S1235R mutation

Question

Good evening,

I am currently in the 13th week of pregnancy, and during the cystic fibrosis screening, the variant c.3705T>G (p.Ser1235Arg, rs34911792) of the CFTR gene (NM_000492.4) was found in heterozygosity. According to the CFTR2 genotype-phenotype correlation database, this variant is classified as non-pathogenic with regard to the development of cystic fibrosis (non CF-causing).

The doctor recommended that my partner should also be tested. What are the chances that our baby will have cystic fibrosis?

Answer

Dear questioner,
The individual was found to be a heterozygous carrier of the c.3705T>G (p.Ser1235Arg) variant in the CFTR gene. According to the CFTR2 database, this variant is classified as non-CF causing, which means that it is not associated with cystic fibrosis, either in the homozygous state or when combined with another pathogenic variant.

Given that full sequencing of the CFTR gene, as well as deletion/duplication analysis, has been performed and this is the only finding, partner testing is not indicated.
Should the partner nonetheless be tested and identified as a carrier of a pathogenic variant, the child would have a 50% probability of being a carrier of the paternal variant. Based on current scientific evidence, the child is not at risk of developing cystic fibrosis due to the variant identified in the mother.
M. Poulou

20.01.2026