 In severe cases, malnutrition disrupts ovulation and causes a lack of menstruation.CF is caused by a mutation in the gene cystic fibrosis transmembrane conductance regulator ("CFTR").The most common mutation, ΔF508, is a deletion (Δ signifying deletion) of three nucleotides that results in a loss of the amino acid phenylalanine (F) at the 508th position on the protein.