Longitudinal follow-up of asthmatic status in a French-Canadian cohort

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The objective of this study was to analyze the evolution of asthma and related phenotypes over time by evaluating new diagnoses as well as changes in respiratory status and comorbidities in a subsample of the cohort. family of SLSJ asthma. When examining changes in asthma status, seven new cases of asthma in the subsample of this cohort were found, which represents 12% of people without asthma at the time of recruitment. This is consistent with the literature. In fact, the onset of asthma in adulthood occurs in about 10% of the population.17.18. It is interesting to note that only one individual (#6) out of the seven has a profile in accordance with the recommendations of the Global Initiative for Asthma (GINA) for a non-asthmatic becoming asthmatic (atopy, methacholine PC20 12% reversibility in airway obstruction after bronchodilators)4.

Atopy and BMI as risk factors for asthma

A study by Toskala et al. showed that atopy was a risk factor in the development and persistence of asthma19. This phenomenon was also observed in this study. Indeed, four of the seven individuals who developed asthma had allergies at recruitment and follow-up, and one developed atopy during this same period, representing 71% of individuals with a new diagnosis of asthma. However, not all allergic asthmatics see their symptoms persist.19. Indeed, three asthmatics saw their symptoms disappear and two of them were atopic at recruitment. The prevalence of allergic asthma phenotype across all participants was persistent over time. The unchanged proportion of atopic phenotype in people with asthma at follow-up could be explained by the relatively stable concentration of IgE levels between the two periods (about 2.5 times higher than in people without asthma). This is consistent with the literature indicating that dysregulation of the immune system in allergic asthma results in elevated serum IgE levels.19. Remarkably, no significant changes were observed for circulating IgE levels, regardless of age, asthma status and medications, which changed over the same period.

Another important risk factor is obesity20. Obesity is often associated with increased asthma severity, adult onset of asthma, and poor asthma control due to decreased response to medications5.21. In the present study, an increase in BMI between recruitment and follow-up was observed in all groups. At follow-up, the mean BMI was 27.06 kg/m2, who is considered overweight. However, the average BMI of individuals with a change in their respiratory status was greater than 30 kg/m2, who is considered obese. Four of seven adults with asthma had a BMI between 30 and 40 kg/m2. These people therefore presented an important risk factor linked to their new respiratory state.

Asthma severity indices

FEV11/FVC ratio is a respiratory parameter that determines the degree of airway obstruction22with a value generally less than 4. In this study, the average FEV11The FVC ratio has decreased in both asthmatic and non-asthmatic people over the years. Therefore, 54% of the decrease in FEV11/FVC pre-BD ratio at follow-up can be explained by a regression model in the SLSJ subsample that includes values ​​at recruitment for percent BD reversibility, percent predicted FEV1, and percent eosinophils. A comparable effect of blood eosinophils on lung function decline was found in a New Zealand young adult population-based cohort among participants aged 21-38 years.23. The study determined that the number of blood eosinophils was associated with a decrease in FEV11/FVC ratio including participants with and without asthma23. Additionally, in a population-based birth cohort that was followed into adulthood (up to age 26), a similar decrease in lung function across all groups, regardless of wheeze, gender or other parameters, has been reported.24. It would therefore be normal to observe a decrease in lung capacity given the two decades separating the two measurements.

FEV11/FVC values ​​reflected results of self-reported asthma severity in the questionnaire at follow-up. People with asthma had an average FEV11 /FVC which corresponds to mild asthma according to the literature4, and the majority rated their asthma as very mild or mild. Asthma severity can also be determined by the class of medication taken to relieve symptoms and exacerbations4. The drugs prescribed in the subsample are mainly short-acting beta-agonists and ICS, which also correspond to mild asthma4. However, there has been a marked increase (31%) in the prescription of long-acting beta-agonists, typically prescribed to people with moderate asthma.4, and the prescription of ICS (11%) during follow-up. Changes in the use of respiratory medications could be due to changes in GINA guidelines since recruitment; in 2019, ICS-formoterol was recommended for intermittent asthma and mild persistent asthma4. Whereas in the 2002 GINA report, it was recommended to introduce ICS only in mild persistent asthma4. This could indicate that symptoms are well controlled by the medication, resulting in participants’ self-reported asthma severity as very mild and mild.

Smoking has a significant impact on asthma, for example via epigenetic changes3. The number of smokers decreased significantly (from 22 to 4) between recruitment and follow-up. However, the risk of developing asthma in adulthood due to this exposure remains3. For people who had a new asthma status at follow-up, five out of seven participants were either ex-smokers or current smokers. Moreover, 58% of the 24 people with adult asthma at the time of recruitment were either former smokers or current smokers. Among the 24 individuals at recruitment and the 7 individuals at follow-up with adult asthma, 4 developed obstructive sleep apnea and 3 had or had psychological disorders (depression and anxiety disorder). These comorbidities can be found in people with severe asthma, as can gastroesophageal reflux disease and chronic infections, and may be associated with difficult asthma outcomes.25.26. The respiratory infections noted in these participants were neither recurrent nor chronic. Since the SLSJ Family Asthma Cohort is primarily comprised of participants with mild to moderate asthma, it is expected that there will be few comorbidities in the subsample.

Development of COPD in participants with asthma

A study by Mirabelli et al. demonstrated the presence of COPD in 29% of a population with a history of asthma27. People with asthma who smoked are more likely to develop COPD as they age and therefore may develop asthma-COPD overlap phenotypes (ACO)3.28. In this study, five participants with asthma at the time of enrollment (7%) developed COPD and all were ex-smokers or current smokers. For all, PC20was also very low at recruitment, four of the five individuals who developed COPD had values ​​below 0.25 mg/ml, which corresponds to severe AHR, and one had a value of 0.5 mg/ml, which is considered a moderate AHR29. This suggests that this risk factor may have contributed to the development of COPD30.31. These results contribute to a better understanding of COA, which is essential since patients affected by both diseases have more exacerbations, a poorer quality of life and a more rapid decline in lung function, as well as a higher mortality rate than patients with only asthma or COPD.22,32,33,34,35.

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