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Subject: Cystic Fibrosis (CF) Mutation Assay
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CF assay identifies mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. To date, more than 1,700 mutations have been identified for CF (OMIM# 219700). Current guidelines, revised by the American College of Medical Genetics (ACMG) in 2004, recommend for routine screening a 23-mutation panel. CF screening also may identify the 5T/7T/9T variants in the CFTR gene. Complete analysis of the CFTR gene by DNA sequencing is appropriate for patients with a clinical diagnosis consistent with CF, patients with a family history of CF, males with congenital bilateral absence of the vas deferens, or newborns with a positive newborn screening result when mutation testing, using the standard 23-mutation panel, has a negative result.
Normal values: negative or no mutations are found.
Confirmatory diagnostic testing
Carrier testing (for the identification of heterozygotes)
Available tests can be grouped as
Targeted mutation analysis tests.
23-mutation panel recommended by the ACMG in 2004.
Panels testing for more than 23 mutations.
Reflex testing for the poly T variant (5T/7T/9T), a string of thymidine bases located in intron 8, is recommended for individuals having the R117H mutation or an adult male patient who is being evaluated for congenital absence of the vas deferens (CAVD). The 5T variant is thought to decrease the efficiency of intron 8 splicing.
Sequence analysis: Analysis of the entire coding region, promoter exon–intron boundaries, and specific intronic regions—testing to identify rare mutant alleles.
Deletion analysis: By MLPA (multiplex ligation–dependent probe amplification) or other molecular method.
Next-generation sequencing represents an integration of carrier screening and diagnostic testing in one lab test. Differentiation between CF screening and CF diagnostic testing occurs during the software analysis. CF screening software allows viewing of sequencing results according to a predetermined panel of clinically relevant CFTR mutations. CF diagnostic software allows one to see all variants found within the CFTR gene. The complexity of the interpretation of the results is much higher for the diagnostic test than for carrier screening test.
The results of a genetic test may be affected by DNA rearrangements, blood transfusion, bone marrow transplantation, or rare sequence variations.