Cystic Fibrosis

The discovery of the CFTR gene raised hopes that the detection of mutations at the DNA level could supplement the traditional sweat test for CF diagnosis and, more importantly, might be used to identify carriers in the general population so that they could be offered genetic counseling. Unfortunately, these goals have been hampered by the large number of possible mutations in the gene, since present-day DNA tests can detect only a small subset of them. As in most recessive diseases, the vast majority of carriers have no family history of the disorder and do not discover that they are carriers until they happen to have a child with another carrier, giving birth to their first affected child.

CF is an appealing target for population carrier screening simply because of the relatively high carrier frequency in the general population. One in twenty-nine Caucasians, one in forty-six Hispanics, one in sixty-five African Americans, and one in ninety Asian Americans are carriers. It is not known why the mutation frequency is so high, especially in European populations. Some have proposed, using the analogy of the sickle-cell gene conferring relative resistance to malaria, that the mutations must have a protective effect against some disease appearing in European history, such as cholera or tuberculosis.

But all of this is just speculation. DNA screening of the entire adult population could potentially identify those couples at risk, who could then be offered prenatal diagnosis, affording couples the opportunity to consider their options. After several pilot studies and much debate at the national level, it has now been recommended that screening for the twenty-five most frequent CFTR mutations be offered to all couples expecting a child or planning a pregnancy. So most of the students reading this book will eventually be offered this DNA test!