Abstract
differing diagnosticcriteria. In a systematictwin study (47 same-sex pairs, 22 monozygotic-25 dizygoticpairs) with index-twinsbelonging to psychosesof the schizophrenicspectrum,we investigatedtwin concordancerates, family loadingwith psychosesand frequencyand severity of birth complicationsbased on Leonhard’snosology.The Leonhardclassification is a highlyoperationalizeddiagnosticsystem dealing with hierarchical symptom clusters. Interrater reliability among experiencedpsychiatrists is about Kappa 0.9. The results of the twin study point to the existence of three genetically different groups: cycloid psychoses,unsystematicand systematic schizophrenias. In cycloid psychosis genetic loading is subordinate (pairwise concordance:MZ2770,DZ 18Yo) but birth complicationsmayhave an important role in the etiology. Unsystematic schizophrenias are predominantlyinherited (pairwise concordance:MZ 82%, DZ 25%) and “environmental”factors are not very prominent. Interestingly, MZ twins with a diagnosisof systematic schizophreniahave not yet heen found, whereas 24% of DZ index-twins (p<.001) received a diagnosis of systematic schizophrenia.All of the latter were discordant and the ill twins had threefold more and severe birth complications than their healthy partners.
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