T. Lundman

Concordance for mortality with special reference to ischaemic heart disease and cerebrovascular disease. A study on the Swedish Twin Registry.

The Swedish Twin Registry contains about 11 000 same-sexed twin pairs born between 1886 and 1925 with both members alive when the registry was formed in 1961. During the years 1962 to 1973, 2780 deaths occurred. 727 deaths were due to ischaemic heart disease (IHD), 345 due to cerebrovascular disease (CVD), and 727 due to cancer. The rate of concordance for the whole twin population revealed a significantly (p < 0.05) higher concordance rate for IHD among the male monozygotic (MZ) pairs as compared to the dizygotic (DZ) pairs (15.8% versus 8.0%). The corresponding figures for the female pairs were 11.0% (MZ) and 7.5% (DZ), respectively. With regard to death in CVD and cancer, the rates of concordance were about the same for MZ and DZ pairs in both males and females. When subgrouping was made for age groups, the difference in concordance rate for IHD in males was still more pronounced for the younger age group, born 1901–1925, (16.1% versus 5.4%). These data may indicate the existence of a genetic determination on death in IHD, especially in males, whereas a genetic determination on death in CVD and cancer seems more uncertain.

Mortality in Twins in Relation to Smoking Habits and Alcohol Problems

Results are presented from an 11-year study on 9,000 pairs. On a nonpair basis, a significant hypermortality was related to smoking in men and women. Among 706 male dizygotic smoking-discordant pairs born 1901 to 1925, 55 deaths or “first deaths” occurred in a high smoking group, against 31 in a low smoking group. Among 246 corresponding monozygotic male pairs, the numbers were 18 vs 18. For women, the numbers were 42 vs 31 among 781 dizygotic pairs, and 14 vs 13 among 326 monozygotic pairs. The hypermortality was mainly due to coronary heart disease, lung cancer, suicides, and accidents. Nonsmokers were registered at 10% in a nationwide “alcohol registry” as against 30% for high smokers. The mortality among the registered subjects was significantly higher than among the nonregistered, regardless of smoking. Data imply that part of the hypermortality among smokers is not due to smoking per se, but to factors associated with smoking.

Mortality in smoking discordant monozygotic and dizygotic twins. A study on the Swedish Twin Registry.

Among 706 male, dizygotic, smoking discordant twin pairs born in 1901 to 1925, 13 deaths occurred among nonsmokers or less exposed partners against 34 among smokers or more exposed. In 246 corresponding monozygotic pairs the figures were 14 against 9. The excess mortality among male dizygotic smokers was not associated with any specific cause of death. Four cases of lung cancer among males occurred only in smokers. Accidents and suicides seemed to be associated with smoking, supporting the hypotheses regarding differences in personality typebetween smokers and nonsmokers. Only time will show whether trends found are stable. The data suggest, however, that part of the greater mortality in smokers is not due to smoking per se but to factors associated with smoking.

Complex segregation analysis of the Lp(a)/pre-ß1-lipoprotein trait

Complex segregation analysis of the LpCaypre‐β1‐lipoprotein trait in 229 nuclear families gave strong evidence for a major gene with complete dominance for pre‐β+and gene frequency q = 0.10. The penetrance is 0.917. There was no evidence for either polygenic heritability or environment common to sibs.

Biological and cultural determinants of blood pressure.

A path analytic study of blood pressure in Swedish families gave evidence for genetic heritability (0.18 for systolic, 0.13 for diastolic) and for cultural heritability, with evidence for an intergenerational difference giving higher estimates of cultural heritability in adults (0.19 for systolic, 0.08 for diastolic). A maternal effect for cultural inheritance was evident for systolic blood pressure but not for diastolic pressure. (Hypertension 4: 725-728, 1982)

The Validity of the Questionnaire Diagnosis

Validation of a mailed questionnaire concerning angina pectoris has been performed using 69 male twins with the diagnosis “angina pectoris” according to the questionnaire. Of these, 22% could be verified at the clinical examination. If all clinically suspected cases were included together with the cases with a pathological electrocardiogram the confirmation rate was 57%. The confirmation rate was higher, but not significantly so, if the criteria for angina pectoris were altered so that only those with central chest pain were included. The frequency of pathological ECGs in cases with a clinical diagnosis of angina pectoris was significantly higher than in those with a questionnaire diagnosis, which indicates that the validity of the clinical diagnosis is greater. The results indicate that the questionnaire is very useful for screening cases with coronary heart disease. If it is used at prevalence studies or effect studies, one has to be aware of the relatively high frequency of false-positives.