The Genetic Liability to Disability Retirement: A 30-Year Follow-Up Study of 24,000 Finnish Twins

Abstract

BackgroundNo previous studies on the effect of genetic factors on the liability to disability retirement have been carried out. The main aim of this study was to investigate the contribution of genetic factors on disability retirement due to the most common medical causes, including depressive disorders.MethodsThe study sample consisted of 24 043 participants (49.7% women) consisting of 11 186 complete same-sex twin pairs including 3519 monozygotic (MZ) and 7667dizygotic (DZ) pairs. Information on retirement events during 1.1.1975–31.12.2004, including disability pensions (DPs) with diagnoses, was obtained from the Finnish nationwide official pension registers. Correlations in liability for MZ and DZ twins and discrete time correlated frailty model were used to investigate the genetic liability to age at disability retirement.ResultsThe 30 year cumulative incidence of disability retirement was 20%. Under the best fitting genetic models, the heritability estimate for DPs due to any medical cause was 0.36 (95% CI 0.32–0.40), due to musculoskeletal disorders 0.37 (0.30–0.43), cardiovascular diseases 0.48 (0.39–0.57), mental disorders 0.42 (0.35–0.49) and all other reasons 0.24 (0.17–0.31). The effect of genetic factors decreased with increasing age of retirement. For DP due to depressive disorders, 28% of the variance was explained by environmental factors shared by family members (95% CI 21–36) and 58% of the variance by the age interval specific environmental factors (95% CI 44–71).ConclusionsA moderate genetic contribution to the variation of disability retirement due to any medical cause was found. The genetic effects appeared to be stronger at younger ages of disability retirement suggesting the increasing influence of environmental factors not shared with family members with increasing age. Familial aggregation in DPs due to depressive disorders was best explained by the common environmental factors and genetic factors were not needed to account for the pattern of familial aggregation.

Psychosocial working conditions, occupational groups, and risk of disability pension due to mental diagnoses: a cohort study of 43 000 Swedish twins

“…Moreover, both mental disorders (34)(35)(36) and DP due to mental diagnoses (37,38) have been shown to be moderately heritable in earlier studies. However, whether choice of occupation and, hence, type of working conditions are heritable or not has so far not been studied.…”

Disability pension due to musculoskeletal diagnoses: importance of work-related factors in a prospective cohort study of Finnish twins

“…In addition to these work-related factors, genetic factors and shared family environment contribute to the risk for DP (12,13). These familial factors (that is both genetics and shared environment mainly in childhood) may therefore confound some observed epidemiological associations since these familial effects may influence the characteristics influencing DP due to musculoskeletal diagnoses.…”

Advantages of linking national registries with twin registries for epidemiological research

“…Only two Swedish (Narusyte et al, 2011, Svedberg et al, 2012 and a Finnish study (Harkonmäki et al, 2008) had been conducted before on the phenotypes separately using a twin design. These countries were most likely the first to look into these phenotypes using twins due to their excellent population-and twin registry data.…”

“…As explained above, twin data can be used to investigate to what extent family and rearing environment (C) plays a part in this association. The few genetically informative studies that had been conducted on medical benefits also mostly included individuals older than 40 years (Harkonmäki et al, 2008, Narusyte et al, 2011, Svedberg et al, 2012. Knowledge on etiological factors for medical benefits for young adults was therefore lacking.…”