Neonatologists and some new mothers have suspected it for years.
But a new study by Danish researchers of more than 700,000 babies found that jaundiced newborns are 67% more likely than others to be later diagnosed with autism.
Newborn jaundice is a fairly common condition in which the baby's skin turns yellowish due to the buildup of a substance called bilirubin, derived from the breakdown of hemoglobin in red blood cells.
Rikke Damkjaer Maimburg, lead author of the study published in the medical journal Pediatrics, told USA Today that while "doctors have long known that premature babies have a higher risk of autism, this study found a link between jaundice and autism among full-term infants."
The new research offers "no smoking gun" evidence that baby jaundice leads inevitably to a diagnosis of autism, says Vinod Bhutani, a Stanford neonatologist and an expert on the diagnosis and treatment of bilirubin-related disorders, who was not involved in the study. "But there's a strong enough association that we have to take a prospective look at this. We can't dismiss it. And I think we may find that bilirubin plays an important role in the development of autism."
Of course, he said, it's important not to panic.
Guidelines from the American Academy of Pediatrics now suggest universal screening of bilirubin levels on all newborns before leaving the hospital, and for the vast majority of babies, even moderate to high levels can be treated using photo therapy, or special lights. If bilirubin escalates to dangerous levels, babies can undergo blood transfusion.
(An aside: one reason the guidelines are now in place is due to the efforts of Susan Sheridan, a mom from Eagle Idaho. Her son, Cal, was healthy at birth, but his elevated bilirubin levels were not tested and treated properly and due to that failure, he ultimately developed kernicterus, a rare neurological disorder that causes brain damage. I profiled Ms. Sheridan in The Wall Street Journal back in 2007, while she was still fighting with the pediatrics academy to change the guidelines so that all babies would be screened. Last year, the pediatrics group finally did revise the guidelines to encourage universal testing.)
Ms. Sheridan, who organized a support group for parents of children with kernicterus, says for the past 10 years she's been asked by mothers if there might be a connection between high bilirubin levels and autism. "I've heard from a bunch of mothers who wondered if the conditions are in some way related," she says.
While there hasn't been much data on the topic, Dr. Bhutani says that a few earlier studies have made the connections between jaundice, and elevated bilirubin levels, and diminished brain function. This data suggests that bilirubin toxicity can cause subtle changes in cognitive performance. "In the olden days (the 50s, 60s, 70s) it used to be called 'minimal brain damage,'" Dr Bhutani says. "There were issues with language development, hearing abnormalities, poorer IQ and the ability to process information."
These earlier studies all support the possible link between high bilirubin levels and autism, he said. One small study in 2001 looked at babies with moderately high bilirubin values and found abnormal neurologic signs — for instance, difficulty focusing and learning disabilities. Another lab experiment looked at neurons and how they grow. When moderate and high bilirubin was added to these brain cells, researchers found that maturation didn't proceed well and the cells didn't develop properly. "It's like a tree that fails to bloom," Dr. Bhutani says.
This program aired on October 14, 2010. The audio for this program is not available.