatal detection.