As obesity rates climb, fatty livers are emerging as a serious threat to children's health.
By Karen Ravn, Special to The Times
March 26, 2007
It's often said, these days, that we're a nation of fatties. And, not coincidentally, we're also a nation of fatty livers.
Increasingly, millions of those livers belong to children — though most of them don't know it, and neither do their parents and doctors.
Usually, no symptoms show up until damage has been done, damage that may ultimately lead to cirrhosis of the liver, liver cancer and end-stage liver disease.
Until the 1990s, no one knew that fatty livers were a problem in children, and now, doctors say, the situation has become serious. "If you were to go into any large California high school with a couple thousand students and screen, you'd expect 200 children with fatty livers," says Dr. Jeffrey Schwimmer, director of the Fatty Liver Clinic at Rady Children's Hospital in San Diego and associate professor of pediatrics at UC San Diego.
Schwimmer was lead author of a study published in the journal Pediatrics in October 2006 that found evidence that nearly 10% of children between 2 and 19 years old in San Diego County have fatty livers. If that percentage holds throughout the U.S., 6.5 million children are affected.
The data show that fatty livers in children are highly correlated with weight. About 80% of kids with the condition are obese or overweight. Nearly 40% of obese children have fatty livers.
"It's the most common serious complication of childhood obesity," Schwimmer says. And doctors fear it may cause serious problems for these children as adults. In a study published in the October 2006 issue of the journal Hepatology, researchers in Sweden followed up on adult patients an average of 14 years after they were diagnosed with fatty livers and found that most of them had diabetes or impaired glucose tolerance. Many had end-stage liver disease.
Experts say it is likely that children with fatty livers have a head start on these problems and may be at risk for developing them while still young.
To date, biopsies are the only effective diagnostic test for fatty livers. Diet and exercise are the only effective treatments. And it's a mystery why the condition can be harmless for many, yet dangerous for others.
People with fatty livers are said to have nonalcoholic fatty liver disease. By definition, this disease occurs when 5% or more of the liver is fat. Often no damage is done, but in about 20% to 25% of cases, excess fat in the liver results in cell destruction and inflammation. At that point it becomes a condition known as nonalcoholic steatohepatitis, a form of hepatitis caused not by a virus but by too much fat.
People can have nonalcoholic fatty liver disease, even nonalcoholic steatohepatitis, without symptoms. "And they won't have until they show up in the emergency room with a life-threatening problem," Schwimmer says.
Nonalcoholic steatohepatitis can sometimes lead to cirrhosis of the liver, a scarring of tissue that impairs function. These days, doctors have even seen cases of 8-year-olds with cirrhosis of the liver.
Besides weight, the disease is related to age, ethnicity and gender. It's more prevalent in adolescents than in younger children, most prevalent in Latinos (12%) and least in blacks (less than 2%) and more prevalent in boys than girls.
Schwimmer's study, the only prevalence study to date, was done by reviewing autopsy records over 10 years, which is perhaps the only way to obtain that kind of data right now. Some screening for fatty liver disease is possible with blood tests that look for elevated levels of liver enzymes, as well as ultrasound or magnetic resonance imaging. But these methods are very imprecise. Accurate diagnosis requires a biopsy.
"We need a good diagnostic test that's simple, cheap and reliable," says Dr. Ariel Feldstein, assistant professor of molecular medicine at Ohio's Cleveland Clinic. Feldstein heads a team that may have developed such a diagnostic, at least for nonalcoholic steatohepatitis: a simple blood test that proved accurate in a small study published in the journal Hepatology in July 2006.
The test is based on the discovery that patients with nonalcoholic steatohepatitis have a fragment of a protein called cytokeratin-18 in their blood, as a byproduct of the type of liver cell death that nonalcoholic steatohepatitis causes. A larger study of this test is ongoing.
Research also is underway at UC San Diego to develop accurate, noninvasive diagnostic methods for nonalcoholic fatty liver disease, including the use of spectroscopy.
So far, diet and exercise are the only effective treatments for correcting fatty livers so that more damage, at least, isn't done. "Unfortunately, people aren't good at doing those things," says Dr. Jean Molleston, clinical professor of pediatrics at the Indiana University School of Medicine/Riley Hospital for Children.
作者:admin@医学,生命科学 2011-01-10 20:40