Cytomegalovirus (CMV) is a common virus, which affects around 90% of adults. In most cases, it is completely harmless and at most causes a little fever. Sometimes, however, it turns into a lethal infection despite the person being apparently healthy. A study led by Dr. Jean-Laurent Casanova, of Rockefeller University, has perhaps revealed why.
The team investigated the case of a 54-year-old Iranian man affected by the lethal version of the cytomegalovirus. The man's immune system was in excellent condition and, in theory, he would have had to fight the virus without problems. Nonetheless, the man did not respond to treatment and continued to deteriorate. A little over two years after the diagnosis, he therefore inexplicably died of respiratory failure.
Scientists analyzed the patient's immune system and DNA, looking for an explanation. Despite the excellent health conditions, humans presented a rare variation in the NOS2 gene. The mutation causes an error in the coding of the gene, which produces a non-functioning version of the enzyme. When the enzyme does not work, macrophages are not helpless in the face of certain types of viruses.
To prove their thesis, scientists observed NOS2-free guinea pigs. Their immune system was in excellent condition, in appearance. On contact with the cytomegalovirus, it proved to be non-functional. In fact, it was as if the guinea pigs were immunosuppressed. For this reason, new treatments designed specifically for such cases will be needed.