Testing Information
Cystic Fibrosis
Cystic fibrosis (CF) is one of the most common genetic diseases, occurring in1 out of every 2,500 - 3,300 newborns. CF results from mutations in the CFTR gene, which is important for maintaining chloride balance in the cell. CF affects the mucus and sweat glands of the body and is caused by a defective gene. Thick mucus is formed in the breathing passages of the lungs and this predisposes the person to chronic lung infections. Cystic fibrosis can also affect the sweat glands and the male reproductive system.
The CFTR gene that causes cystic fibrosis is a recessive gene, which means in order to get the disease you must inherit the gene from both of your parents. If you only inherit the gene from one parent, you become a carrier (you will not get the disease, but you can pass the gene on to your children). If you are a carrier and you and another person who is a carrier have a baby together, each child will have a 25 percent chance of having the disease and a 50 percent chance of being a carrier.
Common symptoms of CF include:
- coughing/wheezing
- infections/ pneumonia
- nasal polyps (bumps inside the nose)
- digestive problems
- poor growth
- salty tasting skin
- infertility
The symptoms and severity of CF differ from person to person. Most patients have both respiratory and digestive problems, while others only have respiratory problems. CF does not affect a person's intelligence.
| Ethnic Group | Carrier Rate |
|---|---|
| Caucasian (non-Hispanic/non-Ashkenazi Jewish) | 1 in 25 |
| Ashkenazi Jewish | 1 in 25 |
| Hispanic | 1 in 46 |
| African American | 1 in 65 |
| Asian | 1 in 90 |
There are two main methods for CF testing, Sweat Chloride and Genetic Assessment. Traditionally, diagnosing CF has been through evaluation of the patient's clinical picture backed up by a positive Sweat Chloride test; but genetic testing has become less difficult to perform and more cost effective than in the past.
Genetic Testing:
The CF (cystic fibrosis) transmembrane conductance regulator (CFTR) gene was tested for the presence of 46 specific mutations, including the 25 mutations recommended by the American College of Obstetricians and Gynecologists (ACOG) and the American College of Medical Genetics (ACMG), by genotyping to determine if they are negative, heterozygous, or homozygous for the mutation. This test will detect the F508C MUTATION, a non-cystic fibrosis (CF)-causing variant. When the F508C mutation is paired with a CF-causing mutation, it has been associated with congenital bilateral absence or atresia of the vas deferens (CBAVD). The CYSTIC GEN assay tests following mutations:
| Mutations | |||||
|---|---|---|---|---|---|
| ΔF508 | R334W | F508C | R347P | W1282X | I148T |
| 3849+10kbC>T | R347P | R1162X | D1152H | N1303K | R560T |
| 1717-1G>A | 1078delT | G85E | G542X | 621+1G>T | 394delITT |
| D1270N | V520F | 3849+4A>G | 3120+1G>A | 1898+1G>A | R347H |
| R117H | 711+1G>T | 3659delC | 2789+5G>A | 2184delA | Y122X |
| IVS8-5T | G551D | R553X | A455E | Q493X | E60X |
| IVS8-7T | 3876delA | Y1092X C>A | 3905insT | 2183AA>G | IVS8-9T |
| S549R A>C | Y1092X C>G | ?I507 | S549N | ||
Who should be tested:
- Confirmation of diagnosis in affected individuals
- Carrier identification in persons with a family history
- Carrier identification in persons currently pregnant or considering pregnancy
- Screening of sperm and egg donors
- Abnormal fetal ultrasound (i.e. echogenic bowel)
- Male infertility (congenital absence of the vas deferens)