Inborn Metabolic Diseases Diagnosis and Treatment - part 5 pot

16 217 22. deGrauw TJ, Cecil KM, Byars AW et al (2003) The clinical syndrome of creatine transporter deficiency. Mol Cell Biochem 244:45-48 23. Hahn KA, Salomons GS, Tackels-Horne D et al (2002) X-linked mental retardation with seizures and carrier manifestations is caused by a mutation in the creatine-transporter gene (SLC6A8) located in Xq28. Am J Hum Genet 70:1349-1356 24. Salomons GS, van Dooren SJ, Verhoeven NM et al (2003) X-linked creatine transporter defect: an overview. J Inherit Metab Dis 26:309- 318 25. Rosenberg EH, Almeida LS, Kleefstra T et al (2004) High preval ence of SLC6A8 deficiency in X-linked mental retardation. Am J Hum Genet 75:97-105 26. Cecil KM, DeGrauw TJ, Salomons GS et al (2003) Magnetic re sonance spectroscopy in a 9-day-old heterozygous female child with creatine transporter deficiency. J Comput Assist Tomogr 27:44-47 27. Salomons GS, Wyss M, Jakobs C (2004) Creatine. In: Coats PM (ed) Encyclopedia of dietary supplements. Dekker, New York, pp 151- 158 28. Stöckler S, Marescau B, De Deyn PP et al (1997) Guanidino com- pounds in guanidinoacetate methyltransferase deficiency, a new inborn error of creatine synthesis. Metabolism 46:1189-1193 29. Item CB, Stromberger C, Muhl A et al (2002) Denaturing gradient gel electrophoresis for the molecular characterization of six patients with guanidinoacetate methyltransferase deficiency. Clin Chem 48:767-769 30. Item CB, Mercimek-Mahmutoglu S, Battini R et al (2004) Charac- terisation of seven novel mutations in seven patients with GAMT deficiency. Hum Mutat 23:524 31. Carducci C, Leuzzi V, Carducci C et al (2000) Two new severe mutations causing guanidinoacetate methyltransferase deficiency. Mol Genet Metab 71:633-638 32. Almeida LS, Verhoeven NM, Roos B et al (2004) Creatine and guanidinoacetate: diagnostic markers for inborn errors in creatine biosynthesis and transport. Mol Genet Metab 82:214-219 33. Cognat S, Cheillan D, Piraud M et al (2004) Determination of guanidinoacetate and creatine in urine and plasma by liquid chromatography-tandem mass spectrometry. Clin Chem 50:1459- 1461 34. Ilas J, Mühl A, Stöckler-Ipsiroglu S (2000) Guanidinoacetate methyltransferase (GAMT) deficiency: non-invasive enzymatic diagnosis of a newly recognized inborn error of metabolism. Clin Chim Acta 290:179-188 35. Bodamer OA, Bloesch SM, Gregg AR, Stockler-Ipsiroglu S, O`Brien WE (2001 ) Analysis of guanidinoacetate and creatine by isotope dilution electrospray tandem mass spectrometry. Clin Chim Acta 308:173-178 36. Verhoeven NM, Schor DS, Roos B et al (2003) Diagnostic enzyme assay that uses stable-isotope-labeled substrates to detect L-arginine:glycine amidinotransferase deficiency. Clin Chem 49:803-805 37. Verhoeven NM, Roos B, Struys EA et al (2004) Enzyme assay for diagnosis of guanidinoacetate methyltransferase deficiency. Clin Chem 50:441-443 38. Stöckler-Ipsiroglu S, Stromberger C, Item CB et al (2003) In: Blau N, Duran M, Blaskovics ME, Gibson KM (eds) Physician’s guide to the laboratory diagnosis of metabolic diseases. Springer, Berlin Heidel- berg New York, pp 467-480 39. Schulze A, Ebinger F, Rating D, Mayatepek E (2001) Improving treatment of guanidinoacetate methyltransferase deficiency: reduction of guanidinoacetic acid in body fluids by arginine restriction and ornithine supplementation. Mol Genet Metab 74:413-419 40. Stöckler-Ipsiroglu S, Battini R, de Grauw T, Schulze A (2006) Dis- orders of creatine metabolism. In: Blau N, Hoffmann GF, Leonard J, Clarke JTR (eds) Physician‹s guide to the treatment and follow up of metabolic diseases. Springer, Berlin Heidelberg New York (in press) References IV Disorders of Amino Acid Metabolism and Transport 17 Hyperphenylalaninaemia – 221 John H. Walter, Philip J. Lee, Peter Burgard 18 Disorders of Tyrosine Metabolism – 233 Anupam Chakrapani, Elisabeth Holme 19 Branched-Chain Organic Acidurias/Acidemias – 245 Udo Wendel, Hélène Ogier de Baulny 20 Disorders of the Urea Cycle and Related Enzymes – 263 James V. Leonard 21 Disorders of Sulfur Amino Acid Metabolism – 273 Generoso Andria, Brian Fowler, Gianfranco Sebas tio 22 Disorders of Ornithine Metabolism – 283 Vivian E. Shih, Matthias R. Baumgartner 23 Cerebral Organic Acid Disorders and Other Disorders of Lysine Catabolism – 293 Georg F. Hoffmann 24 Nonketotic Hyperglycinemia (Glycine Encephalopathy) – 307 Olivier Dulac, Marie-Odile Rolland 25 Disorders of Proline and Serine Metabolism – 315 Jaak Jaeken 26 Transport Defects of Amino Acids at the Cell Membrane: Cystinuria, Lysinuric Protein Intolerance and Hartnup Disorder – 321 Kirsti Näntö-Salonen, Olli Simell 17 Hyperphenylalaninaemia John H. Walter, Philip J. Lee, Peter Burgard 17.1 Introduction – 223 17.2 Phenylalanine Hydroxylase Deficiency – 223 17.2.1 Clinical Presentation – 223 17.2.2 Metabolic Derangement – 223 17.2.3 Genetics – 223 17.2.4 Diagnostic Tests – 224 17.2.5 Treatment and Prognosis – 224 17.3 Maternal Phenylketonuria – 227 17.3.1 Clinical Presentation – 227 17.3.2 Metabolic Derangement – 227 17.3.3 Management – 227 17.3.4 Prognosis – 228 17.4 Hyperphenylalaninaemia and Disorders of Biopterin Metabolism – 229 17.4.1 Clinical Presentation – 229 17.4.2 Metabolic Derangement – 229 17.4.3 Genetics – 229 17.4.4 Diagnostic Tests – 229 17.4.5 Treatment – 230 17.4.6 Outcome – 230 References – 231 Chapter 17 · Hyperphenylalaninaemia IV 222 Phenylalanine Metabolism Phenylalanine (PHE), an essential aromatic aminoacid, is mainly metabolized in the liver by the PHE hydroxylase (PAH) system ( . Fig. 17.1). The first step in the irreversible catabolism of PHE is hydroxylation to tyrosine by PAH. This enzyme requires the active pterin, tetrahydrobiopterin (BH 4 ), which is formed in three steps from GTP. During the hydroxylation reaction BH 4 is converted to the inactive pterin-4a-carbinolamine. Two enzymes regenerate BH 4 via q-dihydrobiopterin (qBH 2 ). BH 4 is also an obligate co-factor for tyrosine hydroxylase and tryptophan hydroxylase, and thus necessary for the production of dopamine, catecholamines, melanin, sero tonin, and for nitric oxide synthase. Defects in either PAH or the production or recycling of BH 4 may result in hyperphenylalaninaemia, as well as in deficiency of tyrosine, L-dopa, dopamine, melanin, catecholamines, and 5-hydroxytryptophan. When hydroxylation to tyrosine is impeded, PHE may be transaminated to phenylpyruvic acid (a ketone excreted in increased amounts in the urine, hence the term phenylketonuria or PKU), and further reduced and decarboxylated. . Fig. 17.1. The phenylalanine hydroxylation system including the synthesis and regeneration of pterins and other pterin-requiring enzymes. BH 2 , dihydrobiopterin (quinone); BH 4 , tetrahydrobiopterin; DHPR, dihydropteridine reductase; GTP, guanosine triphosphate; GTPCH, guanosine triphosphate cyclohydrolase; NO, nitric oxide; NOS, nitric oxide synthase; P, phosphate; PAH , PHE hydroxylase; PCD, pterin-4a-carbinolamine dehydratase; PTPS, pyruvoyl-tetra hydrobiopterin synthase; SR, sepiapterin reductase; TrpH, trypto phan hydroxylase; TyrH , tyrosine hydroxylase. The enzyme defects are depicted by solid bars across the arrows 17 223 Mutations within the gene for the hepatic enzyme phenylalanine hydroxylase (PAH) and those involving enzymes of pterin metabolism are associated with hyperphenylalaninaemia (HPA). Phenylketonuria (PKU) is caused by a severe deficiency in PAH activity and untreated leads to permanent central nervous system damage. Dietary restriction of phenylalanine (PHE) along with aminoacid, vitamin and mineral supplements, started in the first weeks of life and continued through childhood, is an effective treatment and allows for normal cognitive development. Continued dietary treatment into adulthood with PKU is generally recommended but, as yet, there is insufficient data to know whether this is necessary. Less severe forms of PAH deficiency may or may not require treatment depending on the degree of HPA. High blood levels in mothers with PKU leads to fetal damage. This can be prevented by re- ducing maternal blood PHE throughout the pregnancy with dietary treatment. Disorders of pterin metabolism lead to both HPA and disturbances in central nervous system amines. Generally they require treatment with oral tetrahydrobiopterin and neurotransmitters. 17.1 Introduction Defects in either phenylalanine hydroxylase (PAH) or the production or recycling of tetrahydrobiopterin (BH 4 ) may result in hyperphenylalaninaemia. Severe PAH deficiency which results in a blood phenylalanine (PHE) greater than 1200 µM when individuals are on a normal protein intake, is referred to as classical phenylketonuria (PKU) or just PKU. Milder defects associated with levels between 600 µM and 1200 µM are termed HPA and those with levels less than 600 µM but above 120 µM mild HPA. Disorders of biopterin metabolism have in the past been called malignant PKU or malignant HPA. However such disorders are now best named according to the underlying enzyme deficiency. 17.2 Phenylalanine Hydroxylase Deficiency 17.2.1 Clinical Presentation PKU was first described by Følling in 1934 as »Imbecillitas phenylpyruvica«[1]. The natural history of the disease is for affected individuals to suffer progressive, irreversible neurological impairment during infancy and childhood [2]; untreated patients develop mental, behavioural, neurological and physical impairments. The most common outcome is severe mental retardation (IQ d 50), often associated with a mousy odour (resulting from the excretion of phenyl acetic acid), eczema (20–40%), reduced hair, skin, and iris pig- mentation (a consequence of reduced melanin synthesis), reduced growth and microcephaly, and neurological impairments (25% epilepsy, 30% tremor, 5% spasticity of the limbs, 80% EEG abnormalities) [3]. The brains of patients with PKU untreated in childhood have reduced arborisa- tion of dendrites, impaired synaptogenesis and disturbed myelination. Other neurological features that can occur include pyramidal signs with increase d muscle tone, hyper- reflexia, Parkinsonian signs and abnormalities of gait and tics. Almost all untreated patients show behavioural problems which include hyperactivity, purposeless movements, stereotypy, aggressiveness, anxiety and social withdrawal. The clinical phenotype correlates with PHE blood levels, reflecting the degree of PAH deficiency. 17.2.2 Metabolic Derangement Although the pathogenesis of brain damage in PKU is not fully understood it is causally related to the increased levels of blood PHE. Tyrosine becomes a semi-essential amino acid with reduced blood levels leading to impaired synthesis of other biogenic amines including melanin, dopamine, and norepinephrine. Increase d blood PHE levels result in an imbalance of other large neutral amino acids (LNAA) within the brain, resulting in decreased brain concentrations of tyrosine and serotonin. The ratio of PHE levels in blood/brain is about 4:1 [4]. In addition to the effects on amino acid transport into the brain, PHE impairs the metabolism of tyrosine hydroxylation to dopamine and tryptophan decarboxylation to serotonin. The phenylketones phenylpyruvate, phenylacetate and phenyllactate are not abnormal metabolites but appear in increased concentration and are excreted in the urine. 17.2.3 Genetics PAH deficiency is an autosomal recessive transmitted disorder. The PAH gene is located on the long arm of chromo- some 12. At the time of writing nearly 500 different mutations have been described (see http://www.pahdb.mcgill. ca). Most subjects with PAH deficiency are compound heterozygous harbouring two different mutations. Although there is no single prevalent mutation certain ones are more common in different ethnic populations. For example the R408W mutation accounts for approximately 30% of alleles within Europeans with PKU whereas in Orientals the R243Q mutation is the most prevalent accounting for 13% of alleles. Prevalence of PAH deficiency varies between different populations (for example 1 in 1 000 000 in Finland and 1 in 4 200 in Turkey). Overall global prevalence in screened populations is approximately 1 in 12 000 giving an estimated carrier frequency of 1 in 55. 17.2 · Phenylalanine Hydroxylase Deficiency Chapter 17 · Hyperphenylalaninaemia IV 224 Genotypes correlate well with biochemical phenotypes, pre-treatment PHE levels, and PHE tolerance [5, 6]. How- ever due to the many other factors that effect clinical phenotype correlations between mutations and neurological, intellectual and behavioural outcome are weak. Mutation analysis is consequently of limited practical use in clinical management but may be of value in determining genotypes associated with possible BH 4 responsiveness. 17.2.4 Diagnostic Tests Blood PHE is normal at birth in infants with PKU but rises rapidly within the first days of life. In most Western nations PKU is detected by newborn population screening. There is variation between different countries and centres in the age at which screening is undertaken (day 1 to day 10), in the me thodology used (Guthrie microbiological inhibition test, enzymatic techniques, HPLC, or tandem mass spectro metry) and the level of blood PHE that is taken as a positive result requiring further investigation (120 to 240 µmol/l but with some laboratories also using a PHE/tyrosine ratio !3). Cofactor defects must be excluded by investigation of pterins in blood or urine and DHPR in blood ( 7 later). Per- sistent hyperphenylalaninaemia may occasionally be found in preterm and sick babies, particularly after parenteral feeding with amino acids and in those with liver disease (where blood levels of methionine, tyrosine, leucine/isoleucine and PHE are usually also raised). In some centres the diagnosis is further characterised by DNA analysis. PAH deficiency may be classified according to the concentration of PHE in blood when patients are on a normal protein containing diet or after a standardized protein chal- lenge [7–9]: 4 classical PKU (PHE t1200 µmol/l; less than 1% residual PAH activity), 4 hyperphenylalaninaemia (HPA) or mild PKU (PHE >600 µmol/l and <1200 µmol/l; 1–5% residual PAH activity), and 4 non-PKU-HPA or mild hyperphenylalaninaemia (MHP) (PHE ≤ 600 µmol/l; >5% residual PAH acti v- ity). Although in reality there is a continuous spectrum of sever- ity, such a classification has some use in terms of indicating the necessity for dietary treatment. Although rarely requested, prenatal diagnosis is possible by PAH DNA analysis on CVB or amniocentesis where the index case has had mutations identified previously. 17.2.5 Treatment and Prognosis Principles of Treatment The principle of treatment in PAH deficiency is to reduce the blood PHE concentration sufficiently to prevent the neuropathological effects. Blood PHE is primarily a func- tion of residual PAH activity and PHE intake. For the majority of patients with PKU the former cannot be altered so that blood P HE must be reduced by restricting dietary PHE intake. A PHE blood level while on a normal protein containing diet defines the indication for treatment with some minor differences in cut-offs; UK (>400 µmol/l), Ger- many (>600 µmol/l), and USA (>360–600 µmol/l). In all published recommendations for treatment target blood PHE levels are age related. . Table 17.1 shows such recommendations for UK [10], Germany [11] and the USA [12]. The degree of protein restriction required is such that in order to provide a nutritionally adequate diet a semi- synthetic diet is necessary. This is composed of the follow- ing: 4 Unrestricted natural foods with a very low PHE content (<30 mg/100 g; e.g. carbohydrate, fruit and some vege- tables). 4 Calculated amounts of restricted natural and manu- factured foods with medium PHE content (>30 mg/ 100 g; e.g. potato, spinach, broccoli; some kinds of special bread and special pasta). In the United Kingdom . Table 17.1. Daily phenylalanine (PHE) tolerances and target blood levels for three different recommendations Age PHE tolerance mg/day Target blood PHE (µmol/l) Germany UK USA 0–2 years a 130–400 40–240 120–360 120–360 3–6 years a 200–400 7–9 years a 200 –400 120–480 10–12 years a 350–800 40–900 13–15 years a 350–800 120–700 120–600 Adolescents/adults a 450–1000 40–1200 120–900 17 225 17.2 · Phenylalanine Hydroxylase Deficiency a system of ›protein exchanges‹ is used with each 1g of natural protein representing a PHE content of approximately 50 mg. 4 Calculated amounts of PHE-free amino acid mixtures supplemented with vitamins, minerals and trace elements. Intake of these three components – including the PHE-free amino acid mixture – should be distributed as evenly as possible during the day. Those foods with a higher concentration of PHE (e.g. meat, fish, cheese, egg, milk, yoghurt, cream, rice, corn) are not allowed. Aspartame (L-aspartyl L-phenylalanine methyl ester), a sweetener for foods (e.g. in soft-drinks) contains 50% PHE, and therefore is inappropriate in the diet of patients with PKU. PHE free amino acid infant formulas which also con- tain adequate essential fatty acids, mineral and vitamins are available. Human breast milk has relatively low PHE content; in breast fed infants, PHE-free formulas are given in measured amounts followed by breast-feeding to appetite. In the absence of breast feeding a calculated quantity of a normal formula is given to provide the essential daily re- quirement of PHE. With intercurrent illness, individuals may be unable to take their prescribed diet. During this period high- energy fluids may be given to counteract catabolism of body protein. Monitoring of Treatment The constraints of a diet that is ultimately focused at the threshold of a calculated PHE intake bears the risk of nu- trient deficiency. Therefore, the treatment must be moni- tored by regular control of dietary intake, as well as neurological, physical, intellectual and behavioural development. . Table 17.2 summarizes recommendations for monitoring treatment and outcome of PKU. Alternative Therapies/Experimental Trials Although dietary treatment of PKU is highly successful it is difficult and compliance is often poor, particularly as individuals reach adolescence. Hence there is a need to develop more acceptable therapies. 4 Gene therapy. Different PAH gene transfer vehicles have been tried in the PAH enu2 mouse. These have included non-viral vectors, recombinant adenoviral vector, recombinant retroviral vector and recombinant adeno- associated virus vector[13]. So far none of these experiments has resulted in sustained phenotypic correction, either due to poor efficiency of gene delivery, the production of neutralizing antibodies, or the lack of cofactor in non hepatic target organs. The development of a safe and more successful gene transfer vector is still required before clinical trials in humans are likely to become possible. 4 Liver transplanta tion fully corrects PAH deficiency but the risks of transplantation surgery and post transplantation immune suppressive medication are too high for it to be a realistic alternative to dietary treatment. 4 Phenylalanine ammonia lyase. Animal experiments have been performed with a non-mammalian enzyme, PHE ammonia lyase (PAL), that converts PHE to a harmless compound, transcinnamic acid. In the PAH enu2 mouse enteral administration, intraperitoneal injection and recombinant E.coli cells expressing PAL have all led to a significant fall in blood PHE [14, 15]. However it is likely to be some time before clinical trials are attempted. 4 The large neutr a l aminoacids (phenylalanine, tyrosine, tryptophan, leucine, isoleucine, and valine) compete for the same transport mechanism (the L-type amino - acid carrier) to cross the blood brain barrier. Studies in the PAH enu2 mouse model and in patients have reported a reduction in brain PHE levels when LNAAs (apart from PHE) have been given enterally [16, 17]. 4 Recently it has been shown that in certain patients or al BH 4 monotherapy (7–20 mg/kg bw) can reduce blood PHE levels into the therapeutic range [18]. Up to two- thirds of patients with mild PKU are potentially BH 4 - responsive and might profit from cofactor treatment. PAH is a homotetrameric enzyme where each mono- mer has a regulatory, a catalytic, and an oligomerization domain. According to Blau and Erlandsen [19] there are four postulated mechanisms for BH 4 -responsiveness. BH 4 therapy might (a) increase the binding affinity of the mutant PAH for BH 4 , (b) protect the active tetramer . Table 17.2. Recommendations for monitoring treatment and outcome of PKU Age Monitoring Blood PHE levels Clinical monitoring 1 0–3 years WeeklyEvery 3 months 4–6 years FortnightlyEvery 3-6 months 7–9 years FortnightlyEvery 6 months 10–15 years MonthlyEvery 6 months Adolescents/ adults 2–3-monthly Yearly 1 Length/height, head circumference, general status of health, neurology and psychological development. When phenylalanine (PHE) levels are within the recommended range, in general no additional routine laboratory analysis is necessary. A complete fasting profile of all amino acids, minerals, vitamins and trace elements, blood count, Ca-, P-metabolism, fatty acids may be indicated in individuals with poor compliance. Chapter 17 · Hyperphenylalaninaemia IV 226 from degradation, (c) increase BH 4 biosynthesis, and (d) up-regulate PAH expression. The most likely hypo- thesis is that BH 4 responsiveness is multifactorial but needs further research. From experience of treatment of BH 4 deficient patients it can be expected that long- term application of BH 4 has no significant side effects. However, clinical studies are not available to demonstrate long-term therapeutic efficacy, and BH 4 is expen- sive and not available for all patients. Compliance with Treatment Compliance with treatment is most often satisfactory in infancy and childhood. However the special diet severely interferes with culturally normal eating habits, particularly in older children and adolescents and this often results in problems keeping to treatment recommendations. It has been shown that up to the age of 10 years only 40% of the sample of the German Collaborative Study of PKU has been able to keep their PHE levels in the recommended range [20] and that after the age of 10 years 50 to 80% of all blood PHE levels measured in a British & Australian sample were above recommendation [21]. Dietary treatment of PKU is highly demanding for patients and families, and is almost impossible without the support of a therapeutic team trained in special metabolic treatment. This team should consist of a dietician, a metabolic paediatrician, a biochemist running a metabolic laboratory and a psychologist skilled in the behavioural problems related to a life long diet. It is of fundamental impor- tance that all professionals, and the families themselves, fully understand the principle and practice of the diet. The therapeutic team should be trained to work in an inter- disciplinary way in a treatment centre which should care for at least 20 patients to have sufficient expertise [22]. Outcome The outcome for PKU is dependent upon a number of variables which include the age at start of treatment, blood PHE levels in different age periods, duration of periods of blood PHE deficiency, and individual gradient for PHE transport across the blood brain barrier. Further unidenti- fied co-modifiers of outcome are also likely. However, the most important single factor is the blood PHE level in infancy and childhood. Longitudinal studies of development have shown that start of dietary treatment within the first 3 weeks of life with average blood PHE levels d 400 µmol/l in infancy and early childhood result in near normal intellectual development, and that for each 300 µmol/l increase during the first 6 years of life IQ is reduced by 0.5 SD, and during age 5 to 10 years reduction is 0.25 SD. Furthermore, IQ at the age of 4 years is reduced by 0.25 SD for each 4 weeks delay of start of treatment and each 5 months period of insufficient PHE intake. After the age of 10 years all studies show stable IQ performance until early adulthood irrespec- tive of PHE levels, and normal school career if compliance during the first 10 years has been according to treatment recommendations [23–26]. However, longitudinal studies covering middle and late adulthood are still lacking. Complications in Adulthood Neurological Abnormalities Neuropsychological studies of reaction times demonstrate a life-long but reversible, vulnerability of the brain to increased concurrent PHE levels [27]. Nearly all patients show white matter abnormalities in brain MRI after longer periods of increased PHE levels. However, these abnormalities are not correlated to intellectual or neurological signs and are reversible after 3 to 6 months of strict dietary treatment [28]. Patients with poor dietary control during infancy show behavioural impairments such as hyperactivity, temper tantrums, increased anxiety and social withdrawal, most often associated with intellectual deficits. Well-treated subjects may show an increased risk of depressive symptoms and low self-esteem. However, without correlation to concurrent PHE levels causality of this finding remains obscure but is hypothesized to be a consequence of living with a chronic condition rather than a biological effect of increased PHE levels [29]. A very small number of adolescent and adult patients have developed frank neurological disease which has usually improved on returning to dietary treatment [30]. These individuals appear to usually have had poor control in childhood. The risk to those who have been under good control in childhood and who have subsequently relaxed their diet is probably very small. In some cases neurological deterioration has been related to severe vitamin B 12 deficiency ( 7 below) compounded by anaesthesia using nitrous oxide [31]. Dietary Deficiencies Vitamin B 12 deficiency can occur in adolescents and adults who have stopped their vitamin supplements but continue to restrict their natural protein intake [32]. For patients on strict diet there have been concerns regarding possible deficiencies in other vitamins and minerals including selenium, zinc, iron, retinol and polyunsaturate d fatty acids. However such deficiencies are inconsistently found and it is unclear whether they are of any particular clinical significance. Low calcium, osteopenia and an increased risk of fractures have also been reported. Diet for Life For historical reasons clinical experience with early and strictly treated PKU does not go beyond early and middle adulthood. In view of the non-clinical life-long vulner ability of the brain to increased PHE levels, the neuropsychological findings, in particular, have been interpreted as possible markers of long-term intellectual and neurological impair- 17 227 ments. For reasons of risk-reduction, guidelines for treatment of PKU recommend diet for life, and where this is not possible at least monitoring for life. 17.3 Maternal Phenylketonuria 17.3.1 Clinical Presentation Although it was recognised that the offspring born to mothers with PKU are at risk of damage from the terato genic effects of PHE over 40 years ago [33], it was not until the publication of the seminal paper by Lenke and Levy in 1980 that the maternal PKU syn drome became recognised [34]. High PHE concentrations are associated with a distinct syndrome: facial dysmorphism, microcephaly, develop mental delay and learning difficulties, and congenital heart disease ( . Table 17.3). The facial features resemble those of the fetal alcohol syndrome with small palpebral fissures, epicanthic folds, long philtrum and thin upper lip. Other malformations also can occur in higher than expected frequency e.g. cleft lip and palate, oesophageal atresia and tracheo-oesophageal fistulae, gut malrotation, bladder extrophy and eye defects. As a result of these data, the prospective North American and German Maternal PKU Collaborative Study was initi- ated to assess the impact of dietary PHE restriction on the fetal outcome [35]. In the United Kingdom, data were collected within the National PKU Registry to look at the maternal PKU syndrome [36] and subsequently a Medical Research Council Working Party recommended that women with PKU should commence a diet pre-con- ceptually to protect against these effects [37]. The North American and German maternal PKU Collaborative Study examined the outcome of 572 pregnancies from 382 women with hyperphenylalaninaemia. It was found that optimum outcomes occur when maternal blood PHE of 120 to 360 µmol/l were achieved by 8-10 weeks gestation and subsequently maintained throughout pregnancy. The UK data looked at 228 pregnancies and found that pre- conceptual diet improved birth head circumference, birth weight and neuropsychometric outcome at 4 and 8 years. Interestingly outcome was better in those pregnancies managed in the more experienced centres. 17.3.2 Metabolic Derangement Fetal PHE concentrations are one and a half to twice those in the mother, due to active transport from the mother to the fetus [38]. PHE competes for placental transport with other large neutral amino acids and affects fetal development in a variety of as yet unknown ways. On the other hand, low PHE concentrations may limit fetal brain protein synthesis and be detrimental. Thus there is a need to aim to keep maternal blood PHE concentrations within a safe range. From the North American data this range is 120 to 360 µmol/l, whilst in the UK it is 100 to 250 µmol/l. 17.3.3 Management The issue of maternal PKU needs to be addressed at an early stage with the parents of children with PKU throughout childhood. Indeed, young girls from 5 years onwards can understand a simple explanation of the problem and then as they move into the reproductive years, counselling can be directed towards them. The aim of this education is to provide them with a basic understanding of conception and PKU and the need for a strict diet ideally before conception. Genetics of PKU should be discussed, highlighting the relative low recurrence risk of 1 in 100, assuming a carrier frequency of 1 in 50. The need for close contact with the metabolic clinic into adulthood is stressed so that the young women are able to contact appropriate support in a timely fashion. Contraception must be discussed with teen- age girls and reviewed frequently. If they become pregnant whilst on a normal diet, they must feel free to be able to contact the clinic immediately rather than wait until the pregnancy has proceeded for a significant length of time. Experience has shown that the most successful pregnancies are those that are planned ahead of time and in which a supportive partner is involved in the counselling process, as well as the dietary therapy. Starting Diet for Pregnancy Many women with PKU choosing to start a family have been on normal dietary intakes for many years because this was recommended at the time. They need, ideally, to be admitted to hospital for intensive education and institution of a PHE-restricted diet. If suitable facilities for admission are not available, they require very close supervision in their own homes or serial visits to see the dietitian. The woman, and her partner, need to be able to carefully plan menus, . Table 17.3. Pregnancy outcome in women with classical phenylketonuria (off-diet phenylalanine >1200 µmol/l). Com- parison between data of Lenke and Levy (1980) in which 0.5% pregnancies were treated [34] and Koch et al (2003) ) in which 26% were treated pre-conception, 46% from the first trimester and 9% from the second trimester [35] Untreated [34]Treated [35] Mental retardation 92% 28% Microcephaly 73% 23% Congenital heart disease 12% 11% Birth weight <2.5 kg 40% 21% Spontaneous abortion 24% 17% 17.3 · Maternal Phenylketonuria [...]... 19.1 .5 Clinical Presentation – 247 Metabolic Derangement – 249 Genetics – 250 Diagnostic Tests – 251 Treatment and Prognosis – 251 19.2 3-Methylcrotonyl Glycinuria – 256 19.2.1 19.2.2 19.2.3 19.2.4 19.2 .5 Clinical Presentation – 256 Metabolic Derangement – 256 Genetics – 257 Diagnostic Tests – 257 Treatment and Prognosis – 257 19.3 3-Methylglutaconic Aciduria Type I – 257 19.4 Short/Branched-Chain Acyl-CoA... Deficiency – 258 19 .5 2-Methyl-3-Hydroxybutyryl-CoA Dehydrogenase Deficiency – 258 19.6 Isobutyryl-CoA Dehydrogenase Deficiency – 259 19.7 3-Hydroxyisobutyric Aciduria – 259 19.8 Malonic Aciduria – 259 19.8.1 19.8.2 19.8.3 19.8.4 19.8 .5 Clinical Presentation – 259 Metabolic Derangement – 259 Genetics – 259 Diagnostic Tests – 260 Treatment and Prognosis – 260 References – 260 246 Chapter 19 · Branched-Chain... 4-hydroxyphenylpyruvate, -lactate, -acetate is highly elevated and N-acetyl- tyrosine and 4-tyramine are also increased The diagnosis can be confirmed by enzyme assay on liver biopsy or by mutation analysis 18.2 .5 Treatment and Prognosis Treatment consists of a phenylalanine and tyrosine-restricted diet, and the skin and eye symptoms resolve within weeks of treatment [44, 47] Generally, skin and eye symptoms... action of 2-( 2nitro-4-trifluoromethylbenzoyl )-1 , 3- cyclohexanedione (NTBC), its toxicology and development as a drug J Inherit Metab Dis 21:49 850 6 31 Holme E, Lindstedt S (2000) Nontransplant treatment of tyrosinemia Clin Liver Dis 4:80 5- 8 14 32 Hall MG, Wilks MF, Provan WM et al (2001) Pharmacokinetics and pharmacodynamics of NTBC ( 2-( 2-nitro- 4- fluoromethylbenzoyl)1,3-cyclohexanedione) and mesotrione,... + - + Selegiline (l-deprenyl) 0.1–0.25mg/day 3 to 4 divided doses (as adjunct to 5HT & L-dopa – see text) ± ± - ± Entacapone 15mg/kg/day in 2 to 3 divided doses ± ± - ± calcium folinate (folinic acid) 15 mg/day once daily - - - + BH4, tetrahydrobiopterin; CNS, central nervous system; DHPR, dihydropterin reductase; GTPCH, guanosine triphosphate cyclohydrolase I; 5HT, 5- hydroxytrytophan; PCD, pterin-4a-carbinolamine... cholesterol, and bacterial gut activity also contribute to the formation of propionyl-CoA Fig 19.1 Pathways of branched-chain amino acid catabolism 1, Branched-chain 2-keto acid dehydrogenase complex; 2, isovaleryl-coenzyme A (CoA) dehydrogenase; 3, 3-methylcrotonyl-CoA carboxylase; 4, 3-methylglutaconyl-CoA hydratase; 5, 3-hydroxy3-methylglutaryl-CoA lyase; 6, short/branched-chain acyl-CoA dehydrogenase;... dehydrogenase; 7, 2-methyl-3-hydroxybutyryl-CoA dehydrogenase; 8, 2-methylacetoacetyl-CoA thiolase; 9, isobutyryl-CoA dehydrogenase; 10, 3-hydroxyisobutyryl-CoA deacylase; 11, 3-hydroxyisobutyric acid dehydrogenase; 12, methylmalonic semialdehyde dehydrogenase; 13, acetyl-CoA carboxylase (cytosolic); 14, propionyl-CoA carboxylase; 15, malonyl-CoA decarboxylase; 16, methylmalonyl-CoA mutase Enzyme defects... Transient Tyrosinaemia – 240 18 .5 Alkaptonuria – 240 18 .5. 1 18 .5. 2 18 .5. 3 18 .5. 4 18 .5. 5 Clinical Presentation – 240 Metabolic Derangement – 241 Genetics – 241 Diagnostic Tests – 241 Treatment and Prognosis – 241 18.6 Hawkinsinuria – 241 18.6.1 18.6.2 18.6.3 18.6.4 18.6 .5 Clinical Presentation – 241 Metabolic Derangement – 241 Genetics – 241 Diagnostic Tests – 241 Treatment and Prognosis – 242 References... Thieme, Stuttgart, pp 20 3-2 35 42 Heidemann DG, Dunn SP, Bawle E, V, Shepherd DM (1989) Early diagnosis of tyrosinemia type II Am J Ophthalmol 107 :55 956 0 43 Paige DG, Clayton P, Bowron A, Harper JI (1992) I Richner-Hanhart syndrome (oculocutaneous tyrosinaemia, tyrosinaemia type II) J R Soc Med 85: 75 9-7 60 44 Rabinowitz LG, Williams LR, Anderson CE et al (19 95) Painful keratoderma and photophobia: hallmarks... ocular signs and symptoms Am J Ophthalmol 132 :52 2 -5 27 48 Barr DG, Kirk JM, Laing SC (1991) Outcome in tyrosinaemia type II Arch Dis Child 66:124 9-1 250 49 Cerone R, Fantasia AR, Castellano E et al (2002) Pregnancy and tyrosinaemia type II J Inherit Metab Dis 25: 31 7-3 18 50 Francis DE, Kirby DM, Thompson GN (1992) Maternal tyrosinaemia II: management and successful outcome Eur J Pediatr 151 :196199 51 Chitayat . guanidinoacetate and creatine in urine and plasma by liquid chromatography-tandem mass spectrometry. Clin Chem 50 :1 45 9- 1461 34. Ilas J, Mühl A, Stöckler-Ipsiroglu S (2000) Guanidinoacetate methyltransferase. care. J Pediatr 1 45: 5 3 -5 7 23. Smith I, Beasley MG, Ades AE (1990) Intelligence and qual ity of dietary treatment in phenylketonuria. Arch Dis Child 65: 47 2- 478 References . Table 17 .5. Medication. 240 18 .5. 2 Metabolic Derangement – 241 18 .5. 3 Genetics – 241 18 .5. 4 Diagnostic Tests – 241 18 .5. 5 Treatment and Prognosis – 241 18.6 Hawkinsinuria – 241 18.6.1 Clinical Presentation – 241 18.6.2 Metabolic

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