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The Genetics of Schizophrenia

  • Patrick F Sullivan
  • Published: July 26, 2005
  • DOI: 10.1371/journal.pmed.0020212

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Schizophrenia Adoption Studies

Posted by plosmedicine on 30 Mar 2009 at 23:54 GMT

Author: Jonathan Leo
Position: Associate Professor of Neuroanatomy
Institution: No affiliation was given
E-mail: jleo1@tampabay.rr.com
Submitted Date: May 15, 2006
Published Date: May 25, 2006
This comment was originally posted as a “Reader Response” on the publication date indicated above. All Reader Responses are now available as comments.

Patrick Sullivan cites twin and adoption studies as justification for searching for schizophrenia genes [1]. In his words, "Both adoption and twin studies indicate that the familiality of schizophrenia is due mainly to genetic effects." To support this he provides a table (table 1, p. 615) briefly summarizing these studies. Under Adoption Studies he mentions, "Adoptees with schizophrenia: increased risk in biological vs. adoptive parents (OR = 5.0;95% CL 2.4-10.4)". However, rather than a comparison between biological vs. adoptive parents, the original investigators made comparisons between index biological relatives versus control biological relatives.

In the schizophrenia literature there have been three studies using this design; the lead author of all three was Seymour Kety (1968, 1975, and 1994). All three started with finding people who grew up as adopted children and were later diagnosed with a "schizophrenia spectrum disorder". The goal was to then examine the rate of schizophrenia spectrum disorders among those adoptees' biological family members (with whom they did not grow up) and compare that rate to the rate among the biological relatives of control adoptees, who were not diagnosed with a schizophrenia spectrum disorder [2].

According to Kety himself, a comparison between index adoptees' biological and adoptive relatives is "improper" and "fallacious" [3, p. 964] [4]. Indeed, in Kety's first adoption study (1968) there was no significant elevation of chronic schizophrenia, or of schizophrenia spectrum disorders, among his index biological versus index adoptive relatives. (This is based on the data; the investigators did not make this comparison.)

In addition, Kety and his colleagues did not limit themselves to only looking at parents. If they had done so, their conclusions would have been very different. For instance, in the 1975 study there were 5 index biological relatives diagnosed with chronic schizophrenia, but 4 of these 5 were half-siblings. The other diagnosis was given to a biological parent. In the 1968 Kety study, not a single index biological parent was diagnosed with chronic schizophrenia.

In his conclusion Sullivan says that the treatment of the mentally ill mirrors the humanity of a society. True, yet it then becomes difficult to rationalize the treatment of schizophrenia in this country in light of the World Health Organization studies showing that, doctors in third world countries use less medication yet have a higher success rate than doctors in America. This is well documented in Robert Whitaker's book, "Mad in America: Bad Medicine, Bad Science, and Enduring Mistreatment of the Mentally Ill" [5].

References
1. Sullivan PF (2005) The genetics of schizophrenia. PLoS Med 2(7); e212.
2. Leo J, Joseph J (2002) Schizophrenia: Medical students are taught it's all in the genes, but are they hearing the whole story? Ethical Human Sciences and Services 4:17- 30.
3. Kety SS (1983) Dr. Kety responds [Letter to the editor] American Journal of Psychiatry, 140, 964.
4. Joseph J (2006) The missing gene: Psychiatry, heredity, and the fruitless search for genes. Algora Publishing.
5. Whitaker R (2002) Mad in America: Bad science, bad medicine, and the enduring mistreatment of the mentally ill. Cambridge, MA: Perseus Publishing. 334 p.

Competing interests declared: none