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.

Fucosidosis is an autosomal recessive lysosomal storage disease caused by defective alpha-L-fucosidase with accumulation of fucose in the tissues. Clinical features include angiokeratoma, progressive psychomotor retardation, neurologic signs, coarse facial features, and dysostosis multiplex. Fucosidosis has been classified into 2 major types. Type 1 is characterized by rapid psychomotor regression and severe neurologic deterioration beginning at about 6 months of age, elevated sweat sodium chloride, and death within the first decade of life. Type 2 is characterized by milder psychomotor retardation and neurologic signs, the development of angiokeratoma corporis diffusum, normal sweat salinity, and longer survival (Kousseff et al., 1976).

Isolated hyperchlorhidrosis (HYCHL) is an autosomal recessive condition in which excessive salt wasting in sweat can result in severe infantile hyponatremic dehydration and hyperkalemia (summary by Muhammad et al., 2011).

Bronchiectasis with or without elevated sweat chloride-1 (BESC1) is characterized by dilation of the airways arising from chronic bronchial inflammation accompanied by chronic cough, purulent sputum, and recurrent respiratory tract infections. Severity is variable, and some patients may be identified in adulthood and have normal respiratory function (Sheridan et al., 2005, Fajac et al., 2008). Genetic Heterogeneity of Bronchiectasis with or without Elevated Sweat Chloride Bronchiectasis with or without elevated sweat chloride-2 (BESC2; 613021) is caused by mutation in the gene encoding the alpha subunit of the epithelial sodium channel (SCNN1A; 600228) on chromosome 12p13, and BESC3 (613071) is caused by mutation in the gene encoding the gamma subunit (SCNN1G; 600761) on chromosome 16p12. Bronchiectasis and elevated sweat chloride associated with pancreatic exocrine dysfunction and infertility are also features of cystic fibrosis (CF; 219700), which is caused by mutation in the CFTR gene (602421).

Patients with bronchiectasis with or without elevated sweat chloride-2 (BESC2) have bronchiectasis and chronic bronchitis of varying severity. Pancreatic insufficiency may be present (Azad et al., 2009). For discussion of genetic heterogeneity in bronchiectasis with or without elevated sweat chloride, see BESC1 (211400).

Congenital pancreatic lipase deficiency is a rare, monoenzymatic form of exocrine pancreatic failure. All reported patients have presented with similar symptoms and clinical findings, including oily/greasy stools from infancy or early childhood and the absence of discernible pancreatic disease. Failure to thrive has not been observed. Analyses of duodenal contents consistently show a marked decrease of pancreatic lipolytic activity (summary by Figarella et al., 1980).

Primary ciliary dyskinesia-29 is an autosomal recessive disorder characterized by early childhood onset of recurrent respiratory infections due to defective mucociliary clearance. Patients do not have situs inversus (summary by Wallmeier et al., 2014). For a phenotypic description and a discussion of genetic heterogeneity of primary ciliary dyskinesia, see 244400.

Recurrent respiratory infections and failure to thrive with or without diarrhea (RIFTD) is characterized by neonatal onset of chronic cough, episodic wheezing, recurrent lower respiratory tract infections, chronic diarrhea, and failure to thrive. Despite the resemblance to cystic fibrosis (CF; 219700), these patients have normal sweat chloride and pancreatic elastase tests (Bertoli-Avella et al., 2022).