However, several works published between 1998 and 2008 have been questioned since, on the basis that they report contradictory results [3–6]; furthermore, they had limitations that included incorrectly diagnosing asthma, using emergency registry databases, detecting just a single CFTR gene mutation and analysing different populations with unequal comparisons in terms of sex and age [5, 6]. Here, CFTR is linked to asthma.