Ann Bowron

C677T (thermolabile alanine/valine) polymorphism in methylenetetrahydrofolate reductase (MTHFR): its frequency and impact on plasma homocysteine concentration in different European populations

A common polymorphism has been described in the methylenetetrahydrofolate reductase (MTHFR) gene, substituting an alanine (A) for a valine (V), where the V allele results in a thermolabile enzyme with reduced activity. This polymorphism is easily detectable by PCR amplification and digestion with HinfI restriction enzyme. We describe the use of the MADGE high throughput genotyping system for rapid typing of this polymorphism. Seven hundred and eighty five individuals participating in the European Atherosclerosis Research Study II (EARS II), aged 22-25 from 14 universities in 12 countries across Europe were genotyped for this polymorphism. The frequency of the V allele was 0.32 overall (95% CI; 0.30-0.35), but was significantly lower in the Baltic countries (0.23; 95% CI; 0.19-0.28) compared with the other regions of Europe (0.37; 95% CI; 0.32-0.38) (P < 0.001). Individuals homozygous for the V allele had statistically significant (P < 0.001) higher plasma homocysteine (16.5 micromol/l) compared with those heterozygous for an A allele (10.4 micromol/l) or homozygous for an A allele (10.0 micromol/l). This effect was seen in all countries and regions of Europe. Mean plasma homocysteine levels were significantly higher in the South compared to the Baltic, UK and Middle regions (P = 0.001), but this difference was not explained by the difference in the frequency of the V allele in the samples. This polymorphism explained 12.3% of the total sample variance in plasma homocysteine, other measured factors (smoking, alcohol consumption, systolic blood pressure, physical activity) explained 0.7%. This study demonstrates the large and consistent impact of the thermolabile MTHFR variant on plasma homocysteine levels in different European populations, and shows a regional difference in the levels of homocysteine that must be explained by other genetic or environmental factors.

Cerebrospinal fluid concentrations of pterins and metabolites of serotonin and dopamine in a pediatric reference population.

ABSTRACT: Accurate diagnosis and management of inborn errors of monoamine neurotransmitter and tetrahydrobiopterin metabolism depend on reliable reference ranges of key metabolites. Cerebrospinal fluid (CSF) was collected in a standardized way from 73 children and young adults with neurologic disease, with strict exclusions. In each specimen, concentrations of homovanillic acid (HVA), 5-hydroxyindoleacetic acid (HIAA), total neopterin, 7,8-dihydrobiopterin, and tetrahydrobiopterin (BH4) were measured using HPLC. There was a continuous decrement in CSF HVA, HIAA, and BH4 during the first few years of life; this was independent of height (or length). Age-related reference ranges for each metabolite are given. Extensive correlations between HVA, HIAA, 7,8-dihydrobiopterin, and BH4 were further analyzed by multiple regression. Age and CSF BH4 were significant explanatory variables for CSF HIAA, but CSF HVA had only HIAA as a significant explanatory variable.

Interlaboratory variation in 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 is significantly improved if common calibration material is used.

Measurements of 25-hydroxyvitamin D2 (D2)1 and 25-hydroxyvitamin D3 (D3) are used to detect vitamin D deficiency and monitor vitamin D supplementation. Interlaboratory variation within the same method groups makes it impossible to apply standardized reference intervals or published clinical cutoff values. Laboratories therefore must develop site-specific reference intervals. Advances in the routine use of liquid chromatography–tandem mass spectrometry (LC-MS/MS) in clinical chemistry laboratories have enabled the development of methods for measuring D2 and D3 individually (1). Despite the superior performance of LC-MS/MS methods compared with HPLC and immunoassay approaches, an examination of the UK Vitamin D External Quality Assessment Scheme (DEQAS) data for the LC-MS/MS user group indicates that interlaboratory variation exists within this method group. Calibration of D2 and D3 assays has been a continuing problem because there is no certified reference material available to test method accuracy. A recent Letter to the Editor in this journal pointed out that calibration is not the only concern with vitamin D assays. Laboratories also do not have common standard operating procedures and use a wide variety of instrumentation (2). We used commercially available calibration material (Chromsystems, …

Cardiolipin fingerprinting of leukocytes by MALDI-TOF/MS as a screening tool for Barth syndrome

Barth syndrome (BTHS), an X-linked disease associated with cardioskeletal myopathy, neutropenia, and organic aciduria, is characterized by abnormalities of cardiolipin (CL) species in mitochondria. Diagnosis of the disease is often compromised by lack of rapid and widely available diagnostic laboratory tests. The present study describes a new method for BTHS screening based on MALDI-TOF/MS analysis of leukocyte lipids. This generates a “CL fingerprint” and allows quick and simple assay of the relative levels of CL and monolysocardiolipin species in leukocyte total lipid profiles. To validate the method, we used vector algebra to analyze the difference in lipid composition between controls (24 healthy donors) and patients (8 boys affected by BTHS) in the high-mass phospholipid range. The method of lipid analysis described represents an important additional tool for the diagnosis of BTHS and potentially enables therapeutic monitoring of drug targets, which have been shown to ameliorate abnormal CL profiles in cells.

Barth syndrome without tetralinoleoyl cardiolipin deficiency: a possible ameliorated phenotype

Barth syndrome (BTHS) is an X-linked disorder characterised by cardiac and skeletal myopathy, growth delay, neutropenia and 3-methylglutaconic aciduria (3-MGCA). Patients have TAZ gene mutations which affect metabolism of cardiolipin, resulting in low tetralinoleoyl cardiolipin (CL4), an increase in its precursor, monolysocardiolipin (MLCL), and an increased MLCL/CL4 ratio. During development of a diagnostic service for BTHS, leukocyte CL4 was measured in 156 controls and 34 patients with genetically confirmed BTHS. A sub-group of seven subjects from three unrelated families was identified with leukocyte CL4 concentrations within the control range. This had led to initial false negative disease detection in two of these patients. MLCL/CL4 in this subgroup was lower than in other BTHS patients but higher than controls, with no overlap between the groups. TAZ gene mutations in these families are all predicted to be pathological. This report describes the clinical histories of these seven individuals with an atypical phenotype: some features were typical of BTHS (five have had cardiomyopathy, one family has a history of male infant deaths, three have growth delay and five have 3-MGCA) but none has persistent neutropenia, five have excellent exercise tolerance and two adults are asymptomatic. This report also emphasises the importance of measurement of MLCL/CL4 ratio rather than CL4 alone in the biochemical diagnosis of the BTHS.

Increased HVA detected on organic acid analysis in a patient with Costello syndrome

SummaryUrine organic acid analysis is routinely performed to investigate inborn errors of metbolism; however, interpretation can be difficult owing to the detection of compounds derived from other disease states or from nonpathological causes. We describe the finding of elevated homovanillc acid (HVA) on urine organic acid analysis which was not associated with medication or a neuroendocrine tumour but with Costello syndrome.

Cost-effective strategy for the serological investigation of coeliac disease

Increased numbers of requests for serological investigation of coeliac disease, and a local trend to request both anti-gliadin antibodies (AGA) and anti-endomysium antibodies (AEA) simultaneously, resulted in cost pressures that prompted a review of our practice. Serology results from all patients (771 children, 511 adults) investigated for coeliac disease over a 3-year period were compared with small intestine histology where available. IgG AGA and IgA AGA were measured by enzyme-linked immunosorbent assay (in-house), IgA AEA by immunofluorescence (send-away contract). Overall diagnostic performance was as follows: AGA sensitivity 84%, specificity 88%, positive predictive value (PPV) 24%, negative predictive value (NPV) 99%; AEA sensitivity 88%, specificity 97%, PPV 65%, NPV 99%. Results showed AGA, with its high NPV, to be a suitable first-line test to exclude coeliac disease. The high specificity of AEA makes it a suitable confirmatory test when AGA is positive. Introduction of this step-wise approach to coeliac disease investigation resulted in cost savings of at least £5000 per year without detriment to the clinical service.

Addition of 3-Deazaadenosine to Vacutainer Tubes Stabilizes Whole-Blood Homocysteine for At Least 6 Hours at Ambient Temperature

Increased plasma homocysteine is now well established as a risk factor for cardiac, cerebral, and peripheral vascular disease (1). Despite this, the test is not widely available. This is partly because of practical difficulties in sample collection. The homocysteine concentration increases in whole blood by up to 10% per hour unless samples are kept on ice and separated within 60 min. The introduction of containers with 3-deazaadenosine (3-dad; DS30 Homocysteine Blood Collection Tubes; Drew Scientific Ltd.), described in a recent report (2) in the Journal, may solve the problem, but they are not in widespread …