Evidence, from Combined Segregation and Linkage Analysis, That a Variant of the Angiotensin I-converting Enzyme (ACE) Gene Controls Plasma ACE Levels

The hypothesis of a genetic control of plasma angiotensin I-converting enzyme (ACE) level has been suggested both by segregation analysis and by the identification of an insertion/deletion (I/D) polymorphism of the ACE gene, a polymorphism contributing much to the variability of ACE level. To elucidate whether the I/D polymorphism was directly involved in the genetic regulation, plasma ACE activity and genotype for the I/D polymorphism were both measured in a sample of 98 healthy nuclear families. The pattern of familial correlations of ACE level was compatible with a zero correlation between spouses and equal parent-offspring and sib-sib correlations (.24 +/- .04). A segregation analysis indicated that this familial resemblance could be entirely explained by the transmission of a codominant major gene. The I/D polymorphism was associated with marked differences of ACE levels, although these differences were less pronounced than those observed in the segregation analysis. After adjustment for the polymorphism effects, the residual heritability (.280 +/- .096) was significant. Finally, a combined segregation and linkage analysis provided evidence that the major-gene effect was due to a variant of the ACE gene, in strong linkage disequilibrium with the I/D polymorphism. The marker allele I appeared always associated with the major-gene allele s characterized by lower ACE levels. The frequency of allele I was .431 +/- .025, and that of major allele s was .557 +/- .041. The major gene had codominant effects equal to 1.3 residual SDs and accounted for 44% of the total variability of ACE level, as compared with 28% for the I/D polymorphism.(ABSTRACT TRUNCATED AT 250 WORDS)