the autonomy of the cycloid psychoses was substantiated by neurophysiological and morphometric studies. in a systematic twin study, he provided evidence that in cycloid psychosis monozygotic pairs had similar concordance rates to dizygotic pairs, pointing to a low heritability. these findings were confirmed by a controlled family study, where first-degree relatives of patients with cycloid psychoses were found to show a similar low frequency of secondary cases to relatives of a population-based control sample.