Steve E. Humphries

A review on the diagnosis, natural history, and treatment of familial hypercholesterolaemia

BACKGROUNDnFamilial hypercholesterolaemia (FH) affects approximately 1 in 500 people (10 million world-wide) and the elevated serum cholesterol concentrations lead to a more than 50% risk of fatal or non-fatal coronary heart disease by age 50 years in men and at least 30% in women aged 60 years. Based on a systematic literature search, we review the natural history of FH, describe the diagnostic criteria, and consider the effectiveness of treatment.nnnMETHODSnA comprehensive review was conducted of the literature on the diagnosis of FH, the morbidity and mortality related to treated and untreated FH, and the evidence on the effectiveness of treatment of FH in adults and children. Treatment options have changed since statin treatment became available, and we have not considered pre-statin therapy studies of treatment effectiveness.nnnFINDINGS AND DISCUSSIONnA clinical diagnosis of FH is widely used, but a definitive diagnosis can be made by genetic screening, although mutations are currently only detected in 30-50% of patients with a clinical diagnosis. Under-diagnosis of FH has been reported world-wide ranging from less than 1% to 44%. The relative risk of death of FH patients not treated with statins is between three and fourfold but treatment is effective, and delays or prevents the onset of coronary heart disease. Early detection and treatment is important. Aggressive LDL therapy is more effective in the regression of the carotid intima media thickness than conventional LDL therapy. Diagnosis at birth is problematic, and should be delayed until at least 2 years of age. Statins are not generally recommended for the treatment of children up to adolescence. Resins may be used but poor adherence is a problem. Technical advances in mutation detection, and the identification of other genes that cause FH, are likely to have important implications for the cost effectiveness of genetic diagnosis of FH.

Endothelial nitric oxide synthase genotype and ischemic heart disease: meta-analysis of 26 studies involving 23028 subjects

Background—Polymorphisms in the endothelial nitric oxide synthase (eNOS) gene may influence the risk of ischemic heart disease (IHD), but data from published studies with individually low statistical power are conflicting. To evaluate the role of polymorphisms in the eNOS gene in IHD, we considered all available studies in a meta-analysis. Methods and Results—Case-control studies evaluating the association between the Glu298Asp, −786T>C, and intron-4 polymorphisms and IHD were searched in MEDLINE and EMBASE up to January 2003. The principal prior hypothesis was that homozygosity for eNOS Asp298, the −786C allele in the promoter, or the intron-4 (a allele) would be associated with an increased risk of IHD. Data were available for 9867 cases and 13 161 controls from 26 studies. Homozygosity for the Asp298 was associated with an increased risk of IHD (OR, 1.31; 95% CI, 1.13 to 1.51). Although there was significant heterogeneity among studies of Asp298 (PHet=0.0002), which was largely accounted for by a single study, the increase in risk was still significant after exclusion of that study from analysis. Homozygosity for the intron-4 a allele was also significantly associated with higher risk of IHD (OR, 1.34; 95% CI, 1.03 to 1.75). However, no significant association was found with the −786C allele (OR, 1.06; 95% CI, 0.89, 1.25). Conclusions—Individuals homozygous for the Asp298 and intron-4 a alleles of eNOS are at moderately increased risk of IHD. These findings support the proposal that common genetic variations in the eNOS gene contribute to atherosclerosis susceptibility, presumably by effects on endothelial NO availability.

Nonfasting Apolipoprotein B and Triglyceride Levels as a Useful Predictor of Coronary Heart Disease Risk in Middle-Aged UK Men

Objective—The Apolipoprotein-related Mortality Risk (AMORIS) study concluded that the apolipoprotein (apo)B/apoA-I ratio was the best predictor of coronary heart disease (CHD) risk. We have compared the pairwise combinations of total cholesterol, triglycerides (TGs), apoB, high density lipoprotein (HDL) cholesterol, low density lipoprotein cholesterol, and apoA-I on CHD risk prediction in middle–aged men. Methods and Results—Healthy middle-aged men (n=2508), free of CHD at baseline, were examined prospectively. Over 6 years of follow-up, there were 163 CHD events (including acute myocardial infarction, coronary artery surgery, and ECG evidence of silent myocardial infarction). The relative risk (RR) of CHD associated with cholesterol, TGs, apoB, apoA-I, apoB/apoA-I, low density lipoprotein cholesterol, and HDL cholesterol were examined by survival analysis. The apoB/apoA-I ratio was associated with the strongest effect on the RR (3.58, 95% CI 2.08 to 6.19). In multivariate analysis, apoA-I had no significant effect on risk. Examining RR by quartiles, apoB and HDL in combination (RR 8.38, 95% CI 3.21 to 21.92) were better predictors of CHD risk than apoB and TGs (RR 4.05, 95% CI 1.57 to 6.23). However, apoB and TGs in combination added risk information over and above lifestyle factors, whereas apoB and HDL cholesterol did not. Conclusions—The combined evaluation of apoB with TGs provides useful diagnostic criteria for CHD risk.

Association of telomere length with type 2 diabetes, oxidative stress and UCP2 gene variation

Objective High oxidative stress potentially leads to accelerated telomere shortening and consequent premature cell senescence, implicated in type 2 diabetes (T2D) development. Therefore, we studied the association of leukocyte telomere length (LTL) with the presence of T2D, as well as the effect on the patients’ LTL of plasma oxidative stress and of variation in UCP2, a gene involved in the mitochondrial production of reactive oxygen species. Methods Mean LTL was determined in 569 Caucasian, 103 South Asian and 70 Afro-Caribbean T2D patients aged from 24 to 92 years, 81 healthy Caucasian male students aged from 18 to 28 years and 367 healthy Caucasian men aged from 40 to 61 years by real-time PCR. Plasma total antioxidant status (TAOS) was measured in the T2D patients by a photometric microassay. The patients were also genotyped for the UCP2 functional variants −866G>A and A55V. Results Afro-Carribeans had 510 bp longer mean length compared to Caucasians (p < 0.0001) and 500 bp longer than South Asians (p = 0.004). T2D subjects displayed shorter age-adjusted LTL compared to controls [6.94(6.8–7.03) vs. 7.72(7.53–7.9), p < 0.001] with subjects in the middle and the lowest tertile of LTL having significantly higher odds ratios for T2D compared to those in the highest tertile [1.50(1.08–2.07) and 5.04(3.63–6.99), respectively, p < 0.0001]. In the patients, LTL was correlated negatively with age (r = −0.18, p < 0.0001) and positively with TAOS measures (r = 0.12, p = 0.01) after adjusting for age, while carriers of the UCP2 −866A allele had shorter age-adjusted LTL than common homozygotes [6.86(6.76–6.96) kb vs. 7.03(6.91–7.15) kb, p = 0.04]. Conclusion The present data suggest that shorter LTL is associated with the presence of T2D and this could be partially attributed to the high oxidative stress in these patients. The association of the UCP2 functional promoter variant with the LTL implies a link between mitochondrial production of reactive oxygen species and shorter telomere length in T2D.

Interleukin-6 −174G>C Polymorphism and Risk of Coronary Heart Disease in West of Scotland Coronary Prevention Study (WOSCOPS)

Interleukin (IL)-6 plays an important role in the pathogenesis of coronary heart disease (CHD). Two functional polymorphisms in the IL-6 promoter have been identified (−174G>C and −572G>C), with both the rare alleles being associated with higher plasma levels of IL-6 after bypass surgery and one of them (−174G>C) associated with CHD risk. We have studied the contribution of these polymorphisms to CHD risk in the West of Scotland Coronary Prevention Study (WOSCOPS), a primary prevention trial that demonstrated the effectiveness of pravastatin in reducing morbidity and mortality from CHD. Four hundred ninety-eight cases (consisting of individuals experiencing a cardiovascular event during 4.8 years of follow-up) and 1109 controls (individuals matched for age and smoking habits) were genotyped. In the placebo group, there was no significant evidence of higher risk associated with the −174CC genotype compared with the GG+GC group. However, in the pravastatin-treated group, CC homozygotes had a significantly lower risk of CHD compared with the GG+GC placebo group (odds ratio 0.46, 95% CI 0.27 to 0.79), and this remained statistically significant after adjustment for classic risk factors. Compared with the GG+GC group, men with the CC genotype had modestly, but not significantly, higher baseline levels of IL-6, C-reactive protein, or fibrinogen but showed a significantly greater fall in LDL cholesterol with statin treatment (P =0.036). The −572G>C polymorphism was not significantly associated with any plasma trait or CHD risk. Thus, in subjects under pravastatin treatment, the −174CC genotype was associated with a lower risk of CHD. These results demonstrate the importance of the inflammatory system in determining the risk of CHD and support the nonlipid effect of statins on risk.

Physiology: The ACE gene and muscle performance

Angiotensin-converting enzyme in human skeletal muscle can be encoded by either of two variants of the ACE gene, one of which carries an insertion of 287 base pairs. This longer allele gives rise to lower enzyme activity, and is associated with enhanced endurance performance and an anabolic response to intense exercise training. Here we examine training-related changes in the mechanical efficiency of human skeletal muscle (energy used per unit power output) and find that the presence of this ACE allele confers an enhanced mechanical efficiency in trained muscle.

Contribution of APOA5 gene variants to plasma triglyceride determination and to the response to both fat and glucose tolerance challenges

The aim of this study was to investigate the influence of APOA5 variants on fasting lipids and to the response to both an oral fat tolerance test (OFTT) and an oral glucose tolerance test (OGTT). The association of two APOA5 SNPs [S19W (SNP5), -1131T>C (SNP3)] and an APOA4/A5 intergenic SNP [-12238T>C (SNP4)] were examined in healthy young men (n=774) who had undergone both an OFTT and an OGTT. Both -1131T>C and S19W rare alleles were associated with triglyceride (TG)-raising effects (11%, P=0.008; 21% (in cases), P<0.026, respectively) and showed additive effects on TG. None of the variants influenced the responsiveness to the OFTT after correcting for baseline TG. Homozygosity for the -12238T>C rare allele was associated with higher waist to hip ratio (P<0.0006), systolic blood pressure (P=0.012) and AUC and peak of insulin after OGTT (P=0.003 and P=0.027, respectively), traits that define the metabolic syndrome. Our results strongly support the role of APOA5 in determining plasma TG levels in an age-independent manner and highlight the importance of the APOC3/A4/A5 gene cluster in both TG and metabolic homeostasis.

Genetic Variants of Angiotensin II Receptors and Cardiovascular Risk in Hypertension

Abstract—Renin-angiotensin systems may mediate cardiovascular disease pathogenesis through a balance of actions of angiotensin II on (potentially proatherogenic) constitutive type 1 (AT1R) and (potentially antiatherogenic) inducible type 2 (AT2R) receptors. We explored such potential roles in a prospective candidate gene association study. Cardiovascular end points (fatal, nonfatal, and silent myocardial infarction and coronary artery bypass surgery/angioplasty) were documented among 2579 healthy UK men (mean age, 56.1±3.5 years; median follow-up, 10.1 years) genotyped for the AT1R1166A>C and the X chromosome located AT2R1675A>G and 3123C>A polymorphisms. Baseline characteristics, including blood pressure, were independent of genotype. The AT1R1166CC genotype was associated with relative cardiovascular risk (hazard ratio, 1.65 [1.05 to 2.59]; P =0.03) independent of blood pressure. Systolic blood pressure was associated with risk (P =0.0005), but this association was restricted to AT2R1675A allele carriers (P <0.00001), with G allele carriers protected from the risk associated with blood pressure (P =0.18). Hypertensive carriers with the AT2R1675A/3123A haplotype were at most risk, with 37.5% having an event. This is the first study to demonstrate an association of AT2R genotype with coronary risk, an effect that was confined to hypertensive subjects and supports the concept that the inducible AT2R is protective. Conversely, the AT1R1166CC genotype was associated with cardiovascular risk irrespective of blood pressure. These data are important to our understanding of the divergent role of angiotensin II acting at its receptor subtypes and coronary disease pathogenesis and for the development of future cardiovascular therapies.

Apal polymorphism in insulin-like growth factor II (IGF2) gene and weight in middle-aged males.

In 1474 healthy Caucasoid men aged 45–65u2005y, insulin-like growth factor II (IGF2) Apal AA homozygotes showed a mean body weight 4u2005kg lower than Apal GG homozygotes (77.6±10.9u2005kg vs 81.6±11.5u2005kg, P=0.003) with heterozygotes (GA) intermediate (80.1±11.9u2005kg). The mean serum IGF-II concentration in 44 Apal AA individuals was significantly higher than in 48 Apal GG individuals (683.3±146.9u2005ng/ml vs 614.0±124.0u2005ng/ml, P=0.01). An INS Pstl polymorphism showed no association with weight and it was also found to be in minimal linkage disequilibrium with the IGF2 Apal site (coefficient 0.016). The IGF2 Apal AA genotype is therefore associated with lower mean body weight but higher serum IGF-II concentrations than the GG genotype. Apal GG homozygotes incur a 1.67-fold risk of pathological Body Mass index (BMI) (>30u2005kg/m2) compared with AA homozygotes.

Genetic and environmental determinants of plasma high density lipoprotein cholesterol and apolipoprotein AI concentrations in healthy middle-aged men.

The effects of common variants of cholesteryl ester transfer protein (CETP) (TaqIB), hepatic lipase (HL) (−514C>T), lipoprotein lipase (LPL) (S447X) and lecithin cholesterol acyl transferase (LCAT) (S208T) on the determination of high density lipoprotein cholesterol (HDL‐C) and apolipoprotein AI (apoAI) levels were examined in 2773 healthy middle‐aged men participating in the second Northwick Park Heart Study. The extent of gene:gene, gene:smoking and gene:alcohol interactions were determined. For HDL‐C levels, only CETP genotype was associated with significant effects (p<0·0001), with the B2 allele being associated with higher levels in both smokers and non‐smokers. This interaction was significant at the lowest tertile of TG, suggesting that TG levels were rate limiting. As previously reported, CETP, LPL and HL genotypes were all associated with significant effects on apoAI levels (all p<0·01), with carriers of the rare alleles having higher levels and with no evidence of heterogeneity of effects in smokers and non‐smokers. LCAT genotype was not associated with significant effects on either trait. There was no significant interaction between any of the genotypes and alcohol consumption on either HDL‐C or apoAI levels. All genotypic effects were additive for HDL‐C and apoAI. Environmental and TG levels explained more than 20% and 5·5% of the variance in HDL‐C and apoAI, respectively. The novel aspect of this finding is that genetic variation at these loci explained in total only 2·5% of the variance in HDL‐C and 1·89% of the variance in apoAI levels. Thus despite the key roles played by these enzymes in HDL metabolism, variation at these loci, at least as detected by these common genotypes, contributes minimally to the variance in HDL‐C and apoAI levels in healthy men, highlighting the polygenic and multifactorial control of HDL‐C.