Source Of Jaundice Studied Researchers See Interaction Of 2 Genes As Trigger In Babies

One of the more startling outcomes of birth is jaundice in the newborn, which often is of no consequence. Sometimes, however, jaundice can be serious, even fatal, and as scientists now are finding, can have deep roots in the genes.

Reporting in today’s issue of the Proceedings of the National Academy of Sciences, researchers in Israel have homed in on the genes that lead to a condition called kernicterus. It occurs when the brain and spinal cord are infiltrated by bilirubin, a yellow-pigmented substance produced by the breakdown of hemoglobin, the iron-containing pigment of red blood cells.

Not all jaundice in newborns is caused by kernicterus. Only rarely is jaundice attributed to that condition - which can be prevented when blood tests reveal bilirubin levels and the pigment’s prevasiveness in the bloodstream.

“Many babies break a little bit of their blood,” referring to the hemoglobin breakdown, and “that makes them look yellow. So (jaundice) is common even in the normal full-term baby,” said Dr. Sharon Buckwald, a neonatologist at North Shore University Hospital in Manhasset, N.Y. Still, the invasive condition can worry doctors and petrify parents. “That’s when the jaundice is so severe that bilirubin goes across the blood brain barrier and damages the brain,” Buckwald said.

Dr. Michael Kaplan and his colleagues in the department of medical genetics at Shaare Zadek Medical Center in Jerusalem found that an interaction between two genes produced an increased likelihood of jaundice in which bilirubin breaches the blood brain barrier.

The barrier is a membrane between the circulating blood and the brain that, like a sieve, allows nutrients in and usually keeps most harmful substances out.

Unfortunately, the blood brain barrier is not always failsafe.

Deficiency of an enzyme known as G-6-PD, which affects millions worldwide, has long been associated with severe jaundice in newborns. But Kaplan and his team have found that G-6-PD infants are only at heightened risk for severe jaundice when they also have reduced levels of a second enzyme, called UDPGT1. Both enzyme deficiencies are caused by gene mutations.

Alone, each mutation is harmless. Combined, there is an increased risk for potentially fatal jaundice.

But Buckwald said prevention strategies are so effective that even when doctors suspect kernicterus, babies still can be saved.

First-line treatment for all jaundice in newborns is phototherapy - exposing the baby to sunlight or artificial light, which reduces bilirubin in the blood.

When that doesn’t work, then an exchange transfusion is performed in which 87 percent of the newborn’s blood supply is replaced. This can rectify the emergency, she said.