What is Cystic Fibrosis?

Cystic fibrosis of the pancreas (or mucoviscidosis) is due to one of the many known 'inborn errors of metabolism' that are fundamentally the result of aberrations in the structure of the genetic material. It is classed as lethal because of the very poor prognosis afforded to sufferers. The inheritance is autosomal recessive, so that an affected child must inherit one defective gene from each of the parents to be homozygotic. Such parents must then at the least be carriers (heterozygotes). The distribution of the genetic anomaly varies with racial types. It is predominantly associated with Caucasians in whom it occurs in about 1 in every 1500 to 2000 live births.

The symptoms of the disease are manifold; however, they are not strictly specific and hence physicians often have difficulty in distinguishing CF from other childhood diseases on the basis of medical diagnosis alone. The most serious clinical features are the pulmonary problems stemming from abnormally viscous exudates in the lungs, requiring urgent physiotherapy and antibiotic treatment to offset the ever-present risk of pneumonia. The pancreas is also affected by over-viscous secretions that reduce its output of digestive enzymes; thus, the child tends to fail to thrive because the food ingested passes through the alimentary canal without the normal enzymic breakdown necessary for absorption of nutrients. Fortunately, the latter problem is relatively easily corrected by the addition of animal pancreatic extracts to the diet. The use of “pancreas” in the disease name arose because of the identification (in 1938) of pancreatic abnormalities during post-mortem examination of children that had died with a set of symptoms that were not as yet associated with a specific illness. It should be noted here that CF sufferers may differ quite widely in the degree to which they exhibit the various symptoms. Some may be relatively less affected in the respiratory airways; others may show more serious pancreatic problems. A feature of the inheritance is that carriers do not exhibit the symptoms of CF.

In 1953, it was found that children afflicted by the disease are prone to acute hyponatremia during hot weather. Investigations on the cause of the loss of sodium showed that the eccrine sweat of children with CF contains 3 to 4 times as much salt as that of unaffected subjects. Subsequent work showed that this salt increase is not observed in presumed carriers. This was the first intimation that a laboratory test for the disease was conceivable. The sweat test was born and remains to this day the principal laboratory diagnostic test for this disease. In recent years the discovery of “the CF gene” promised a new laboratory diagnostic approach. Intensive studies of this gene have revealed hundreds of variants that may, or may not, produce the typical CF symptoms.

There is no doubt that in the future, this research will illuminate the effects of different genetic abnormalities on the biochemical patterns of the individual. However, the sweat test will remain the definitive laboratory diagnostic test for some time yet.