15 genomic regions could be involved in the development of depression. PamelaJoeMcFarlane/iStock

Fifteen regions of the genome may be involved in the development of depression. Although major depressive disorder (MDD) has been shown in the past to be highly inheritable, this is the first time that a study describes so many significant genetic associations with MDD in individuals from European descent.

Commonly known as depression, MDD is a disease that affects many people around the globe. In the UK alone, between 4% and 10% of the population suffer from it at some point in their lifetime.

The problem is efforts to develop new treatments and psychotherapy interventions have been limited by the fact there is still much to learn about the neurobiology and genetic determinants of the disease.

Depression is thought to involve both genetic and environmental factors, with genetics playing a larger role in severe and recurrent depression. However, it is not entirely clear exactly what genes are involved or how.

Previous genome-wide association studies have failed to clearly identify genes involved in depression. Scientists blame this on the disease's heterogeneity, saying it makes it very difficult to draw generic conclusions about depression.

This new research, published in Nature Genetics different points of the genome that are likely to be involved in causing the psychiatric disorder.

Analysis of large samples

To succeed where others had failed, and find areas of the genome – or loci – involved in depression, the scientists decided to look at much bigger cohorts as a way to reduce the variability in the illness.

They focused on a very large group of patients – 75,607 individuals reporting clinical diagnosis of depression – comparing them with an equally large control group constituted of 231,747 individuals who had never experienced the disease. Genetic data was collected through consumer genomics company 23andMe. All the participants were of European descent, a change from the past, as the most effective studies so far had involved Asian subjects.

The scientists identified 15 loci that showed statistically significant associations with MDD. A preliminary analysis of these regions suggests that they are enriched for genes that are expressed in the nervous system or involved in neurodevelopment. There was also some overlap with regions previously identified in the context of other psychiatric disorders, such as schizophrenia.

However, there are are a number of limits to these findings. First of all, they may only apply to Europeans, as other ethnic groups were not taken into account in the analysis. Additionally, the scientists only identified genomic regions involved in depression, and not specific genes within each regions. Further research is thus needed to identify the genes within the region and determine which ones may be having an effect.

These results are nevertheless a step forward, in the sense that they pinpoint what areas scientists should work on in future studies. If specific genes are subsequently identified, it would greatly improve the odds of finding novel, effective therapy.