Ready To Rock
3 weeks ago
The Bipolar Schizophrenic Overlap
Mo's blog linked to this Lancet article. Interest in the much-debated possibility of genetic overlap between schizophrenia and bipolar disorder has been restimulated by molecular genetic studies, which have led to reappraisal of previous evidence from genetic epidemiology. Most previous genetic epidemiological studies have been underpowered to investigate the question of diagnostic overlap. This study, however, included more than 2 million nuclear families; the researchers merged data from the Swedish multigeneration population register and the Swedish hospital discharge register. The results clearly show increased risks of both schizophrenia and bipolar disorder for first-degree relatives of probands with either disorder. Furthermore, evidence from half-siblings and offspring adopted away shows that this is due substantially to genetic factors.
The Kraepelinesque Dichotomy is dead! (I've always wanted to say that.) Kraepelin, as you all know, differentiated what he called Manic-Depressive Insanity from Dementia Praecox (what we now call schizophrenia). In fact, though, Kraepelin later said: No experienced psychiatrist will deny that there is an alarmingly large number of cases in which it seems impossible, in spite of the most careful observation to make a firm diagnosis... it is becoming increasingly clear that we cannot distinguish satisfactorily between these two illnesses and this raises the suspicion that our formulation of the problem may be incorrect. (1920)
Seriously, it has been on the cards for a while. The overlap has been highlighted recently (to my certain knowledge) since at least 1995 (Eysenck: Genius, the Natural History of Creativity - you can read some of the book here - quite interesting, and refreshingly straightforward (why are psychologists more readable than psychiatrists?) though I may have been feeling mildly grandiose when I ordered it from Amazon). Various studies comparing people with schizophrenia and manic depression with the likelihood of their children inheriting either condition: Rosenthal (1970), Penrose (1968), Powell et al (1973), Elsasser (1952), Schulz (1940), Pollock and Maltzberg (1940), Slater (1953), etc, etc, etc... all of these show that one type of illness may beget the other to a significantly higher degree than would be expected by chance (eg, Rosenthal found that the children of manic depressives had a 2.3% chance of being schizophrenic, compared to 0.8% in the general population).
On the other hand - there is evidence that there is a difference between the two conditions. I commented on Mo's blog: "if there were five genes, and four of them (say ABCD) made you schizophrenic and another four (say BCDE) made you bipolar" then it would be easy to see how the shared likelihood of transmission could occur, but still differentiate the two conditions. Some studies, Kant (1942), Weingberg and Lobstein (1943), Vaillant (1962) found that relatives of schizophrenics who didn't recover showed a greater ratio in first degree relatives of schizophrenia to manic depression, compared to relatives of recovered schizophrenics, where the ratio was reversed. The ratios varied between 5:1/1:5 and 7:1/1:7. Studies have been carried out seeing how often different psychiatrists' diagnoses accord with each other. The figures for agreement are generally around 59%. Or on the other hand, 41% of the time, someone gets it wrong. This obviously (?) cannot purely be down to incompetence (thus he prays).
However, this Swedish study seems very large, and hopefully should make more of a splash in the murky waters of the pond.I've rambled on long enough to little purpose. I'll finish with a quote from Eysenck:
"As regards the generality of 'psychosis', it seems clear that there are definite genetic links between different diagnostic categories (schizophrenia, manic-depressive disorder, schizo-affective disorder, unipolar disorder) which make it impossible to regard them as entirely separate disease entities. Some specificity there undoubtedly is, but there is also a generality of disorder which links all these disorders and their sub-classifications and diagnoses together to form one end of the psychoticism continuum, with a severity gradient placing schizophrenia at the extreme end, followed by schizo-affective disorder, manic-depressive disorder and finally unipolar illness."
Back to the schizoaffective spectrum, eh? Or since that was written in the mid 90s, that should be towards the schizoaffective spectrum.P.S. On a brighter note, I hope this will reduce the stigma that gets shoved at schizophrenia. I find it irritates me when I read someone with (say) manic depression 'writing off' people with something 'worse'. Our 'shared heritage' he said, raising an eyebrow in sympathetic amusement, should give us pause.