What's on the Test

Prenatal Screening for Cystic Fibrosis

WHAT IS IT?

Genetic screening for cystic fibrosis (CF) has been recommended in the US for over a decade

CF screening should be offered to all pregnant women or those considering pregnancy
CF is caused by a change in the CFTR gene
- The CFTR gene instructs a cell to build a protein that helps control how salts move through cells
Damage to the CFTR gene can lead to thick, sticky mucus

Lungs
- Clogged and damaged airways resulting in breathing difficulties and multiple infections
Bowel/Digestive Systems
- Meconium ileus: Some affected babies can have intestine blockage that can be detected on ultrasound or occur after birth
- Pancreas: An important organ that helps digest food and produces insulin
  - Blockages can result in serious digestive problems such as malnutrition and a form of diabetes

Note: The above are the more common findings, however other organs may be affected

All people carry a few variants (changes or mutations in their DNA) that may impair the function of an important enzyme or protein
Thankfully, all genes come in pairs and as long as one copy of the CFTR gene is working, enough protein is available to maintain heath
- A ‘carrier’ describes someone who has a serious change in one CFTR gene copy of a gene pair
- Because the other CFTR gene copy is working well, there is enough CFTR protein so that ‘carriers’ are healthy
- If one parent (usually the mother is tested first) is found to be a carrier, then the other parent will be offered testing as well
A baby will be affected with cystic fibrosis if
- Both parents are carriers and
- Both of the baby’s gene copies are damaged (one non-working copy inherited from the mother and the other non-working copy from the father)
- Because neither gene copy is making enough normal CFTR protein, the baby’s mucous is no longer helping to lubricate parts of the body, but becomes sticky

CF ‘screening’ tests will be offered by your obstetric provider during your office visit and applies to average risk women – those without any family or personal history
Genetic counseling services are appropriate for
- Individuals with a personal or family history of CF
- A woman and her partner are both CF carriers
If only one partner is a CF carrier, the baby is not at risk for CF
If both partners are CF carriers, the risk to the baby of being affected with CF is ¼ or 25%
States may test for CF at birth
- The newborn screening test will identify babies with CF but can’t tell whether or not either parent is a carrier
A prenatal CF screening test can identify if parents are carriers but, during pregnancy, only a diagnostic test such as amniocentesis or CVS can confirm if a baby is affected