Extended gene analysis can increase specificity of neonatal screening for cystic fibrosis

To assess whether carriers and patients can be accurately identified by extended gene analysis for cystic fibrosis (CF) in dried blood spots.

A blinded analysis was performed in 10-mm2 blood spots on Guthrie cards, punched as if to remove material for the IRT test, from 10 CF patients and 10 carriers with known CF mutations. Genomic DNA was isolated. Aliquots of 1 microl dissolved DNA were used for subsequent PCRs. Analysis of the deltaF508 mutation was followed by an oligonucleotide ligation assay. Denaturing gradient gel electrophoresis of the whole CFTR gene was carried out in samples with only one identified mutation. Amplicons revealing an aberrant pattern were sequenced.

In all cases, the blood-spot genotype was identical to that previously determined from whole-blood analysis. Estimated time needed to complete the procedure in a series of Guthrie cards was 3-4 wk.

Extended gene analysis in dried blood spots can discriminate CF patients and carriers. If proven equally reliable in larger series, an approach to neonatal screening in which tests are only considered as screen positive when two CF mutations are found is possible. This can increase the specificity of the screening programme, and carrier detection can practically be avoided.