A multivariate Swedish national twin-sibling study in women of major depression, anxiety disorder, [FM], and [IBS] 2025 Kendler, Rosmalen et al

Females only, as there weren't enough males with fibromyalgia

So lifetime prevalence, up until the time of sampling.

That's a huge sample. In the Full Sibs group, which is the biggest group, prevalences in the female Swedish population are
Major depressive disorder 20.8%
Anxiety disorder 19.4%
IBS 6%
Fibromyalgia 1.2%

I'm constantly amazed at the high amount of depression and anxiety disorder diagnoses in general populations around the world. These numbers would be bigger if they were for whole of life. This high background prevalence needs to be kept in mind when interpreting statistics finding that depression and anxiety are common in people with ME/CFS.

 

The authors seem to be completely certain that IBS and fibromyalgia are functional disorders. I thought it was worth noting who they are:

Kenneth S. Kendler 1
Henrik Ohlsson 2
Michael Neale 1
Hanna van Loo 3
Judith Rosmalen 3
Jan Sundquist 2, 4, 5
Kristina Sundquist 2, 4, 5

1: Virginia Institute for Psychiatric and Behavioural Genetics, Virginia Commonwealth University, USA
2. Center for Primary Health Care Research, Lund University, Malmö, Sweden
3. Department of Psychiatry, University Medical Center Groningen, Groningen, Netherlands
4. University Clinic Primary Care Skåne, Region Skåne, Malmö, Sweden
5. Center for Community-Based Healthcare Research and Education (CoHRE), Department of Functional Pathology, School of Medicine, Shimane University, Japan

So, Rosmalen is involved, and people from the US, Sweden, Netherlands. University Clinic Primary Care Skåne looks like a place to avoid. Shimane University in Japan with its Department of Functional Pathology is likely to show up on the functional radar again.

 

To be clear, they didn't actually do any genetic analysis, or anything particularly complicated at all.

They have these sets of pairs:
Identical twins
Fraternal twins
Fraternal siblings raised together
Half siblings raised together
Half siblings raised apart

Just by the way - I find that possibly horrifying - they were able to match up individual health records with census data on cohabitation status. I hope data was deidentified, but surely reidentification would be possible with all of that information?

So, they are assuming commonality of genetics of 100% for identical twins, 50% for full siblings and 25% for half siblings.
And they give a shared home a rating of 1 for shared environment, and a 0 for a non-shared home. (Their exclusion criteria excluded people who had a mixed history of shared home and not shared home.)

And then they make a model to explain the differences in the prevalence of the 4 disorders in the pairs.

 

The data in that top panel could be used to support a hypothesis of childhood trauma increasing the incidence of these conditions.
Rates of the conditions are somewhat higher for half siblings (who perhaps faced issues of parental death, divorce or discord) than for full siblings. For example, rates of depression in the full siblings raised together were 20.8% and 28.9% for half siblings raised together. That's probably not surprising for diagnoses of depression and anxiety.

The rate of fibromyalgia in full siblings raised together was 1.2%, but 2.3% in half siblings raised together. The difference for IBS was minimal though (6% for full siblings and 7%/6.4% for half siblings). I didn't see any information given on the statistics - we don't know if these reported prevalences are statistically significant.

The data could also be used to support other hypotheses such as an increased incidence of childhood poverty in families with half siblings, with that poverty directly impacting on things like childhood quality of housing and exposure to pathogens, and indirectly through an increased likelihood of adult poverty acting on those environmental factors.)

 

Within-disorder cross-relative (the second panel)
(I'm not completely sure what the correlations mean, but I'm assuming they are saying something about how likely the second member of the pair is to have a specified disorder if you know what specified disorder the first member of the pair has.)

The stand out for me there is the enormous implication of a genetic cause of fibromyalgia with a correlation of 0.63 in identical twins. The correlation was only 0.29 in full siblings raised together. The correlation between the depression diagnoses of an identical twin with the depression diagnosis of the second twin was only 0.46 and 0.21 in full siblings raised together.

Just to indicate how much noise there probably is in the data, the correlation in identical twins for IBS was 0.39 and in non-identical twins 0.06. That suggests a significant genetic component and relatively little effect of a shared childhood environment. But the correlation for full siblings raised together was 0.11. Those full siblings could be expected to share a similar amount of genetic variation as the non-identical twins and probably less childhood environmental similarities, and yet the correlation was doubled.

I think there is interesting information here, and would like to hear what people who have looked at a lot of twin studies think about the results.

 

Cross-disorder within-relative (the third panel)
I think this means, if you know a person has, for example, a diagnosis of depression, what does that tell you about the likelihood of them having, for example, a diagnosis of anxiety. So, the analysis is of the individual.

As would be expected, the correlations are pretty similar across the pair types.

Not surprisingly, there is a big correlation between depression and anxiety diagnoses (around 0.69 in all the pair types). It looks like they are, to a large extent, a package deal. I think that tells us more about the habits of diagnosing doctors and the vagueness of depression and anxiety definitions than anything else.

Correlations between other pairs of disorders all seem to be around the 0.3 mark. I don't think there is much to be made of that. It's a shame that disorders with more obviously physical aetiologies weren't included to give a sense of what relationship we might expect between, for example, depression and a chronic disabling physical condition.

***

It occurs to me that this sort of information is a gold mine for insurance companies, i.e. being able to look at the medical history of a potential applicant for insurance and at the medical history of their siblings and having a very good idea what other diagnoses they are likely to get, and what sort of claims they will make. And then there is actual genetic information.

I imagine academics who provide the data for the ever increasingly detailed modelling of risk will do very well out of support from the insurance industry.

 

That sounds very vague. Is there any requirement to list out all the sources of funding for an investigation? I wonder to what extent insurers influence decisions about what health investigations are funded with public money.

 

MadinAmerica article about the first author
Kenneth Kendler: “Implausible” That Psychiatric Diagnoses Even “Approximately True”
I find myself agreeing with him:

Possibly this current study was designed to find that IBS and FM are just variations of depression and anxiety, but I don't think it shows that, even though I suspect the likelihood of a woman who has IBS or FM symptoms getting a depression and/or anxiety disorder label is high.