The genetic aetiology of somatic distress

Background. Somatoform disorders such as neurasthenia and chronic fatigue s yndrome are characterized by a combination of prolonged mental and physical fatigue. This study aimed to investigate the heritability of somatic distr ess and determine whether this dimension is aetiologically distinct from me asures of depression and anxiety. Method. Measures of anxiety, depression, phobic anxiety, somatic distress a nd sleep difficulty were administered in a self-report questionnaire to a c ommunity-based sample of 3469 Australian twin individuals aged 18 to 28 yea rs. Factor analysis using a Promax rotation, produced four factors: depress ion, phobic anxiety, somatic distress and sleep disturbance. Multivariate a nd univariate genetic analyses of the raw categorical data scores for depre ssion, phobic anxiety and depression were then analysed in Mx1.47. Results. Univariate genetic analysis revealed that an additive genetic and non-shared environmental (AE) model best explained individual differences i n depression and phobic anxiety scores, for male and female twins alike, bu t could not resolve whether additive genes or shared environment were respo nsible for significant familial aggregation in somatic distress. However, m ultivariate genetic analysis showed that an additive genetic and non-shared environment (AE) model best explained the covariation between the three fa ctors. Furthermore, 33 % of the genetic variance in somatic distress was du e to specific gene action unrelated to depression or phobic anxiety. In add ition, 74 % of the individual environmental influence on somatic distress w as also unrelated to depression or phobic anxiety. Conclusion. These results support previous findings that somatic symptoms a re relatively aetiologically distinct both genetically and environmentally from symptoms of anxiety and depression.