Genetic Protection Against Schizophrenia?
On November 12, 2013, Molecular Psychiatry published online Evidence That Duplications of 22q11.2 Protect Against Schizophrenia, by Rees et al. The print version was published last month – January 2014.
Here’s the authors’ summary:
“A number of large, rare copy number variants (CNVs) are deleterious for neurodevelopmental disorders, but large, rare, protective CNVs have not been reported for such phenotypes. Here we show in a CNV analysis of 47 005 individuals, the largest CNV analysis of schizophrenia to date, that large duplications (1.5–3.0 Mb) at 22q11.2—the reciprocal of the well-known, risk-inducing deletion of this locus—are substantially less common in schizophrenia cases than in the general population (0.014% vs. 0.085%, OR=0.17, P=0.00086). 22q11.2 duplications represent the first putative protective mutation for schizophrenia.”
The idea of a genetic mutation that would protect one from schizophrenia aroused a good deal of interest and enthusiasm.
Schizophrenia Research Forum, for instance, ran the headline Protection From Schizophrenia – Too Much 22q11.2 is a Good Thing on an article dated November 22 2013, and Genetic protection Against schizophrenia on another article on the same date.
The Simons Foundation Autism Research Initiative used the headline Duplication of chromosome 22 region thwarts schizophrenia on a January 2, 2014, piece.
The Rees et al paper has added some impetus to psychiatry’s claim that the condition known as schizophrenia is a genetic disease. For this reason, I thought it might be helpful to take a closer look at the study.
Let’s start by examining what the authors’ summary actually says.
Copy number variants (CNVs) are essentially sections of the DNA string that contain variations from normal. The DNA is the “blueprint” of the organism, so variations in the string always have the potential to cause variations in the structure of the organism.
There are two kinds of CNVs: deletions and duplications. In deletions, a small piece of the normal code is omitted; in duplications, a piece is inserted twice.
When the authors write that a number of CNVs are deleterious for neurodevelopmental disorders, what they mean is that there is an association between having the CNV and having the disorder. Rees et al focused on the part of the genome designated 22q11.2: a small section near the middle of chromosome 22.