Cystic fibrosis (CF) is a multisystem disease affecting epithelia of the respiratory tract, exocrine pancreas, intestine, hepatobiliary system, and exocrine sweat glands. Morbidities include recurrent sinusitis and bronchitis, progressive obstructive pulmonary disease with bronchiectasis, exocrine pancreatic deficiency and malnutrition, pancreatitis, gastrointestinal manifestations (meconium ileus, rectal prolapse, distal intestinal obstructive syndrome), liver disease, diabetes, male infertility due to hypoplasia or aplasia of the vas deferens, and reduced fertility or infertility in some women. Pulmonary disease is the major cause of morbidity and mortality in CF.

Any congenital myasthenic syndrome in which the cause of the disease is a mutation in the SLC18A3 gene.

An extremely rare autosomal recessive gastroenterological disorder reported in three families so far characterized by meconium ileus without any further stigmata of cystic fibrosis including pulmonary or pancreatic manifestations. Two of the reported patients developed chronic diarrhea in infancy. Homozygous mutations in the GUCY2C gene (12p12) leading to marked reduction or absence of enzymatic activity of guanylate cyclase 2C were found in the affected patients. The disease was reported to show partial penetrance.