European intersocietal recommendations for the biomarker-based diagnosis of neurocognitive disorders

The recent commercialisation of the first disease-modifying drugs for Alzheimer's disease emphasises the need for consensus recommendations on the rational use of biomarkers to diagnose people with suspected neurocognitive disorders in memory clinics. Most available recommendations and guidelines are either disease-centred or biomarker-centred. A European multidisciplinary taskforce consisting of 22 experts from 11 European scientific societies set out to define the first patient-centred diagnostic workflow that aims to prioritise testing for available biomarkers in individuals attending memory clinics. After an extensive literature review, we used a Delphi consensus procedure to identify 11 clinical syndromes, based on clinical history and examination, neuropsychology, blood tests, structural imaging, and, in some cases, EEG. We recommend first-line and, if needed, second-line testing for biomarkers according to the patient's clinical profile and the results of previous biomarker findings. This diagnostic workflow will promote consistency in the diagnosis of neurocognitive disorders across European countries.

European consensus for the diagnosis of MCI and mild dementia: Preparatory phase

INTRODUCTION

Etiological diagnosis of neurocognitive disorders of middle-old age relies on biomarkers, although evidence for their rational use is incomplete. A European task force is defining a diagnostic workflow where expert experience fills evidence gaps for biomarker validity and prioritization. We report methodology and preliminary results.

METHODS

Using a Delphi consensus method supported by a systematic literature review, 22 delegates from 11 relevant scientific societies defined workflow assumptions.

RESULTS

We extracted diagnostic accuracy figures from literature on the use of biomarkers in the diagnosis of main forms of neurocognitive disorders. Supported by this evidence, panelists defined clinical setting (specialist outpatient service), application stage (MCI-mild dementia), and detailed pre-assessment screening (clinical-neuropsychological evaluations, brain imaging, and blood tests).

DISCUSSION

The Delphi consensus on these assumptions set the stage for the development of the first pan-European workflow for biomarkers' use in the etiological diagnosis of middle-old age neurocognitive disorders at MCI-mild dementia stages.

HIGHLIGHTS

Rational use of biomarkers in neurocognitive disorders lacks consensus in Europe. A consensus of experts will define a workflow for the rational use of biomarkers. The diagnostic workflow will be patient-centered and based on clinical presentation. The workflow will be updated as new evidence accrues.

Inter-Laboratory Comparisons and EQA in the Mediterranean Area

The role of Proficiency Testing schemes (PT) or External Quality Control programs (EQA), involves the use of inter-laboratory comparisons for the determination of laboratory performance. EQA-PT schemes are of primordial importance to the analytical quality, standardization of methods and harmonization of the results. Laboratories are familiar with EQA-PT schemes as they are a prerequisite for their accreditation according to the ISO/IEC 15189 standard. The IFCC Committee on Proficiency Testing (C-PT) conducted a survey among the colleagues of the Mediterranean countries in order to evaluate the status of the EQA-PT providers in the region, their acceptance among laboratories, and possible issues in their implementation. The survey was organized electronically and we received 59 replies from colleagues (IFCC National Representatives and affiliated EQA-PT providers), from 17 of the 23 countries (74%) of the Mediterranean area. We concluded that there is a broad difference in the application of the rules of External Quality Control programs or Proficiency Testing schemes, among the Laboratories in the Mediterranean countries. Moreover, as the Accreditation of the Laboratories is not mandatory in the majority of these countries, there is no valid reason for participation in EQA-PT schemes.

EurA1c: The European HbA1c Trial to Investigate the Performance of HbA1c Assays in 2166 Laboratories across 17 Countries and 24 Manufacturers by Use of the IFCC Model for Quality Targets

BACKGROUND

A major objective of the IFCC Committee on Education and Use of Biomarkers in Diabetes is to generate awareness and improvement of HbA1c assays through evaluation of the performance by countries and manufacturers.

METHODS

Fresh whole blood and lyophilized hemolysate specimens manufactured from the same pool were used by 17 external quality assessment organizers to evaluate analytical performance of 2166 laboratories. Results were evaluated per country, per manufacturer, and per manufacturer and country combined according to criteria of the IFCC model for quality targets.

RESULTS

At the country level with fresh whole blood specimens, 6 countries met the IFCC criterion, 2 did not, and 2 were borderline. With lyophilized hemolysates, 5 countries met the criterion, 2 did not, and 3 were borderline. At the manufacturer level using fresh whole blood specimens, 13 manufacturers met the criterion, 8 did not, and 3 were borderline. Using lyophilized hemolysates, 7 manufacturers met the criterion, 6 did not, and 3 were borderline. In both country and manufacturer groups, the major contribution to total error derived from between-laboratory variation. There were no substantial differences in performance between groups using fresh whole blood or lyophilized hemolysate samples.

CONCLUSIONS

The state of the art is that 1 of 20 laboratories does not meet the IFCC criterion, but there are substantial differences between country and between manufacturer groups. Efforts to further improve quality should focus on reducing between-laboratory variation. With some limitations, fresh whole blood and well-defined lyophilized specimens are suitable for purpose.

Neurophil gelatinase-associated lipocalin as a new biomarker in laboratory medicine

Neutrophil gelatinase-associated lipocalin (NGAL) is a 25 kDa protein of the lipocalin superfamily. This protein is expressed and secreted by immune cells, hepatocytes, and renal tubular cells in various pathologic states. NGAL has recently generated great interest as an early biomarker of renal injury. However, like many other endogenous biomarkers it is not produced by just one cell type and it exists in more than one molecular form. As recent research has shown different pathological conditions may involved in the production of this molecule. This review summarizes the current knowledge about the biology of NGAL and examines the role of this molecule of acute renal injury as well as in other pathologic conditions like neoplasia, anemia, pregnancy, cardiovascular disease chronic kidney disease and in cardiorenal syndrome. Commercial and research immunoassays are used to measure NGAL in both plasma and urine but these assays are not standardized. The existence of different molecular forms of NGAL and their expression at various disease states further complicates the interpretation of the results. Pre analytical issues and biological variation are also not fully elucidated.

Connection between telomerase activity in PBMC and markers of inflammation and endothelial dysfunction in patients with metabolic syndrome

Metabolic syndrome (MS) is a constellation of metabolic derangements associated with vascular endothelial dysfunction and oxidative stress and is widely regarded as an inflammatory condition, accompanied by an increased risk for cardiovascular disease. The present study tried to investigate the implications of telomerase activity with inflammation and impaired endothelial function in patients with metabolic syndrome. Telomerase activity in circulating peripheral blood mononuclear cells (PBMC), TNF-α, IL-6 and ADMA were monitored in 39 patients with MS and 20 age and sex-matched healthy volunteers. Telomerase activity in PBMC, TNF-α, IL-6 and ADMA were all significantly elevated in patients with MS compared to healthy volunteers. PBMC telomerase was negatively correlated with HDL and positively correlated with ADMA, while no association between TNF-α and IL-6 was observed. IL-6 was increasing with increasing systolic pressure both in the patients with MS and in the healthy volunteers, while smoking and diabetes were positively correlated with IL-6 only in the patients' group. In conclusion, in patients with MS characterised by a strong dyslipidemic profile and low diabetes prevalence, significant telomerase activity was detected in circulating PBMC, along with elevated markers of inflammation and endothelial dysfunction. These findings suggest a prolonged activity of inflammatory cells in the studied state of this metabolic disorder that could represent a contributory pathway in the pathogenesis of atherosclerosis.

The organization of an educational program for specialists in clinical chemistry by the Greek Society of Clinical Chemistry-Clinical Biochemistry

In Greece, there is no officially organized training in clinical chemistry for scientists. The Greek Society of Clinical Chemistry-Clinical Biochemistry decided to organize an intensive educational program of 18 seminars on clinical chemistry content as it is described in the EC4 Syllabus. The duration of each seminar was about 6 hours and consisted of 6 to 9 lectures. At the end of each seminar there was a voluntary written examination, comprised of 24 multiple choice questions. Successful completion of the Educational program was leading to a Certificate of Competence. Two cycles of the 18 seminars were performed: 1st cycle from October 2003 to December 2005 and 2nd cycle from March 2005 to October 2007. One hundred eighty nine colleagues was the mean attendance per seminar for the seminars of the 1st cycle and 38 colleagues for the seminars of the 2nd cycle. The mean participation to the examination for each seminar was almost 80% for the 1st cycle and 68% for the 2nd cycle. More than 80% of the participants performed Good or Very good in the examination in both cycles. It is estimated that more than 40% of the scientists who practice Clinical Chemistry in Greece, participated to this educational activity. This program is now provided as an e-learning application, and it is open for all scientists who want to follow the discipline of clinical chemistry.

Study of insulin resistance, TNF-α, total antioxidant capacity and lipid profile in patients with chronic heart failure under exercise

Gluco-metabolic syndrome, oxidative stress and inflammation are common in chronic heart failure (CHF). Exercise training programmes are known to improve oxidative status, insulin sensitivity and endothelial function. In this study, the effects of walking on improving lipid and glucose metabolism in CHF patients, under statin treatment, were investigated. Fasting glucose, serum insulin, tumor necrosis factor-α (TNF-α), total antioxidant capacity (TAC), uric acid (UA), total cholesterol, triglycerides, high-density lipoproteins (HDL), direct low-density lipoproteins (LDL-dir), apolipoprotein-B, apolipoprotein-A1, and lipoprotein-a (Lp(a)) were monitored. Insulin resistance was depicted by fasting insulin resistance index (FIRI) (FIRI≥2.94±1.41). HDL significantly increased with walking and was positively correlated with the non-significant triglyceride decrease and significant Lp(a) decrease. Significant correlations were found in all CHF patients at baseline between FIRI and New York Heart Association (NYHA) functional class, ejection fraction, HDL, triglycerides and TNF-α. All non-diabetic CHF patients were characterized by insulin resistance. Serum insulin and fasting glucose significantly decreased with walking, while decrease in FIRI was positively associated with patients' adherence to the walking program. Elevated uric acid and TNF-α levels also significantly decreased. In conclusion, the present study demonstrated that moderate, unsupervised, everyday physical activity was able to ameliorate the lipid and glycemic profile of CHF patients, with simultaneous attenuation of inflammation and oxidative stress.

The Greek way to the Register: the establishment and operation of the Register for Clinical Chemists-Clinical Biochemists in Greece

In Greece, there is no officially organized training in clinical chemistry for scientists. The Greek Society of Clinical Chemistry-Clinical Biochemistry (GSCC-CB), following the encouragement of the EC4/RC decided to organize a voluntary Register for specialists in clinical chemistry. The following criteria for registration were defined: 1) University degree in Chemistry, Biochemistry, Biology, Medicine, Pharmacy or other relevant subject. 2) A total of 9 years of university studies and postgraduate specialization in clinical chemistry-clinical biochemistry. 3) A minimum of 4 years of postgraduate specialization in clinical chemistry-clinical biochemistry on the job. 4) The candidate must be practicing clinical chemistry-clinical biochemistry in a laboratory in a medical environment in Greece. The postgraduate specialization in clinical chemistry-clinical biochemistry includes the laboratory training and the theoretical education. The laboratory training is organized by the GSCC-CB according to the Professional Training Dossier. The theoretical education was organized in a series of 18 "Seminars" which was the content of the "Educational program" of the GSCC-CB. Successful completion of the Educational program leads to a Certificate of Competence. The Greek Register has gained equivalence with the EC4 Register and it has 218 members, more than 80 of whom are European clinical chemists.

Association of neutrophil gelatinase-associated lipocalin with the severity of coronary artery disease

Serum neutrophil gelatinase-associated lipocalin (NGAL) concentrations were measured in 73 consecutive patients who underwent first-time angiography for suspected coronary artery disease (CAD), and their associations with angiographic indexes of the severity of CAD (i.e., number of diseased vessels and modified Gensini score) were estimated. Median serum NGAL levels in patients with angiographically confirmed CAD were significantly higher than those in patients with normal coronary arteries (29.0 ng/ml [interquartile range 25.2 to 36.8] vs 22.4 ng/ml [interquartile range 17.34 to 32.0], p = 0.004). Statistically significant correlations were observed between serum NGAL level and the number of diseased vessels (r(s) = 0.390, p = 0.01) and modified Gensini score (r(s) = 0.356, p = 0.002). Using multivariate analysis, serum NGAL level was independently associated with the presence and severity of CAD. In conclusion, serum NGAL levels are significantly higher in the presence of CAD and are correlated with the severity of the disease. Further clinical studies are needed to confirm the use of NGAL as a biomarker for the detection and extent of CAD.

Relationship between mean blood glucose and glycated haemoglobin in Type 2 diabetic patients

AIMS

To correlate the values of MBG to HbA(1c) in Greek patients with Type 2 diabetes and/or metabolic syndrome.

METHODS

We followed up 140 Greek adult patients: 92 patients with Type 2 diabetes treated with insulin or oral glucose-lowering medication, and 48 patients with newly diagnosed Type 2 diabetes or metabolic syndrome not receiving any treatment. MBG was calculated for each patient from self-measurements of blood glucose using a portable glucometer, made six times a day (before eating and 2 h after a meal), three times a week for 1 month. HbA(1c) was determined by HPLC at 0 and 12 weeks.

RESULTS

HbA(1c) at 0 (x) and 12 weeks (y) correlated strongly (y = 0.790x + 1.115, r = 0.92), confirming that the patient's glycaemic status remained stable during the whole period of follow-up. Linear regression was performed on MBG values; HbA(1c) at 12 weeks, sex, age, body mass index (BMI) and patient status (Type 2 diabetes treated or not) were used as independent variables. None of the independent variables reached statistical significance in the model, with the exception of HbA(1c) at 12 weeks. The final model was: MBG (mg/dl) = (34.74 x HbA(1c)) - 79.21, r = 0.93; or MBG (mmol/l) = 1.91 x HbA(1c) - 4.36, r = 0.93.

CONCLUSIONS

Our results establish for the first time a strong correlation between MBG and HbA(1c) in Type 2 diabetic patients and support the idea of expressing HbA(1c) results as MBG. This will help patients to gain a clearer interpretation of the result, with less confusion. This simplification will allow every person with diabetes using home glucose-monitoring to understand his or her own target level.

Does diagnostic coronary angiography induce significant coronary microembolization in stable, ischemic patients? A prospective study

BACKGROUND

Although microembolization during percutaneous coronary interventions is a frequent event, the extent of possible microembolization during diagnostic coronary angiography is unknown. The aim of the study was to investigate whether diagnostic coronary angiography results in coronary microembolization and consequent subtle, subclinical myocardial necrosis with enzyme elevations.

METHODS

Fifty-three consecutive patients underwent diagnostic coronary angiography due to inducible ischemia. Creatine kinase MB isoenzyme (CK MB) and cardiac troponin I (cTnI) were used as sensitive surrogate markers of myocardial necrosis. Serial measurements, before, and 6 and 24 hours following a diagnostic procedure, were performed.

RESULTS

Baseline cTnI was below the limits of detection in all patients (<0.20 ng/mL), except for one patient with 1.31 ng/mL. Baseline median CK-MB was 1.05 ng/mL (interquartile range, 0.80-1.56 ng/mL) (Fig. 1). Both at 6 and 24 hours, no patients had any increase in cTnI, with the exception of a minor increase to 0.22 ng/mL at 24 hours in one patient. At 6 hours, 25 patients had decreases in CK MB, while 22 had increases (exact P = 0.77). At 24 hours, 26 patients had decreases in CK MB and 19 patients had increases.

CONCLUSIONS

Detectable embolization with subsequent subclinical myonecrosis is an unlikely event.

Measurement of glycated hemoglobin (HbA1c) with an automated POCT instrument in comparison with HPLC and automated immunochemistry method: evaluation of the influence of hemoglobin variants

Our study evaluates a fast and easy way to perform point-of-care testing (POCT) measurements of glycated hemoglobin HbA1c in comparison with an immunoassay on an automated biochemistry analyzer and cation exchange chromatography, the two methods routinely used in clinical laboratories for the measurement of HbA1c. A significant finding of our study is that although the POCT instrument insert claims that the method is not affected by the presence of HbS in the heterozygous state or in combination with beta-thalassemia, discrepant results were found in some cases with such hemoglobinopathies. In these cases, the two POCT and laboratory immunoassay methods showed clinically significant positive interferences with samples containing the HbS trait. We conclude that samples with the HbS trait should be interpreted with caution when tested using the POCT instrument.

C-Reactive protein concentrations and angiographic characteristics of coronary lesions

BACKGROUND

C-Reactive protein (CRP) is a strong predictor of clinical outcome in coronary artery disease (CAD), and inflammation has been implicated in the process. We aimed to evaluate whether CRP concentrations measured with a new, automated particle-enhanced immunoturbidimetric method for high-sensitivity CRP may be related to specific high-risk angiographic features of coronary lesions.

METHODS

In a cross-sectional study, we examined 103 consecutive patients undergoing cardiac catheterization for suspected CAD. We assessed the association of preprocedural CRP concentrations with clinical presentation (unstable angina) and angiographic features of coronary lesions.

RESULTS

Twenty patients had unstable angina. Independent predictors of unstable angina included increased CRP [odds ratio (OR), 2.93 per 10-fold increase in CRP; 95% confidence interval (CI), 1.28-6.69; P = 0.01] and the presence of macroscopic thrombus (OR, 7.08; 95% CI, 1.33-37.8; P = 0.02). Thirty-two culprit lesions had macroscopic thrombus or eccentric/irregular discrete morphology without total occlusion. Increased CRP was the strongest predictor of such features (OR, 2.04 per 10-fold increase in CRP; 95% CI, 1.03-4.04; P = 0.04), and the effect was independent of the presence of unstable angina.

CONCLUSIONS

Among patients with suspected CAD undergoing coronary angiography, increased CRP is strongly associated with unstable angina and with specific high-risk features of the culprit coronary lesions.

C-Reactive Protein Concentrations and Angiographic Characteristics of Coronary Lesions

Background: C-Reactive protein (CRP) is a strong predictor of clinical outcome in coronary artery disease (CAD), and inflammation has been implicated in the process. We aimed to evaluate whether CRP concentrations measured with a new, automated particle-enhanced immunoturbidimetric method for high-sensitivity CRP may be related to specific high-risk angiographic features of coronary lesions.

Methods: In a cross-sectional study, we examined 103 consecutive patients undergoing cardiac catheterization for suspected CAD. We assessed the association of preprocedural CRP concentrations with clinical presentation (unstable angina) and angiographic features of coronary lesions.

Results: Twenty patients had unstable angina. Independent predictors of unstable angina included increased CRP [odds ratio (OR), 2.93 per 10-fold increase in CRP; 95% confidence interval (CI), 1.28–6.69; P = 0.01] and the presence of macroscopic thrombus (OR, 7.08; 95% CI, 1.33–37.8; P = 0.02). Thirty-two culprit lesions had macroscopic thrombus or eccentric/irregular discrete morphology without total occlusion. Increased CRP was the strongest predictor of such features (OR, 2.04 per 10-fold increase in CRP; 95% CI, 1.03–4.04; P = 0.04), and the effect was independent of the presence of unstable angina.

Conclusions: Among patients with suspected CAD undergoing coronary angiography, increased CRP is strongly associated with unstable angina and with specific high-risk features of the culprit coronary lesions.

Pretreatment with aspirin and ticlopidine confers lower thrombogenic potential of radiofrequency catheter ablation

In the present study we pretreated 31 patients undergoing radiofrequency catheter ablation (RFA) with combined aspirin and ticlopidine for 3 days before the procedure, whereas 37 patients did not receive pretreatment. D-dimer levels reflecting the thrombogenic potential of RFA were significantly lower in the pretreated group at each stage before, during, and after the procedure, whereas there were no significant differences between the 2 groups in the number of RFA lesions or duration of the procedure.

Detection of the cytomegalovirus by the polymerase chain reaction DNA amplification in a kidney transplanted patient

Cytomegalovirus injection is common in kidney transplanted patients. Viremia is the only marker of active CMV infection, but the use of cell culture for the direct detection of the virus is time-consuming and not very sensitive, while the detection of CMV by measuring the titre of antibodies is difficult due to the immunosuppression these patients undergo. Thus the ability to amplify CMV DNA by the polymerase chain reaction from blood or urine samples of the patients becomes a valuable diagnostic tool for the detection of CMV in the early stages of the infection. Using a set of primers specific for the amplification of a 435 bp region of the IE-1 gene, we detected CMV DNA in blood leucocytes of a kidney transplanted patient who received the transplant from a CMV-seropositive donor, 45 days after the operation, while the antibody titre showed no evidence of active CMV infection.

H-ras oncogene mutations in the urine of patients with bladder-tumors - description of a noninvasive method for the detection of neoplasia

Bladder cancers are usually curable, by surgical or transurethral excision, if diagnosed at an early stage. Tumor derived mutations in oncogenes potentially provide specific markers for the detection of surgically resectable tumors. The detection of point mutations of H-ras oncogene correlated with this disease. DNA sequences produced by the Polymerase Chain Reaction (PCR) can be considered for this application, because theoretically bladder tumors should shed cells containing this mutation into the urine. We examined urine from 21 individuals with bladder cancer before any treatment, as well as tissue specimens from the excised tumor and we found 10 mutations of the H-ras gene at codon 12 in the urine (47.61%) and 14 mutations in the tumor specimens (66.66%). We were able to detect nearly 50% of the patients with bladder tumors using this method. We also studied two relapses; in one case (which presented the mutation in the original tumor and the urine) the relapse grade had progressed from II to III. In the other case the relapse grade stayed at III but it presented for the first time the studied mutation in the urine. These results provide the theoretical and technical basis for the detection of bladder tumors by a non-invasive method and possibly for the evaluation of the invasiveness of the disease.

Detection of hepatitis-B virus-DNA at high-frequency in liver neoplasias using a PCR technique

Hepatocellular carcinoma is the most frequent liver cancer and hepatitis B virus is included among the risk factors for the development of this type of neoplasia. Direct detection of this virus is difficult due to the lack of a simple tissue culture system for growing the virus. Amplification of HBV nucleic acid sequences with the Polymerase Chain Reaction technique leads to the direct detection of the virus, but involves several critical steps and it is prone to false positive results due to inter sample contaminations. We overcame these shortcomings by using a simple boiling method for extracting DNA from histological slides of tissues coupled with double ('nested') PCR amplification. In this study we evaluated the frequency of presence of HBV nucleic acid sequences in samples of neoplastic liver tissues from patients in Greece. We studied 20 DNA samples from hepatocellular carcinomas and we found 11 positive for HBV DNA and 8 DNA samples from hepatoblastomas and we found 3 positive for the viral DNA.

K-ras oncogene mutations in neoplasias of kidney transplanted patients: preliminary results with a new technique

K-ras oncogene activations by point mutations are frequent in many forms of human cancers but there is a special category of cancers occurring in immunosuppressed patients after kidney transplantation in which the frequency of K-ras oncogene activation has not been fully studied. We used a new sensitive and easy method for the detection of this mutation, and in 8 DNA samples studied from various neoplasias of 8 patients after kidney transplantation, we found 4 mutations. Our preliminary results indicate that the activation of K-ras oncogene at codon 12, is a common event among the kidney transplanted patients who present a neoplasia, even in the least aggressive forms of the disease, contrary to the sporadic cases.

Frequency of the major CF mutation in French CF patients

We have studied 124 patients of French origin, whose CF status had already been clearly established. These children belong to families previously tested with restriction fragment length polymorphism (RFLP) markers in our laboratory for genetic counselling. The most common mutation (delta F508) accounts for 67% in this population sample.

Ras activation in myelodysplastic syndromes: clinical and molecular study of the chronic phase of the disease

We studied N-ras and Ki-ras point mutations respectively at codons 12-13 and 12 in 15 patients with myelodysplastic syndromes (MDS) using the polymerase chain reaction (PCR) method for DNA amplification, and slot blot hybridization to allele specific oligonucleotide (ASO) probes. We analysed peripheral blood and bone marrow samples collected at diagnosis and repeatedly during the chronic phase of the disease to define when the activation occurred and in which haemopoietic cell populations, in order to establish possible relationships between clinical and molecular features. In three cases the N-ras oncogene was mutated at codon 12 in every cell population, both at diagnosis and throughout the chronic phase. Point mutations were not seen at the 12 codon of the Ki-ras oncogene. In patients lacking activated ras oncogene at diagnosis, mutations were not discovered during the entire period of observation. Therefore in our cases disease progression and leukaemic transformation did not correlate with the presence of the activated N-ras. Our data suggest that ras activation occurs early in the pathogenesis of MDS and involves a haemopoietic progenitor with multiple differentiative capacity, without however conferring an apparent proliferative advantage on its progeny.

Detection of minority point mutations by modified PCR technique: a new approach for a sensitive diagnosis of tumor-progression markers

The detection of point mutations correlated with diseases, in enzymatically amplified DNA sequences (Polymerase Chain Reaction), is currently performed by digestion of PCR products when an existing restriction site disappears at least in one allele of the amplified mutated sequence or by allele specific radiolabeled probes in all other cases. These methods are the most sensitive but they cannot detect a mutation if it is present in less than 5% of the studied cells. We describe here a method based on the introduction of an artificial restriction site, using a modified primer during the PCR, which creates a RFLP indicative of the studied mutation. This RFLP is detected by a radiolabeled oligonucleotide probe which is not related to the mutation. Our approach multiplies the sensitivity by a factor of 1000 and it is practical for use in screening purposes and the detection, after treatment, of the residual disease in human malignancies. Using this method we detected 20% more mutations at codon 12 in the Ki ras oncogene in DNA from colorectal cancers that were undetectable with all the previous methods.

Modification of enzymatically amplified DNA for the detection of point mutations

Images

Usefulness of linkage disequilibrium of KM-19 and XV-2c DNA probes for genetic counselling in a high-risk CF family

A French couple with an individual risk of carrying the cystic fibrosis (CF) mutation of 1/2 sought genetic counselling. From the DNA haplotypes generated by XV-2c and KM-19 RFLPs, it could be deduced that only one subject was a carrier, lowering the risk of having a CF baby from 1/16 to 1/200. The strong linkage disequilibrium between these RFLPs and the CF allele observed in France reduced the risk to 1/1600.