New method for detection of C34-T mutation in the AMPD1 gene causing myoadenylate deaminase deficiency

Performance enhancing genetic variants, oxygen uptake, heart rate, blood pressure and body mass index of elite high altitude mountaineers

AIM

To analyse and compare the ACE (angiotensin-converting enzyme), ACTN3 (actinin-3) and AMPD1 (adenosine monophosphate deaminase 1) genetic variants, oxygen uptake (VO2max), heart rate (HR), blood pressure (BP) and body mass index (BMI) of elite high altitude mountaineers and average athletes.

METHODS

Elite Bulgarian alpinists (n = 5) and control group of athletes (n = 72) were recruited. VO2max was measured using a treadmill graded protocol. HR, BP and BMI were recorded. Genotyping was done by polymerase chain reaction (PCR) amplification followed by agarose gel electrophoresis. Chi2-test and Fisher's exact test were used for statistical analysis.

RESULTS

Alpinists showed significantly higher frequencies of 60% ACE I allele (p = 0.002), 50% ACTN3 X allele (p = 0.032) and 30% AMPD1 T allele (p = 0.003) compared to controls - 39%, 36%, 13%, respectively. ACE ID genotype prevalence and null DD genotype were observed in mountaineers. Higher absolute VO2max, but no differences in VO2max ml kg-1 min-1, HR, oxygen pulse, blood pressure and BMI were found.

CONCLUSIONS

The ID genotype and higher frequencies of ACE I allele could contribute to successful high altitude ascents in mountaineers. The genetic make-up of the two mountaineers who made the summit of Mt Everest was distinctive, revealing ACE ID genotype, mutant ACTN3 XX and AMPD1 TT genotypes.

Association between AMPD1 Gene Polymorphism and Coagulation Factors in Patients with Coronary Heart Disease

The aim of this study was to investigate whether the C34T and G468T variations in the adenosine monophosphate deaminase-1 (AMPD1) gene were associated with intima-media thickness of the carotid and brachial artery, endothelial function of the brachial artery, glucose metabolism, haemostatic variables and cardiac hypertrophy in patients (n = 109) with coronary heart disease. The plasminogen activator inhibitor-1 activity and the von Willebrand factor were higher in the CC homozygote group compared to the CT/TT group (p < 0.05). There were no differences between the groups regarding intima-media complex of the carotid and brachial artery, presence of plaque in the carotid region, flow-mediated dilatation, ejection fraction or dimensions of the heart. In conclusion, there were no differences between the mutant AMPD1 allele carriers and CC homozygotes regarding surrogate values for atherosclerosis, endothelial function, dimensions and ejection fraction of the heart, glucose tolerance and other well-known cardiovascular risk factors, whereas plasminogen activator inhibitor-1 activity and von Willebrand levels were lower in the mutant AMPD1 allele carriers.

A Polymorphism of the Gene Encoding AMPD1: Clinical Impact and Proposed Mechanisms in Congestive Heart Failure

A vast array of gene polymorphisms have been described, and further discovery of these gene variants will continue as the human genome is defined. Therefore, selection of a single polymorphism to investigate in relation to disease evolution or outcome must be motivated by specific physiologic, pathophysiologic, or epidemiologic associations. A significant gene polymorphism may result in an alteration of protein function, or be associated with disease incidence or outcome. Prevalence of the polymorphism in the general population is of extreme importance, as it must be common enough to warrant interest in its clinical impact. The polymorphism of the gene encoding for the enzyme adenosine monophosphate deaminase 1 results in an abnormal protein necessary in skeletal muscle metabolism. While its physiologic effects are not completely understood, it has been associated with improved morbidity and mortality in patients with cardiovascular disease.

Evaluation of AMPD1 C34T genotype as a predictor of mortality in heart failure and post-myocardial infarction patients

BACKGROUND

The AMPD1 gene C34T polymorphism has previously been associated with prolonged survival in small cohorts of heart failure (HF) and coronary artery disease patients. This study aimed to corroborate the association of the AMPD1 C34T polymorphism with survival in larger myocardial infarction (MI) and HF cohorts.

METHODS

Genotypes were obtained for 935 post-MI (PMI) and 433 patients with established HF, with median follow-up times of 5.4 and 3.1 years, respectively. At admission, cardiac function was assessed by nuclear ventriculography (PMI) and echocardiography (HF) and plasma cardiac neurohormones were assayed.

RESULTS

Differences in mortality by AMPD1 genotype did not achieve significance, either for the overall HF (P = .07) or the overall PMI group (P = .28), but AMPD1 genotype predicted mortality in patients of both cohorts with a history of MI (HxMI). In contrast to previous studies, the mutant T allele was associated with poorer outcome. Mortality in HF HxMI patients was significantly different between genotype groups (n = 144, mortality CC 56.5%, CT/TT 77.8%, P = .027), but not in patients without HxMI. In PMI patients, the association of genotype with survival in the HxMI subgroup trended toward significance (n = 147, mortality CC 29.8%, CT/TT 45.5%, P = .093). Multivariate analysis of combined PMI and HF cohorts showed that HxMI patients with CT/TT genotype were at greater risk than all other groups (P < .001).

CONCLUSION

This study suggests that AMPD1 C34T genotype is not a predictor of survival in heart disease patients, except possibly those with HxMI.

The Role of a Common Adenosine Monophosphate Deaminase (AMPD)-1 Polymorphism in Outcomes of Ischemic and Nonischemic Heart Failure

BACKGROUND

A common variant of the adenosine monophosphate deaminase (AMPD)-1 gene (C34T) results in enzymatic inactivity and may increase adenosine in cardiac muscle and confer cardioprotection through ischemic preconditioning.

METHODS AND RESULTS

We hypothesized that AMPD1 carriers with ischemic heart failure (HF) in the Beta-Blocker Evaluation of Survival Trial (BEST) might have a relative survival advantage. Patients (n = 1038, 20% black) with ischemic (58%) and nonischemic (42%) HF were followed for an average of 2.0 years for cardiovascular mortality. DNA was purified from blood using phenol/chloroform. Genotyping was performed by polymerase chain reaction with 5' exonuclease chemistry. Differences in survival were assessed by comparing Kaplan-Meier curves with the log-rank test. Genotype frequencies differed by ethnicity (P < .001) but not by disease etiology. AMPD1 genotype did not significantly modify survival in the entire study population (hazard ratio [HR] = 0.91, 95% CI = 0.61-1.37), among ischemics (HR = 0.73, CI = 0.44-1.22, P = .23), or ischemic non-blacks (HR = 0.74, CI = 0.44-1.24, P = .25). Genotype did not modify the effect of bucindolol on mortality.

CONCLUSIONS

Results of this study failed to confirm a reported survival benefit among HF patients carrying the AMPD1 T-allele. However, further studies in larger, more homogeneous populations should explore the possibility of a modest survival advantage for patients with ischemic HF.

A common variant of the AMPD1 gene predicts improved survival in patients with ischemic left ventricular dysfunction

BACKGROUND

A recent retrospective study suggested that the adenosine monophosphate deaminase (AMPD)-1 gene variant C34T predicts outcome in heart failure patients. This variant might lead to ischemic preconditioning by increasing tissue adenosine. We tested whether the survival benefit of C34T occurs preferentially in the setting of ischemic left ventricular dysfunction.

METHODS AND RESULTS

A consecutive cohort of patients (n=390) with left ventricular ejection fraction <40% was evaluated. In the ischemic patient subgroup (n=210) multivariate analysis identified AMPD1 T allele carriage (hazard ratio=0.43, confidence interval=0.20-0.94, P=.035) as an independent predictor of transplant-free cardiovascular survival. No benefit was found in the nonischemic group although the number of events was too small to reliably exclude a benefit by genotype.

CONCLUSION

The AMPD1 C34T polymorphism influences transplant-free cardiovascular survival in the setting of ischemic left ventricular dysfunction.

A G468-T AMPD1 mutant allele contributes to the high incidence of myoadenylate deaminase deficiency in the Caucasian population

Myoadenylate deaminase deficiency is the most common metabolic disorder of skeletal muscle in the Caucasian population, affecting approximately 2% of all individuals. Although most deficient subjects are asymptomatic, some suffer from exercise-induced myalgia suggesting a causal relationship between a lack of enzyme activity and muscle function. In addition, carriers of this derangement in purine nucleotide catabolism may have an adaptive advantage related to clinical outcome in heart disease. The molecular basis of myoadenylate deaminase deficiency in Caucasians has been attributed to a single mutant allele characterized by double C to T transitions at nucleotides +34 and +143 in mRNA encoded by the AMPD1 gene. Polymerase chain reaction-based strategies have been developed to specifically identify this common mutant allele and are considered highly sensitive. Consequently, some laboratories preferentially use this technique over other available diagnostic tests for myoadenylate deaminase deficiency. We previously identified a G468-T mutation in one symptomatic patient who was only heterozygous for the common AMPD1 mutant allele. In this report, nine additional individuals with this compound heterozygous genotype are revealed in a survey of 48 patients with documented deficiency of skeletal muscle adenosine monophosphate deaminase and exercise-induced myalgia. Western blot analysis of leftover biopsy material from one of these individuals does not detect any immunoreactive myoadenylate deaminase polypeptide. Baculoviral expression of the G468-T mutant allele produces a Q156H substitution enzyme exhibiting labile catalytic activity. These combined results demonstrate that the G468-T transversion is dysfunctional and further indicate that AMPD1 alleles harboring this mutation contribute to the high incidence of partial and complete myoadenylate deaminase deficiency in the Caucasian population. Consequently, genetic tests for abnormal AMPD1 expression designed to diagnose patients with metabolic myopathy, and to evaluate genetic markers for clinical outcome in heart disease should not be based solely on the detection of a single mutant allele.

A common variant of the AMPD1 gene predicts improved cardiovascular survival in patients with coronary artery disease

OBJECTIVE

We tested whether a common AMPD1 gene variant is associated with improved cardiovascular (CV) survival in patients with coronary artery disease (CAD).

BACKGROUND

Reduced activity of adenosine monophosphate deaminase (AMPD) may increase production of adenosine, a cardioprotective agent. A common, nonsense, point variant of the AMPD1 gene (C34T) results in enzymatic inactivity and has been associated with prolonged survival in heart failure.

METHODS

Blood was collected from 367 patients undergoing coronary angiography. Genotyping was done by polymerase chain reaction amplification and restriction enzyme digestion, resulting in allele-specific fragments. Coronary artery disease was defined as > or =70% stenosis of > or =1 coronary artery. Patients were followed prospectively for up to 4.8 years. Survival statistics compared hetero- (+/-) or homozygotic (-/-) carriers with noncarriers.

RESULTS

Patients were 66 +/- 10 years old; 79% were men; 22.6% were heterozygous and 1.9% homozygous for the variant AMPD1(-) allele. During a mean of 3.5 +/- 1.0 years, 52 patients (14.2%) died, 37 (10.1%) of CV causes. Cardiovascular mortality was 4.4% (4/90) in AMPD1(-) allele carriers compared with 11.9% (33/277) in noncarriers (p = 0.046). In multiple variable regression analysis, only age (hazard ratio, 1.11/year, p < 0.001) and AMPD1(-) carriage (hazard ratio, 0.36, p = 0.053) were independent predictors of CV mortality.

CONCLUSIONS

Carriage of a common variant of the AMPD1 gene was associated with improved CV survival in patients with angiographically documented CAD. The dysfunctional AMPD1(-) allele may lead to increased cardiac adenosine and increased cardioprotection during ischemic events. Adenosine monophosphate deaminase-1 genotyping should be further explored in CAD for prognostic, mechanistic and therapeutic insights.

Myoadenylate deaminase deficiency. A common inherited defect with heterogeneous clinical presentation

Myoadenylate deaminase deficiency is a clinically heterogeneous metabolic disorder that is commonly diagnosed in a variety of neurologic settings. Although the molecular basis for this purine nucleotide catabolic derangement may typically be attributed to the inheritance of a single prevalent mutant allele, the clinical spectrum in the absence of other definable abnormalities can range from asymptomatic to mild exercise-induced myalgia. Moreover, myoadenylate deaminase deficiency is also found associated with other definable neuromuscular disorders. The myoadenylate deaminase deficiency in these latter cases may, in part, be precipitated by pathologic change or act synergistically in combination with another metabolic disease.

Genetic and other determinants of AMP deaminase activity in healthy adult skeletal muscle

AMPD1 genotype, relative fiber type composition, training status, and gender were evaluated as contributing factors to the reported variation in AMP deaminase enzyme activity in healthy skeletal muscle. Multifactorial correlative analyses demonstrate that AMPD1 genotype has the greatest effect on enzyme activity. An AMPD1 mutant allele frequency of 13.7 and a 1.7% incidence of enzyme deficiency was found across 175 healthy subjects. Homozygotes for the AMPD1 normal allele have high enzyme activities, and heterozygotes display intermediate activities. When examined according to genotype, other factors were found to affect variability as follows: AMP deaminase activity in homozygotes for the normal allele exhibits a negative correlation with the relative percentage of type I fibers and training status. Conversely, residual AMP deaminase activity in homozygotes for the mutant allele displays a positive correlation with the relative percentage of type I fibers. Opposing correlations in different homozygous AMPD1 genotypes are likely due to relative fiber-type differences in the expression of AMPD1 and AMPD3 isoforms. Gender also contributes to variation in total skeletal muscle AMP deaminase activity, with normal homozygous and heterozygous women showing only 85-88% of the levels observed in genotype-matched men.

Myoadenylate deaminase deficiency, hypertrophic cardiomyopathy and gigantism syndrome

We report a 20-year-old man with gigantism syndrome, hypertrophic cardiomyopathy, muscle weakness, exercise intolerance, and severe psychomotor retardation since childhood. Histochemical and biochemical analysis of skeletal muscle biopsy revealed myoadenylate deaminase deficiency; molecular genetic analysis confirmed the diagnosis of primary (inherited) myoadenylate deaminase deficiency. Plasma, urine, and muscle carnitine concentrations were reduced. L-Carnitine treatment led to gradual improvement in exercise tolerance and cognitive performance; plasma and tissue carnitine levels returned to normal, and echocardiographic evidence of left ventricular hypertrophy disappeared. The combination of inherited myoadenylate deaminase deficiency, gigantism syndrome and carnitine deficiency has not previously been described.

Clinical heterogeneity and molecular mechanisms in inborn muscle AMP deaminase deficiency

Lack of the muscle-specific isoform of AMP deaminase (myoadenylate deaminase deficiency) can cause a metabolic myopathy, with exercise-induced muscle symptoms such as early fatigue, cramps and/or myalgia. It is the most common muscle enzyme defect in man, found in about 2-3% of all muscle biopsies. The genetic basis of the inherited defect is the nonsense mutation C34-T in the AMPD1 gene encoding myoadenylate deaminase. The mutation results in a premature stop of the enzyme synthesis. In a healthy German population, the frequency of the mutant allele was 0.1, and 1% of this population is expected to be homozygous for the mutation. In people with muscle symptoms, the allele frequency was significantly higher (0.145). The correlation between allele frequency and muscle symptoms underscores the clinical significance of this defect. However, the vast majority of homozygous subjects do not develop a metabolic myopathy. This clinical heterogeneity may be due to molecular genetic factors such as alternative splicing of the exon harbouring the mutation, or due to metabolic conditions such as pathways compensating for the defect. The real basis for the high percentage of asymptomatic homozygous subjects remains to be revealed.