Molecular Diagnostics

Cystic fibrosis mutation analysis is useful in a variety of clinical settings including (1) diagnosis, (2) newborn screening, (3) prenatal diagnosis for at-risk pregnancies, and (4) carrier detection. The majority of CF mutation analyses are for carrier detection and risk revision. Mutation analysis is a useful adjunct to sweat testing for diagnosis of CF, particularly for patients with borderline sweat tests, patients with atypical clinical presentations with normal sweat electrolytes, and at-risk newborns for whom sufficient quantities of sweat cannot be collected. Mutation analysis is also useful for a diagnosed proband in order to identify the familial mutation for carrier risk revision for at-risk relatives. With respect to newborn screening, both genetic and sweat testing are used after measuring immunoreactive trypsinogen.

Population screening for the purpose of identifying CF mutation carriers has begun in the United States. Using available data from over 20,000 CF patients, the ACMG (American College of Molecular Genetics) and ACOG (American College of Obstetrics and Gynecology) recommended a pan-ethnic panel of 25 mutations that occur at a frequency >0.1% in any of the major US ethnic groups and 4 reflex sequence variants (55) (Table 1).

As an established recommendation, CF carrier screening requires newer methods and technologies to support such a national program. Several assays are commercially available as analyte-specific reagents (ASRs) that utilize different technologies (Table 2). All of these assays include at least the ACMG/ACOG minimum core mutation panel. However, each assay/technology varies considerably with respect to criteria that laboratories consider in choosing a diagnostic platform, such as reagent/royalty costs, footprint, throughput, flexibility, and data analysis. PCR royalty payments are required of all assays except the Invader® platform (Third Wave Technologies, Madison, WI). As an enzymatic reaction (Fig. 1), the Invader assay requires only pipetting steps and is easily automated using a liquid handler. This assay should be more cost-effective than other ASRs because it eliminates an amplification step and uses a detection system that requires only a plate reader. For all other ASRs, reagent costs per patient are significant as are labor costs. This latter issue is being addressed by semiautomated platforms that allow for greater throughput and less "hands-on" time.

Two of the more commonly used assays are based on reverse blotting technologies (Fig. 2). The Linear Array CF Gold 1.0

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