Utilizing twins as controls for non-twin case-materials in genome wide association studies

Changes in self-reported sleep duration with age - a 36-year longitudinal study of Finnish adults

BACKGROUND

Sleep deprivation is often claimed to be increasingly common, but most studies show small changes in sleep duration over the last decades. Our aim was to analyze long-term patterns in self-reported sleep duration in a population-based cohort.

METHODS

Members of the Older Finnish Twin Cohort have responded to questionnaires in 1975 (N = 30,915 individuals, response rate 89%, mean age 36 years), 1981 (24,535, 84%, 41 years), 1990 (12,450, 77%, 44 years), and 2011 (8334, 72%, 60 years). Weibull regression models were used to model the effects of follow-up time and age simultaneously.

RESULTS

Sleep duration has decreased in all adult age groups and in both genders. The mean duration was in men 7.57 h in 1975 and 7.39 in 2011, and in women 7.69 and 7.37, respectively. The decrease was about 0.5 min in men and 0.9 in women per year of follow-up. In the age-group 18-34 years, mean sleep length was 7.69 h in 1975 and 7.53 in 1990. Among 35-54-year-old it was 7.57 h in 1975 and 7.34 in 2011, and in the age group of 55+ year olds 7.52 and 7.38, correspondingly. The change was largest in middle-aged group: about 23 min or about 0.6 min per year of follow-up.

CONCLUSIONS

There has been a slight decrease in mean sleep duration during the 36-year follow-up. Although the sleep duration was longer in 1970s and 1980s, the probable main cause for the change in this study population is the effect of aging.

A psychometric validation study of the Impulsive-Compulsive Behaviours Checklist: A transdiagnostic tool for addictive and compulsive behaviours

The occurrence of repetitive behaviours that are often harmful has been attributed to traits traditionally described as "impulsive" or "compulsive" e.g. substance dependence, excessive gambling, and hoarding. These behaviours are common and often co-occur in both the general population and psychiatric populations. The lack of measures to concurrently index a range of such behaviours led to the development of the Impulsive-Compulsive Behaviours (ICB) Checklist. This study aims to validate the ICB Checklist in a general community sample. Factor analyses revealed a two-factor structure, demonstrating good model fit in two independent samples. These were labelled Impulsive-Compulsions and Compulsive-Impulsions, comprising of classically compulsive and impulsive behaviours respectively. Reliability and construct validity were further confirmed using correlations with existing measures of impulsivity and compulsivity. Results suggest that the ICB Checklist is a valid and practical assessment that can be used to monitor behavioural clusters characterised by deficits in inhibition.

Heritability assessment of cartilage metabolism. A twin study on circulating procollagen IIA N-terminal propeptide (PIIANP)

OBJECTIVE

The aim of this investigation was to estimate the heritability of circulating collagen IIA N-terminal propeptide (PIIANP) by studying mono- and dizygotic healthy twin pairs at different age and both genders.

DESIGN

598 monozygotic (MZ) and dizygotic (DZ) twin individuals aged 18-59 years were recruited from the Danish Twin Registry. PIIANP was measured by competitive ELISA. The similarity of circulating PIIANP among MZ and DZ twins was assessed by intraclass correlations according to traits. The heritability was estimated by variance component analysis accounting for additive and dominant genetic factors as well as shared and non-shared environment but ignoring epistasis (genetic inter-locus interaction) and gene-environment interaction.

RESULTS

The intraclass correlation of PIIANP in MZ and DZ twins was 0.69 (0.60-0.76) and 0.46 (0.34-0.58) respectively indicating a significant genetic impact on PIIANP in serum. Additive genetic effects explained 45% (21-70%), shared environment 24% (7-53%) and non-shared environment 31% (24-39%) of the total variance. The heritability estimate did not differ across ages and between genders.

CONCLUSIONS

The study shows that approximately 45% of the collagen IIA synthesis as assessed by the collagen IIA N-terminal propeptide in serum is attributable to genetic effectors while individual and shared environment account for 24% and 31% respectively. The heritability does not differ between genders or according to age.