J.-M. Lalouel

Haplotypes of Angiotensinogen in Essential Hypertension

The M235T polymorphism of the angiotensinogen gene (AGT) has been associated with essential and pregnancy-induced hypertension. Generation of haplotypes can help to resolve whether the T235 allele itself predisposes to the development of hypertension or acts as a marker of an unknown causal molecular variant. We identified 10 diallelic polymorphisms at the AGT locus and genotyped both a series of 477 probands of hypertensive families and 364 controls, all French Caucasians, as well as a series of 92 hypertensives and 122 controls from Japan. Despite a large ethnic difference in gene frequency, a significant association of T235 with hypertension was observed both in Cancasians (.46 vs. .38, P = .004) and in Japanese (.91 vs. .76, P = .002). In both groups, the G-->A substitution located at position -6 upstream of the initial transcription site occurred at the same frequency and in complete linkage disequilibrium with the T235 allele. No other polymorphism was found to be consistently associated with hypertension. Five informative haplotypes subdividing the T235 allele were generated. Whereas two of them were associated with hypertension in Caucasians, none of these two haplotypes (H3 and H4) reached statistical significance in Japanese. The analysis of the AGT-GT repeat revealed marked linkage disequilibriums between each of the diallelic polymorphisms and some (GT)n alleles, with similar patterns in the two populations. The strong disequilibrium between M235 and (GT)16 explained the increased frequency of that particular allele in French controls compared with hypertensives (.42 vs. .36, P < .01). The haplotype combining the M235T and G-6A polymorphisms appears as the ancestral allele of the human AGT gene and as the one associated with hypertension.

Genotyping and sequence analysis of apolipoprotein E isoforms

Apolipoprotein E (apoE), a polymorphic plasma protein, is essential for catabolism of lipoproteins by receptor-mediated endocytosis. One of the apoE isoforms (E2) differs in its binding affinity to specific receptors and contributes to variations in lipoprotein metabolism. Diagnosis of apoE isoforms is done by isoelectric focusing, but it is hindered by various degrees of post-translational sialylation of the apoE protein. Electrophoretically silent structural variations may also escape detection by this technique. We describe a method for genotyping apoE based on hybridization of allele-specific oligonucleotides with enzymatically amplified genomic DNA, which permits unambiguous diagnosis of six common apoE phenotypes within 24 h. Among 100 E2 alleles present in 81 unrelated individuals genotyped by this technique, we found two rare structural mutants of apoE in addition to the common E2 form, E2(158Arg----Cys). Automated sequencing of amplified DNA identified the rare mutants as E2(136Arg----Ser) and E2(145Arg----Cys). The genotypic method may complement or even replace isoelectric focusing for routine determination of apoE phenotypes and for identification of rare structural variants.

Angiotensin-Converting Enzyme Gene Polymorphism Is Associated With Myocardial Infarction but Not With Development of Coronary Stenosis

BACKGROUND Although both genetic and nongenetic factors contribute to the pathogenesis of coronary artery disease, the identification of specific genetic lesions has lagged behind the identification of critical environmental risk factors. A reported association between myocardial infarction (MI) and the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene in European men suggests a critical role for this genomic region. However, the generality of this association remains to be determined. It also is not clear at what stage in disease progression the association with the ACE I/D polymorphism becomes important. METHODS AND RESULTS We evaluated the ACE I/D polymorphism in patients who had undergone coronary angiography (402 men and 295 women) and in 203 representative control subjects. After polymerase chain reaction amplification, genotypes were determined by agarose gel sizing and by hybridization with allele-specific oligonucleotides. After patients were categorized by the degree of coronary artery stenosis and the occurrence of an MI, the distribution of ACE I/D genotypes was evaluated by log linear analysis. Patients were genetically representative of the regional population, and patients with > 60% stenosis of their coronary arteries had the same distribution of ACE I/D genotypes as did patients with < 10% stenosis. However, among patients with stenosis, the occurrence of an MI was significantly associated with the D allele in all patients (odds ratio [OR], 1.59; P = .002) and in men alone (OR, 1.63; P = .006). The lack of significance in women (OR, 1.40; P = .263) is probably due to the fact that only 36 women in the present study had experienced an MI. Furthermore, the association between MI and the ACE I/D polymorphism was independent of blood pressure, smoking habits, and body mass index. CONCLUSIONS Segregation of the ACE I/D polymorphism is a pervasive genetic risk factor for MI in whites but has no evident effect on the events leading to stenosis of the coronary arteries. This suggests that risk of MI is influenced by two independent processes--atherogenesis that leads to coronary stenosis followed by conversion to MI. The renin-angiotensin system appears to confer significant risk of infarction by influencing the conversion to MI but has no apparent effect on the development of atherostenosis.

A primary genetic linkage map for human chromosome 12.

A primary genetic map for human chromosome 12 has been constructed from data on 23 restriction fragment length polymorphic systems collected in 38 normal families with large sibships. Linkage analysis of the genotypic data has ordered 16 loci into a continuous genetic map of 111 cM in males and 258 cM in females. Although most of the genetic map reflects a higher rate of recombination in females relative to males, significantly more frequent recombination was observed in males than in females in intervals between loci on the distal portion of the short arm of the chromosome. The mapping data shown here will serve as a first step toward a high-resolution genetic map for human chromosome 12.

Genetic linkage between lipoprotein(a) phenotype and a DNA polymorphism in the plasminogen gene

Coronary heart disease risk correlates directly with plasma concentrations of lipoprotein(a) (Lp(a)), a low-density lipoprotein-like particle distinguished by the presence of the glycoprotein apolipoprotein(a) (apo(a)), which is bound to apolipoprotein B-100 (apoB-100) by disulfide bridges. Size isoforms of apo(a) are inherited as Mendelian codominant traits and are associated with variations in the plasma concentration of lipoprotein(a). Plasminogen and apo(a) show striking protein sequence homology, and their genes both map to chromosome 6q26-27. In a large family with early coronary heart disease and high plasma concentrations of Lp(a), we found tight linkage between apo(a) size isoforms and a DNA polymorphism in the plasminogen gene; plasma concentrations of Lp(a) also appeared to be related to genetic variation at the apo(a) locus. We found free recombination between the same phenotype and alleles of the apoB DNA polymorphism. This suggests that apo(a) size isoforms and plasma lipoprotein(a) concentrations are each determined by genetic variation at the apo(a) locus.

Lipoprotein lipase and hepatic triglyceride lipase: molecular and genetic aspects

Lipoprotein lipase and hepatic triglyceride lipase exert their actions at critical stages of the catabolism of plasma lipoproteins. Structural or biochemical studies of normal enzymes and molecular analyses of enzyme deficiencies unraveling a growing number of lesions should ultimately help clarify

Isolation and mapping of a polymorphic DNA sequence pMCK2 on chromosome 10 [D10S15]

REFERENCES: 1. Y. NaXamura et al., Science 235: 1616-1622 (1987) 2. G.M. Lathrop et al., Am. J. Hum. Genet. 37:482-498 (1985) 3. K.-H. Grzeschik and H.H. Kazazian, Cytogenet. Cell Genet. 40:179-205 (1985) 4. M. Litt et al., Nucleic Acids Research 15:2783 (1987) 5. G.I. Liou et al., Nucleic Acids Research 15:3196 (1987) 6. Y. Nakamura et al., abstract submitted to Human Gene Mapping Workshop 9. Cytogenet. Cell Genet., in press