Health
One in every 20 cases of the serious condition of pregnancy, pre-eclampsia, may be linked to increased levels of the air pollutant ozone during the first three months, suggests a large study published in the online journal BMJ Open.
Mothers with asthma may be more vulnerable, the findings indicate.
Pre-eclampsia is characterized by raised blood pressure and the presence of protein in the urine during pregnancy. It can cause serious complications, if left untreated.
The authors base their findings on almost 121,000 singleton births in Greater Stockholm, Sweden, between 1998 and 2006; national data on the prevalence of asthma among the children’s mothers; and levels of the air pollutants ozone and vehicle exhaust (nitrogen oxide) in the Stockholm area.
There’s a growing body of evidence pointing to a link between air pollution and premature birth, say the authors, while pregnant women with asthma are more likely to have pregnancy complications, including underweight babies and pre-eclampsia.
In all, 4.4 percent of the pregnancies resulted in a premature birth and the prevalence of pre-eclampsia was 2.7 percent.
There was no association between exposure to levels of vehicle exhaust and complications of pregnancy, nor were any associations found for any air pollutants and babies that were underweight at birth.
But there did seem to be a link between exposure to ozone levels during the first three months of pregnancy and the risk of premature birth (delivery before 37 weeks) and pre-eclampsia, after adjusting for factors likely to influence the results and seasonal variations in air pollutants, although not spatial variations in exposure.
Each rose by 4 percent for every 10 ug/m3 rise in ambient ozone during this period, the analysis indicated.
Mothers with asthma were 25 percent more likely to have a child born prematurely and 10 percent more likely to have pre-eclampsia than mums without this condition.
Asthma is an inflammatory condition and ozone may therefore have worsened respiratory symptoms and systemic inflammation, so accounting for the larger increase in the risk of premature birth among the mums with asthma, suggest the authors.
But after taking account of the mother’s age, previous births, educational attainment, ethnicity, asthma, season and year of conception, the authors calculated that one in every 20 (5%) cases of pre-eclampsia were linked to ozone levels during early pregnancy.
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A newly identified genetic variant doubles the risk of calcium buildup in the heart’s aortic valve. Calcium buildup is the most common cause of aortic stenosis, a narrowing of the aortic valve that can lead to heart failure, stroke, and sudden cardiac death.
An international genomics team called CHARGE (Cohorts for Heart and Aging Research in Genomic Epidemiology) found the variant in the gene for lipoprotein(a), a cholesterol-rich particle that circulates in the blood.
CHARGE oversees genomic studies of five large study populations in the United States and Europe, including the Framingham Heart Study (FHS), which is a part of the National Heart, Lung, and Blood Institute (NHLBI) at the National Institutes of Health.
The findings will be published in the Feb. 7 issue of The New England Journal of Medicine.
“No medications tested to date have shown an ability to prevent or even slow progression of aortic stenosis, and treatments are limited beyond the major step of replacing the aortic valve,” said study co-author Christopher O’Donnell, M.D., M.P.H., senior director for genome research at the NHLBI and associate director of the FHS. “By identifying for the first time a common genetic link to aortic stenosis, we might be able to open up new therapeutic options.”
The CHARGE researchers conducted a genome-wide analysis of 2.5 million known genetic variants in a group of nearly 7,000 white participants. The analysis identified a variant in the lipoprotein(a), or Lp(a), gene that was highly correlated with calcification of the aortic valve, as measured by computed tomography (CT) scanning.
Followup analysis in more than 6,000 additional participants, including Hispanics, African-Americans, and Chinese-Americans, confirmed this correlation.
The variant was present in about 7 percent of the study population and the people who carry it generally had higher amounts of Lp(a) circulating in their blood. The function of Lp(a) is unknown, but it is associated with an elevated risk of heart disease.
Another independent analysis carried out by CHARGE followed participants in Sweden and Denmark, and found that people with the Lp(a) variant had higher risks of clinical heart valve disease and of needing valve replacement surgery.
“What makes these findings provocative is that we linked the genetic variant with a physiological change in lipoprotein levels, disease precursor in the form of calcium buildup, and fully diagnosed aortic valve disease, across multiple ethnicities,” O’Donnell said. “The study suggests a causal relation between Lp(a) and aortic valve disease, but further work will be needed to see whether medications that lower Lp(a) levels can lower the risk or slow the development of valve disease.”
In addition to the FHS, this work included data from the NHLBI’s Multi-Ethnic Study of Atherosclerosis, the Age Gene/Environment Susceptibility Study, the Heinz Nixdorf Recall Study, the Malmo Diet and Cancer Study, and the Copenhagen City Heart Study.
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