Estimated GFR is biased by non-traditional cardiovascular risk factors.

BACKGROUND: Estimated glomerular filtration rate (eGFR) based on either cystatin C or creatinine performs similarly in estimating measured GFR, but associate differently with cardiovascular disease (CVD) and mortality. This could be due to confounding by non-GFR-related traits associated with cystatin C and creatinine levels. We investigated non-GFR-related associations between eGFR and two types of nontraditional risk factors for CVD and death: L-arginine/dimethylarginine metabolism and insulin resistance. METHODS: GFR was measured via iohexol clearance in a cross-sectional study of 1,624 middle-aged persons from the general population without CVD, diabetes or chronic kidney disease. The dimethylarginines were measured using liquid chromatography tandem mass spectrometry (LC-MSMS). Insulin resistance was determined by the homeostasis model assessment (HOMA-IR). RESULTS: Asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA), the L-arginine/ADMA ratio and insulin resistance were associated with creatinine-based eGFR after accounting for measured GFR in multivariable adjusted analyses. The cystatin C-based eGFR showed a similar residual association with SDMA; an oppositely directed, borderline significant association with ADMA; and a stronger residual association with insulin resistance compared with eGFR based on creatinine. CONCLUSION: Both creatinine- and cystatin C-based eGFR are influenced by nontraditional risk factors, which may bias risk prediction by eGFR in longitudinal studies.

Lactase persistence genotyping: rapid detection of seven sequence variants in a single tube with melting curve analyses.

BACKGROUND: Lactase persistence is an inherited autosomal dominant trait that confers the ability to digest lactose after weaning. Lactose persistence is caused by single nucleotide variants in a regulatory element for the lactase gene (LCT). In Europeans, lactase persistence is associated with the nucleotide variant LCT -13910C>T. Ethnic groups from Africa and the Arabian Peninsula have other lactase persistence variants in close proximity to the -13910C>T variant. Current hybridisation probe analysis methods have been limited by the inability to detect all the known nucleotide variants. The aim of this study was to devise a method based on hybridisation probes and melting curve analysis for rapidly detecting LCT variants. METHODS: We designed hybridisation probes for producing melting curve profiles that could identify seven LCT nucleotide variants: -13907C>G, -13910C>T, -13913T>C, -13914G>A, -13915T>G, -14009T>G, and -14010G>C. To validate the assay, we generated plasmid standards of all the alleles and mixed them to create artificial heterozygote samples. RESULTS: All genotypes could be detected in a single tube assay. Rare genotypes were confirmed in a second assay with probes that had different complementary sequences. CONCLUSIONS: This assay can be used for rapidly genotyping lactase persistence in multi-ethnic populations.

Leber Hereditary Optic Neuropathy Case Report: Clinical Presentation and Treatment with Idebenone Reinforce the Evidence for m.3866T>C as a Causative Variant.

Introduction: Leber hereditary optic neuropathy (LHON) is a mitochondrial disorder that typically presents with painless, central visual loss, hyperaemia of the optic nerve head, and peripapillary telangiectasias. Most LHON cases are due to one of three variants, but several less common variants also exist. We describe a clinical case of LHON associated with the variant m.3866T>C, which is possibly linked to LHON. Case Presentation: A 59-year-old Caucasian woman experienced acute, bilateral, and painless visual loss. She reported cigarette smoking, and elevated phosphatidylethanol suggested harmful alcohol consumption. Her best-corrected visual acuity (BCVA) was 20/100 for the right eye and 20/50 for the left eye. She could only read the Ishihara demonstration plate, and threshold perimetry demonstrated reduced central sensitivity bilaterally. Her optic nerve heads were hyperaemic, with peripapillary telangiectasias. The visual symptoms and clinical findings suggested LHON. Magnetic resonance imaging demonstrated a tuberculum sella meningioma and two cerebral aneurysms, which we regarded as incidental findings. Genetic testing did not identify common LHON variants but a rare homoplasmic variant, m.3866T>C, which studies suggest might cause LHON or act in synergy with other variants to increase the disease penetrance. After initiating test-of-treatment with idebenone 900 mg per day, the patient's BCVA improved to 20/32 for both eyes and then stabilized. Conclusion: This case strengthens the evidence for m.3866T>C as a causative LHON variant. The case also raises the question as to whether this particular variant can respond favourably to treatment with idebenone.

Increased levels of BAFF in patients with systemic lupus erythematosus are associated with acute-phase reactants, independent of BAFF genetics: a case-control study.

OBJECTIVES: To determine whether increased levels of B-cell activating factor (BAFF) in patients with SLE are due to disease activity or genetic variations in the promoter region of the BAFF gene and BAFF gene expression. METHODS: The case-control study included 101 SLE patients and 111 healthy controls. Five single nucleotide polymorphisms (SNPs) in the BAFF promoter region were investigated by melting point analysis: c.-2841 (T > C), c.-2704 (T > C), c.-2701 (A > T), c.-871 (C > T) and c.-514 (A > G). BAFF mRNA levels were determined by real-time PCR (BAFF-RQ) and serum BAFF (s-BAFF) levels were measured by ELISA. Independent predictors that might be correlated with increased s-BAFF in SLE patients were analysed by multivariate regression methods. RESULTS; Although s-BAFF levels were increased in SLE patients (1.73 vs 0.98 ng/µl, P < 0.001), no specific BAFF genotype was found to associate with SLE. The different genotypes defined by the investigated SNPs were identified both in SLE patients and healthy controls with similar frequencies. No association was found between BAFF genotype and BAFF-RQ. s-BAFF was independent of other factors, correlated with CRP (ß = 0.40, P < 0.001) and physician's visual analogue score (R = 0.21, P = 0.046) and inversely with haemoglobin (ß = -0.32, P < 0.001) and IgA (ß = -0.33, P = 0.001). CONCLUSIONS: Increased s-BAFF levels in SLE patients are associated with the acute-phase responses, CRP and haemoglobin, but probably not dependent on BAFF genotype or expression. This indicates that s-BAFF production occurs at sites of inflammation.

Real-time detection and quantification of mitochondrial mutations with oligonucleotide primers containing locked nucleic acid.

BACKGROUND: The phenotypic expression of disorders caused by point mutations, deletions or depletions within the mitochondrial genome (mtDNA) is heterogeneous. This relates to the phenomena of heteroplasmy, tissue threshold as well as the distribution of mutant DNA among tissues. Hence, the diagnostics of these disorders demands highly specific, sensitive and quantitative methods. METHODS: We have developed an allele-specific quantitative real-time PCR method for the detection of two of the most prevalent disease causing mitochondrial mutations, m.3243A>G (MELAS) and m.8993T>G (NARP). Locked Nucleic Acid (LNA) modified primers were used to obtain high allele specificity. In order to monitor mtDNA depletion a real-time method for mtDNA/nuclear DNA copy number ratio determination was developed. RESULTS: Rapid and sensitive detection and quantification of MELAS and NARP mtDNA alleles were achieved. Heteroplasmy levels as low as 0.01% could be detected, and the mtDNA/nuclear DNA ratio could be determined. CONCLUSIONS: The present method that allows simultaneous determination of heteroplasmy levels and mtDNA/nuclear DNA copy number ratio, will provide a useful tool in molecular diagnostics and in future epidemiological studies of mitochondrial diseases.