Rhena Delport

The effect of a subnormal vitamin B-6 status on homocysteine metabolism.

Homocysteine, an atherogenic amino acid, is either remethylated to methionine or metabolized to cysteine by the transsulfuration pathway. The biochemical conversion of homocysteine to cysteine is dependent upon two consecutive, vitamin B-6-dependent reactions. To study the effect of a selective vitamin B-6 deficiency on transsulfuration, we performed oral methionine load tests on 22 vitamin B-6-deficient asthma patients treated with theophylline (a vitamin B-6 antagonist) and 24 age- and sex-matched controls with a normal vitamin B-6 status. Both groups had normal circulating vitamin B-12 and folate concentrations. Methionine loading resulted in significantly higher increases in circulating total homocyst(e)ine (P < 0.01) and cystathionine (P < 0.05) concentrations in vitamin B-6-deficient patients compared with controls. 6 wk of vitamin B-6 supplementation (20 mg/d) significantly (P < 0.05) reduced post-methionine load increases in circulating total homocyst(e)ine concentrations in deficient subjects, but had no significant effect on the increase in total homocyst(e)ine concentrations in controls. The increases in post-methionine load circulating cystathionine concentrations were significantly (P < 0.01) reduced in both groups after vitamin supplementation. It is concluded that a vitamin B-6 deficiency may contribute to impaired transsulfuration and an abnormal methionine load test, which is associated with premature vascular disease.

Assessment of professionalism: Recommendations from the Ottawa 2010 Conference

Over the past 25 years, professionalism has emerged as a substantive and sustained theme, the operationalization and measurement of which has become a major concern for those involved in medical education. However, how to go about establishing the elements that constitute appropriate professionalism in order to assess them is difficult. Using a discourse analysis approach, the International Ottawa Conference Working Group on Professionalism studied some of the dominant notions of professionalism, and in particular the implications for its assessment. The results presented here reveal different ways of thinking about professionalism that can lead towards a multi-dimensional, multi-paradigmatic approach to assessing professionalism at different levels: individual, inter-personal, societal–institutional. Recommendations for research about professionalism assessment are also presented.

Frequency Distributions of Apolipoprotein(a) Kringle IV Repeat Alleles and Their Effects on Lipoprotein(a) Levels in Caucasian, Asian, and African Populations: The Distribution of Null Alleles Is Non-Random

A size polymorphism (K IV VNTR) and largely unknown sequence variation in the apolipoprotein(a) [apo(a)] gene on chromosome 6q26–q27 together determine most of the extreme variation in apo(a) glycoprotein expression and lipoprotein(a) [Lp(a)] plasma concentration in Caucasians. We have determined Lp(a) plasma concentrations, the number of kringle IV (K IV) repeats in the apo(a) gene and the expression of the apo(a) glycoprotein in four ethnic groups (Khoi San, South African Blacks, Hong Kong Chinese and Caucasians from the Tyrol, total n = 788). The distributions of Lp(a) concentrations, the frequencies of expressed and non-expressed apo(a) K IV alleles, and the impact of the size polymorphism on Lp(a) concentrations were all heterogeneous across populations. In contrast, the effect of the K IV repeat alleles appeared homogeneous. Lp(a) concentrations were higher in Africans and Chinese than in Caucasians, but this was not explained by differences in K IV repeat allele frequencies among populations. Lp(a) concentrations were highest in Khoi San, suggesting that high Lp(a) is an old African trait. When expressed as Spearman rank correlations the impact of the size polymorphism was smallest in African Blacks (R = −0.386) and largest in the Chinese (R = −0.692). In all four populations, the distribution of non-expressed apo(a) alleles was non-random. Rather they were significantly associated with distinct size alleles and overall positively with high K IV repeat numbers. The negative correlation of K IV repeat length with Lp(a) concentration was nonlinear in Khoi San and the average apo(a)-size-allele-associated Lp(a) concentrations were markedly different between all populations. We conclude that besides the apo(a) size variation, other factors affect Lp(a) concentrations to different degrees in the study populations. Most likely, this is sequence variation in apo(a) which is not the same in the different ethnic groups.

Evaluation of next generation mtGenome sequencing using the Ion Torrent Personal Genome Machine (PGM).

Insights into the human mitochondrial phylogeny have been primarily achieved by sequencing full mitochondrial genomes (mtGenomes). In forensic genetics (partial) mtGenome information can be used to assign haplotypes to their phylogenetic backgrounds, which may, in turn, have characteristic geographic distributions that would offer useful information in a forensic case. In addition and perhaps even more relevant in the forensic context, haplogroup-specific patterns of mutations form the basis for quality control of mtDNA sequences. The current method for establishing (partial) mtDNA haplotypes is Sanger-type sequencing (STS), which is laborious, time-consuming, and expensive. With the emergence of Next Generation Sequencing (NGS) technologies, the body of available mtDNA data can potentially be extended much more quickly and cost-efficiently. Customized chemistries, laboratory workflows and data analysis packages could support the community and increase the utility of mtDNA analysis in forensics. We have evaluated the performance of mtGenome sequencing using the Personal Genome Machine (PGM) and compared the resulting haplotypes directly with conventional Sanger-type sequencing. A total of 64 mtGenomes (>1 million bases) were established that yielded high concordance with the corresponding STS haplotypes (<0.02% differences). About two-thirds of the differences were observed in or around homopolymeric sequence stretches. In addition, the sequence alignment algorithm employed to align NGS reads played a significant role in the analysis of the data and the resulting mtDNA haplotypes. Further development of alignment software would be desirable to facilitate the application of NGS in mtDNA forensic genetics.

Hyperhomocysteinemia and the response to vitamin supplementation.

SummaryThe long-term vitamin requirements of men (n=22) with moderate hyperhomocysteinemia (plasma total homocysteine concentration > 16.3 μmol/1) were investigated over a period of 48 weeks. An initial 6-week period of vitamin supplementation (1.0 mg folic acid, 10 mg pyridoxine, 0.05 mg cyanocobalamin) reduced plasma homocysteine levels 54.7% (P<0.001). However, 18 weeks after vitamin therapy was discontinued, only seven participants (subgroup A) still had plasma homocysteine levels of 16.3 μmol/l or lower. The remainder of the participants (subgroup B) required a second 6-week period of vitamin therapy to normalize the elevated plasma homocysteine levels. Substitution of vitamin supplementation by dietary guidelines to increase folate intake from food products failed to maintain normal plasma homocysteine levels in participants from subgroup B. Long-term vitamin supplementation may be required in some individuals to prevent hyperhomo-cysteinemia.

High frequency of the apo ɛ4 allele in Khoi San from South Africa

Variation at the apolipoprotein E (apo E) gene locus affects cholesterol concentrations, the risk for atherosclerosis and Alzheimer disease (AD), and is associated with longevity in Caucasians. We have determined apo E gene frequencies and effects on cholesterol levels in Khoi San (Bushmen) from South Africa. The frequency of the apo ɛ4 allele (0.37), which confers dose-dependent susceptibility to atherosclerosis and AD in Caucasians, was twice as high, and apo E4 homozygotes were 3–5 fold more frequent in the Khoi San (≈ 10%) compared with Caucasians (2%–3%). No significant effect of apo E variation on cholesterol concentration was noted in this non-Westernized population with low plasma cholesterol (mean cholesterol 149 mg/dl). This suggests that Bushmen carry a heavy genetic burden for these late-onset disorders if exposed to a Western lifestyle.

The effect of Simvastatin on the plasma antioxidant concentrations in patients with hypercholesterolaemia

The aim of this study was to monitor the antioxidant status of patients with hypercholesterolaemia during treatment with Simvastatin. Forty-seven patients, of whom 25 had confirmed familial hypercholesterolaemia (FH), were treated with 10 or 20 mg of Simvastatin per day for 14 weeks. As expected, total cholesterol and LDL cholesterol concentrations decreased considerably, while HDL cholesterol concentrations increased during drug treatment. In neither FH nor non-FH patients were any significant changes observed for retinol status, while plasma vitamin C concentrations were also not adversely affected by the drug therapy. In both patient groups Simvastatin therapy led to a significant decrease in plasma alpha-tocopherol (P < 0.05) concentrations, however, the alpha-tocopherol/total cholesterol ratio increased by 9.1 (P < 0.01) and 12.1% (P < 0.01) in FH and non-FH patients, respectively, during the 14-week treatment period. The coenzyme Q10/total cholesterol ratio did not change significantly in non-FH patients, but was significantly lower (P < 0.05) than the baseline ratio after 4 and 14 weeks of Simvastatin treatment in FH patients. The alpha-tocopherol/total cholesterol ratio of FH patients remained consistently and significantly lower (P < 0.01) compared with non-FH patients, indicating that LDL from the former group may be more vulnerable to free radical-mediated damage and lipid peroxidation. Our results suggest that the significant decline in circulating alpha-tocopherol and coenzyme Q10 concentrations was mainly a function of the decrease in serum total cholesterol concentrations.

Folate status, homocysteine metabolism, and methylene tetrahydrofolate reductase genotype in rural South African blacks with a history of pregnancy complicated by neural tube defects.

The birth incidence of neural tube defects (NTDs) in South Africa is threefold to sixfold higher in rural compared with urban blacks. We investigated whether folate deficiency and aberrant homocysteine metabolism could explain the high NTD incidence in rural black populations. Plasma folate and total homocyst(e)ine (tHcy) concentrations were determined in apparently healthy rural black women (n = 107), rural black women with a history of pregnancy complicated by NTDs (n = 54), and urban blacks (n = 101). Methionine load tests were performed on the 54 women with a history of NTD-affected pregnancy and 54 controls matched for age and body mass. The presence of the 677C --> T mutation in the methylene tetrahydrofolate reductase (MTHFR) gene was investigated in both groups by a polymerase chain reaction (PCR) of genomic DNA and HinfI digestion of the PCR product. Apparently healthy urban black women (n = 101) had a lower (P < .001) plasma folate concentration compared with rural black women (n = 107). Women with a history of NTD-affected pregnancy did not differ significantly from controls with respect to plasma folate, fasting homocyst(e)ine, methionine, and the post-methionine load increase in plasma homocyst(e)ine. More than 50% of both of the latter groups had a post-methionine load increase in plasma tHcy less than the fifth percentile as observed in a healthy white control group. No homozygotes for the 677C --> T mutation in the MTHFR gene were found in black mothers with NTD-affected offspring or controls. It is concluded that black urbanization is characterized by a diminished folate status that is paradoxically associated with a lower NTD birth incidence. Homozygosity for the 677C --> T mutation in the gene coding for MTHFR does not constitute a genetic risk factor for NTDs in blacks. No aberrant homocysteine metabolism could be demonstrated in black women with NTD-affected pregnancies.

Ethnic immunity to coronary heart disease

Dietary fat intake is often regarded as a major determinant of coronary heart disease (CHD) rate and it has been deemed unnecessary to invoke racial or other factors to explain the differences in CHD rates among different ethnic groups. Despite a high prevalence of CHD risk factors such as hypertension, obesity, and smoking, CHD remains a rarity in westernized black Africans. Cord blood total cholesterol (TC), low density lipoprotein cholesterol (LDLC) and apolipoprotein B (apo B) levels were measured and found to be respectively 12.1%, 18.3% and 22.4% lower in black neonates when compared to white neonates. These differences were again studied in a group of young black African males and a comparable group of age-matched whites who had been exposed to the same environment and western diet for at least 2 years. Although the body mass indices and serum albumin concentrations in the adult males were not significantly different, serum levels of TC, LDLC and apo B were 10.7%, 18.7% and 39.7% lower in the blacks, respectively. Furthermore, high density lipoprotein cholesterol (HDLC) and Apolipoprotein AI were 20.2% and 9.5% higher, homocysteine 45.6% lower and coagulation factor VII 26.6% lower in the adult black Africans. It is concluded that blacks are biochemically less responsive to an atherogenic diet than whites and these differences are already present at birth.

Simultaneous exposure to low concentrations of dichlorodiphenyltrichloroethane, deltamethrin, nonylphenol and phytoestrogens has negative effects on the reproductive parameters in male Spraque-Dawley rats

Many reports suggest that male reproductive health has deteriorated over the last decades, possibly due to environmental contaminants that act as endocrine disruptors. This hypothesis was tested in Sprague‐Dawley rats using a modified Organization for Economic Cooperation and Development 415 one‐generation test. Group A received cottonseed oil as control, and Groups B, C and D received deltamethrin (DM); DM and dichlorodiphenyltrichloroethane (DDT); and DM, DDT, phytoestrogens and p‐nonylphenol, respectively. Rats were exposed in utero and then received the substances for 10 weeks. The seminal vesicle mass (Group B; P = 0.046) and sperm count [Groups C (P = 0.013) and D (P = 0.003)] were lower and the anogenital distance [Group B (P = 0.047) C (P = 0.045) and D (P = 0.002)] shorter compared with the control group. The seminiferous tubule diameter [Groups B (P = <0.001), C (P = <0.001) and D (P = <0.001)] and epithelium thickness [Groups B (P = 0.030), C (P = <0.001) and D (P = <0.001)] were smaller compared with the control. The histology of the testes showed signs of apical sloughing and vacuolisation. Liver weights [Groups C (P = 0.013) and D (P = 0.005)] and liver enzymes [Group D (P = 0.013)] were also affected. These findings may indicate that simultaneous exposure to endocrine disrupting compounds contributes to the deterioration observed in male reproductive health.