WEDNESDAY, Feb. 27 (HealthDay News) -- The incidence of cystic fibrosis may be decreasing, and a more severe form of the disease caused by one particular gene also appears to be on the decline.
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Those are the two main findings from a Massachusetts study that found the overall incidence of cystic fibrosis dropped from between 25 and 35 babies a year before 2003 to less than 20 babies each year for most years after 2003.
The study also found that the incidence of a severe form of the disease, caused by the genotype ΔF508/ΔF508, also dropped dramatically. Before 2003, at least 10 babies were born with this form of cystic fibrosis each year. In 2003 and beyond, only about five babies were born annually with this type of cystic fibrosis in the Massachusetts area, according to the study.
"The most severe genotype has dropped out dramatically. The new mix has some severe genotype, but overall, it's a milder group of kids, though not everyone has mild disease," said one of the study's authors, Anne Marie Comeau, deputy director of the New England Newborn Screening Program in Jamaica Plain, and an associate professor of pediatrics at the University of Massachusetts Medical School in Worcester.
The findings were published as a letter in the Feb. 28 issue of the New England Journal of Medicine.
Cystic fibrosis is an inherited disorder that affects mucus production and the sweat glands, making mucus sticky and thick, and sweat becomes extremely salty. The disorder affects many major organs, such as the lungs, pancreas and intestines. Mucus can clog the lungs, causing breathing problems and making it easy for bacteria to grow, leading to lung infections and lung damage.
While there's no cure for cystic fibrosis, treatments have improved greatly in recent years. Until the 1980s, most deaths from the disorder occurred in children and teens. Today, people live, on average, to be more than 35 years old, according to the U.S. Library of Medicine.
Both parents must be carriers of a cystic fibrosis gene for a child to be born with the disorder. However, carriers have no symptoms and often have no idea that they carry the cystic fibrosis gene. Even when both parents carry a cystic fibrosis gene, the chances are only one in four that a child will be born with the disorder, according to the U.S. National Heart, Lung, and Blood Institute (NHLBI).
About 30,000 Americans have cystic fibrosis, and it's most common in white people of Northern European descent, although people from all races can be born with cystic fibrosis, according to NHLBI.
The new research included data from the New England Newborn Screening Program and the Massachusetts Cystic Fibrosis Newborn Screening Work Group.
Comeau said the researchers believe that the decrease in the incidence of the ΔF508/ΔF508 type, as well as other forms of cystic fibrosis, owes to prenatal screening to see if parents are carriers of a cystic fibrosis gene.
She said the most important implication of this research, however, is for people evaluating treatments for cystic fibrosis. She said it's very important for such researchers to know that "the cohort of children may be changing. If you test a treatment on kids inherently bound to have a less severe disease, you have to be careful when applying those findings to all kids," Comeau said.
Dr. David Orenstein, director of the Antonio J. and Janet Palumbo Cystic Fibrosis Center at Children's Hospital of Pittsburgh, said, "This study raises an interesting possibility. There have been some other geographic areas where this same trend toward lower birth rates or fewer children born with cystic fibrosis has been observed, and so it's possible that it's real. But, these things do go up and down a bit naturally."
Orenstein said he'd have liked to have seen the data broken down by ethnic groups, since the disease is more prevalent in people of Northern European descent. But, he also pointed out that the numbers of children included in this study were very small, which means the findings need to be confirmed.
SOURCES: Anne Marie Comeau, Ph.D., deputy director, New England Newborn Screening Program, Jamaica Plain, and associate professor of pediatrics, University of Massachusetts Medical School, Worcester; David Orenstein, M.D., director, Antonio J. and Janet Palumbo Cystic Fibrosis Center, Children's Hospital of Pittsburgh; Feb. 28, 2008, New England Journal of Medicine
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