Numerous CFTR gene variants, characterized by variable or even unknown clinical consequences, were identified in patients with negative (<30 mmol/L) or borderline (30–59 mmol/L) sweat tests: this could explain the difficulty in diagnosing CF in adulthood [24] and the need for more widespread sensitive tests to define CF diagnosis, in case of a lacking confirmatory CFTR gene sequencing. Here, CFTR is linked to cystic fibrosis.