The reason why non-Europeans are more at risk of developing lupus is genetic, scientists have confirmed. They have also identified 10 new loci – locations of genes' DNA sequence on chromosomes – associated with the disease.
Lupus is a complex and still poorly understood autoimmune condition. Though there are types of lupus that only affect the skin, the term is more commonly used to describe a more severe form of the condition called systemic lupus erythematosus (SLE), which can affect many parts of the body, including the skin, joints and internal organs.
For reasons which scientists still struggle to understand, the immune system in people with SLE starts to attack and inflame healthy cells, tissue and organs.
It is thought that lupus is caused by a mix of environmental and genetic factors, but in this latest study, published in Natures Genetics, the researchers have focused their investigations on the latter.
Comparing the genome of European and Chinese individuals, they have discovered that non-Europeans have a higher frequency of the gene variants that increase the risk of lupus. This may explain why this group is usually burdened by higher rates of the disease.
Genome-wide association study
The research team looked at genetic data from 22,670 Europeans, 13,174 Chinese as well as data from South Asian, east Asian and African recorded in the 1000 genomes Project – the largest public database of human variation and genotype data.
A meta-analysis of these data revealed that over half of the gene variants – or alleles – thought to contribute to the risk of developing lupus were present in the different populations. However, non-European populations, especially Chinese – presented a higher number of these alleles.
"Lupus is a very poorly understood condition. The confirmation that the condition's increased prevalence in non-Europeans has a genetic basis is an important step towards developing better predictive and diagnostic tools and may eventually help us to develop personalised treatments too", says lead author Professor Tim Vyse from King's College London.
Furthermore, the team identified 10 previously loci associated to lupus, a step which could also help scientists to improve their ability to predict and diagnose the condition.
Investigate environmental factors
The fact that lupus clearly has genetic origins should not lead scientists to ignore the fact that environment also plays an important part in the development of the disease. More research on this aspect should be carried out in a near-future, to get a complete picture of what may trigger the disease.
"For the first time we've shown that Chinese populations have a higher number of risk alleles than their European counterparts, but we don't understand why this susceptability hasn't diminished over time for non-Europeans", concludes co-author Dr David Morris.
"When thinking about whether someone might develop lupus, we use evidence from Twins studies which has shown that genetic factors account for two-thirds of the picture and environmental factors make up the final third. Our study advances our understanding of the genetic component, but more work needs to be done to better understand the environmental factors."