Nasal potential difference testing showed a borderline response to CFTR stimulation, which was suggestive of at least partial CFTR dysfunction following stimulation with isoprotenerol (a Δlow chloride/isoproterenol value of 6.5 mV [normal value, >6 mV]), whereas CF diagnostic scores were within abnormal range (Sermet score of 0.14 [normal score, >0.27]; Wilschanski index of 0.57 [normal value, <0.7]). The gene discussed is CFTR; the disease is cystic fibrosis.