Lung function measurements in children - copsac

Discussion
Twin study
We found no difference within co-habiting MZ twin pairs discordant for hospitalization
for RSV bronchiolitis in infancy on the asthma prevalence, baseline lung function,
bronchial responsiveness; biomarker of airway inflammation (F E NO) and sensitization 7
years after such severe RSV bronchiolitis.
Limitations and Strengths of the study design
Monozygotic twins were useful for investigating the role of genetic and environmental
factors on asthma because of their identical genetic background and similar childhood
environmental exposures. However, comparison of MZ twin pairs discordant to
hospitalization for RSV bronchiolitis was prone to a number of biases.
We had no evidence to prove that the twin serving as control was actually infected with
RSV, but rely on very high virulence of RSV among cohabitating twins previously
estimated to 93-96% (115) though this could not be verified. In an optimal study there
would have been comparable nasopharyngeal aspirates from the twin pair to quantify
RSV virus load (136-138) or a blood sample measuring RSV serum antibodies to detect
any difference in association to disease severity (139). Thomsen et al. (2008) reported
that in the whole twin cohort the proband-wise concordance rate of hospitalization for
RSV-bronchiolitis was significantly higher in MZ (0.66) than in DZ twin pairs (0.53),
p=0.02 (115).
The decision to hospitalize may have been influenced by local policies such as number
of available rooms and the assessment of disease severity varied by different physicians,
but this would not influence the fact that only one twin was hospitalized and the other
was not.
We do not have positive evidence that the control twin had milder symptoms, but rely
on the fact that one was hospitalized while the other was not. Danish children are
generally only admitted with RSV infection if they need support with feeding tube,
suction of upper airways, mask inhalations or nasal continuous positive airway pressure.
Yet, this could be biased from registration practice. Indeed, fifty-four% of the parents
answered retrospectively that the hospitalized RSV proband twin suffered more severe
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