Angiotensin-converting enzyme insertion/deletion polymorphism and cerebrovascular disease

BACKGROUND AND PURPOSE

There is evidence that an allelic variation in the angiotensin-converting enzyme (ACE) gene may confer an increased risk of vascular disease. The roles of the ACE insertion/deletion polymorphism and circulating ACE levels are unknown in cerebrovascular disease.

METHODS

We studied an insertion/deletion polymorphism within intron 16 of the ACE gene by polymerase chain reaction and plasma ACE activity in 467 cases of stroke, the pathological type of which was established by cranial CT, and 231 control subjects. ACE genotype and activity were related to stroke type and mortality at 4 weeks and 3 months.

RESULTS

No difference in genotype frequency was observed between all subjects with stroke and control subjects or between control subjects and subjects with cerebral infarction or cerebral hemorrhage. Plasma ACE activity was significantly lower in stroke patients at presentation (64.1 IU/L) than in control subjects (79.6 IU/L; P<.0001). Twenty-one patients (4.5%) with cerebral infarction died within 4 weeks and 56 patients (12%) within 3 months. These patients had significantly lower plasma ACE activity than patients who survived. There was some evidence that risk of death within 4 weeks increased with the number of D alleles (P=.02). Among survivors, plasma ACE activity showed a mean increase of 6.9 IU/L (95% confidence interval, 3.0 to 10.8) between levels at presentation and at 3 months (73.6 IU/L), the latter being similar to ACE activity in control subjects.

CONCLUSIONS

Low ACE activity at sroke presentation and possession of the D allele may be associated with increased risk of early death from acute cerebral infarction.

Commingling analysis of the distribution of a phenotype conditioned on two marker genotypes: application to plasma angiotensin-converting enzyme levels

Commingling analysis is a statistical method for distinguishing between one (usually normal) distribution and a mixture of two or more distributions. It is used in genetic studies, since one mechanism giving rise to a mixture of distributions is the effect of a major gene. Plasma levels of angiotensin-converting enzyme (ACE) have been shown to be related to an insertion/deletion (I/D) polymorphism in the ACE gene. Recently, Cambien et al. [(1994) Circulation 90:669-676] used commingling analysis in a study of ACE, extending the method to condition on information about the I/D polymorphism in the gene. A further common polymorphism has been discovered recently by our group [Foy et al. (1995) Blood Coagulation Fibrinolysis 6:590] in the promoter region of the gene. In this paper we extend the method of commingling analysis to condition on two marker loci. The method is illustrated by application to plasma ACE levels in subjects for whom genetic information at both the I/D and promoter loci has been recorded. The results confirm strong evidence for a mixture of three normal distributions in preference to one or two, and also show that neither polymorphism is identical to a putative functional polymorphism. To assess the performance of the method, a simulation study was carried out. Parameters may be estimated more efficiently conditioning on two marker loci than on one or none, but this is not always the case if the underlying distributions are well separated. Conditioning on marker loci can increase the power to distinguish between alternative hypotheses of interest.

Analysis of breast cancer pedigrees using affected sibship methods

Haplotype-sharing was examined in sets of affected siblings in the Breast Cancer Linkage Consortium pedigrees [Easton et al., 1993], using both identity-by-descent and identity-by-state methods. Linkage of the disease susceptibility locus to markers on chromosome 17 was confirmed. Substantial genetic heterogeneity was found, with more young cases being attributable to the putative gene. No differences were found between breast and ovarian cancer, and there was no evidence against a simple dominant mode of inheritance.

Genetic mapping based on radiation hybrid data

Radiation hybrid mapping is a recently developed technique for constructing high-resolution maps of mammalian chromosomes. The chromosome of interest is exposed to X rays, which cause it to break into numerous fragments. The fragments are randomly recovered into hamster cells. The resulting hybrids are then analyzed for the presence or absence of DNA markers of interest. A simple method for using this information to order the markers on the chromosome is developed here. For any particular ordering of the loci, the least number of breaks consistent with the data can be determined. The best order is taken to be that which minimizes this number of obligatory breaks. Some statistical properties of the method are examined, both theoretically and by use of a simulation study. Except for some extreme cases, the method gives good results, which compare well with results obtained by a full maximum likelihood analysis. The method is used to order a set of 14 loci on chromosome 21 with encouraging results.

Dosimetric intercomparison in the British Institute of Radiology fractionation study of 3F/week versus 5F/week in radiotherapy of laryngo-pharynx cancer

A dose intercomparison was carried out by the National Physical Laboratory between the seven radiotherapy centres which contributed the largest number of patients to the British Institute of Radiology fractionation study of three fractions per week versus five fractions per week in clinical cancer treatment. Six of the centres showed remarkable agreement within the acceptable limits of error of the measurements. In one centre there appeared to be a physical dose discrepancy of 2.8% which was materially less than could be detected clinically.

An Additional (Third and Separate) Head of the Pronator Teres Muscle

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