How long will it take to have the results of genotype testing

Question

We know that my brother and his son are carrier of the Nordic CF deletion (c394del TT). My partner and I are planning to use ICSI. Because I may well be a CF carrier, we would like to be tested before we continue with this ICSI treatment. We however can only get an appointment with clinical genetics next year. My question is how long will it take for us to have the test results (are we carriers?) so that we know whether to continue with ICSI. Are we talking in days weeks or months? Thank you for your answer.

Answer

Dear E-Corn user,

Since your brother is a carrier, you -his sister- indeed have an increased chance to be carrier of the mutation 394delTT i.e. your chance of carrying this mutation is 1 in 2.
As for your partner there is an important remark. Mutations in the CFTR gene can give rise to a rare form of infertility, that is, infertility by congenital absence of the vas deferens. Men with this condition often carry one severe CF mutation plus one mild CF mutation (every individual has 2 CFTR genes: one inherited via the father, one inherited via the mother).
Because an ICSI procedure is planned in your couple and because you may carry a severe CF mutation it is important that the risk of being a carrier is examined in both of you.
More than 1500 CF mutations are known. Only about 30 mutations are frequent and are being tested for routinely. This routine test will discover about 90% of CF carriers and will also detect the presence of the mutation 394delTT running in your family.
Your partner should also be tested for the presence of CF mutations. The combination of a severe mutation such as 394delTT together with a mild mutation can lead to infertility without any other sign of cystic fibrosis. This type of infertility is caused by absence of the vas deferens and you should discuss with your doctor whether this is the case in your partner. Many of the mild CF mutations are not discovered on routine screening so it cannot be tested with 100% certainty that your partner does not carry a CF mutation. The test sensitivity is about 90% in our population: in case of a negative result (=no mutation found with the routine CFTR mutation test) there will still be a chance that your partner carries a CF mutation and this chance will be 1/250 to 1/300.
The routine test takes about 1 to 2 weeks. It is possible to do more sensitive tests i.e. detect CFTR mutations by sequencing the total DNA code of the CFTR gene. This is however very time consuming (result available after 2 weeks to 3 months) and costly (about 1500 Euro) and therefore not done routinely.
Yours sincerely,
Prof. K. De Boeck

26.01.2009