Sleep bruxism based on self-report in a nationwide twin cohort

The relative roles of genetic and environmental factors in bruxism are not known. In 1990 a questionnaire sent to the Finnish Twin Cohort yielded responses from 1298 monozygotic and 2419 dizygotic twin pairs aged 33–60 years. We used structural equation modelling to estimate genetic and environmental components of variance in the liability to bruxism. There was a significant gender difference both in childhood (P =0.001) and adult (P =0.007) bruxism. Females compared to males reported childhood bruxism ‘often’ 5.2% vs 4.1% and ‘sometimes’ 17.4% vs 17.3%, and as adults ‘weekly’ 3.7% vs 3.8% and ‘monthly’ 3.9% vs 4.6%, respectively. Bruxism in childhood and adulthood is highly correlated (0.86 in males and 0.87 in females). The proportion of total phenotypic variance in liability to bruxism attributed to genetic influences in childhood bruxism was 49% (95% CI 37–60%) in males and 64% (55–71%) in females, and for adults 39% (27–50%) among males and 53% (44–62%) among females. The correlation between the genetic effects on childhood bruxism and the genetic effects on adult bruxism was estimated in a bivariate model to be 0.95 (95% CI 0.94–0.96) in males and 0.89 (0.88–0.90) in females. Bruxism appears to be quite a persistent trait. There are substantial genetic effects on bruxism both in childhood and as adults, which appear to be highly correlated.     

Daytime sleepiness in an adult, Finnish population

Hublin C, Kaprio J, Partinen M, Heikkilä K, Koskenvuo M (Departments of Psychiatry and Neurology and the Department of Public Health (The Finnish Twin Cohort), University of Helsinki, Helsinki; and the Department of Public Health, University of Turku, Turku; Finland). Daytime sleepiness in an adult, Finnish population. J Intern Med 1996; 239: 417–23.
Objectives. To investigate the prevalence of and the factors associated with daytime sleepiness occurring every or almost every day.
Design. A cross-sectional, questionnaire survey.
Subjects. A total of 11354 adults (aged 33–60 years) representative of the Finnish population.
Main outcome measures. Frequency of daytime sleepiness, naps and sleep attacks; occurrence of emotion-associated muscle weakness, sleep debt, insomnia, sleep apnoeas and type of snoring; Beck Depression Inventory score; and the use of hypnotics and tranquillisers.
Results. A total of 11.0% of women and 6.7% of men suffered from daytime sleepiness every or almost every day. Amongst those with sleepiness ( n = 1026) 19.5% of women and 42.3% of men reported snoring 3 nights per week, 25% had scores suggesting moderate to severe depression, 11% used hypnotics or tranquilizers on more than 180 days per year, and 9% reported insufficient sleep. Insomnia at least every other day was reported by 20.7% of women and by 28.6% of men. Amongst those with sleepiness, narcolepsy was found in 0.3%, with the diagnosis confirmed in a sleep laboratory evaluation.
Conclusions. Daytime sleepiness occurring daily or almost daily is most often associated with depression, insomnia and sleep-disordered breathing. In most cases, indications of the cause of sleepiness can be obtained by using simple screening questions.     

ALCOHOL-RELATED DISEASES ASSOCIATED WITH ISCHAEMIC HEART DISEASE: A THREE-YEAR FOLLOW-UP OF MIDDLE-AGED MALE HOSPITAL PATIENTS

Mortality and morbidity from ischaemic heart disease (IHD) wasstudied in 5404 Finnish males aged 35–64 years who hadbeen hospitalised for alcohol-related disease in 1972 withoutany admissions for IHD during that same period. By record-linkage,morbidity and mortality were followed up to the end of 1975.The mortality of patients with alcohol-related diseases wascompared to 1120 patients with acute appendicitis by calculatingindirectly age-standardised mortality ratios (SMR). The mortalityand morbidity of 5963 patients with acute myocardial infarctionor angina pectoris was also studied. The following SMRs forIHD mortality, non-fatal-MD-hospitalisation and for mortalityfrom all causes respectively, were found: acute myocardial infarction11.6, 7.2 and 7.2; alcohol intoxication 6.0, 4.5 and 4.5; anginapectoris 5.2, 10.5 and 3.4; liver cirrhosis 2.2, 2.5 and 11.8;alcoholism 1.9, 1.9 and 3.6; pancreatitis 1.8, 1.2 and 4.4;alcohol psychosis 1.7, 2.5 and 4.2. IHD mortality and morbidityappeared to be more prevalent in patients hospitalised withalcohol intoxication than in patients with other alcohol-relateddiseases. This suggests that rapid drinking predisposes bothto serious intoxication and to fatal disturbances of cardiacrhythm     

Hay fever, asthma and number of older siblings — a twin study

Background It has been suggested that allergic sensitization is inversely related to the number of siblings in the family. Objectives To study whether a similar relation can be observed for hay fever and asthma among Finnish adolescents in a population with relatively low prevalence of atopic diseases. Methods A questionnaire mailed to a nationwide sample of 1849 families with 16-year- old twins assessing the cumulative incidence of doctor-diagnosed hay fever and asthma among the adolescents and the number of older siblings in the family by parental report. Results The cumulative incidence of hay fever was significantly lower among the adolescents with three or more older siblings (3.9%, 95% CI= 1.2–6.5%) compared with adolescents with fewer older siblings (12.7%, 95% CI=11.4–14.0%). There was no difference in the cumulative incidence of asthma among the adolescents according to the number of older siblings in the family. Conclusions Large number of older siblings appears to be protective against the development of hay fever.     

Narcolepsy-like symptoms among adult twins

The genetic architecture of narcolepsy is poorly known. Genetic and environmental components of symptoms characteristic of narcolepsy, excessive sleepiness and cataplexy were assessed in a population-based sample of middle-aged like-sexed twin pairs. Questionnaire assessment of the 11-item Ullanlinna Narcolepsy Scale (UNS), a validated screening instrument for narcolepsy [ J. Sleep Res . (1994) 3 , 52–59] and two subscales (sleepiness and cataplexy-like symptoms) was obtained from both twins of 3785 pairs aged 33–60 y (541 male MZ pairs, 1089 male DZ pairs, 781 female MZ and 1374 female DZ pairs) from the population-based Finnish Twin Cohort. For the UNS scores, the intraclass correlation for male MZ pairs was 0.365 and for male DZ pairs 0.072, while for female pairs the MZ correlation was 0.375 and for DZ pairs 0.155. Structural equation model fitting indicated that a model with additive and non-additive genetic effects, and idiosyncratic environmental effects best accounted for the pattern of twin resemblance in both men and women. Genetic effects accounted for 35% (in men) and for 39% (in women) of total phenotypic variance in UNS. Analysis of the subscales suggested that there may be a greater genetic component to the sleepiness subscale, while environmental components play more of a role in the development of cataplexy-like symptoms. Further investigation of the complex genetic architecture of narcolepsy and its symptoms is warranted.