CFTR and cystic fibrosis: First, CFTR could globally lower levels of insulin-like growth factor 1 (IGF1), which are decreased in both CF pigs as well as CF infants.29 People with Laron syndrome, who are unable to produce IGF1, have sinus hypoplasia and decreased skull size.30 However, this possibility seems unlikely because CF pigs have small sinuses yet normal skull volumes.