Assessment of CFTR function in homozygous R117H-7T subjects
R117H is a frequent missense mutation included in most CFTR mutation panels. However knowledge about the residual function of R117H-CFTR channels in cystic fibrosis-affected organs, e.g. airways, intestines and sweat glands is presently lacking. We evaluated clinical CF symptoms and assessed CFTR function by sweat tests, nasal potential difference and intestinal current measurements in 2 homozygous R117H individuals (7T variant). The CFTR activity in airways and intestine was within the normal range. However both individuals presented with a borderline sweat test and the male patient was infertile. The lack of impact of the R117H mutation on chloride secretion in intestine and nose contrasts with the ~80% loss of CFTR activity reported in patch clamp studies. Apparently CFTR activity is not rate-limiting for chloride secretion in both tissues at levels >20% of normal, or compensatory factors may operate that are absent in heterologous host cells in vitro.