The aim of the study was to screen for the common deltaF508 mutation and the poly T polymorphism and to determine their frequency in the cystic fibrosis transmembrane conductance regulator (CFTR) gene among the suspected CF cases referred to our clinical care centre for sweat chloride tests.
Sweat and EDTA blood samples were obtained from 23 clinically suspected cystic fibrosis (CF) cases. Sweat was estimated by pilocarpine iontophoresis procedure. Poly T polymorphism was detected by the multiplex-PCR based on ARMSTM technique and deltaF508 mutation by PCR-mediated site-directed mutagenesis method.
Five cases, mainly with respiratory abnormalities and followed by steatorrhea had elevated sweat chloride levels (> 60 mmol/l), three of them, each with nutritional, respiratory and pancreatic abnormalities were borderline (40-60 mmol/l) and the remaining 15 clinically suspected CF cases had normal sweat chloride levels (< 40 mmol/l). The 9T variant was frequently observed (75%) in cases with elevated sweat chloride, including those exhibiting borderline values; with no 5T variant. The 7T was the most common variant (77%) observed in the cases with normal sweat chloride, with only one 5T variant (33%). Of the five cases with high sweat chloride, four cases were homozygous for deltaF508, whereas one was heterozygous with borderline sweat chloride, thus showing an overall frequency of 56.25% in the CF chromosome. DeltaF508 was found to be present with the 9T variant in all the instances.
The presence of the 9T variant along with elevated sweat chloride levels can be used to predict a high risk of the individual harboring the severe deltaF508 mutation. It would be advisable to test for to the deltaF508 mutation along with the sweat chloride estimation in all the critically suspected CF cases diagnose CF with a higher degree certainty.
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