Why are some twin pairs concordant for schizophrenia whereas others are not? There must be factors other than genes that contribute to the development of schizophrenia. Another creative way of studying heredity is through adoption studies.
One of the first large adoption studies was the Heston Study in 1966. Heston identified 47 adopted children whose biological mothers had schizophrenia. He compared these children to a group of children from the same foster homes whose biological mothers did not have schizophrenia. Heston found that 16.6 percent of the children of schizophrenic mothers became schizophrenic as adults, compared to none of the control children.
Thus, even though none of the children were raised by schizophrenic parents, the children who had schizophrenia in their biological families were more likely to develop the disorder.
The Genain Quadruplets
Perhaps one of the most remarkable examples of the complex
interaction of genes and environment in schizophrenia is the
case of the Genain Quadruplets. The Genain Quadruplets, four
identical twin girls born in 1930, became a focus of clinical
interest in the 1960s when each sister was diagnosed with
schizophrenia. Genain, a fictitious name used in order to pro-
tect the family’s identity, comes from the Greek term meaning
“dire birth.” The fictitious names of the girls, Nora, Iris, Myra,
and Hester, were chosen to mimic the four letters in NIMH, the
National Institute of Mental Health.
Although one might conclude that the Genains are evidence
of the hereditary nature of schizophrenia, the fact that each
girl’s illness was unique in its symptoms, severity, course, and
outcome confirms that environmental factors are integral to the
disorder’s development. Nora, the firstborn, while identified as
the brightest of the four girls, was hospitalized at 22 and never
lived independently for an extended period of time. Iris, the
second sister, spent 12 years in a psychiatric hospital starting at
the age of 22. Myra, the third sister, is the only one to marry and
have children. It is not certain whether she has schizoaffective
disorder or schizophrenia, and she did not experience delusions
or hallucinations until she was in her forties. Hester, the young-
est sister, is the most severely ill. She was taken out of school in
the eleventh grade and never worked outside the home.
Dr. David Rosenthal and the staff at the National Institute of
Mental Health spent many years following this family. In addi-
tion to the girls, many family members had some form of mental
illness. Mr. Genain, the father of the girls, was paranoid and
most likely an alcoholic. He was frequently unemployed and
was irritable and withdrawn. He was concerned that the girls
would be raped unless he kept them at home. Investigators at
the NIMH believed that Mr. Genain himself raped at least two of
the girls, despite his concern for their innocence. Mrs. Genain
did not appear to interfere on behalf of her daughters and
protect them from the real threat of their father. Mrs. Genain’s
mother, the girls’ grandmother, appeared to have suffered some
form of a “breakdown” and experienced what investigators
believed to be paranoid schizophrenia. The four sisters were
dealt a double blow, a genetic predisposition to schizophrenia
from both sides of the family, and a family environment that
was cruel and stressful.
Another large adoption study is the Danish study by Kenneth Kendler and colleagues that began in the 1980s. Kendler identified adults with schizophrenia who had been adopted when they were infants and compared them to other adoptees who did not have schizophrenia. He found that 13.3 percent of the biological relatives of the schizophrenic adoptees had schizophrenia disorders, compared to 1.3 percent of the relatives of the healthy adoptees. This may be interpreted as even more evidence for a biological component of schizophrenia.
What factors in the environment increase the likelihood that schizophrenia will develop? In 1997 Dr. Karl-Erik Wahlberg and colleagues of the University of Oulu in Finland studied the qualities of the adoptive family to help determine why some children with a biological family history of schizophrenia developed the disorder while others did not. Wahlberg was interested in the way in which adoptive families communicated with one another and studied communication deviance. Family members who use speech that is unclear and difficult to follow are considered to be high in communication deviance. In the Finnish adoption study, biological children of schizophrenic mothers who were raised in adoptive families with high communication deviance were more likely to become schizophrenic than children raised in families with low communication deviance. This evidence suggests that the combination of genes and a stressful family environment makes schizophrenia more likely.
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