Heritability of severe mental illness may be underestimated

By Joanna Lyford, Senior medwireNews Reporter

Around one in three children of parents with a severe mental illness (SMI) – schizophrenia, bipolar disorder, or major depressive disorder – will develop such a disorder themselves by early adulthood, a meta-analysis has found.

While the children were most likely to develop the same condition suffered by their parent, familial transmission was only partly diagnosis-specific.

“As a result, the total risk of SMI and any mental illness in offspring of parents with psychotic or major mood disorders are higher than previously thought,” write Rudolf Uher (Dalhousie University, Halifax, Nova Scotia, Canada) and co-authors. “This should be reflected in genetic counseling and information provided by clinicians.”

The researchers identified 33 studies involving 3863 children of parents with an SMI (high-risk children) and 3158 children of parents without an SMI (controls).

Overall, 55% of high-risk children suffered from a diagnosed mental health disorder. Meta-analysis found that high-risk children were 2.5 times more likely to develop an SMI in their lifetime compared with control children.

High-risk children had an 18% chance of developing an SMI between the age of 10 and 19 years and a 32% chance once they were aged 20 years and above.

There was evidence of partial specificity of familial transmission, note Uher et al, such that children who developed an SMI were most likely to have the same diagnosis as their parent (risk ratio[RR]=3.59).

However, there was also evidence of general familial risk, meaning that high-risk children were at increased risk for developing any of the disorders studied (RR=1.92).

Uher et al say that their analysis suggests that the widely cited figure of one in 10 for the risk for familial transmission of SMIs is an underestimate, and that the real figure is around one in three.

However, they warn that their findings should be considered preliminary and conclude: “Cross-diagnostic research may be needed to advance the knowledge of etiology and plan effective preventive interventions.”

The study is published in Schizophrenia Bulletin.

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  1. Mohammed Athari Mohammed Athari United States says:

    We now know that neurotoxins such as lead and mercury cause injury to the brain, which manifest as complex disorders of the brain such as ADHD, autism and schizophrenia. Psycho-socialists (eugenic movement) have been claiming, like the authors here, that “genes”, whatever that means, can cause complex disorders of the brain.  What has been lacking from this irresponsible claim is any explanation as to how or why. So how is it possible that some studies were showing that our children are more likely to have the same complex disorder of the brain that we know is also caused by injury to the brain?

    A group of real scientists began to look into this.  They found out that there were clusters of areas, old houses with lead paint or the communities surrounding a chemical or coal plant, where there was striking similarity of complex disorders of the brain between parents and their children!  These studies clearly debunked the use of deductive reasoning (or measured guess) used by the eugenic movement as proof of the heritability of complex disorders of the brain by showing that the similarity was because of the clustering of people around the neurotoxic agent!

    On another front, more real scientists began understanding and mapping out the human genome (GWAS), and their studies began finding that there are no genes for these complex disorders of the brain and that even if you clustered a million genes together, you still could not explain anything.  In fact, the variance based on genes was less than 1% between us all.  The reason was simple, there was no linear connection between genes and complex disorders of the brain!

    How is it that 20 to 40% of our population now has such complex disorders of the brain, where a hundred years ago, incidents of mental illness were almost non existent except for known mendelian diseases.  Did our genes somehow go into the toilet, exponentially increasing the rates of mental disorders, in a mere 100 years?  No. The answer is we have been dumping insane amounts of toxins into our environment for the last century. For example, we dumped so much mercury into our waterways that eating more than one serving of fish a week is hazardous to our health.  We took another neurotoxin, lead, and put it into our gasoline and brought it into our homes by painting our walls with it.  We are now contaminating our water supply with millions of tons of antifreeze and neurotoxins to make methane.

    Genetics is one very small piece of a puzzle that has ten thousand pieces.  We are all 99.9% genetically equal or we would not be able to mate.  The real scientists always knew that mapping the genome would expose this “missing heritability”. This meta analysis simply takes these unscientific eugenic studies that did not confound for neurotoxic exposure to begin with, clumps them together, and repeats the false conclusions they previously drew.  No competent news organization should report the results of this illogical and irrational guesswork these authors attempt to pass off as scientific.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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