heritability of schizophrenia

Mike Miller mbmiller at SIRRONALD.WUSTL.EDU
Wed May 22 10:55:39 EST 1996

On Mon, 20 May 1996, Irina Razin wrote (regarding schizophrenia in both
families of a man and women considering marriage):

> They haven't actually gotten married yet, and this genetic problem is
> important for their decision.
> Father's side: his grandfather's son (from another woman, NOT from his
> grandmother) is very seriously ill. The grandfather himself is not
> really ill and was very successful in life (was managing a 100 people
> company), but in private life he is very annoying and has obsessive
> ideas. Both the father in question and his grandfather are half-Jewish
> (I heard that it matters).
> This grandfather is on the mother's side.
> Mother's side: her younger brother got schizoaffective disorder (has not
> yet been diagnozed with real schizophrenia), and also her
> great-grandfather (mother's grandfather) was ill. The mother herself is
> smart and successful academically but is a little strange. She is also
> half-Jewish.
> The question is, how likely their children are to be affected.

First, I don't know any evidence that Jewish people are any more or less
likely to have schizophrenia.  So I don't think that is important.  (It
can be extremely important for some genetic diseases, e.g., Tay Sachs, but
probably not for schizophrenia.)

Second, you did not mention the man's mental health, but you said that the
woman is "a little strange."  Perhaps you consider the man to be not
strange.  The mental health of the man and woman is surely more important
for prediction of mental health of their child than is the mental
health of their other relatives.

As I said before, it is not really possible to make a probability
statement without use of some model of transmission.  We also know very
little about the behavior of the affected people and have to rely on your

It sounds like the offspring of this potential marriage would have a
maternal uncle with schizoaffective disorder, a maternal great-great-
grandfather who "was ill," and a paternal half granduncle who was
"severely ill."  His/her parents would seem to be well, but his/her mom
might be "a little strange."  Most of these ill relatives are fairly
distant ones and don't add much, if anything, to the risk of psychosis.
The schizoaffective maternal uncle contributes most to the risk, but the
mom is not ill, so that contribution is not as strong as the doubling of
risk (from 1% to 2%) usually observed in the nieces and nephews of someone
with schizophrenia.

It is a very inexact science, but I would advise that they not worry over
the possibility that they might have a schizophrenic child.  They are not
mentally ill themselves and most of their ill relatives are distant ones. 
The risk to their children is not great.

Michael B. Miller, M.S., Ph.D., M.P.E.
Department of Psychiatry (Box 8134)
Washington University School of Medicine
4940 Children's Place,  St. Louis, MO 63110
WWW Homepage: ftp://sirronald.wustl.edu/pub/mbmiller/mike.htm

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