A pilot study of sibling resemblance in later life

Behavioural genetic studies of later life are strictly limited. We carried out a community-based pilot study of sibling resemblance with the primary aims of establishing the feasibility of such work in this population and estimating genetic influence on depression and its risk factors.

Data were collected on surviving siblings of individuals interviewed in previous phases of an epidemiological study of the elderly (the Gospel Oak survey); scales relevant to the investigation of late life depression and its risk factors were utilized. Since families tend to be geographically scattered, the interview was conducted by telephone. Comparisons were made between data relating to the siblings and those obtained on the probands. Variability in phenotypic traits and environmental measures was partitioned into between- and within-family variation, in order to distinguish familial and non-familial sources of variation. Intraclass correlations were used to estimate the strength of genetic influences on continuous measures, while pairwise concordances were calculated for dichotomous traits.

Thirty-two siblings from 20 families were ultimately identified and interviewed. Intraclass correlations for the Depression and Dementia Diagnostic Scales and the Handicap Scale were 0, 0.27 and 0.22, respectively. Those for number of life events, number of friends in contact and number of neighbours in contact were 0.08, 0.03 and 0, respectively. Concordance for both depression caseness and dementia caseness was 0.

There were difficulties carrying out this study, which are discussed. The study is the first of its kind to examine familial resemblance for the common disorders of old age. Establishing ways of engaging elderly families with research will be a challenge that future research will need to meet.