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A chip off the old block, a kid inherits a multitude of his or her parents' traits, such as eye and hair color. But new evidence suggests that parents may also pass on a common virus to their offspring hereditarily. Researchers estimate that one of every 116 newborns may have human herpesvirus 6 (HHV-6) infections that originated when the virus inserted its genetic material into that of their parents' DNA.
HHV-6 is the virus responsible for roseola—a mild childhood infection resulting in high fevers and occasionally associated with a rash. In rare cases the infection is accompanied by seizures as well as respiratory and gastrointestinal complications. By age three, nearly all children have acquired the virus, most likely passed through the saliva of caretakers or other kids.
About 1 percent of all infants in the U.S. are born with asymptomatic infections. Scientists have long believed that they were infected in utero when viral particles from their pregnant mothers crossed the placental barrier. But a recent study published in Pediatrics documents a new mechanism for infection in which HHV-6 integrated into parental DNA is passed on at conception.
Following childhood infection HHV-6 remains latent in the human body, although it may reactivate in immunocompromised patients, potentially triggering complications, such as pneumonia or encephalitis (inflammation of the brain and spinal cord). In less than 1 percent of all adults, the virus can also quietly slip its own DNA into the human genome—making it possible for mothers and fathers to pass HHV-6 to their offspring if these insertions are present in their eggs or sperm.
For the study, researchers examined 254 children, ranging in age from newborn to 3 years of age, for signs of congenital HHV-6 infection. Of the 43 infants found to harbor the infection, six contracted it through the placenta, whereas the remaining 37 contracted it from chromosomally integrated virus. Babies that inherited the virus from either parent's DNA exhibited much high levels of virus in their system with urine, blood and even hair follicles testing positive.
"With chromosomal integration, all cells have the virus from the beginning," says senior study author Caroline Hall, a pediatrician at the University of Rochester. But, she adds, it is unclear whether the presence of the virus during development affects a child's health. Even the ability of integrated HHV-6 to replicate producing new infectious virus remains an open question. Researchers have discovered, however, that HHV-6 inserts itself into telomeres, DNA regions at chromosome ends that are important for immune regulation and aging.
Viral integration into telomeres can disrupt chromosome function and spark a plethora of complications, including cancers, says Steven Jacobson, chief of viral immunology at the National Institute of Neurological Disorders and Stroke, who was not involved in the work. In fact, preliminary evidence already exists that HHV-6 may be associated with some lymphomas, a diverse set of cancers affecting the cells of the immune system.
HHV-6 also has been a suspected culprit in neurological disorders, including epilepsy, multiple sclerosis and chronic fatigue syndrome. Preliminary evidence even suggests that antiviral therapies could successfully treat central nervous system dysfunctions in patients with chromosomally integrated HHV-6, according to Stanford University infectious disease specialist Jose Montoya and his student Mitchell Lunn, who presented their unpublished work at a recent conference. Undoubtedly, Hall’s latest research will spur other scientists to test more widely for the presence of integrated HHV-6 in patients suffering from these disorders.
For now, Hall and her colleagues plan to continue following the congenitally infected infants to determine if their development is adversely affected by the presence of HHV-6 in their genomes. The good news, Hall notes, is that physicians have the tools to diagnose these inherited infections at birth, empowering families to take preventive measures if further study reveals that HHV-6 adversely affects kids who carry it.