Lung function measurements in children - copsac
Lung function measurements in children - copsac
Lung function measurements in children - copsac
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wheeze compared with controls (162). This supports the belief that RSV is the cause of<br />
respiratory illness <strong>in</strong> <strong>in</strong>fancy.<br />
A more recent publication based on 8,280 tw<strong>in</strong> pairs showed that a model <strong>in</strong> which<br />
asthma “causes” RSV hospitalization fitted significantly better than a model <strong>in</strong> which<br />
RSV hospitalization “causes” asthma (163). On the other hand Wu and colleagues<br />
concluded <strong>in</strong> another recent paper that they have shown strong evidence for causal<br />
relationship of w<strong>in</strong>ter viruses and early childhood asthma (figure 8) (118). In the light of<br />
these two particular papers Kuehni et al. discussed the causal l<strong>in</strong>k between RSV<br />
<strong>in</strong>fection and asthma <strong>in</strong> an editorial (164). The editorial concluded the new data were<br />
more <strong>in</strong> favor of the hypothesis that the association between RSV and asthma is due to<br />
shared predisposition rather than to a causal effect of RSV. However, the authors<br />
po<strong>in</strong>ted out that the asthma phenotype was poorly def<strong>in</strong>ed <strong>in</strong> both studies. The GINA<br />
guidel<strong>in</strong>es have def<strong>in</strong>ed three categories: transient early wheez<strong>in</strong>g, persistent early-onset<br />
wheez<strong>in</strong>g and late-onset wheez<strong>in</strong>g/asthma (86).<br />
Cohort studies have suggested that the association between RSV <strong>in</strong>fections and later<br />
wheeze wanes with time (age) (96, 99). Huge epidemiological studies have power but<br />
difficulty gett<strong>in</strong>g certa<strong>in</strong> asthma outcomes (e.g. lung <strong>function</strong> <strong>measurements</strong>), therefore<br />
it is also important to supplement with smaller cl<strong>in</strong>ical studies such as this tw<strong>in</strong> study.<br />
We found no differential effect from severity of RSV <strong>in</strong>fection on asthma and allergy 7<br />
years after the <strong>in</strong>fection. This may suggest that some undisclosed environmental factor<br />
<strong>in</strong>stead could be responsible for the different severities of RSV <strong>in</strong>fection. A study of the<br />
whole tw<strong>in</strong> cohort showed that the severity of RSV <strong>in</strong>fection was determ<strong>in</strong>ed partly by<br />
genetic factors (16%); family environment accounted for 73% and nonshared<br />
environment for 11% of the <strong>in</strong>dividual susceptibility to develop severe respiratory<br />
syncytial virus <strong>in</strong>fection (115). The nature of such exposure is unknown and surpris<strong>in</strong>g<br />
<strong>in</strong> monozygotic tw<strong>in</strong>s, maybe this study material (subgroup) was unique at some level.<br />
Scientists have discussed the theory of epigenetic, which refers to heritable changes <strong>in</strong><br />
phenotype (appearance) or gene expression caused by mechanisms other than changes<br />
<strong>in</strong> the underly<strong>in</strong>g DNA sequence. Monozygotic tw<strong>in</strong> sibl<strong>in</strong>gs frequently present many<br />
phenotypic differences, such as their susceptibility to disease. Recent studies suggest<br />
that phenotypic discordance between monozygotic tw<strong>in</strong>s is to some extent due to<br />
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