Cystic Fibrosis Screen

• Heterozygous means the individual carries 1 copy of a variant on 1 chromosome. If the variant is associated with a recessive disease such as cystic fibrosis (CF), these individuals are called carriers. Carriers are typically unaffected; that is, they show no symptoms of the disease.
• Homozygous means the individual carries 2 copies of the same variant, 1 on each chromosome. If the variant is associated with a recessive disease such as CF, these individuals are typically affected; that is, they show symptoms of the disease. However, the diagnosis is made based on clinical features and other laboratory studies.
• Compound heterozygous means the individual carries 1 copy each of 2 different variants, 1 on each chromosome. If the variants are associated with a recessive disease such as CF, these individuals are typically affected. 

For pregnant patients, guidelines recommend performing a CF screen on the male partner.¹ If he is also a CF carrier, the fetus has a 25% risk of being affected with CF.^1,2 Guidelines recommend offering the couple genetic counseling and prenatal testing if both partners are CF carriers.^1,2 If her male partner’s result is negative, his residual risk of being a CF carrier is reduced, and the risk that the fetus is affected with CF is also reduced. The percent risk reduction is based on ethnicity, because the CF screen sensitivity varies by ethnic group.

For patients suspected of having CF, additional genetic testing may be considered to determine whether a second rare variant, not detected by the standard CF screen, is present. Rare variants may be detectable through 2 other assays. The Cystic Fibrosis Complete Rare Mutation Analysis, Entire Gene Sequence test (test code 10917) can detect point mutations in the CFTR gene. The Cystic Fibrosis Gene Deletion or Duplication test (test code 16080) can detect deletions or duplications of the gene.

Please, call Quest Genomics Client Services at 1.866.GENE.INFO (1.866.436.3463) to discuss the case and additional testing options. 

Yes, the risk to offspring of this couple is still 25%.^1,2 CF is a recessive disease, so when offspring inherit any 2 disease-causing CF variants, risk of CF and CF-related conditions is increased. 

Providing patient ethnicity does not change the CF result. A positive result is still positive, and a negative result is still negative, regardless of ethnicity provided. For negative results, the residual risk that a patient is still a CF carrier is provided in a table in the report, which is broken down by ethnicity.¹

No; please call Quest Genomics Client Services at 1.866.GENE.INFO (1.866.436.3463) to discuss this case with a genomic science specialist to ensure appropriate testing is used based on the family history. 

For patients with a clinical diagnosis of CF, additional genetic testing may be considered to determine whether rare variants not detected by the standard CF screen are present. Rare variants can be detected using 2 other assays. The Cystic Fibrosis Complete Rare Mutation Analysis, Entire Gene Sequence test (test code 10917X) can detect point mutations in the CFTR gene. The Cystic Fibrosis Gene Deletion or Duplication test (test code 16080) can detect deletions or duplications of the gene.

Please call Quest Genomics Client Services at 1.866.GENE.INFO (1.866.436.3463) to discuss the case and additional testing options.