A genome-wide scan for coronary heart disease suggests in Indo-Mauritians a susceptibility locus on chromosome 16p13 and replicates linkage with the metabolic syndrome on 3q27

Prevalence of coronary heart disease (CHD), of type 2 diabetes (T2DM) and of the metabolic syndrome are in Mauritius amongst the highest in the world. As T2DM and CHD are closely associated and have both a polygenic basis, we conducted a 10 cM genome scan with 403 microsatellite markers in 99 independent families of North-Eastern Indian origin including 535 individuals. Families were ascertained through a proband with CHD before 52 years of age and additional sibs with myocardial infarction (MI) or T2DM. Model-free two-point and multipoint linkage analysis were performed using the Mapmarker-Sibs (MLS) and maximum-likelihood-binomial (MLB) programs for autosomal markers and the Aspex program for chromosome X markers. In a second step, additional markers were studied to increase the genetic map density in three regions on chromosomes 3, 8 and 16 where initial indication for linkage was found. Our data show suggestive linkage with CHD on chromosome 16p13-pter with the MLS statistics at 8.69 cM (LOD = 3.06, P = 0.00017) which partially overlaps with a high pressure (HBP) peak. At the same locus, a nominal indication for linkage with T2DM was found in 35 large T2DM Pondicherian families also having Indian origin. With respect to region 8q23, we found suggestive linkage with T2DM (LOD = 2.55, P = 0.00058) as well as with HBP. On 3q27, we replicated previous indication for linkage found in Caucasians (for the metabolic syndrome and for diabetes) according to the categorized trait for CHD and MI with the MLB statistics (LOD = 2.13, P = 0.0009). The genome scan also revealed nominal evidence of linkage with CHD on 10q23 (LOD = 2.06, P = 0.00188). Interestingly, we detected in the same region overlapping linkages with three QTLs: age of onset of CHD (LOD = 2.03), HDL cholesterol (LOD = 1.48) and LDL/HDL ratio (LOD = 1.34). Ordered-subset analysis based on family body mass index ranking replicated finding on 2q37 for T2DM (at Calpain 10 locus). These results show the first evidence for susceptibility loci that predispose to CHD, T2DM and HBP in the context of the metabolic syndrome.

Genetic and environmental nature of the insulin resistance syndrome in Indo-Mauritian subjects with premature coronary heart disease: contribution of beta3-adrenoreceptor gene polymorphism and beta blockers on triglyceride and HDL concentrations

AIMS/HYPOTHESIS

Insulin resistance syndrome is an important risk factor for developing premature coronary heart disease. It is a complex syndrome which could arise from the interaction of several genes modulated by environmental factors. The Trp64Arg polymorphism in the beta3-adrenoreceptor gene has been found to be associated with insulin resistance, obesity or with earlier onset of Type II (non-insulin-dependent) diabetes mellitus in different populations. We aimed to study whether features of the insulin resistance syndrome are associated with this polymorphism in Indo-Mauritian patients with premature coronary heart disease.

METHODS

We carried out a case control study using PCR-RFLP techniques, of consecutive Indo-Mauritian patients (n = 338) with premature coronary heart disease (onset below age of 60 years) and unrelated control subjects (n = 148) of the same ethnicity.

RESULTS

In Indo-Mauritian patients with premature coronary heart disease who were not treated by beta blockers, triglyceride concentrations were lower (median: 1.44 vs 1.93 mmol/l, p < 0.008) and HDL cholesterol concentrations higher (mean: 0.98 vs 0.85 mmol/l, p < 0.015) in those carrying the wild type of the beta3-adrenoreceptor gene than in those carrying the Trp64Arg variant. The latter genotype specific effect on HDL was inverse in patients treated with beta blockers.

CONCLUSION/INTERPRETATION

The beta3-adrenoreceptor gene variant seems to modulate the effects of beta blockers on triglyceride and HDL cholesterol concentrations in this group of Indo-Mauritian population. Dyslipidaemia, a key component of the metabolic syndrome has a heterogeneous nature in Indo-Mauritian subjects. This potent risk factor for early-onset coronary heart disease is influenced by the interaction between genetic and environmental effects.

Mutation screening of the PPARalpha gene in type 2 diabetes associated with coronary heart disease

The peroxisome proliferator-activated receptor alpha (PPARalpha) is a ligand-activated transcription factor belonging to the nuclear hormone receptor superfamily. PPARalpha plays a key role in lipid and glucose metabolism, inflammatory response and energy homeostasis. The aim of our study was to screen the PPARalpha gene for mutations, and to test the genetic contribution of PPARalpha in diabetes and its vascular complications. The first two non coding exons and the coding region of the PPARalpha gene were screened by single strand conformation polymorphism (SSCP) and sequencing in 74 unrelated Type 2 diabetic patients with history of coronary heart disease (CHD) (18 Caucasian and 56 Indian subjects). A total of 7 nucleotide variants were detected: two single amino acid substitutions, a silent mutation, four intron base changes. Association studies were undertaken in two populations of Type 2 diabetic patients from Pondichery and from France, to test the distribution of allelic frequencies for L162V (exon 5) and A268V (exon 7) polymorphisms. No association was found between these PPARalpha variants and diabetes or CHD. However, in the Caucasian diabetic male population with CHD, the Val162 allele carriers showed higher concentrations of total cholesterol and Apo B when compared to non-carriers (p =0.01 and p =0.005, respectively). A trend toward elevated concentrations of total cholesterol and Apo B was also observed in the Caucasian diabetic male patients without CHD carrying Val162 allele. In conclusion, it is likely that PPARalpha gene does not have a major role in diabetes and CHD in our populations, although we can not exclude a minor contribution of the PPARalpha gene to the risk of CHD associated with Type 2 diabetes through a modulation of atherogenic plasma lipids.

Asthma mortality in Mauritius: 1982-1991

BACKGROUND

Bronchial asthma is a common problem in the island of Mauritius and its prevalence seems to be increasing.

OBJECTIVE

In order to appreciate the magnitude of the problem, patterns of asthma mortality were studied during a period of 10 years.

METHOD

All death certificates issued in the island from 1982 to 1991 were reviewed and all cases of asthma deaths were selected.

RESULTS

The global asthma mortality rate was found to be 20/100,000 in 1982, and it decreased to 12/100,000 in 1991. Similarly the asthma death rate for the 0 to 4 year age group decreased from 20/100,000 in 1982 to 5/100,000 in 1991. For the 5 to 34 year age group, it decreased from 2.6/100,000 in 1982 to 1.02/100,000 in 1991. There was no statistically significant difference between the various ethnic groups.

CONCLUSION

Our study showed that in a developing country such as Mauritius asthma death rates may be high but may show decreasing trends. Nevertheless, it is generally perceived that the prevalence of the disease is increasing.

Lack of association of angiotensin I-converting enzyme gene polymorphism and premature myocardial infarction in Mauritian Indians

Eighty-five young Mauritian Indians, male survivors of premature myocardial infarction (MI) and thus belonging to a high risk group, were compared with 108 stringently selected controls for a possible association between premature MI and an insertion/deletion (I/D) polymorphism in the gene encoding angiotensin I-converting enzyme (ACE). The frequency of the D allele was 0.42 in the MI group and 0.43 in the control group, and thus no association between I/D polymorphism of ACE with susceptibility to early-onset MI was found in this population group. Other gene components of the renin-angiotensin system and lipid metabolism need to be explored to understand the genetic factors involved in causing MI at an early age.

A new visual analogue scale for assessment of dyspnoea in congestive heart failure

A new (quality of life) visual analogue scale of dyspnoea has been designed to evaluate the severity of dyspnoea in patients with congestive heart failure (CHF). The index has 10 numerical values, rated on a scale from 0-10, each value corresponding to an intensity of breathlessness. Since dyspnoea is a primary symptom that restricts the quality of life in patients with congestive heart failure, the new scale provided a simple, easily comprehensible and inexpensive instrument to assess the severity of breathlessness. We also report the sensitivity of the visual scale of dyspnoea before and after the administration of intravenous injection of a diuretic (frusemide) in CHF patients.