Environmental causes of congenital heart defects?

Congenital heart defects are the most common type of birth defect (at least in the United States). Around 1% of all babies that born in each year have some type of a heart defect, though that percentage halves (0.6%) if you only consider moderate to severe heart defects like tricuspid atresia or hypoplastic left heart syndrome (Hoffman and Kaplan 2002 J American College of Cardiology 39, 1890-1900; Reller et al., 2008 J of Pediatrics 153, 807-813).

As you can see, many parents or friends/relatives of patients with heart defects are left wondering why this happened to them if it is so rare. Sadly, some more recent studies have noticed an upward trend in the incidence of heart defects. For example, from 1968-1997 the incidence of moderate-severe congenital heart defects was 6.2/1000 births (0.62%) but from 1995-1997, the incidence was 9/1000 births (0.9%: Botto et al., Pediatrics 107). Some of this increase is obviously because our ability to detect minor or major congenital heart defects has increased over this period of time. But other features about our environment have changed and they are an easy target to blame the incidence or rise in the incidence of congenital heart defects.

In a new paper by Liu et al. (2013, Environmental Health 12) titled “Association between maternal exposure to housing renovation and offspring with congenital heart disease: a multi-hospital case-control study”, the authors report the correlation/association between being exposed to housing renovation during pregnancy and the incidence of congenital heart defects in the resulting children. We tend to worry more about the level of pollution outside our home than inside our home, yet we spend most of our days inside. Also, during a home renovation or after moving into a new house, occupants can be exposed to a variety of synthetic substances that are released from the materials used in the housing renovation or construction of the new home (e.g., volatile organic compounds, formaldehyde, heavy metals). This form of “indoor pollution” can arise from new paint on the walls, new caulk, new carpet or plastic flooring  (volatile organic compounds) or from cabinets or other furniture made from pressed wood (formaldehyde). Basically, bad stuff that people should avoid but especially pregnant women.

A few recent studies have looked at how such exposure to these renovation materials may increase in the incidence of congenital heart defects in children. A recent study concluded that exposure to new paint (volatile organic compounds) may be associated with the formation of congenital heart defects (Hjortebjerg et al., 2012, Environmental Health 11, 54). In the present study by Liu et al., the authors identified patients in four hospitals in China and screened their babies for fetal defects with ultrasound. They identified a group carrying babies with congenital heart defects and a control group from the same hospital during the same study period. They then gave both groups a questionnaire about their perceived non-occupational exposure to organic solvents or other such compounds. They excluded individuals who stated that they thought they had high occupational exposure to these toxins or if they had chromosomal abnormalities. Finally, they had a face-to-face interview with these pregnant women and asked about their exposure to housing renovations during three time periods: 7-12 months before pregnancy, 4-6 months before pregnancy, 0-3 months before pregnancy, or during the first trimester. Their criteria for housing renovation was that it involved installing at least one or more of the following list: marble surfaces, laminated board, plywood, carpets, ceramic tiles, paints, or wallpapers.

What did this study show about environmental causes of congenital heart defects?

1) Women with a fetus with a congenital heart defect were more likely to have been exposed to a housing renovation. Around 30% of the women that were pregnant with a fetus with a congenital heart defect had been exposed to a housing renovation project compared to 19% of the women without a fetus with a congenital heart defect. Not huge effect sizes but a statistical difference.

2) Mothers that smoke were more likely to be carrying a baby with a congenital heart defect (CHD). Around 46% of women carrying a fetus with a CHD smoked or were exposed to smoke compared to 30% of women carrying a fetus without a CHD.

3) Mothers living near a factory or landfill were more likely to be carrying a baby with a congenital heart defect. Around 30% of women carrying a fetus with a CHD lived near a factor/landfill whereas about 18% of women carrying a fetus without a CHD did so.

4) The overall risk of fetus developing a congenital heart defect was increased with exposure to indoor housing renovations. The odds of a fetus developing a CHD were on average 1.89 times higher if they were exposed to indoor housing renovations prior to or soon into pregnancy compared to mothers not exposed to such indoor pollution. These results are similar to a previous study in Denmark where being exposed to paint fumes during the first trimester was associated with an increased (though very slight) risk of producing a fetus with a congenital heart defect (Hjortebjerg et al., 2012 Environmental Health 11, 54-61).

5) The timing of exposure to housing renovations was important in affecting the risk of a fetus developing a congenital heart defect. Mothers exposed to a housing renovation that occurred within i) 3 months before pregnancy or ii) during the first trimester had an increased risk of producing a fetus with a CHD but only if they had moved into a house that had had a renovation within 1 month previous. Given that much of the heart development happens during the first trimester (e.g., both of the ventricles and atria are formed by 32 days after conception: Bruneau, 2008 Nature 451, 943-948), it is not necessarily surprising that being exposed to such indoor pollution in the first trimester was associated with an increased incidence of CHD. However, it is surprising that women that were exposed to indoor pollution (renovation) 3 months before pregnancy had a higher incidence of producing a fetus with a CHD. The second interesting point was that mothers (either 3 months prior to conception or 1st trimester) that moved in to a house that had been renovated within the previous month had a higher incidence of producing a fetus with a CHD. The authors discuss how this is also not surprising given that the amount of volatile organic compounds and other substances declines as the amount of time since renovation increases.

Conclusion: First, this is of course a correlational study and can only suggest associations between environmental variables and the incidence of congenital heart defects. However, recent studies suggest that ~12% of patients with a congenital heart defect have a chromosomal abnormality (e.g., Hartman et al., 2011 Pediatric Cardiology 32, 1147-1157), so there may also be a genetic basis to the development of some CHDs. However, it is important to emphasize that 1) such genetic studies are also associations and 2) this doesn’t necessarily mean that ~88% of patients with a CHD have an environmental (rather than genetic) basis. Most genes have small effects on the characteristics of an individual such that there could be many genes of small effect that interact to increase the incidence of CHD. However, this study by Liu et al. and others (Hjortebjerg et al., 2012 Environmental Health 11, 54-61) clearly provide quantitative support for common sense. That is, don’t paint your house while you are pregnant and consider the consequences of indoor pollution. This study supports the idea that effective campaigns for preventing CHD’s should involve promoting awareness of the negative consequences of indoor pollution produced by housing renovations.

Link to this paper:

http://www.ehjournal.net/content/12/1/25/abstract

Advertisements

One thought on “Environmental causes of congenital heart defects?

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s