Dairena Gaffney

Regulation of plasma HDL cholesterol and subfraction distribution by genetic and environmental factors. Associations between the TaqI B RFLP in the CETP gene and smoking and obesity.

This study investigated in a healthy population (n = 220) the association of the TaqI B restriction fragment length polymorphism (RFLP) in the cholesteryl ester transfer protein (CETP) gene with plasma high-density lipoprotein (HDL) cholesterol concentration and subfraction distribution. A raised HDL cholesterol level was found in B2B2 homozygotes (B2 cutting site absent) and was associated specifically with a 45% increase in HDL2 compared with B1B1 homozygotes (B1B1, 77 +/- 39 mg/100 mL, mean +/- SD; B2B2, 112 +/- 59 mg/100 mL; P < 0.01). Total plasma, very-low-density lipoprotein, and HDL triglyceride levels did not differ among the genotype groups, nor did plasma apolipoprotein AI levels (B1B1, 1.45 +/- 0.35 mg/mL, mean +/- SD; B2B2, 1.56 +/- 0.33 mg/mL). Thus, the genetic variation appeared to be independent of metabolic factors that are known to regulate HDL levels. Plasma CETP exchange activity was unlikely to be the cause of the association, since it did not differ between genotype groups and was not correlated with HDL2 concentration. Multivariate analysis demonstrated that the TaqI B polymorphism had an effect on HDL cholesterol and HDL2 that was independent of age, sex, body mass index, oral contraceptive use, exercise, alcohol consumption, and plasma triglycerides. In smokers, the presence of the B2B2 genotype did not result in increased HDL cholesterol or HDL2, whereas in obese subjects, the difference between B1B1 and B2B2 individuals was diminished. We conclude that the TaqI B RFLP is associated with a quantitatively significant effect on plasma HDL2 levels that is independent of plasma triglycerides and interacts with lifestyle factors.

Independent Mutations at Codon 3500 of the Apolipoprotein B Gene Are Associated With Hyperlipidemia

The apoB arginine-to glutamine change at codon 3500 has become established as a cause of failure of binding of the LDL particle to its receptor and the consequent hypercholesterolemia of familial defective apoB 100. A search for further similar mutations was undertaken by systematic screening of a candidate region of the apoB gene from individuals with hypercholesterolemia. Polymerase chain reaction and denaturing gradient gel electrophoresis were used. We describe two families in which a different mutation in the codon 3500 causes an arginine-to-tryptophan substitution. Most adults in these families who have this mutation have hypercholesterolemia. LDL derived from all who have inherited the mutation is dysfunctional in that it allows only poor growth of an LDL cholesterol-dependent cell line. We conclude that this arginine 3500 is essential to the function of apoB and that its loss and replacement by glutamine or tryptophan is responsible for the hypercholesterolemia of familial defective apoB 100.

Clinical and laboratory features of calcium-sensing receptor disorders: a systematic review

Mutations in the calcium-sensing receptor gene (CaSR) may result in disorders of calcium homeostasis manifesting as familial benign hypocalciuric hypercalcaemia (FBHH), neonatal severe hyperparathyroidism (NSHPT) or autosomal dominant hypocalcaemia with hypercalciuria (ADHH). FBHH may have a population prevalence as high as one in 16 000, and ADHH one in 70 000. NSHPT is very rare. The FBHH condition is usually asymptomatic. Parathyroidectomy does not result in normal serum calcium, and no active treatment is indicated. To differentiate FBHH from primary hyperparathyroidism (PHPT), a guideline which includes measurement of serum calcium, intact parathyroid hormone (PTH), magnesium and fasting urinary calcium excretion is proposed. Screening of family members for hypercalcaemia, and occasionally a search for mutations in the CaSR gene, may be required. The NSHPT condition may manifest with hypercalcaemia, (usually) very elevated serum PTH concentration, subperiosteal erosions and fractures. Milder cases may be managed medically, but respiratory failure, extreme hypercalcaemia and failure to thrive are indications for early parathyroidectomy. The ADHH condition may result in asymptomatic hypocalcaemia, but some affected family members have minor symptoms, and a minority experience seizures in infancy which can recur into adulthood. A significant proportion of cases previously reported as idiopathic hypoparathyroidism (IHP) may in fact be due to mutations in the CaSR gene. In a moderately hypocalcaemic patient with no other clearly discernible cause, an elevated urine calcium:creatinine ratio is suggestive of ADHH, as is the presence of a first-degree relative with hypocalcaemia. If treatment with vitamin D analogues is undertaken, serum and urine calcium should be monitored, advice which applies equally to ADHH and IHP.

Wilson's disease: acute and presymptomatic laboratory diagnosis and monitoring

Wilsons disease, the most common inherited disorder of copper metabolism, is a recessive genetic condition. The clinical presentation of Wilsons disease is very variable. It is characterised by low serum copper and caeruloplasmin concentrations coupled with the pathological accumulation of copper in the tissues. However, there are diagnostic difficulties and these are discussed. The current value of DNA diagnosis, both in gene tracking in families or as applied to de novo cases, is examined. Wilsons disease can be treated successfully but treatment must be life long. Patients are best treated by specialist centres with experience and expertise in the condition.

Genetic variation in the cholesteryl ester transfer protein and apolipoprotein A-I genes and its relation to coronary heart disease in a Sri Lankan population

The influence of variation in the genes for cholesteryl ester transfer protein and apolipoprotein A-I was investigated in 95 patients with coronary heart disease and 95 matched control subjects of South East Asian extraction. Restriction fragment length polymorphisms (RFLPs) linked to the cholesteryl ester transfer protein gene TaqIA and TaqIB, and to the apolipoprotein A-I gene SstI, were examined to investigate the extent of genetic variation at these loci. None of the alleles defined by these RFLPs were associated with increased coronary risk. Analysis of the data by division of high density lipoprotein-cholesterol levels into tertiles showed a trend of a higher frequency of B1 allele (presence of the TaqIB site) with reduced high density lipoprotein levels. The B1 allele was more frequent in control subjects, with low high density lipoprotein levels (P less than 0.02), but not in coronary heart disease patients. The differences became significant for both groups (P less than 0.05) when the data of non-smokers were analysed separately.

Apolipoprotein E and cholesteryl ester transfer protein polymorphisms in normal and preeclamptic pregnancies

OBJECTIVES To evaluate the association of apolipoprotein (apo) E polymorphism and a cholesteryl ester transfer protein (CETP) polymorphism (CETP/TaqIB) with preeclampsia and with lipid/lipoprotein profile in pregnancy. MATERIALS AND METHODS A group of 144 normal pregnant women (67 in the third trimester) were compared with 51 cases of preeclampsia in the third trimester of gestation. Apo E and CETP genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism. Serum lipids, lipoproteins and apolipoproteins were evaluated using commercially available kits. LDL size was assessed by gradient gel electrophoresis. RESULTS No differences were found in the distribution of subjects with respect to genotypes, in the apo E and CETP polymorphisms, between control and pathologic groups. In the third trimester of gestation (both control and case groups considered), apo E polymorphism, but not CETP polymorphism, was associated with different lipid and lipoprotein levels. Patients carrying the E2 allele (E2+) presented with significantly lower values of LDL cholesterol (LDLc) compared with carriers of E4 (E4+) and E3/3 individuals. E2+ also presented with the highest triglyceride (TG) level, although this was not statistically significant. On the other hand, HDL cholesterol (HDLc) and apo A-I levels were significantly reduced in E4+, compared with E3/3. Furthermore, E4+ presented with the highest total cholesterol and LDL and therefore LDLc/HDLc and apo B/apo A-I ratios were significantly higher in this group compared with the other two. CONCLUSIONS Neither of our candidate genes showed association with preeclampsia. However, apo E genotype was associated with changes in lipid and lipoprotein profiles in pregnant women.

Polymorphisms in VKORC1 have more impact than CYP2C9 polymorphisms on early warfarin International Normalized Ratio control and bleeding rates.

Poor warfarin control with resultant high International Normalized Ratios (INRs) and bleeding events is most common during the first months of treatment. The effects of genetic polymorphisms at the vitamin K epoxide reductase [VKORC1] and cytochrome P450 2C9 [CYP2C9] loci have been increasingly acknowledged as contributory factors of enhanced warfarin sensitivity. In our prospective, blinded study, 557 patients (49·1% male, mean age 65·4 years, range 18–91 years) commencing warfarin (target INR 2·5) were genotyped and monitored through the first 3 months of anticoagulation. Homozygosity for the −1639 G>A single nucleotide functional promoter polymorphism of the VKORC1 gene (genotype AA; 14·5% of cases) was associated with a significantly shortened time to therapeutic INR ≥ 2 (P < 0·01), reduced stable warfarin dose (P < 0·01), and an increased number of INRs > 5 (P < 0·001) and occurrence of bleeding events (P < 0·01) during the first month, as compared to the GG genotype. CYP2C9 genetic variations *2 and *3 were not associated with significant effect on these factors. Neither VKORC1 nor CYP2C9 polymorphisms influenced these parameters beyond the first month of treatment. These findings imply possible benefits of assessing VKORC1 polymorphisms prior to anticoagulation, particularly as a low dose induction regime in VKORC1 AA individuals appears to reduce the incidence of high INRs.

Comparison of apolipoprotein B metabolism in familial defective apolipoprotein B and heterogeneous familial hypercholesterolemia

Both defective LDL receptors (familial hypercholesterolaemia, FH) and mutations in apolipoprotein B (apoB) on LDL (familial defective apoB, FDB) give rise to a phenotype of elevated LDL cholesterol. We sought to compare the metabolic basis of the two conditions by examining apoB turnover in FDB and FH subjects. A group comprising three heterozygous and one homozygous FDB subjects were compared with five FH heterozygotes and 17 control subjects using a deuterated leucine tracer. Kinetic parameters were derived by multicompartmental modelling. FH heterozygotes had a reduced delipidation rate for VLDL, which led to a moderate increase in plasma triglyceride. Compared with controls and FH, the FDB subjects converted 44% less IDL to LDL. The LDL FCR was reduced to a similar extent in FDB and FH. In all subjects LDL plasma levels appeared to be regulated by the LDL FCR and the rate of production of small VLDL. We conclude that disturbances in IDL metabolism provide the basis for understanding why FDB is less severe than FH. Our findings suggest that an apoB-LDL receptor interaction is important in the IDL to LDL conversion.

Haemochromatosis gene mutations and risk of coronary heart disease: a west of Scotland coronary prevention study (WOSCOPS) substudy

Objectives: To measure the frequency of genotypes of the HFE (haemochromatosis) gene in patients recruited to the west of Scotland coronary prevention study (WOSCOPS), and relate them to the subsequent occurrence of coronary clinical events. Design: Nested case–control study, drawing samples of DNA from the biological bank of a cohort study. Patients: Men aged 45–64 years in 1989, with moderate hypercholesterolaemia and no evidence of coronary heart disease at baseline. Interventions: Follow up for a mean period of 4.9 years. Typing for C282Y and H63D mutations of the HFE gene in 482 subjects with a subsequent coronary event and 1104 without an event. Results: The C282Y mutation was present in 81 of 482 cases (16.8%) and 182 of 1104 controls (16.5%). Comparing the prevalence of gene mutations in the cases and controls, there were no significant differences. The hazard ratio for C282Y heterozygotes was 1.03 (95% confidence interval (CI) 0.77 to 1.36) and for C282Y/H63D compound heterozygotes 1.04 (95% CI 0.50 to 2.14). Prespecified subgroup analyses of the pravastatin, placebo, smoking, and non-smoking groups showed no significant differences between cases and controls. Repeating the analyses after adjusting for possible confounding factors produced no change in the results. Conclusions: In a population of moderately hypercholesterolaemic middle aged Scottish men who did not have any evidence of coronary heart disease at baseline, the presence of a C282Y mutation in the HFE gene did not predict the occurrence of coronary events over a mean follow up of 4.9 years.

Whose TPMT activity is it anyway

Determination of thiopurine S-methyltransferase (TPMT) activity prior to starting azathioprine therapy is used to identify individuals with low or deficient TPMT activities who are at risk of severe complications and even death This case describes a patient treated with azathioprine without prior knowledge of TPMT status. Pancytopaenia developed over several months and at this point TPMT activity was determined and found to be low at 16 nmol 6-methyl thioguanine (6-MTG)/g Hb/h, which is within the reference interval associated with heterozygosity for TPMT mutant alleles. On repeating the TPMT measurement 3 months later, the TPMT activity was 2 nmol 6-MTG/g Hb/h, consistent with deficient TPMT activity (homozygosity for TPMT mutant alleles), suggesting the patient is at high risk of myelosuppression if treated with thiopurine drugs. Retrospectively, it was found that the patient had received transfusions of red blood cell and platelets 6 days before TPMT activity was first measured. This case underlines the importance of determining TPMT activity status prior to azathioprine treatment, rather than taking a dose incrementation approach. It also highlights the caution that must be taken in interpreting TPMT activity in patients who have recently been transfused.