L-arginine regulates asymmetric dimethylarginine metabolism by inhibiting dimethylarginine dimethylaminohydrolase activity in hepatic (HepG2) cells.

An increase in circulating asymmetric dimethylarginine (ADMA) and a decreased L-arginine/ADMA ratio are associated with reduced endothelial nitric oxide (NO) production and increased risk of vascular disease. We explored relations between ADMA, L-arginine and dimethylarginine dimethylaminohydrolase (DDAH) in liver (HepG2) cells. DDAH is the principle enzyme for the metabolism of ADMA. HepG2 cells metabolised 44.8 nmol/h of ADMA per 3.6 x 10(6) cells in the absence of L-arginine. The metabolism of ADMA at physiological (1mu mol/l, p < 0.01) and at pathological (100mumol/l, p < 0.01) levels was inhibited dose-dependently by L-arginine (0-400mumol/l) in cultured HepG2 cells and increased intracellular ADMA (p = 0.039). L-arginine competitively inhibited DDAH enzyme activity to 5.6 +/- 2.0% of the untreated level (p < 0.01). We conclude that L-arginine regulates ADMA metabolism dose-dependently by competing for DDAH thus maintaining the metabolic balance of L-arginine and ADMA, and endothelial NO homeostasis.

Overview of inherited metabolic disorders causing cardiovascular disease.

Inherited metabolic disorders contribute importantly to adverse cardiovascular outcomes and affect all tissue types. This review summarizes some of the more important aspects. In the venous system, heterozygosities for the factor V Leiden and prothrombin 20210G > A mutations are common and occur in 4% and 1%, respectively, of caucasians. They confer a 2- to 3- fold increase in risk of venous, but not arterial, thrombosis. Marfan syndrome affects the systemic circulation and has a population prevalence of about 1 in 4000. The more than 200 mutations responsible are in the fibrillin-1 gene (15q21.1) and mediate the characteristic skeletal, lens and aortic changes. There are two potentially lethal inherited disorders of cardiac conduction, the long QT and Brugada syndromes. The prevalence for each is about 1 in 10,000. On the other hand, autosomal dominant hypertrophic cardiomyopathies are relatively common, at 1 in 500, but with variable penetrance. Mutations are in the sarcomere proteins and more than 140 are known. Hypertrophic cardiomyopathy may be confused with Fabry disease, for which effective treatment is now available. Mutations in several genes have been shown to produce dilated cardiomyopathy in the young, but there is as yet no specific treatment. In fatty acid oxidation disorders, arrhythmias and cardiomyopathy occur during acute decompensation. An important recently established cause of cardiomyopathy is carnitine transporter defect; it is treated effectively with oral carnitine. The autosomal dominant arrhythmogenic right ventricular dysplasia occurs with a prevalence of about 1 in 15,000 and presents with arrythmias and a dilated right ventricle. The mutations responsible have been mapped to chromosomes 1, 2, 10 and 14. Lysosomal storage disorders, the Ehlers-Danlos syndrome and other connective-tissue disorders affect cardiac valves and vessels. In addition to the relatively common inherited lipoprotein disorders familial hypercholesterolaemia and familial combined hyperlipidaemia, an important dominantly inherited lipid variable contributing to coronary risk is lipoprotein(a). The gene is localized to chromosome 6 and there is full expression in childhood. Elevated lipoprotein(a) levels contribute to the occurrence and severity of early-onset coronary disease and add to the already enhanced risk in patients with familial hypercholesterolaemia.

Strong association between N-acetyltransferase 2 genotype and PD in Hong Kong Chinese.

BACKGROUND: The slow acetylator genotype for N-acetyltransferase 2 (NAT2 genotype) may be associated with PD in white subjects and the genotype is common in both white and Chinese populations. Whether there is a relationship between NAT2 genotype and PD in Chinese subjects is not known. OBJECTIVE: To investigate the association between the slow acetylator genotype for N-acetyltransferase 2 and PD in a Chinese population. METHODS: The authors obtained DNA samples and documented sex, age, and smoking history in 99 Chinese patients with PD and in 126 control subjects from two major Hong Kong hospitals. PCR-restriction fragment length polymorphism was used to identify M1, M2, and M3 mutant polymorphisms of the slow acetylator genotype for N-acetyltransferase 2. Logistic regression analyses were carried out to investigate the relationships between the different variables and PD. RESULTS: The frequency of the slow acetylator genotype for N-acetyltransferase 2 in the PD group was significantly higher than that of the control group (68.7% vs 28.6%) with an OR of 5.53 (95% CI 3.08 to 9.92) after adjusting for age, sex, and smoking history. In a subgroup analysis smoking had no modifying effect on the association between genotype and PD. CONCLUSIONS: There is a significant association between PD and the slow acetylator genotype for N-acetyltransferase 2 in Hong Kong Chinese. The OR found is among the highest reported so far in all susceptibility gene studies for PD in both Chinese and white subjects and provides evidence for a possible functional relationship between NAT2 slow acetylator genotype and PD in both racial groups.

Vascular outcome in patients with homocystinuria due to cystathionine beta-synthase deficiency treated chronically: a multicenter observational study.

An inborn error of metabolism, homocystinuria due to cystathionine beta-synthase deficiency, results in markedly elevated levels of circulating homocysteine. Premature vascular events are the main life-threatening complication. Half of all untreated patients have a vascular event by 30 years of age. We performed a multicenter observational study to assess the effectiveness of long-term homocysteine-lowering treatment in reducing vascular risk in 158 patients. Vascular outcomes were analyzed and effectiveness of treatment in reducing vascular risk was evaluated by comparison of actual to predicted number of vascular events, with the use of historical controls from a landmark study of 629 untreated patients with cystathionine beta-synthase deficiency. The 158 patients had a mean (range) age of 29.4 (4.5 to 70) years; 57 (36%) were more than 30 years old, and 10 (6%) were older than 50 years. There were 2822 patient-years of treatment, with an average of 17.9 years per patient. Plasma homocysteine levels were markedly reduced from pretreatment levels but usually remained moderately elevated. There were 17 vascular events in 12 patients at a mean (range) age of 42.5 (18 to 67) years: pulmonary embolism (n=3), myocardial infarction (n=2), deep venous thrombosis (n=5), cerebrovascular accident (n=3), transient ischemic attack (n=1), sagittal sinus thrombosis (n=1), and abdominal aortic aneurysm (n=2). Without treatment, 112 vascular events would have been expected, for a relative risk of 0.09 (95% CI 0.036 to 0.228; P<0.0001). Treatment regimens designed to lower plasma homocysteine significantly reduce cardiovascular risk in cystathionine beta-synthase deficiency despite imperfect biochemical control. These findings may be relevant to the significance of mild hyperhomocysteinemia that is commonly found in patients with vascular disease.

Influence of an inducible nitric oxide synthase promoter variant on clinical variables in patients with coronary artery disease.

Pathophysiological processes in coronary artery disease (CAD) are influenced by genetic factors. Since (i) inducible nitric oxide synthase (iNOS) has important cardiovascular effects, and (ii) the promoter of the iNOS gene (NOS2A) is genetically modulated by a 4 bp insertion/deletion (+/-) polymorphism located 0.7 kb upstream, we decided to examine the influence of this variant on clinical variables in 856 CAD patients of Anglo-Celtic/Northern European extraction. We found that 2% of CAD patients were homozygous for the + allele, and 19% were heterozygous. Males made up 74% of the patient group, and in these the + allele was associated with 38% higher plasma glucose levels (P=0.005), a 4.8% elevation in the waist/hip ratio (P=0.009) and a 48% greater frequency of unstable angina (P=0.014). The + allele, by influencing iNOS expression, could thus contribute to indices of insulin resistance and angina severity in male CAD patients.

Cytomegalovirus inhibits p53 nuclear localization signal function.

Endothelial cells (EC) infected with the VHL strain of cytomegalovirus (CMV) are resistant to p53-mediated apoptosis, which may be relevant to EC dysfunction and atherogenesis. This resistance to apoptosis may be mediated by cytoplasmic sequestration of p53, which functions only in the nucleus. We explored the hypothesis that CMV sequesters p53 in the cytoplasm by blocking p53 nuclear localization signal (NLS) function. We transfected VHL CMV infected EC with recombinant p53 NLSI conjugated with chicken muscle pyruvate kinase (PK) plasmid. NLSI is responsible for 90% of p53 nuclear localization, and PK is not normally translocated to the nucleus after cytoplasmic production. Thus it cannot be localized in the nucleus without the assistance of the artificial NLSI. A double-labeling immunofluorescence staining method was used to identify the localization of p53 NLSI-conjugated PK in CMV-infected EC. We found that CMV infection sequesters PK and p53 in the cytoplasm by blocking NLSI function. This inactivation of NLSI function is dependent upon infection stage; it occurs only in the early and late phases and not the immediate early phase of infection. These findings may be relevant to endothelial dysfunction and initiation of atherogenesis. Our study also suggests a novel mechanism of the p53 inactivation by virus, which may be important for atherogenesis and tumorgenesis.

Cigarette smoke activates caspase-3 to induce apoptosis of human umbilical venous endothelial cells.

We explored an hypothesis that cigarette smoking-induced endothelial injury is mediated by accelerated apoptosis by treating human endothelial cells with cigarette smoke extracts (CSE). In cells treated with an increasing doses of CSE (0.005-0.03 cigarette equivalents/mL), we found a dose-dependent increase in the proportion of endothelial cells stained positive for apoptotic changes (8.3 +/- 0.7 to 50.7 +/- 2.2%, P < 0.01), accompanied by changes in caspase-3 activities and p53 protein levels. We suggest that excessive endothelial apoptosis may contribute to cigarette smoke-induced endothelial dysfunction and hence atherogenesis.

Vascular complications of severe hyperhomocysteinemia in patients with homocystinuria due to cystathionine beta-synthase deficiency: effects of homocysteine-lowering therapy.

Homocystinuria (HCU) due to cystathionine beta-synthase (CBS) deficiency leads to severe hyperhomocysteinemia (HHcy). Vascular events (VE) remain the major cause of morbidity and mortality in the untreated patients with HCU. The study on the natural history of untreated HCU disclosed that, at the time of maximal risk, in other words beyond 10 years old, there was one event per 25 years. Recent studies from Australia (n = 32), The Netherlands (n = 28), and Ireland (n = 24) have documented the effects of long-term treatment on the vascular outcome of a total of 84 patients with 1314 patient-years of treatment for HCU. The mean (range) age was 27.8 (2.5 to 70) years. Five VE were recorded during treatment; one pulmonary embolism, two myocardial infarctions, and two abdominal aneurysms. All five VE occurred in B6-responsive patients at a mean (range) age of 48.8 (30 to 60) years. In 1314 patient-years of treatment, 53 VE would have been expected if they remained untreated; instead only 5 were documented, relative risk = 0.091 (95% confidence interval [CI] 0.043 to 0.190; p < 0.001). Appropriate homocysteine-lowering therapy for severe HHcy significantly reduced the vascular risk in patients with HCU. VE were rare with treatment despite the fact that the post-treatment homocysteine levels were several times higher than the cutoff point for homocysteine in the normal population. The present findings may have relevance to the current concept of "mild HHcy" as a risk factor for vascular disease, with elevated plasma homocysteine levels considerably lower than that of the post-treatment levels in this group of reported patients.

Homocysteine and cardiovascular disease: cause or effect?

Both markedly and mildly elevated circulating homocysteine concentrations are associated with increased risk of vascular occlusion. Here we review possible mechanisms that mediate these effects. Inborn errors of homocysteine metabolism result in markedly elevated plasma homocysteine (200-300 micromol/L) and thromboembolic (mainly venous) disease: treatment to lower but not to normalize these concentrations prevents vascular events. Mild homocysteine elevation (>15 micromol/L) occurs in approximately 20-30% of patients with atherosclerotic disease. Usually, this is easily normalized with oral folate and ongoing trials are assessing the effect of folate treatment on outcomes. Although there is evidence of endothelial dysfunction with both markedly and mildly elevated homocysteine concentrations, the elevated homocysteine concentration in atherosclerotic patients is also associated with most standard vascular risk factors, and importantly, with early decline in renal function, which is common in atherosclerosis. Decline in renal function alone causes elevated plasma homocysteine (and cysteine). These observations suggest that mild hyperhomocysteinemia could often be an effect rather than a cause of atherosclerotic disease. Data on the common C677T methylenetetrahydrofolate reductase polymorphism supports this, in that, although homozygosity is a frequent cause of mild hyperhomocysteinemia when plasma folate is below median population concentrations, it appears not to increase cardiovascular risk. Indeed, there is recent evidence suggesting an acute antioxidant effect of folic acid independent of its effect on homocysteine concentrations. This antioxidant mechanism may oppose an oxidant effect of homocysteine and be relevant to treatment of patients with vascular disease, especially those with chronic renal insufficiency. Such patients have moderately elevated plasma homocysteine and greatly increased cardiovascular risk that is largely unexplained.

Lp(a) and conventional risk profiles predict the severity of coronary stenosis in high-risk hospital-based patients.

AIMS: To explore predictive power of Lp(a), of conventional lipoprotein profiles and their carrier proteins, and of biometric measurements, for the presence and severity of angiographically documented coronary disease in high-risk patients, and to compare risk profiles in men and women. METHODS: We determined coronary artery disease (CAD) risk factors in 1308 Australian Caucasian patients (313 women and 995 men) aged < or =65 years who consecutively underwent coronary angiography. RESULTS: In univariate analyses of the risk factors, lipid profiles, Lp(a), cigarette smoking, diabetes, hypertension and obesity were all higher in men and women with CAD and changed significantly with the number of significantly diseased vessels (> or =50% luminal obstruction). When stepwise logistic regression analysis was applied, age (OR 1.06, 95% CI: 1.04-1.09), TC/HDL-C (OR 1.29, 95% CI: 1.15-1.45), male gender (OR 2.64, 95% CI: 1.67-4.16), hyperLp(a) (> or =300 mg/L) (OR 2.09, 95% CI: 1.42-3.07), lifetime smoking dose (OR 1.02, 95% CI: 1.01-1.03), diabetes (OR 2.19, 95% CI: 1.14-4.18) and waist/hip ratio (OR 14.53, 95% CI: 1.21-174.90) were predictive of the disease. Both Lp(a) levels and percentage of hyperLp(a) increased linearly with the number of significantly diseased vessels. When the analyses were conducted in men and women separately, hyperLp(a), TC/HDL-C, lifetime smoking dose and age remained as significant predictors in both groups but the waist/hip ratio was only predictive in women. CONCLUSIONS: As Lp(a) is an independent predictor of the occurrence and extent of coronary stenosis and relevant to treatment options, we suggest that it should be measured routinely in the coronary risk profile assessment of high-risk patients.

Elevated circulating homocyst(e)ine levels in placental vascular disease and associated pre-eclampsia.

We examined the hypothesis that hyperhomocyst(e)inaemia in the maternal or fetal circulation is associated with placental vascular disease with either the maternal syndrome of pre-eclampsia and/or fetal syndrome of growth restriction. Maternal plasma homocyst(e)ine levels were significantly higher in pregnancies complicated by pre-eclampsia, pregnancies with evidence of umbilical placental vascular disease, and pregnancies with both complications compared with the normal pregnancy group. In the fetal circulation mean plasma homocyst(e)ine concentration was significantly higher in the pre-eclampsia group compared with the normal group. The results suggest that hyperhomocyst(e)inaemia may be a risk marker for placental vascular disease and maternal pre-eclampsia. The elevated fetal plasma homocyst(e)ine concentrations, found only in the group of pregnancies with pre-eclampsia in the absence of umbilical placental vascular disease, may be due to an effect of placental vascular disease on homocyst(e)ine transfer from the maternal to fetal circulation.

Human cytomegalovirus immediate early proteins upregulate endothelial p53 function.

Infected endothelial cells are found to be resistant to apoptosis possibly mediated by p53 cytoplasmic sequestration. We explored whether the immediate early 84 kDa protein (IE84) of cytomegalovirus (CMV) is responsible for p53 cytoplasmic sequestration. The endothelial cells were transfected with plasmids containing IE1 and 2 coding regions which are known to synthesize IE84 and 72 proteins. Our study found that p53 expression was significantly elevated in endothelial cells transfected with IE1 and 2 plasmids. However, p53 was only found in the nucleus rather than sequestered in the cytoplasm. We have demonstrated that IE84 and 72 are not responsible for p53 dysfunction caused by CMV infection, rather they upregulate p53 function and promote endothelial apoptosis.

Relationship between homocysteine and superoxide dismutase in homocystinuria: possible relevance to cardiovascular risk.

A modest homocysteine elevation is associated with an increased cardiovascular risk. Marked circulating homocysteine elevations occur in homocystinuria due to cystathionine beta-synthase (CbetaS) deficiency, a disorder associated with a greatly enhanced cardiovascular risk. Lowering homocysteine levels reduces this risk significantly. Because homocysteine-induced oxidative damage may contribute to vascular changes and extracellular superoxide dismutase (EC-SOD) is an important antioxidant in vascular tissue, we assessed EC-SOD and homocysteine in patients with homocystinuria. We measured circulating EC-SOD, total homocysteine (free plus bound), and methionine levels during the treatment of 21 patients with homocystinuria, 18 due to CbetaS deficiency, aged 8 to 59 years, and 3 with remethylating defects. We measured total homocysteine by immunoassay, EC-SOD by ELISA, and methionine by amino acid analysis and assessed interindividual and intraindividual relationships. There was a significant, positive relationship between EC-SOD and total homocysteine. For the interindividual assessment, levels were highly correlated, r=0.746, N=21, P<0.0001. This relationship was maintained after taking into account intraindividual patient variation (r=0.607, N=62, P<0.0001). In 2 newly diagnosed CbetaS-deficient patients, treatment that lowered the markedly elevated pretreatment homocysteine level (from 337 to 72 and from 298 to 50 micromol/L) reduced the associated elevated EC-SOD in each by 50%. EC-SOD and methionine levels were unrelated (r=0.148, n=39, P=0.368). The positive relationship between circulating EC-SOD and homocysteine could represent a protective antioxidant response to homocysteine-induced oxidative damage and contribute to reducing cardiovascular risk in homocystinuric patients. EC-SOD levels may be relevant to the pathogenesis of vascular disease in other patient groups.

Plasma levels of extracellular superoxide dismutase in an Australian population: genetic contribution to normal variation and correlations with plasma nitric oxide and apolipoprotein A-I levels.

Extracellular superoxide dismutase (EC-SOD) is a major superoxide scavenger and may be important to normal vascular function and cardiovascular health. We analyzed family data from 610 healthy Australians to detect and quantify the effects of genes on normal variation in plasma levels of EC-SOD and to test for pleiotropy with plasma nitric oxide (NO) and apolipoprotein A-I (apoA-I). Using maximum-likelihood-based variance decomposition methods, we determined that sex, age, and plasma levels of HDL cholesterol, apoA-I, and creatinine accounted for 38.6% of the variance in plasma EC-SOD levels and that additive genes accounted for 35% (P<0.00002). Multivariate analyses of plasma levels of EC-SOD, NO(x) (a measure of basal NO production), and apoA-I detected significant genetic correlations, indicating pleiotropy between EC-SOD and apoA-I (genetic correlation [rho(G)]=-0.45) and between NO(x) and apoA-I (rho(G)=0.58) but not between EC-SOD and NO(x). Genes shared by EC-SOD and apoA-I account for 20% of the genetic variance and, respectively, 7% and 9% of the phenotypic variance in both traits. Shared genes also account for >33% of the genetic variance and 5% and 15% of the respective phenotypic variance in NO(x) and apoA-I. In healthy individuals, over a third of the variance in EC-SOD plasma levels is due to the additive effects of genes. Some genes influence EC-SOD and apoA-I levels. The same is true of NO(x) and apoA-I but not of EC-SOD and NO(x). These patterns of pleiotropy can guide subsequent attempts to identify the genes and physiological mechanisms underlying them.

Body mass index in Australian children: recent changes and relevance of ethnicity.

AIM: To determine changes over time in the body mass index (BMI) profile of Australian primary schoolchildren and to assess the effects of sex and ethnicity. METHODS: Height and weight were measured in 3645 children (1869 girls and 1596 boys), aged 5-12 years from 39 schools in southeastern Sydney during 1994-7. Levels in the four largest ethnic groups of the population were compared with those measured by the 1985 Australian Council on Health, Physical Education, and Recreation (ACHPER) survey. RESULTS: The study population was 59.9% white (north European), 8.5% Mediterranean white, 7.7% Asian, 7.7% other, and 16.2% mixed (mainly Asian-white (36%) and Arab-white (24.7%)). There were sufficient numbers in four groups for analysis and comparison with the ACHPER survey: Mediterranean white, other white, mixed ethnicity, and Asian children. The age and sex adjusted BMI was highest in Mediterranean white, then white, mixed race, and Asian children. There were minimal differences between sexes within each group. However, boys had an age and sex adjusted BMI 1.5-6.5% higher (mean, 3.9%) than in ACHPER in 1985, as did white girls (mean increase, 2.4%). CONCLUSIONS: BMI in southeastern Sydney schoolchildren is related strongly to ethnicity and age; in boys and white girls it is on average 3.9% and 2.4% greater, respectively, than that recorded in the 1985 ACHPER survey. We suggest that this 10 year increase reflects a general trend in developed countries. Because increased BMI in childhood tracks to adulthood and is then associated with adverse effects on health, these findings signal a need for prevention.

Genetic polymorphism of heparan sulfate proteoglycan (perlecan, HSPG2), lipid profiles and coronary artery disease in the Australian population.

Perlecan is one of the three major classes of heparan sulfate proteoglycans (HSPGs) within the cardiovascular system; it interacts with lipid metabolism by binding to lipoprotein lipase (LpL) and apolipoprotein B (apo B) and may be related to vascular disease. We explored interactions between an HSPG2 polymorphism (BamHI marker), and apo B and coronary artery disease (CAD) in patients undergoing coronary angiography. The frequencies of the HSPG2 BamHI +/+, +/-, and -/- genotypes were 4.7, 31.7 and 63.6%, respectively, with a '+' allele frequency of 20.6%. The genotype distribution was in Hardy-Weinberg equilibrium (chi(2)=0.669, P0.05). The +/+homozygotes had the lowest apo B levels (0.74+/-0.06 g/l, n=36) compared to +/- (0.89+/-0.03 g/l, n=241) and -/- (0.93+/-0.02 g/l, n=480) genotypes. Although plasma apo B concentration was the strongest lipid risk factor for significant CAD, the HSPG2 genotypes were not independently associated with the presence of CAD (P=0.640 in males; P=0.224 in females), with significant CAD (P=0.764; P=0.110) or with the number of significantly stenosed coronary arteries (P=0.945; P=0. 335). In Australian Caucasians undergoing coronary angiography the HSPG2 BamHI polymorphism is associated with lower circulating apo B but not with the occurrence or severity of CAD. This may be due to HSPG2-mediated alterations in the HSPG2-apo B-LpL system and requires further exploration.

NADH/NADPH oxidase p22 phox C242T polymorphism and coronary artery disease in the Australian population.

BACKGROUND: Oxidative stress induced by the superoxide anion (.O2-) has been implicated in atherogenesis. The NADH/NADPH oxidase system is involved in.O2- production and p22 phox is an essential component of that system. MATERIAL AND METHODS: We analysed the p22 phox C242T polymorphism in 689 consecutive Australian Caucasians aged

The Glu-298-->Asp (894G-->T) mutation at exon 7 of the endothelial nitric oxide synthase gene and coronary artery disease.

We examined associations between the endothelial nitric oxide synthase (eNOS) gene Glu-298-->Asp (894G-->T) mutation and the occurrence and severity of angiographically defined coronary artery disease (CAD). eNOS mediates basal vascular wall nitric oxide production, and altered nitric oxide production has been implicated in atherosclerosis. The newly identified eNOS Glu-298-->Asp mutation in exon 7 is common and likely to be functional. It was found to be associated with myocardial infarction (MI) in Japanese but not in whites. We genotyped 763 white Australians undergoing coronary angiography for the eNOS Glu-298-->Asp mutation. The frequencies of the eNOS GG, TG and TT genotypes were 47.8%, 41.2% and 11.0% in men and 45.2%, 41.1% and 13.7% in women with CAD, and were not significantly different from those without CAD (43.2%, 40.7% and 16.0%, P=0.423 in men; 40.2%, 48.1% and 11.7%, P=0.582 in women). The mutation was also not associated with MI (P=0.469 in males; P=0.389 in females) or with the number of significantly stenosed vessels (P=0.954; P=0.734). The "T" allele frequency (32.5%) was much greater than that reported for the Japanese population (7.8% in controls and 10.0% in MI patients). In conclusion, the eNOS Glu-298-->Asp mutation is common, occurring with an allele frequency of 32.5%, but is not associated with either the occurrence or severity of CAD in the Australian population or with other established coronary risk factors assessed in our study. The mutation is significantly more frequent in the Australian than in the Japanese.