prenatal testing

Question

When I was a pregnant mother of a 2-year-old CF child I underwent in Warsaw in a year 2000 prenatal testing, which revealed the presence of delF508 mutation (it was a sample of trophoblast) in one of the allels - carrier state. After birth the child underwent screening tests toward CF - the result is normal, the chloride level in the sweat is also normal. Regardig the fact, that genetical testing was done in my child before birth, should I perform also genetical tests from blood sample after birth to make sure?

Answer

Dear Questioner,
CF is an autosomal recessive disorder, which means, that only a person, who has two mutations in both allels of the CFTR gene is sick. Person with a single mutation in one allel of the CFTR gene is a healthy carrier. In situation, when parents are two carriers (both parents “produce” gametes with mutation of CFTR gene), distribution of the disease in offspring is compatibile with Mendelian inheritance: 1 of 4 children has no mutation, 2 of 4 are healthy carriers and 1 of 4 suffers from CF.
In your situation, if in the sick child both mutations in CFTR gene were detected, one should check, if the second child has the same mutations. No other mutations can be found in the second child, if the child has the same parents. If genetic tests were not done in the sick child and both parents, it should be done anyhow.
You wrote, that in the second child in prenatal testing del508 mutation was detected in one allel. So, if there is no mutation in the second allel, the child is a healthy carrier.
Regarding the question about blood test: material for prenatal testing as far as DNA is concerned is exactly the same, because the fetus and fetal membranes are derivatives of a fertilized ovular cell.
I advise you to perform genetical counselling in the whole family.
Yours sincerely, dr med. Natalia Kobelska-Dubiel
Genetic counselling: dr Andrzej Pławski.

05.01.2010