A new study reports that although lung disease in systemic sclerosis (SSc) shares similarities with idiopathic interstitial pneumonia, the disorders do not have a common genetic basis. The article, titled “Genetic susceptibility loci of idiopathic interstitial pneumonia do not represent risk for systemic sclerosis: a case control study in Caucasian patients,“ appeared in the journal Arthritis Research & Therapy.
Systemic sclerosis is an autoimmune and connective tissue disease that affects many different parts of the body, including the lungs. It is characterized by diseased blood vessels (called vasculopathy) and fibrosis — the thickening and scarring of connective tissue. Idiopathic interstitial pneumonia refers to a category of lung diseases of unknown cause that affects the lung interstitium — the network of tissues extending between both lungs.
The researchers, led by Minghua Wu of the Division of Rheumatology and Clinical Immunogenetics, Department of Internal Medicine, at the University of Texas McGovern Medical School at Houston, studied 2,571 systemic sclerosis patients and 4,500 healthy participants. The team included several groups of systemic sclerosis patients and control subjects for the purpose of replicating their initial findings.
The team genotyped 13 interstitial pneumonia-related genes, known as single nucleotide polymorphisms (SNPs), and evaluated whether they were also associated with systemic sclerosis. SNPs are changes in one of the building blocks that make up the DNA. Although these can occur in a person’s DNA without causing problems, SNPs are sometimes associated with increased risk for specific diseases.
Overall, investigators failed to find a link between SNPs known to be related to idiopathic interstitial pneumonia and systemic sclerosis. Although they initially identified several SNPs in the first group of systemic sclerosis patients, when they attempted to replicate the results in other SSc groups, they were unable to do so.
SNPs that were identified in the first group of subjects included: SNP rs6793295 in the LRRC34 gene; SNP rs11191865 in the OBFC1 gene; and SNP rs7934606 in the MUC2 gene. The scientists noted in their article that “… these associations also did not replicate in the validation cohort.”
“Our results add new evidence that systemic sclerosis and systemic sclerosis-related [interstitial lung disease] are genetically distinct from [idiopathic interstitial pneumonia], although they share phenotypic similarities,” the research team concluded in its report.
The results suggested that although similar symptoms exist between these lung diseases, distinct treatments may be needed, particularly if genetic factors are being targeted. Further research into genetic factors contributing to systemic sclerosis-related lung disease are warranted.