Individuals with other variants, including a CF disease-causing variant in trans with a short 5T nucleotide track and extended 12TG or 13TG di-nucleotide track in the intronic region chr7:117,188,661–117,188,689 of the CFTR gene, may present with classic, non-classic or milder forms of CF due to potentially lower levels of functional CFTR protein9, 10, 11, 12, 13, 14, 15, 16, 17, 18. Here, CFTR is linked to cystic fibrosis.