Rapid, simultaneous genotyping of 10 Southeast Asian glucose-6-phosphate dehydrogenase deficiency-causing mutations and a silent polymorphism by multiplex primer extension/denaturing HPLC assay

Rapid detection of twenty-nine common Chinese glucose-6-phosphate dehydrogenase variants using a matrix-assisted laser desorption/ionization-time of flight mass spectrometry assay on dried blood spots

BACKGROUND

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common inherited disease. Current neonatal screening methods for G6PD deficiency primarily rely on the use of biochemical tests. However, only 15%-20% of female carriers were estimated to have been detected using these tests. As a better alternative, DNA-based tests could be used for G6PD deficiency screening. We aimed to develop a matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) assay for G6PD variant detection.

METHODS

A MALDI-TOF MS assay with multiprimer extension (multi-PEX) was developed to rapidly and accurately detect the 29 common G6PD variants in the Chinese population using a dried blood spot as a template. A parallel study screening 571 unrelated neonatal samples using the MALDI-TOF MS and fluorescence quantitative enzymatic assays was performed. All results were confirmed by Sanger sequencing in a blind study.

RESULTS

In 571 unrelated neonatal samples, 34 positive samples, including 26 samples from hemizygous males and eight samples from heterozygous females, were correctly identified, yielding a clinical sensitivity of 100%. The results were validated using Sanger sequencing with 100% concordance. In contrast, the fluorescence quantitative enzymatic assay had a 75% false negative and 88.8% false positive rate for the detection of heterozygous G6PD deficient females.

CONCLUSIONS

We established a reliable MALDI-TOF MS assay for G6PD deficiency screening in the Chinese population maximizing the chance of detection of heterozygous G6PD deficient females and reducing the false negative and false positive rates associated with routinely used newborn screening procedures.

Rapid detection of G6PD mutations by multicolor melting curve analysis

The MeltPro G6PD assay is the first commercial genetic test for glucose-6-phosphate dehydrogenase (G6PD) deficiency. This multicolor melting curve analysis-based real-time PCR assay is designed to genotype 16 G6PD mutations prevalent in the Chinese population. We comprehensively evaluated both the analytical and clinical performances of this assay. All 16 mutations were accurately genotyped, and the standard deviation of the measured Tm was <0.3°C. The limit of detection was 1.0ng/μL human genomic DNA. The assay could be run on four mainstream models of real-time PCR machines. The shortest running time (150min) was obtained with LightCycler 480 II. A clinical study using 763 samples collected from three hospitals indicated that, of 433 samples with reduced G6PD activity, the MeltPro assay identified 423 samples as mutant, yielding a clinical sensitivity of 97.7% (423/433). Of the 117 male samples with normal G6PD activity, the MeltPro assay confirmed that 116 samples were wild type, yielding a clinical specificity of 99.1% (116/117). Moreover, the MeltPro assay demonstrated 100% concordance with DNA sequencing for all targeted mutations. We concluded that the MeltPro G6PD assay is useful as a diagnostic or screening tool for G6PD deficiency in clinical settings.

DNA hypermethylation and X chromosome inactivation are major determinants of phenotypic variation in women heterozygous for G6PD mutations

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked incompletely dominant enzyme deficiency that results from G6PD gene mutations. Women heterozygous for G6PD mutations exhibit variation in the loss of enzyme activity but the cause of this phenotypic variation is unclear. We determined DNA methylation and X-inactivation patterns in 71 G6PD-deficient female heterozygotes and 68 G6PD non-deficient controls with the same missense mutations (G6PD Canton c.1376G>T or Kaiping c.1388G>A) to correlate determinants with variable phenotypes. Specific CpG methylations within the G6PD promoter were significantly higher in G6PD-deficient heterozygotes than in controls. Preferential X-inactivation of the G6PD wild-type allele was determined in heterozygotes. The incidence of preferential X-inactivation was 86.2% in the deficient heterozygote group and 31.7% in the non-deficient heterozygote group. A significant negative correlation was observed between X-inactivation ratios of the wild-type allele and G6PD/6-phosphogluconate dehydrogenase (6PGD) ratios in heterozygous G6PD Canton (r=-0.657, p<0.001) or Kaiping (r=-0.668, p<0.001). Multivariate logistic regression indicated that heterozygotes with hypermethylation of specific CpG sites in the G6PD promoter and preferential X-inactivation of the wild-type allele were at risk of enzyme deficiency.

Rapid genotyping of two common G6PD variants, African (A-) and Mediterranean, by high-resolution melting analysis

OBJECTIVES

The Mediterranean and A(-) G6PD variants are particularly prevalent in Africa and Southern Europe. Our study was aimed to develop an assay for the rapid genotyping of these two variants by HRM.

METHODS

After PCR reactions corresponding to the G6PD Mediterranean (exon 6), G6PD (A-) (exon 4) and G6PD (A-) (exon 5) mutations, amplicons were submitted to HRM. This protocol was applied to a cohort of 132 patients suffering from sickle cell disease.

RESULTS

Wild, homozygous or hemizygous and heterozygous states were fully discriminated by HRM for all three mutations. HRM results were in total accordance with DNA sequencing for 22 patients of our cohort with a 'A' genotype: presence of the (A-) (exon 5) mutation but absence of the (A-) (exon 4) mutation.

CONCLUSIONS

Our HRM protocols allow a rapid, simple and cost-effective screening of G6PD deficiency in patients originating from the Mediterranean and the African areas.

Development and evaluation of a reverse dot blot assay for the simultaneous detection of six common Chinese G6PD mutations and one polymorphism

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a common inherited disorder worldwide including southern China. We developed and validated a reverse dot blot (RDB) assay for the rapid and simultaneous genotyping of six mutations (c.95A>G, c.871G>A, c.1004C>T, c.1024C>T, c.1376G>T and c.1388G>A), that were common mutations in the Chinese G6PD deficiency population, and one polymorphism (c.1311C>T). Reliable genotyping of wild-type and mutant genomic DNA samples was achieved by means of a test strip onto which allele-specific oligonucleotide probe lines are fixed in parallel. This method involves a multiplex PCR amplification of three fragments in the G6PD target sequence and a manual hybridization/detection protocol. The entire procedure starting from blood sampling to the identification of mutations requires less than 6 h. The diagnostic reliability of this reverse dot blot assay was evaluated on 207 pre-typed samples by using direct DNA sequence analysis in a blind study. The reverse dot blot typing was in complete concordance with the reference method. The reverse dot blot assay was proved to be a simple, rapid, highly accurate, and cost-effective method to identify common G6PD mutations in Chinese population.

A panel of multiple markers associated with chronic systemic inflammation and the risk of atherogenesis is detectable in asthma and chronic obstructive pulmonary disease

Asthma and chronic obstructive pulmonary disease (COPD) are both lung diseases involving chronic inflammation of the airway. The injury is reversible in asthma whereas it is mostly irreversible in COPD. Both patients of asthma and COPD are known at risk for cardiovascular disease (CVD) and type 2 diabetes (T2DM), nephropathy, and cancer. We measured multiple risk markers for atherogenesis in 55 patients with asthma and 62 patients with COPD. We wanted to know whether risk markers for atherogenesis corresponding to sequence of events of chronic inflammation were also detectable in the airway inflammatory diseases. Elevation of almost all markers involving inflammation of the endothelial cells in the coronary artery were detectable in asthma and COPD involving the inflammation of the epithelial cell lining of the airway. Both the level and % elevation of all markers were found mostly higher in COPD, the more severe form of the lung disease. We believe that these markers are useful for predicting risk of developing clinical complications such as CVD.

Cosmetic liposuction causes only transient elevation of acute inflammatory response and does not advance to oxidative and nitrosative stress

Cosmetic liposuction is a surgical procedure performed on normal nonobese subjects to remove unwanted fat. We are interested to know whether the impact of acute inflammatory response induced by liposuction differs from that of chronic inflammation and whether acute inflammatory response will also advance further and cause oxidative and nitrosative stress leading to various clinical complications. In our investigation we monitored 15 nonobese women prior to liposuction, and one day and one month after the surgery with multiple markers associated with chronic inflammation and oxidative stress. Our results indicate that liposuction causes only a transient elevation of acute inflammatory markers such as interleukin-6 (IL-6), high sensitive C-reactive protein (hCRP), and serum amyloid A (SAA), and a transient decrease of nitric oxide (NO). Apparently the impact of liposuction for normal subjects did not advance beyond acute inflammatory response; there was little change in the levels of markers corresponding to downstream events of chronic systemic inflammation such as adhesion molecules, urinary microalbumin (uMA), homocysteine (Hcy), uric acid (UA), and markers of oxidative stress, including urinary 8-hydroxydeoxyguanosine (8-OhdG) and 3-nitrotyrosine (3NT). It appears that the acute inflammatory response of cosmetic liposuction does not lead to impaired renal function and oxidative and nitrosative damage, which are frequently associated with chronic inflammation.

Multiple risk markers for atherogenesis associated with chronic inflammation are detectable in patients with renal stones

Patients with renal stones are known to be at risk of clinical complications such as cardiovascular disease (CVD), nephropathy, and cancer. Recently, it has been realized that almost all risk markers for CVD, nephropathy, etc. are all markers associated with the sequence of reactions of chronic inflammation. It has been reported that chronic inflammation is involved not only in the pathogenesis of nephrolithiasis but also contributes to the development of clinical complications in this condition; therefore, we decided to find out whether these multiple markers are detectable in patients with renal stones so that they can be used to predict the risk of clinical complications in these patients. There were 33 patients with nephrolithiasis included in this study. We found that almost all major markers of chronic inflammation were elevated in patients with renal stones, including proinflammatory cytokine, acute inflammation markers, adhesion molecules, urinary microalbumin (uMA), myeloperoxidase (MPO), 8-hydroxydeoxyguanosine (8-OHdG), 3-nitrotyrosine (3NT), and monocyte chemoattractant protein. It appears that it is possible to assess the risk of clinical complications by monitoring these markers in patients with renal stones.

Development of multiple complications in type 2 diabetes is associated with the increase of multiple markers of chronic inflammation

Patients with type 2 diabetes (T2DM) are known at risk for developing cardiovascular disease (CVD), nephropathy, and cancer. We were interested to find out whether multiple markers associated with chronic inflammation are detectable in patients with T2DM and are increased in patients with T2DM who developed additional clinical complications. A sequence of multiple risk markers for atherogenesis, associated with chronic inflammation, was measured in patients with T2DM before and after the development of clinical complications. We found that multiple clinical complications frequently developed simultaneously in patients with T2DM. At the early stage of T2DM, only low levels and low percent elevations of multiple risk markers were detected. However, both the level and the percent elevation of these markers were found to increase with disease progression and the development of clinical complications. We believe that chronic inflammation not only contributes to the pathogenesis of T2DM but also continues to increase in T2DM patients who are developing additional clinical complications. It appears that these multiple markers are potentially useful not only for monitoring the progression of T2DM but also predicting the risk of developing macro- and microvascular disease, nephropathy, and cancer.

Multiplex primer extension reaction screening and oxidative challenge of glucose-6-phosphate dehydrogenase mutants in hemizygous and heterozygous subjects

The primary objective of our study was to provide a simple and reliable assay for identifying the majority of G6PD genetic variants in the Chinese population. We optimized the multiplex primer extension reaction (MPER) assay for simultaneous screening of 14-point mutations in 98 G6PD-deficient subjects. Our data demonstrated that this method is precise, cost-effective and has successfully identified mutations in 97 out of 98 subjects, including all heterozygous mutants. We also detected a relatively high incidence (12.3%) of c.871G > A, and all of them harbored the silent mutation c.1311C > T. Apart from the screening program, the pharmacogenetic relationship between G6PD level and residual reduced glutathione (GSH) level was studied upon oxidative challenge by alpha-naphthol. The GSH levels were correlated with their status of G6PD deficiency, but no significant difference was observed between individual G6PD-deficient groups. Our data demonstrated the potentials of the MPER assay for characterization of G6PD deficiency and other genetic diseases.