Science warns that genetic links between traits are often exaggerated

According to a new study led by UCLA, many estimates of traits and diseases sharing genetic signals may be overstated
.
The study shows that current methods for assessing genetic relationships between traits fail to take into account mating patterns
.

In recent years, by using powerful genome sequencing technology, scientists have tried to understand the genetic link between traits and disease risk, hoping that the discovery of common inheritance could provide clues
to solving the disease.
However, UCLA researchers say their new study, published Nov.
17 in the journal Science, offers a warning
about over-reliance on genetic correlation estimates.
They say this estimate is much more severely disturbed by abiotic factors than previously realized
.

Genetic correlation estimates generally assume that mating is random
.
But in the real world, partners tend to form partners
because of many common interests and social structures.
Thus, in previous studies, some of the genetic correlations attributed to shared biology may represent erroneous statistical assumptions
.
For example, previous estimates of gene overlap between body mass index (BMI) and educational attainment are likely to reflect this type of population structure, caused by "cross-trait selection mating," or the tendency of individuals with one trait to mate with individuals with another trait
.

The study's authors say genetic correlation estimates deserve more scrutiny because they are used to predict disease risk, gather clues for potential treatments, inform diagnostic practice, and shape debates
about human behavior and social issues.
Some in the scientific community place too much emphasis on estimates of gene correlation, the authors say,
arguing that studying genes can overcome confounding factors because genes are immutable.

Richard Border, a postdoctoral fellow in statistical genetics at UCLA, said: "If you only look at two elevated traits in a group of people, you can't conclude that they exist for the
same reason.
" "But there's an assumption that if you can trace genes, then you have cause and effect stories
.
"

Based on their analysis of a large database of the characteristics of two mates, the researchers found that cross-trait selection mating was strongly associated with genetic correlation estimation and reasonably explained the "considerable" portion
of genetic correlation estimation.

"Trait selection and mating affects all of our genomes, and throughout the genome, there are interesting correlations between the DNA you inherit from your mother and the DNA you inherit from your father.
"

The researchers also examined estimates of genetic correlation of psychiatric disorders, which has sparked debate in psychiatry circles because they appear to show genetic relationships between seemingly few similarities between disorders such as attention deficit hyperactivity disorder and schizophrenia
.
The researchers found that the genetic correlation of many unrelated traits can reasonably be attributed to cross-trait selection mating and imperfect diagnostic practices
.
On the other hand, their analysis found stronger links between some trait pairs, such as anxiety disorders and major depressive disorder, suggesting that at least some common biological traits
do exist.

"But even with real signals, we still think we're overestimating the extent of
sharing.
"