Neanderthal DNA has been linked with depression, addiction and psychiatric diseases in modern humans. Further to this, scientists have discovered associations with neurological, immune and skin disorders.
The team, from Vanderbilt University, compared a genome-wide map of Neanderthal haplotypes (gene groups) with the health records of 28,000 people of European ancestry. Publishing their findings in the journal Science, the authors said they managed to find around 135,000 genetic variations in modern humans.
It has been known for many years modern humans share between one and 4% of their DNA with Neanderthals. And scientists are steadily learning more about what we inherited from the species – most recently, it was announced modern human's immune systems were probably given a boost as a result of interspecies sex with Neanderthals, but that this also could have led to some people being more prone to allergies.
In the latest study, the team found Neanderthal DNA could be associated with an increased risk of 12 traits. They believe these genes would have been useful for the species (for example, an ability to ward off pathogens), but that they became detrimental as we evolved in Western environments.
One such finding was that Neanderthal DNA significantly increases the risk of nicotine addiction. They found an association between a neurotransmitter transporter (SLC6A11) responsible for the re-uptake of g-aminobutyric acid (GABA). Nicotine addiction disrupts GABAergic signalling and reduces the expression of SLC6A11.
They also found a number of variants that influence the risk of depression. Some of these had a positive effect, while others a negative. Furthermore, the team said they found a surprising amount of Neanderthal DNA was involved in psychiatric and neurological disorders.
"The significant replicated association of Neanderthal SNPs [single-nucleotide polymorphisms, or a variation at a single position in a DNA sequence] with mood disorders, in particular depression, is intriguing because Neanderthal alleles (one of two or more versions of a gene) are enriched near genes associated with long-term depression, and human-Neanderthal DNA and methylation differences have been hypothesised to influence neurological and psychiatric phenotypes," they wrote.
"Depression risk in modern human populations is influenced by sunlight exposure, which differs between high and low latitudes, and we found enrichment of circadian clock genes near the Neanderthal alleles that contribute most to this association."
Corinne Simonti, first author of the study, added: "The brain is incredibly complex, so it's reasonable to expect that introducing changes from a different evolutionary path might have negative consequences."
Another finding was the Neanderthal DNA variants influence skin biology, in particular the development of keratosis, which are sun-induced skin lesions. Senior author John Capra said: "Our main finding is that Neanderthal DNA does influence clinical traits in modern human. We discovered associations between Neanderthal DNA and a wide range of traits, including immunological, dermatological, neurological, psychiatric and reproductive disease."