Variant analysis of HPD genes from two families showing elevated tyrosine upon newborn screening by tandem mass spectrometry (MS/MS)

Background Alterations in the structure and activity of 4-hydroxyphenylpyruvate dioxygenase (HPD) are causally related to two different metabolic disorders: recessively inherited tyrosinemia type III and dominantly inherited hawkinsinuria. The aim of this study was to provide a new perspective for the clinical understanding of the pathogenesis of tyrosinemia type III or hawkinsinuria. Case presentation A full-term newborn baby born after a safe pregnancy and childbirth with a birth weight of 3200 g and another full-term baby born after a safe pregnancy and childbirth with a birth weight of 2800 g are reported and analysed. DNA extraction, next-generation sequencing, bioinformatics analysis, Sanger sequencing and biochemical analysis were performed. One patient with a heterozygous HPD gene (NM_002150.2) c.460G > A mutation and one patient with a heterozygous HPD gene (NM_002150.2) c.248delG mutation showing elevated tyrosine levels upon newborn screening by tandem mass spectrometry (MS/MS) are reported. Conclusions The HPD gene may not be a strictly autosomal recessive pathogenic gene, which provides a new perspective for the clinical understanding of the pathogenesis of tyrosinemia type III or hawkinsinuria.

A rare case of sterol-C4-methyl oxidase deficiency in a young Italian male: Biochemical and molecular characterization

Inborn defects of cholesterol biosynthesis are metabolic disorders presenting with multi-organ and tissue anomalies. An autosomal recessive defect involving the demethylating enzyme C4-methyl sterol (SC4MOL) has been reported in only 4 patients so far. In infancy, all patients were affected by microcephaly, bilateral congenital cataracts, growth delay, psoriasiform dermatitis, immune dysfunction, and intellectual disability. Herein, we describe a new case of SC4MOL deficiency in which a 19-year-old Italian male was affected by bilateral congenital cataracts, growth delay and learning disabilities, behavioral disorders and small stature, but not microcephaly. Our patient had abundant scalp dandruff, without other skin manifestations. Analysis of the blood sterol profile showed accumulation of C4-monomethyl and C4-dimethyl sterols suggesting a deficiency of the SC4MOL enzyme. Sequencing of the MSMO1 gene (also known as the "SC4MOL" gene) confirmed mutations in each allele (c.731A>G, p.Y244C, which is already known, and c.605G>A, p.G202E, which is a novel variant). His father carried c.731A>G mutation, whereas his mother carried c.605G>A. Thus, the combination of multiple skills and methodologies, in particular, blood sterol profiling and genetic analysis, led to the diagnosis of a new case of a very rare defect of cholesterol biosynthesis. Consequently, we suggest that these two analyses should be performed as soon as possible in all undiagnosed patients affected by bilateral cataracts and developmental delay.

Anti-Neu5Gc and anti-non-Neu5Gc antibodies in healthy humans

Our group previously investigated the levels of anti-Gal and anti-nonGal IgM and IgG in a cohort of 75 healthy humans of various backgrounds, and found some significant differences related to factors such as age, gender, ABO blood group, diet, vaccination history, and geographic location during childhood. We have now expanded our cohort (n = 84) to investigate the levels of anti-Neu5Gc and anti-nonGal/nonNeu5Gc antibodies in healthy humans. Anti-nonGal and anti-nonGal/nonNeu5Gc human IgM and IgG binding to pRBCs and pAECs from GTKO/CD46 and GTKO/CD46/Neu5GcKO pigs were measured by flow cytometry. Anti-Gal and anti-Neu5Gc IgM and IgG levels were measured by ELISA. In summary, (i) the great majority (almost 100%) of humans had anti-Neu5Gc IgM and IgG antibodies that bound to pAECs and approximately 50% had anti-Neu5Gc antibodies that bound to pRBCs, (ii) there was significantly less human antibody binding to pig cells that did not express either Gal or Neu5Gc compared with those that did not express Gal alone, (iii) the levels of both IgM and IgG binding to GTKO/CD46/Neu5GcKO pRBCs and pAECs were low, (iv) the level of anti-Neu5Gc IgG was higher in men than women, (v) the level did not change with age or diet, and there was some variability associated with (vi) previous vaccination history and (vii) the geographic region in which the individual spent his or her childhood. Our study confirms that human antibody binding to RBCs and AECs from GTKO/CD46/Neu5GcKO pigs is greatly reduced compared to binding to GTKO/CD46 cells. However, all humans appear to have a low level of antibody that binds to pAECs that is not directed to either Gal or Neu5Gc. Our findings require consideration in planning clinical trials of xenotransplantation.

Expanding the phenotype of hawkinsinuria: new insights from response to N-acetyl-L-cysteine

Hawkinsinuria is a rare disorder of tyrosine metabolism that can manifest with metabolic acidosis and growth arrest around the time of weaning off breast milk, typically followed by spontaneous resolution of symptoms around 1 year of age. The urinary metabolites hawkinsin, quinolacetic acid, and pyroglutamic acid can aid in identifying this condition, although their relationship to the clinical manifestations is not known. Herein we describe clinical and laboratory findings in two fraternal twins with hawkinsinuria who presented with failure to thrive and metabolic acidosis. Close clinical follow-up and laboratory testing revealed previously unrecognized hypoglycemia, hypophosphatemia, combined hyperlipidemia, and anemia, along with the characteristic urinary metabolites, including massive pyroglutamic aciduria. Treatment with N-acetyl-L-cysteine (NAC) restored normal growth and normalized or improved most biochemical parameters. The dramatic response to NAC therapy supports the idea that glutathione depletion plays a key role in the pathogenesis of hawkinsinuria.

Hawkinsinuria in two unrelated Greek newborns: identification of a novel variant, biochemical findings and treatment

BACKGROUND

Hawkinsinuria is a rare inborn error of tyrosine metabolism.

OBJECTIVES

To study novel hawkinsinuria cases by monitoring their biochemical profile and conducting a mutation analysis.

SUBJECTS AND METHODS

Among 92,519 newborns that underwent expanded newborn screening, two unrelated cases with high tyrosine blood levels were further investigated by chromatographic techniques and via genetic testing for 4-hydroxyphenylpyruvate dioxygenase (HPD) gene.

RESULTS

Elevated levels were monitored for blood/plasma tyrosine and for the specific diagnostic markers in urine. The two newborns were put on a special low tyrosine diet. Till completion of the 1st year of their life, liver function tests and brain MRI were normal. The mutation A33T was identified in both cases, while one neonate carried an additional novel mutation of HPD gene (V212M).

CONCLUSIONS

Two mutations of HPD gene, A33T, which are associated with hawkinsinuria and a novel one (V212M) were detected for the 1st time in Greek newborns.

Why Is N-Glycolylneuraminic Acid Rare in the Vertebrate Brain?

The sialic acids N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc) differ by a single oxygen atom and are widely found at the terminal position of glycans on vertebrate cell surfaces. In animals capable of synthesizing Neu5Gc, most tissues and cell types express both sialic acids, in proportions that vary between species. However, it has long been noted that Neu5Gc is consistently expressed at trace to absent levels in the brains of all vertebrates studied to date. Although several reports have claimed to find low levels of Neu5Gc-containing glycans in neural tissue, no study definitively excludes the possibility of contamination with glycans from non-neural cell types. This distribution of a molecule - prominently but variably expressed in extraneural tissues but very low or absent in the brain - is, to our knowledge, unique. The evolutionarily conserved brain-specific suppression of Neu5Gc may indicate that its presence is toxic to this organ; however, no studies to date have directly addressed this very interesting question. Here we provide a historical background to this issue and discuss potential mechanisms causing the suppression of Neu5Gc expression in brain tissue, as well as mechanisms by which Neu5Gc may exert the presumed toxicity. Finally, we discuss future approaches towards understanding the mechanisms and implications of this unusual finding.

The intracellular redox protein MICAL-1 regulates the development of hippocampal mossy fibre connections

Mical is a reduction-oxidation (redox) enzyme that functions as an unusual F-actin disassembly factor during Drosophila development. Although three Molecule interacting with CasL (MICAL) proteins exist in vertebrate species, their mechanism of action remains poorly defined and their role in vivo unknown. Here, we report that vertebrate MICAL-1 regulates the targeting of secretory vesicles containing immunoglobulin superfamily cell adhesion molecules (IgCAMs) to the neuronal growth cone membrane through its ability to control the actin cytoskeleton using redox chemistry, thereby maintaining appropriate IgCAM cell surface levels. This precise regulation of IgCAMs by MICAL-1 is essential for the lamina-specific targeting of mossy fibre axons onto CA3 pyramidal neurons in the developing mouse hippocampus in vivo. These findings reveal the first in vivo role for a vertebrate MICAL protein, expand the repertoire of cellular functions controlled through MICAL-mediated effects on the cytoskeleton, and provide insights into the poorly characterized mechanisms underlying neuronal protein cell surface expression and lamina-specific axonal targeting.

Knockdown of the fat mass and obesity gene disrupts cellular energy balance in a cell-type specific manner

Recent studies suggest that FTO variants strongly correlate with obesity and mainly influence energy intake with little effect on the basal metabolic rate. We suggest that FTO influences eating behavior by modulating intracellular energy levels and downstream signaling mechanisms which control energy intake and metabolism. Since FTO plays a particularly important role in adipocytes and in hypothalamic neurons, SH-SY5Y neuronal cells and 3T3-L1 adipocytes were used to understand how siRNA mediated knockdown of FTO expression alters cellular energy homeostasis. Cellular energy status was evaluated by measuring ATP levels using a luminescence assay and uptake of fluorescent glucose. FTO siRNA in SH-SY5Y cells mediated mRNA knockdown (−82%), increased ATP concentrations by up to 46% (P = 0.013) compared to controls, and decreased phosphorylation of AMPk and Akt in SH-SY5Y by −52% and −46% respectively as seen by immunoblotting. In contrast, FTO siRNA in 3T3-L1 cells decreased ATP concentration by −93% (p<0.0005), and increased AMPk and Akt phosphorylation by 204% and 70%, respectively suggesting that FTO mediates control of energy levels in a cell-type specific manner. Furthermore, glucose uptake was decreased in both SH-SY5Y (−51% p = 0.015) and 3T3-L1 cells (−30%, p = 0.0002). We also show that FTO knockdown decreases NPY mRNA expression in SH-SY5Y cells (−21%) through upregulation of pSTAT3 (118%). These results provide important evidence that FTO-variant linked obesity may be associated with altered metabolic functions through activation of downstream metabolic mediators including AMPk.

The asparaginyl hydroxylase factor inhibiting HIF-1alpha is an essential regulator of metabolism

Factor inhibiting HIF-1alpha (FIH) is an asparaginyl hydroxylase. Hydroxylation of HIF-alpha proteins by FIH blocks association of HIFs with the transcriptional coactivators CBP/p300, thus inhibiting transcriptional activation. We have created mice with a null mutation in the FIH gene and found that it has little or no discernable role in mice in altering classical aspects of HIF function, e.g., angiogenesis, erythropoiesis, or development. Rather, it is an essential regulator of metabolism: mice lacking FIH exhibit reduced body weight, elevated metabolic rate, hyperventilation, and improved glucose and lipid homeostasis and are resistant to high-fat-diet-induced weight gain and hepatic steatosis. Neuron-specific loss of FIH phenocopied some of the major metabolic phenotypes of the global null animals: those mice have reduced body weight, increased metabolic rate, and enhanced insulin sensitivity and are also protected against high-fat-diet-induced weight gain. These results demonstrate that FIH acts to a significant degree through the nervous system to regulate metabolism.

Precocious puberty with hypothalamic hamartoma and non classical form of congenital adrenal hyperplasia. Report of two cases

Two girls with central precocious puberty (CPP) associated with hypothalamic hamartoma (HH) and non classical form of congenital adrenal hyperplasia (NCAH), are reported. Case 1. The first patient, who showed at age around 4 years the onset of CPP, was submitted in view of some organic lesion to magnetic resonance (MRI) of the brain which documented the presence of HH. The remarkable acceleration of bone age (BA) advanced of 3 SD and some clinical signs of hyperandrogenism suggested the coexistence of NCAH, proved by adrenocorticotropic hormone (ACTH) test and molecular analysis. She resulted carrier of partial 21-hydroxylase deficiency. Case 2. In the second girl with CPP, aged 6.5 years, the remarkable advancement (4 SD) of bone age (BA) alerted to adrenal involvement. ACTH stimulation test and molecular analysis showed NACH due to 21-hydroxylase deficiency. Brain MRI, performed mainly for severe headache, showed the presence of HH. Yearly brain MRI to monitor HH dimensions and neurological examination with EEG, in order to exclude anomalies referable to gelastic epilepsy are advisable, in both cases. The authors' observation emphasizes the need to be careful in young patients with CPP, with fast progression of pubertal development and remarkable BA advancement. The association of CPP with HH and NCAH should be considered, performing not only MRI of the brain, but also ACTH test, beside LHRH test for the diagnosis of CPP. At the authors' knowledge this association has not been reported so far. Further observations are needed to understand if this rare combination is occasional or genetically determined.

Blood-spot 17-hydroxyprogesterone in nonclassical 21-hydroxylase deficiency

The value of blood-spot 17-hydroxyprogesterone (17-OHP) measurements in selective screening for non-classical 21-hydroxylase deficiency (NC 21-OHD) among female patients with postnatal virilization was studied. Early morning basal blood-spot and serum samples, and post-ACTH serum samples for 17-OHP measurement were collected from twenty-seven patients with precocious pubarche, hirsutism and/or menstrual abnormalities (age: 3 to 17 years). Using a two-step extraction method for blood-spot 17-OHP measurements of all the nine patients with NC 21-OHD showed higher values than the eighteen patients without 21-OHD. Blood-spot 17-OHP values of patients with NC 21-OHD showed a diurnal rhythm with pathological high levels between 0500 and 0900 h, and normal or slightly elevated levels between 1700 and 2100 h. In conclusion, early morning blood-spot 17-OHP measurement is a useful method to detect NC 21-OHD in the peripubertal period.

Reversal of physiological deficits caused by diminished levels of peptidylglycine alpha-amidating monooxygenase by dietary copper

Amidated peptides are critically involved in many physiological functions. Genetic deletion of peptidylglycine alpha-amidating monooxygenase (PAM), the only enzyme that can synthesize these peptides, is embryonically lethal. The goal of the present study was the identification of physiological functions impaired by haploinsufficiency of PAM. Regulation of the hypothalamic-pituitary-thyroid axis and body temperature, functions requiring contributions from multiple amidated peptides, were selected for evaluation. Based on serum T(4) and pituitary TSH-beta mRNA levels, mice heterozygous for PAM (PAM(+/-)) were euthyroid at baseline. Feedback within the hypothalamic-pituitary-thyroid axis was impaired in PAM(+/-) mice made hypothyroid using a low iodine/propylthiouracil diet. Despite their normal endocrine response to cold, PAM(+/-) mice were unable to maintain body temperature as well as wild-type littermates when kept in a 4 C environment. When provided with additional dietary copper, PAM(+/-) mice maintained body temperature as well as wild-type mice. Pharmacological activation of vasoconstriction or shivering also allowed PAM(+/-) mice to maintain body temperature. Cold-induced vasoconstriction was deficient in PAM(+/-) mice. This deficit was eliminated in PAM(+/-) mice receiving a diet with supplemental copper. These results suggest that dietary deficiency of copper, coupled with genetic deficits in PAM, could result in physiological deficits in humans.

Vitamin K-induced modification of coagulation phenotype in VKORC1 homozygous deficiency

BACKGROUND

Combined vitamin K-dependent clotting factor (VKCF) deficiency type 2 (VKCFD2) is a rare bleeding disorder caused by mutated vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1) gene.

METHODS AND RESULTS

An Italian patient with moderate to severe bleeding tendency was genotyped, and found to be homozygous for the unique VKORC1 mutation (Arg98Trp) so far detected in VKCFD2. The activity levels of VKCFs were differentially reduced, and inversely related to the previously estimated affinity of procoagulant factor propeptides for the gamma-carboxylase. The normal (factor IX) or reduced antigen levels (other VKCFs) produced a gradient in specific activities. Vitamin K supplementations resulted in reproducible, fast and sustained normalization of PT and APTT. At 24 h the activity/antigen ratios of VKCFs were close to normal, and activity levels were completely (factor VII and IX), virtually (prothrombin, factor X and protein C) or partially (protein S) restored. Thrombin generation assays showed a markedly shortened lag time. The time to peak observed at low tissue factor concentration, potentially mimicking the physiological trigger and able to highlight the effect of reduced protein S levels, was shorter than that in pooled normal plasma. At 72 h the thrombin generation times were normal, and the decrease in activity of procoagulant VKCFs was inversely related to their half-life in plasma. The improved coagulation phenotype permitted the uneventful clinical course after invasive diagnostic procedures.

CONCLUSIONS

Modification of coagulation phenotypes in VKCFD2 after vitamin K supplementation was clinically beneficial, and provided valuable patterns of factor specific biosynthesis, half-life and decay.

Germinal center marker GL7 probes activation-dependent repression of N-glycolylneuraminic acid, a sialic acid species involved in the negative modulation of B-cell activation

Sialic acid (Sia) is a family of acidic nine-carbon sugars that occupies the nonreducing terminus of glycan chains. Diversity of Sia is achieved by variation in the linkage to the underlying sugar and modification of the Sia molecule. Here we identified Sia-dependent epitope specificity for GL7, a rat monoclonal antibody, to probe germinal centers upon T cell-dependent immunity. GL7 recognizes sialylated glycan(s), the alpha2,6-linked N-acetylneuraminic acid (Neu5Ac) on a lactosamine glycan chain(s), in both Sia modification- and Sia linkage-dependent manners. In mouse germinal center B cells, the expression of the GL7 epitope was upregulated due to the in situ repression of CMP-Neu5Ac hydroxylase (Cmah), the enzyme responsible for Sia modification of Neu5Ac to Neu5Gc. Such Cmah repression caused activation-dependent dynamic reduction of CD22 ligand expression without losing alpha2,6-linked sialylation in germinal centers. The in vivo function of Cmah was analyzed using gene-disrupted mice. Phenotypic analyses showed that Neu5Gc glycan functions as a negative regulator for B-cell activation in assays of T-cell-independent immunization response and splenic B-cell proliferation. Thus, Neu5Gc is required for optimal negative regulation, and the reaction is specifically suppressed in activated B cells, i.e., germinal center B cells.

Founder mutation Arg485Pro led to recurrent compound heterozygous GGCX genotypes in two German patients with VKCFD type 1

Congenital combined deficiency of the vitamin-K-dependent coagulation factors (VKCFD) represents a rare autosomal recessive inherited bleeding disorder caused by mutations in either the gamma-glutamyl carboxylase gene (VKCFD type 1) or the vitamin K epoxide reductase gene (VKCFD type 2). Four different mutations of the gamma-glutamyl carboxylase gene (GGCX) have so far been reported in three unrelated patients with VKCFD type 1. Here we report on a fourth patient who presented with two compound heterozygous missense mutations of the GGCX gene, His404Pro and Arg485Pro. The His404Pro mutation has not been described previously, while the Arg485Pro mutation has been reported in another compound heterozygous VKCFD type 1 patient from Germany. Most interestingly, haplotype analysis revealed that Arg485Pro is due to a founder mutation, suggesting that this mutation is present in the German population at some low frequency. The founder mutation explains that the only two compound heterozygous VKCFD type 1 patients known today originated from Germany.

Ablation of the otcC Gene Encoding a Post-polyketide Hydroxylase from the Oxytetracyline Biosynthetic Pathway in Streptomyces rimosus Results in Novel Polyketides with Altered Chain Length

Oxytetracycline (OTC) is a 19-carbon polyketide antibiotic made by Streptomyces rimosus. The otcC gene encodes an anhydrotetracycline oxygenase that catalyzes a hydroxylation of the anthracycline structure at position C-6 after biosynthesis of the polyketide backbone is completed. A recombinant strain of S. rimosus that was disrupted in the genomic copy of otcC synthesized a novel C-17 polyketide. This result indicates that the absence of the otcC gene product significantly influences the ability of the OTC "minimal" polyketide synthase to make a polyketide product of the correct chain length. A mutant copy of otcC was made by site-directed mutagenesis of three essential glycine codons located within the putative NADPH-binding domain. The mutant gene was expressed in Escherichia coli, and biochemical analysis confirmed that the gene product was catalytically inactive. When the mutant gene replaced the ablated gene in the chromosome of S. rimosus, the ability to make a 19-carbon backbone was restored, indicating that OtcC is an essential partner in the quaternary structure of the synthase complex.

Unusual Accumulation of Demethylspheroidene in Anaerobic-Phototrophic Growth of crtA-Deleted Mutants of Rhodovulum sulfidophilum

Rhodovulum sulfidophilum produces carotenoids in the spheroidene pathway. Spheroidene monooxygenase, CrtA, catalyzes the conversion of spheroidene to spheroidenone. crtA-deleted mutants of R. sulfidophilum did not produce spheroidenone and demethylspheroidenone. In these mutants, the ratio of demethylspheroidene to spheroidene increased with exposure to light. One mutant exhibiting a spheroidene-predominant phenotype did not grow under anaerobic-light conditions and was devoid of bacteriochlorophyll a, even under semiaerobic-light conditions There was no difference in the growth of the mutants under aerobic-dark conditions. These data suggest that demethylspheroidene is important for photosynthesis in R. sulfidophilum.

Metabolic profile of nicotine in subjects whose CYP2A6 gene is deleted

Generally, 70-80% of absorbed nicotine is mainly metabolized to cotinine by cytochrome P450 (CYP) 2A6. There is genetic polymorphism in the human CYP2A6 gene. Among several mutated alleles, CYP2A6*4 allele is a whole deleted type. The purpose of the present study was to clarify the metabolic profile of nicotine in subjects whose CYP2A6 gene is deleted. We developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for nicotine and its nine metabolites. Excretion levels of nicotine and its metabolites in 24 h accumulated urine after the chewing of one piece of nicotine gum were evaluated in five Japanese subjects whose CYP2A6 genotype was determined. In three subjects with CYP2A6*1A/CYP2A6*1A, CYP2A6*1A/CYP2A6*1B, and CYP2A6*1A/CYP2A6*4 (group I), nicotine was mainly excreted as cotinine, trans-3'-hydroxycotinine, and their glucuronide (approximately 60%). In contrast, in two subjects with CYP2A6*4/CYP2A6*4 (group II), trace levels of cotinine, cotinine N-glucuronide, and cotinine 1'-N-oxide were detected. Trans-3'-hydroxycotinine and its O-glucuronide were not detected. The excretion levels of nicotine itself, nicotine N-glucuronide, and nicotine 1'-N-oxide were higher than those in the other three subjects. The total excretion levels of these three compounds were approximately 95% in group II versus 35% in group I. However, the sum of the excretion levels of nicotine and all metabolites was similar among these five subjects. This is the first report of the metabolic profile of nicotine in subjects whose CYP2A6 gene is deleted.

Pharmacogenetics of antidepressants and antipsychotics: the contribution of allelic variations to the phenotype of drug response

Genetic factors contribute to the phenotype of drug response. We systematically analyzed all available pharmacogenetic data from Medline databases (1970-2003) on the impact that genetic polymorphisms have on positive and adverse reactions to antidepressants and antipsychotics. Additionally, dose adjustments that would compensate for genetically caused differences in blood concentrations were calculated. To study pharmacokinetic effects, data for 36 antidepressants were screened. We found that for 20 of those, data on polymorphic CYP2D6 or CYP2C19 were found and that in 14 drugs such genetic variation would require at least doubling of the dose in extensive metabolizers in comparison to poor metabolizers. Data for 38 antipsychotics were examined: for 13 of those CYP2D6 and CYP2C19 genotype was of relevance. To study the effects of genetic variability on pharmacodynamic pathways, we reviewed 80 clinical studies on polymorphisms in candidate genes, but those did not for the most part reveal significant associations between neurotransmitter receptor and transporter genotypes and therapy response or adverse drug reactions. In addition associations found in one study could not be replicated in other studies. For this reason, it is not yet possible to translate pharmacogenetic parameters fully into therapeutic recommendations. At present, antidepressant and antipsychotic drug responses can best be explained as the combinatorial outcome of complex systems that interact at multiple levels. In spite of these limitations, combinations of polymorphisms in pharmacokinetic and pharmacodynamic pathways of relevance might contribute to identify genotypes associated with best and worst responders and they may also identify susceptibility to adverse drug reactions.

A Novel Single Nucleotide Polymorphism (SNP) of the CYP2C19 Gene in a Japanese Subject with Lowered Capacity of Mephobarbital 4′-Hydroxylation

We sequenced all nine exons and exon-intron junctions of the cytochrome P450 2C19 (CYP2C19) gene from a Japanese subject with a lowered capacity of CYP2C19-mediated 4'-hydroxylation after an oral administration of mephobarbital. We found a novel single nucleotide polymorphism (SNP) of CYP2C19 gene as follows: SNP, 040110MoritaJ001; GENENAME: CYP2C19; ACCESSION NUMBER: NT_030059.8; LENGTH; 25 bases; 5'-GAGGGCCTGGCCC/TGCATGGAGCTGT-3'. The SNP (168946C>T) induced an amino acid alteration (Arg442Cys) located in exon 9 close to the heme-binding region of CYP2C19, which may result in the decrease in the catalytic properties of CYP2C19. A new allele having this SNP was designated as CYP2C19*16.

Adrenocortical adenoma associated with inadequately treated congenital adrenal hyperplasia

We report a 6 year-old boy with the simple virilizing form of 21-hydroxylase deficiency in whom an adrenal adenoma developed following 5 years of steroid treatment. Extremely high levels of basal serum 17alpha-hydroxyprogesterone as well as an exaggerated response of 17alpha-hydroxyprogesterone to adrenocorticotropic hormone confirmed congenital adrenal hyperplasia at 7 years of age. Initially elevated serum steroid levels were restrained by high dose hydrocortisone therapy, but he chronically tended to take inadequate doses of glucocorticoid. At 12 years of age an adenoma was found in the cortex of the hyperplastic right adrenal gland. The importance of early diagnosis and compliance with medication in the simple virilizing form of 21-hydroxylase deficiency is stressed.

Homozygosity mapping of a second gene locus for hereditary combined deficiency of vitamin K-dependent clotting factors to the centromeric region of chromosome 16

Familial multiple coagulation factor deficiency (FMFD) of factors II, VII, IX, X, protein C, and protein S is a very rare bleeding disorder with autosomal recessive inheritance. The phenotypic presentation is variable with respect to the residual activities of the affected proteins, its response to oral administration of vitamin K, and to the involvement of skeletal abnormalities. The disease may result either from a defective resorption/transport of vitamin K to the liver, or from a mutation in one of the genes encoding gamma-carboxylase or other proteins of the vitamin K cycle. We have recently presented clinical details of a Lebanese family and a German family with 10 and 4 individuals, respectively, where we proposed autosomal recessive inheritance of the FMFD phenotype. Biochemical investigations of vitamin K components in patients' serum showed a significantly increased level of vitamin K epoxide, thus suggesting a defect in one of the subunits of the vitamin K 2,3-epoxide reductase (VKOR) complex. We now have performed a genome-wide linkage analysis and found significant linkage of FMFD to chromosome 16. A total maximum 2-point LOD score of 3.4 at theta = 0 was obtained in the interval between markers D16S3131 on 16p12 and D16S419 on 16q21. In both families, patients were autozygous for 26 and 28 markers, respectively, in an interval of 3 centimorgans (cM). Assuming that FMFD and warfarin resistance are allelic, conserved synteny between human and mouse linkage groups would restrict the candidate gene interval to the centromeric region of the short arm of chromosome 16.

Genetic evidence that oxidative derivatives of retinoic acid are not involved in retinoid signaling during mouse development

Retinoic acid, the active derivative of vitamin A (retinol), is a hormonal signaling molecule that acts in developing and adult tissues. The Cyp26a1 (cytochrome p450, 26) protein metabolizes retinoic acid into more polar hydroxylated and oxidized derivatives. Whether some of these derivatives are biologically active metabolites has been debated. Cyp26a1(-/-) mouse fetuses have lethal morphogenetic phenotypes mimicking those generated by excess retinoic acid administration, indicating that human CYP26A1 may be essential in controlling retinoic acid levels during development. This hypothesis suggests that the Cyp26a1(-/-) phenotype could be rescued under conditions in which embryonic retinoic acid levels are decreased. We show that Cyp26a1(-/-) mice are phenotypically rescued by heterozygous disruption of Aldh1a2 (also known as Raldh2), which encodes a retinaldehyde dehydrogenase responsible for the synthesis of retinoic acid during early embryonic development. Aldh1a2 haploinsufficiency prevents the appearance of spina bifida and rescues the development of posterior structures (sacral/caudal vertebrae, hindgut, urogenital tract), while partly preventing cervical vertebral transformations and hindbrain pattern alterations in Cyp26a1(-/-) mice. Thus, some of these double-mutant mice can reach adulthood. This study is the first report of a mutation acting as a dominant suppressor of a lethal morphogenetic mutation in mammals. We provide genetic evidence that ALDH1A2 and CYP26A1 activities concurrently establish local embryonic retinoic acid levels that must be finely tuned to allow posterior organ development and to prevent spina bifida.

Stereochemistry of the peroxisomal branched-chain fatty acid alpha- and beta-oxidation systems in patients suffering from different peroxisomal disorders

Phytanic acid (3,7,11,15-tetramethylhexadecanoic acid) is a branched-chain fatty acid derived from dietary sources and broken down in the peroxisome to pristanic acid (2,6,10,14-tetramethylpentadecanoic acid) via alpha-oxidation. Pristanic acid then undergoes beta-oxidation in peroxisomes. Phytanic acid naturally occurs as a mixture of (3S,7R,11R)- and (3R,7R,11R)-diastereomers. In contrast to the alpha-oxidation system, peroxisomal beta-oxidation is stereospecific and only accepts (2S)-isomers. Therefore, a racemase called alpha-methylacyl-CoA racemase is required to convert (2R)-pristanic acid into its (2S)-isomer. To further investigate the stereochemistry of the peroxisomal oxidation systems and their substrates, we have developed a method using gas-liquid chromatography-mass spectrometry to analyze the isomers of phytanic, pristanic, and trimethylundecanoic acid in plasma from patients with various peroxisomal fatty acid oxidation defects. In this study, we show that in plasma of patients with a peroxisomal beta-oxidation deficiency, the relative amounts of the two diastereomers of pristanic acid are almost equal, whereas in patients with a defect of alpha-methylacyl-CoA racemase, (2R)-pristanic acid is the predominant isomer. Furthermore, we show that in alpha-methylacyl-CoA racemase deficiency, not only pristanic acid accumulates, but also one of the metabolites of pristanic acid, 2610-trimethylundecanoic acid, providing direct in vivo evidence for the requirement of this racemase for the complete degradation of pristanic acid.

[Refsum's disease: evolution 35 years after diagnosis]

Refsum's disease (Heredopathia atactica polyneuritiformis) is an autosomal recessive disease caused by a defective alpha oxidation of a C20 fatty acid: the phytanic acid. Deficiency of a peroxysomal enzyme called "Phytanoyl-Co-A alpha hydroxylase" leads to an accumulation of phytanic acid. The clinical picture include retinitis pigmentosa, peripheral neuropathy, ataxia and elevated cerebrospinal fluid protein concentration. Firstly described in 1946 by Sigvald Refsum, dietary treatment leads to an improvement of neurological symptoms but does not affect retinal changes. To our knowledge, there is no data in the literature on long term follow-up. A patient with Refsum's disease diagnosed in 1965 presented with facial paralysis. The phytanic acid concentration was low, CSF protein level was normal leading to diagnosis of Bell's palsy. This observation is of particular interest because after 35 years evolution of the disease, the only handicap was visual impairment, with no loss of muscle strength or sensory deficit.

N-glycolylneuraminic acid deficiency in humans

Classic studies suggested that the common mammalian sialic acid N-glycolylneuraminic acid (Neu5Gc) is an oncofetal antigen in humans, being immunogenic in adult humans and yet apparently expressed in human fetuses and tumors. We and others have recently found that the human deficiency of Neu5Gc can be explained by an inactivating mutation in the gene encoding CMP-N-acetylneuraminic acid hydroxylase. Thus, Neu5Gc is not an oncofetal antigen in the classical sense, and other explanations must be found for the observed expression pattern. This review provides an update on this matter, and considers a variety of other old and new questions that arise from it.

The retinoic acid-metabolizing enzyme, CYP26A1, is essential for normal hindbrain patterning, vertebral identity, and development of posterior structures

The active derivative of vitamin A, retinoic acid (RA), is essential for normal embryonic development. The spatio-temporal distribution of embryonic RA results from regulated expression of RA-synthesizing retinaldehyde dehydrogenases and RA-metabolizing cytochrome P450s (CYP26). Excess RA administration or RA deficiency results in a complex spectrum of embryonic abnormalities. As a first step in understanding the developmental function of RA-metabolizing enzymes, we have disrupted the murine Cyp26A1 gene. We report that Cyp26A1-null mutants die during mid-late gestation and show a number of major morphogenetic defects. Spina bifida and truncation of the tail and lumbosacral region (including abnormalities of the kidneys, urogenital tract, and hindgut) are the most conspicuous defects, leading in extreme cases to a sirenomelia ("mermaid tail") phenotype. Cyp26A1 mutants also show posterior transformations of cervical vertebrae and abnormal patterning of the rostral hindbrain, which appears to be partially posteriorly transformed. These defects correlate with two major sites of Cyp26A1 expression in the rostral neural plate and embryonic tail bud. Because all of the Cyp26A1(-/-) abnormalities closely resemble RA teratogenic effects, we postulate that the key function of CYP26A1 is to maintain specific embryonic areas in a RA-depleted state, to protect them against the deleterious effect of ectopic RA signaling.

Aldosterone synthase deficiency type I with no documented homozygous mutations in the CYP11B2 gene

This case report concerns a girl born from non-consanguineous parents and hospitalized in another hospital at the age of 14 days because of a severe salt-losing syndrome (Na=125, K=8.6 mEq/l). In spite of normal genitalia, diagnosis of 21-hydroxylase deficiency was assessed on the basis of a slightly increased 17-OH-progesterone serum level (6.4 ng/ml). The onset of both hydrocortisone and 9alpha-fluorohydrocortisone therapy was followed by a resolution of the clinical picture. At the age of 60 days she was admitted to our clinic for a re-evaluation of the diagnosis. Steroid hormone serum levels were measured after withdrawal of therapy and diagnosis of corticosterone methyl oxidase (CMO) deficiency type I was definitely established in the light of the biochemical results: i.e. very low 18-hydroxycorticosterone (18-OH-B) serum levels (20 pg/ml), an abnormally high corticosterone/18-OH-B serum ratio (306.5) and an abnormally low 18-OH-B/aldosterone serum ratio (2.1). This autosomal recessively inherited disorder can be differentiated from CMO type II and other salt-wasting syndromes only on the basis of the serum steroid hormone pattern. After establishing the diagnosis of CMO I deficiency, hydrocortisone therapy was withdrawn whilst treatment with 9alpha-fluorohydrocortisone was begun again, with a satisfactory clinical and metabolic impact. Direct sequences of the patient's DNA were able to identify only a (heterozygous) amino acid substitution in exon 7 of that gene, which is known to have only a small effect on enzyme activity and cannot be the only cause of the patient's phenotype: valine-386-alanine (V386A) GTG-->GcG. No homozygous mutations in the CYP11B2 gene were observed. This is the first report of a patient with CMO type I who does not carry any homozygous mutation in the entire CYP11B2 alleles, whereas some cases with no mutations in this gene have already been reported in CMO II. The present study seems to be inconsistent with the previously reported correlation of the phenotype and genotype in CMO type I. A reasonable question that might be raised on the basis of our findings in this case report is whether other genes, apart from CYP11B2, are involved in the regulation of terminal aldosterone synthesis.

Homozygous deletion of arginine-173 in the CYP11B2 gene in a girl with congenital hypoaldosteronism. Corticosterone methyloxidase deficiency type II

The first child of consanguineous parents presented with failure to thrive and feeding problems at age 6 weeks. Important laboratory findings were low plasma sodium and elevated potassium and renin. Salt wasting was caused by an enzymatic defect in the terminal aldosterone biosynthesis. The biochemical diagnosis of corticosterone methyloxidase (CMO) deficiency type II was established on the basis of plasma multisteroid analysis, showing a pathologic increase of 18-OH-corticosterone/aldosterone ratio. Sequence analysis of the CYP11B2 gene which encodes aldosterone synthase (P450c11Aldo), the enzyme required for the terminal steps in aldosterone biosynthesis, revealed a hitherto undescribed homozygous deletion of codon 173. CYP11B2 is polymorphic at this position, encoding arginine or lysine. Both parents were heterozygous carriers of the mutation. Amino acid residue 173 in P450c11Aldo is positioned in alpha-helix D. We presume that the secondary structure of the enzyme is changed by the single amino acid deletion. This report describes a novel mutation in the CYP11B2 gene, the third known mutation associated with CMO deficiency type II.

Phytanic acid storage disease (Refsum's disease): clinical characteristics, pathophysiology and the role of therapeutic apheresis in its management

Phytanic acid storage disease (known also as Refsum's Disease) is caused by inherited defects in the metabolic pathway for phytanic acid, a dietary branched-chain fatty acid. Poorly metabolized phytanic acid accumulates in fatty tissues, including myelin sheaths, and in organs including the liver and kidneys. Over time, affected individuals may develop classical diagnostic features of retinitis pigmentosa, cerebellar ataxia, peripheral polyneuropathy and an elevated protein content in the cerebrospinal fluid. Liver, kidney, and heart disease may also develop. Dietary restriction of phytanic acid is useful in preventing acute attacks and arresting the progression of organ impairment, especially in the peripheral nervous system. Therapeutic plasma exchange has been shown to be particularly useful for rapidly lowering plasma phytanic acid levels during acute attacks and may play a significant role as maintenance therapy as well.

Allelic, genotypic and phenotypic distributions of S-mephenytoin 4'-hydroxylase (CYP2C19) in healthy Caucasian populations of European descent throughout the world

Impaired S-mephenytoin 4'-hydroxylation is a well-described genetic polymorphism affecting drug metabolism in humans. The reported population prevalence of the CYP2C19 poor metabolizer phenotype in Caucasians of European descent has been described as ranging from 0.9% to 7.7%. To address the question of whether the difference in the frequency of poor metabolizers represents an ethnic genetic microheterogeneity in the structure and expression of the CYP2C19 gene in Caucasian individuals, we performed a pooled analysis of available studies. Combined data from the 22 homogeneous studies showed that the frequency of poor metabolizers in healthy unrelated Caucasians determined by phenotyping was 2.8% (110 of 3990; 95% confidence interval 2.3-3.3). Data obtained from eight homogeneous studies that determined the frequency of poor metabolizers by genotyping showed that the genotypic frequency of poor metabolizers was 2.1% (28 of 1356; 95% confidence interval 1.3-2.8), consistent with the poor metabolizer frequency determined by phenotyping. In the extensive metabolizers, 26% (471 of 1786; 95% confidence interval 24.4-28.4) were heterozygotes. The observed frequencies of the three Mendelian genotypes were 73% for wt/wt, 26% for wt/m, and 2.1% for m/m. Based on the overall phenotypic poor metabolizer frequency of 2.8%, the expected genotypic frequencies were 69% for wt/wt, 28% for wt/m and 2.8% for m/m, which are in good agreement to the observed values. However, in the 84 Caucasian phenotyped and genotyped poor metabolizers, approximately 10% of the putative poor metabolizer alleles (17 of 168) were unknown. This study provides a systematic overview of the population distribution of the CYP2C19 poor metabolizer phenotype and CYP2C19 alleles and genotypes in healthy Caucasians living in different geographical areas, and shows a similar polymorphic pattern in the structure and expression of the CYP2C19 gene in the worldwide Caucasian populations.

CYP2A6 gene deletion reduces susceptibility to lung cancer

CYP2A6 is an enzyme with a high ability to activate a nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), to its potent and ultimate carcinogen. In the present study, we investigated the relationship between genetic polymorphism of CYP2A6 and lung cancer risk in a case-control study of Japanese subjects. Genotyping of the CYP2A6 gene in both healthy volunteers and lung cancer patients was conducted. The frequency with which the subjects carried homozygotes of the CYP2A6 gene deletion-type mutation (deletion), which causes lack of the enzyme activity, was lower in the lung cancer patients than in the healthy control subjects. The odds ratio (OR) of the group homozygous for the deletion was significantly lower and calculated to be 0.25 (95% CI; 0.08-0.83) when the OR for the population with homozygotes of the CYP2A6 wild-type gene was defined as 1.00. In the allelic-base analysis, there was also a significant decrease in the OR for the deletion allele. These data suggest that deficient CYP2A6 activity due to genetic polymorphism reduces lung cancer risk.

Mortality in patients with congenital adrenal hyperplasia: a cohort study

OBJECTIVE

To determine mortality in patients with congenital adrenal hyperplasia (CAH) compared with that in the general population.

DESIGN

We identified 333 children with CAH, treated at several pediatric endocrinology departments in the United Kingdom since 1964, and monitored their mortality to mid 1996. Standardized mortality ratios were calculated, comparing mortality in the cohort with that in the general population, adjusted for sex, age, and calendar period.

RESULTS

All-cause mortality in the cohort was 3 times that expected. Mortality was significantly increased at ages 1 to 4 years (standardized mortality ratio = 18.3) but not at older ages and was significantly increased in patients of Indian-subcontinent ethnicity (standardized mortality ratio = 20.4), particularly in girls. From case notes and death certificates, it appears that most deaths were caused by adrenal crisis, often after infection.

CONCLUSIONS

Although survival of patients with CAH has greatly improved since steroid therapy has been used, this disease can still have fatal consequences. The high mortality rate in Indian ethnic girls may well reflect lack of parental acceptance and understanding of the disease, as well as of the action required when their child becomes acutely ill. Better communication with and education of parents of children with CAH, especially those from immigrant ethnic minorities, is important.

Molecular genetic study in two patients with congenital hypoaldosteronism (types I and II) in relation to previously published hormonal studies

We performed a molecular genetic study in two patients with congenital hypoaldosteronism. An original study of these patients was published in this Journal in 1982. Both index cases, a girl (patient 1) and a boy (patient 2). presented with salt-wasting and failure to thrive in the neonatal period. Parents of patient 1 were not related, whereas the parents of patient 2 were cousins. Endocrine studies had shown a defect in 18-oxidation of 18-OH-corticosterone in patient 1 and a defect in the 18-hydroxylation of corticosterone in patient 2. Plasma aldosterone was decreased in both patients, whereas 18-OH-corticosterone was elevated in patient 1 and decreased in patient 2. Plasma corticosterone and 11-deoxycorticosterone were elevated in both patients, whereas cortisol and its precursors were in the normal range. According to the nomenclature proposed by Ulick, the defects are termed corticosterone methyl oxidase (CMO) deficiency type II in patient 1, and type I in patient 2 respectively. Genetic defects in the gene CYP11B2 encoding aldosterone synthase have been described in a few cases. In patient 1, we identified only one heterozygous amino acid substitution (V386A) in exon 7, which has no deleterious effect on the enzyme activity. In patient 2 and his older brother, we identified a homozygous single base exchange (G to T) in codon 255 (GAG), causing a premature stop codon E255X (TAG). The mutant enzyme has lost the five terminal exons containing the haem binding site, and is thus a loss of function enzyme. This is only the second report of a patient with CMO deficiency type II without a mutation in the exons and exon-intron boundaries, whereas the biochemical phenotype of the two brothers with CMO deficiency type I can be explained by the patient's genotype.

Mutation THR-185 ILE is associated with corticosterone methyl oxidase deficiency type II

Two boys presenting with infection-triggered, life-threatening salt-loss and hyperkalaemia were published in 1991 in the European Journal of Pediatrics. In both boys, the diagnosis of corticosterone methyl oxidase (CMO) deficiency type II has been established on the basis of determinations of plasma and urinary steroids. We had the opportunity to perform a molecular genetic study in one of the two boys. This boy had an elevated plasma 18-hydroxycorticosterone/aldosterone ratio which is pathognomonic for CMO deficiency type II. Sequence analysis of the CYP11B2 gene revealed a homozygous single base exchange in codon 185 of CYP11B2 causing an amino acid substitution Thr185Ile.

CONCLUSION

A Thr185Ile mutation in the CYP11B2 gene was found in a patient with CMO deficiency type II. This mutation may change the secondary structure of the enzyme leading to its decreased activity.

The incidence of 21 alpha-hydroxylase deficiency in Greek hyperandrogenic women: screening and diagnosis

The purpose of this prospective study was to determine the incidence of any form of 21 alpha-hydroxylase deficiency among Greek women with hyperandrogenic symptoms, and to test the predictive value of basal serum 17-hydroxyprogesterone (17-OHP) in the early follicular phase as a screening index for patient preselection to adrenocorticotropic hormone (ACTH) testing. Eighty-eight unselected women with hyperandrogenic symptoms were examined in the Gynecological Endocrinology Unit of the Second Department of Obstetrics and Gynecology of Athens University. Using the ACTH-stimulated 17-OHP values at 60 minutes (17-OHP60) the study population was divided into four groups (A, B, C and D). Clinical and basal hormonal parameters as well as serum 17-OHP60 values and human leukocyte antigens were studied. Both clinical and basal hormonal parameters could be used to distinguish only patients with severe 21 alpha-hydroxylase deficiency (group A). In contrast, patients with moderate non-classical congenital adrenal hyperplasia (NC-CAH; group B), heterozygotes for NC-CAH (group C), and unaffected females (group D) can be diagnosed and classified only by serum 17-OHP60 values. In conclusion, the incidence of NC-CAH in Greek females with hyperandrogenic symptoms is 3.4%. The positive predictive value of basal 17-OHP is only 13% for this disease. Only 17-OHP60 helps to diagnose and classify moderate and mild forms of NC-CAH. Thus, it seems that ACTH testing is imperative in every subject suspected of this enzymatic disorder.

Randomised controlled trial of growth effect of hydrocortisone in congenital adrenal hyperplasia

The influence of 15 or 25 mg/m2 of daily oral hydrocortisone with fludrocortisone 0.1 mg/day on growth and laboratory findings was evaluated in a prospective randomised crossover trial over 12 months in 26 children with 21-hydroxylase deficiency. Nine non-salt losers had fludrocortisone stopped for a further six month period. Height velocity was significantly decreased during treatment with 25 mg/m2 as compared with 15 mg/m2. This was the most sensitive indicator of corticosteroid treatment excess. A dose dependent effect upon plasma concentrations of 17-hydroxyprogesterone, testosterone, and androstenedione was found but increased values were still detected in more than half of the determinations made during the 25 mg/m2 period. Height velocity and 17-hydroxyprogesterone concentrations were positively correlated. Growth hormone response to clonidine stimulation and insulin-like growth factor-1 concentrations were both within reference values and there was no difference between treatment periods. Withdrawal of fludrocortisone did not result in any difference for the non-salt losers. It was concluded that 25 mg/m2 of hydrocortisone depressed growth in children with congenital adrenal hyperplasia, and that full suppression, or even normalisation, of plasma concentrations of 17-hydroxyprogesterone and androgens should not be considered a treatment goal, but instead an indication of corticosteroid treatment excess.