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Biomedical subjects

P T Clayton

Publications and source records attributed to P T Clayton.

At least 19 recordsLinked to original sources
PubMed2006

Pyridoxal 5'-phosphate may be curative in early-onset epileptic encephalopathy.

Neonatal epileptic encephalopathy can be caused by inborn errors of metabolism. These conditions are often unresponsive to treatment with conventional antiepileptic drugs. Six children with pyridox(am)ine-5'-phosphate oxidase (PNPO) deficiency presented with neonatal epileptic encephalopathy. Two were treated with pyridoxal 5'-phosphate (PLP) within the first month of life and showed normal development or moderate psychomotor retardation thereafter. Four children with late or no treatment died or showed severe mental handicap. All of the children showed atypical biochemical findings. Prompt treatment with PLP in all neonates and infants with epileptic encephalopathy should become mandatory, permitting normal development in at least some of those affected with PNPO deficiency.

Age of Onset↗
PubMed2005

Molecular studies in Portuguese patients with Smith-Lemli-Opitz syndrome and report of three new mutations in DHCR7.

Smith-Lemli-Opitz syndrome (SLO) is an autosomal recessive disorder characterised by craniofacial dysmorphism, mental retardation, multiple congenital anomalies, and increased levels of 7-dehydrocholesterol (7-DHC) in body tissues and fluids. SLO is caused by mutations in the DHCR7 gene which encodes 7-dehydrocholesterol reductase, the last enzyme of cholesterol biosynthesis pathway. In our investigation, we screened 682 dysmorphic/mentally retarded Portuguese patients for abnormal levels of 7-DHC in blood by UV spectrometry. We identified six unrelated patients with SLO (0.87% of total). Mutational analysis of the DHCR7 gene led to the identification of seven distinct mutations, three of which are new (F174S, H301R, and Q98X). The common IVS8-1G > C and T93M variants together with the H301R accounted for 70% of the all SLO alleles in our population. Our findings contribute to the variegate array of pathological changes in the DHCR7 gene among different European populations.

Child↗
PubMed2005

The significance of elevated CSF lactate.

The final diagnosis of 158 patients who had a cerebrospinal fluid (CSF) lactate concentration greater than 2 mmol/l was ascertained. The conditions included seizures, inflammatory changes, and proven metabolic disorders. For the diagnosis of congenital lactic acidoses, CSF lactate should ideally be measured in a seizure free patient after any acute illness.

Acidosis, Lactic↗
PubMed2004

Aromatic L-amino acid decarboxylase deficiency: clinical features, treatment, and prognosis.

BACKGROUND: Deficiency of aromatic L-amino acid decarboxylase (AADC) is associated with severe developmental delay, oculogyric crises (OGC), and autonomic dysfunction. Treatment with dopamine agonists and MAO inhibitors is beneficial, yet long-term prognosis is unclear. OBJECTIVE: To delineate the clinical and molecular spectrum of AADC deficiency, its management, and long-term follow-up. RESULTS: The authors present six patients with AADC deficiency and review seven cases from the literature. All patients showed reduced catecholamine metabolites and elevation of 3-O-methyldopa in CSF. Residual plasma AADC activity ranged from undetectable to 8% of normal. Mutational spectrum was heterogeneous. All patients presented with hypotonia, hypokinesia, OGC, and signs of autonomic dysfunction since early life. Diurnal fluctuation or improvement of symptoms after sleep were noted in half of the patients. Treatment response was variable. Two groups of patients were detected: Group I (five males) responded to treatment and made developmental progress. Group II (one male, five females) responded poorly to treatment, and often developed drug-induced dyskinesias. CONCLUSIONS: The molecular and clinical spectrum of AADC deficiency is heterogeneous. Two groups, one with predominant male sex and favorable response to treatment, and the other with predominant female sex and poor response to treatment, can be discerned.

Adolescent↗
PubMed2004

The significance of a high plasma ammonia value.

At a tertiary referral centre, just over 50% of patients with plasma ammonia values over 200 micro mol/l had inborn errors of metabolism. To distinguish artefactual high values from those requiring treatment, the measurement should be repeated immediately if the result is above 200 micro mol/l and at lower concentrations if the patient is encephalopathic.

Ammonia↗
PubMed2003

Diagnosis of inherited disorders of liver metabolism.

Diagnosis of the metabolic disorder responsible for liver disease can sometimes be straightforward but it can also present a major challenge, particularly if the liver is sufficiently damaged to produce secondary biochemical abnormalities such as galactosuria, hypoglycaemia with hypoketonaemia, or excretion of 3-oxo-delta4 bile acids. It is important to consider the age of the patient, the nature of the liver disease, any extrahepatic clinical features, the imaging and the first-line laboratory tests when prioritizing diagnostic investigations. This article gives some examples of diagnoses made in our unit for patients with liver disease presenting in utero, in the neonatal period, in infancy and the preschool years, and in the school years. The differential diagnoses that should be considered for different clinical presentations are discussed.

Child↗
PubMed2003

Mass spectrometric analysis of glycans in elucidating the pathogenesis of CDG type IIx .

The majority of secreted or membrane-bound proteins are glycosylated. The glycans attached to glycoproteins can affect a range of physicochemical and biological properties of the glycoprotein and appropriate glycosylation is essential for many normal cellular functions, with aberrant glycosylation often leading to disease. This short review briefly outlines the methodology used to release glycans from proteins and analyse them by mass spectrometry. The technology is illustrated by the description of a rapid and sensitive method for profiling glycoproteins of patients with congenital disorders of glycosylation type II. This methodology can rapidly pinpoint the defective step(s) in the processing pathway of N-linked glycans, thereby focusing the biochemical analyses that need to be performed to define the genetic basis of these diseases.

Congenital Disorders of Glycosylation↗
PubMed2003

Short-chain 3-hydroxyacyl-CoA dehydrogenase deficiency associated with hyperinsulinism: a novel glucose-fatty acid cycle?

Hyperinsulinism of infancy is caused by inappropriate insulin secretion in pancreatic beta-cells, even when blood glucose is low. Several molecular defects are known to cause hyperinsulinism of infancy, such as K(ATP) channelopathies and regulatory defects of glucokinase and glutamate dehydrogenase. Although defects of fatty acid oxidation have not previously been known to cause hyperinsulinism, patients with deficiency in SCHAD (short-chain 3-hydroxyacyl-CoA dehydrogenase; an enzyme of mitochondrial beta-oxidation) have hyperinsulinism. A novel link between fatty acid oxidation and insulin secretion may explain hyperinsulinism in these patients.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed2003

Mutations in SRD5B1 (AKR1D1), the gene encoding delta(4)-3-oxosteroid 5beta-reductase, in hepatitis and liver failure in infancy.

BACKGROUND: A substantial group of patients with cholestatic liver disease in infancy excrete, as the major urinary bile acids, the glycine and taurine conjugates of 7alpha-hydroxy-3-oxo-4-cholenoic acid and 7alpha,12alpha-dihydroxy-3-oxo-4-cholenoic acid. It has been proposed that some (but not all) of these have mutations in the gene encoding delta(4)-3-oxosteroid 5beta-reductase (SRD5B1; AKR1D1, OMIM 604741). AIMS: Our aim was to identify mutations in the SRD5B1 gene in patients in whom chenodeoxycholic acid and cholic acid were absent or present at low concentrations in plasma and urine, as these seemed strong candidates for genetic 5beta-reductase deficiency. PATIENTS AND SUBJECTS: We studied three patients with neonatal onset cholestatic liver disease and normal gamma-glutamyl transpeptidase in whom 3-oxo-delta(4) bile acids were the major bile acids in urine and plasma and saturated bile acids were at low concentration or undetectable. Any base changes detected in SRD5B1 were sought in the parents and siblings and in 50 ethnically matched control subjects. METHODS: DNA was extracted from blood and the nine exons of SRD5B1 were amplified and sequenced. Restriction enzymes were used to screen the DNA of parents, siblings, and controls. RESULTS: Mutations in the SRD5B1 gene were identified in all three children. Patient MS was homozygous for a missense mutation (662 C>T) causing a Pro198Leu amino acid substitution; patient BH was homozygous for a single base deletion (511 delT) causing a frame shift and a premature stop codon in exon 5; and patient RM was homozygous for a missense mutation (385 C>T) causing a Leu106Phe amino acid substitution. All had liver biopsies showing a giant cell hepatitis; in two, prominent extramedullary haemopoiesis was noted. MS was cured by treatment with chenodeoxycholic acid and cholic acid; BH showed initial improvement but then deteriorated and required liver transplantation; RM had advanced liver disease when treatment was started and also progressed to liver failure. CONCLUSIONS: Analysis of blood samples for SRD5B1 mutations can be used to diagnose genetic 5beta-reductase deficiency and distinguish these patients from those who have another cause of 3-oxo-delta(4) bile aciduria, for example, severe liver damage. Patients with genetic 5beta-reductase deficiency may respond well to treatment with chenodeoxycholic acid and cholic acid if liver disease is not too advanced.

Chenodeoxycholic Acid↗
PubMed2002

Mutations in the sterol 27-hydroxylase gene (CYP27A) cause hepatitis of infancy as well as cerebrotendinous xanthomatosis.

Follow-up investigations were undertaken on a previously reported patient who had severe familial giant cell hepatitis in infancy associated with substantially increased urinary excretion of bile alcohol glucuronides. By the age of 11 years, he had developed a profile of cholanoids in plasma and urine that closely resembled the pattern seen in cerebrotendinous xanthomatosis (CTX). Sequencing of the sterol 27-hydroxylase gene (CYP27A) showed that he was homozygous for a deletion (525/526delG) that causes a frameshift and a premature stop codon. This genotype has previously been described in an adult female with classical symptoms of CTX (tendon xanthomata, cataracts and deteriorating cognitive function). A review of past medical histories of a group of patients with CTX revealed that prolonged neonatal cholestatic jaundice was common. The family histories also revealed fetal and neonatal deaths among siblings of patients with CTX. We conclude that defective activity of cholesterol 27-hydroxylase can lead to neonatal cholestatic jaundice ('hepatitis of infancy'), which may be self-limiting. After a latent period, however, progressive accumulation of cholesterol and cholestanol can lead to the xanthomata, neurodegeneration, cataracts and atherosclerosis that are typical of CTX.

Adolescent↗
PubMed2001

Analysis by matrix assisted laser desorption/ionisation-time of flight mass spectrometry of the post-translational modifications of alpha 1-antitrypsin isoforms separated by two-dimensional polyacrylamide gel electrophoresis.

The state of protein glycosylation in terms of occupation of potential N-linked glycosylation sites (macroheterogeneity) and type of glycosylation at that site (microheterogeneity) is important when investigating the consequences of aberrant glycosylation in the pathophysiology of disease. Protocols have been developed to permit characterisation of the site-specific glycosylation of individual isoforms of glycoproteins after separation by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and analysis of the peptide mixture by peptide mass fingerprinting using matrix-assisted laser desorption/ionisation-time of flight mass spectrometry (MALDI-TOF). High resolution of the individual isoforms of alpha 1-antitrypsin was achieved by using narrow range (4.5-5.5) p/strips. The individual isoforms were then subjected to sequential digestion with a recombinant N-glycanase followed by a protease. Using this strategy it was possible not only to increase the coverage of the amino acid sequence but also to monitor the occupancy of all three putative N-linked glycosylation sites. Glycans were enzymatically released from alpha 1-antitrypsin which had been separated in gels formed with a low percentage of bis-acrylamide cross-linker and analysed. Profiles of the N-linked glycans of the individual isoforms of alpha 1-antitrypsin were obtained by MALDI-TOF.

Amino Acid Sequence↗
PubMed2001

New synthesis of (+/-)-alpha-CMBHC and its confirmation as a metabolite of alpha-tocopherol (vitamin E).

There is currently interest in the metabolism of the various compounds which make up the vitamin E family, especially with regards to the possible use of vitamin E metabolites as markers of oxidative stress and adequate vitamin E supply. A number of vitamin E metabolites have been described to date and we have recently developed a method to extract and quantitate a range of vitamin E metabolites in human urine. During the development of this method a new metabolite of alpha-tocopherol was identified, which we tentatively characterised as 5-(6-hydroxy-2,5,7,8-tetramethyl-chroman-2-yl)-2-methyl-pentanoic acid (alpha-CMBHC).(1) Here we describe the synthesis of alpha-CMBHC as a standard and confirm that it is a metabolite of alpha-tocopherol.

Chromatography, Gas↗
PubMed2001

Features of carnitine palmitoyltransferase type I deficiency.

Carnitine palmitoyltransferase type I (CPT I) is unique among long-chain fatty acid oxidation enzymes in that there are two tissue-specific isoforms, 'hepatic' and 'muscle', which are encoded by two separate genes. The 'hepatic' isoform is expressed in liver, kidney and fibroblasts and at low levels in the heart, while the other isoform occurs in skeletal muscle and is the predominant form in heart. Reported patients with CPT I deficiency lack activity of the hepatic isoform and present before 30 months of age with hypoketotic hypoglycaemia, hepatomegaly with raised transaminases, seizures and coma. We discuss four new cases in three families showing, variously, renal tubular acidosis, transient hyperlipidaemia and, paradoxically, myopathy with elevated creatinine kinase or cardiac involvement in the neonatal period as additional features that deserve wider recognition.

Acidosis, Renal Tubular↗
PubMed2001

Applications of mass spectrometry in the study of inborn errors of metabolism.

During the twentieth century, and particularly in its last decade, there have been major advances in mass spectrometry (MS). As a result, MS remains one of the most powerful tools for the investigation of genetic metabolic disease. Analysis of organic acids by gas chromatography-mass spectrometry (GC-MS) and analysis of acylcarnitines by tandem mass spectrometry are still leading to the discovery of new disorders. Tandem mass spectrometry is increasingly being used for neonatal screening. New methods for lipid analysis have opened up the fields of inborn errors of cholesterol synthesis, of bile acid synthesis and ofleukotriene synthesis. The latest developments in MS allow it to be used for determination of the amino acid sequence and posttranslational modifications of proteins. There are still some major hurdles to be overcome, but soon it should be possible to detect mutant proteins directly rather than by cDNA or genomic DNA analysis. Measurement of which proteins are overexpressed and underexpressed ('proteomics') should provide further information on the pathogenesis of complications of inborn errors, e.g. hepatic cirrhosis. The use of stable isotopes in conjunction with MS allows us to probe metabolic pathways. As an example, evidence is presented to support the contention that vitamin E and its oxidation product are catabolized by peroxisomal beta-oxidation. Mass spectrometry also has a major role in monitoring new forms of treatment for inborn errors.

Amino Acid Sequence↗