Delta F508 mutation is recognized as the most common genotype of cystic fibrosis (CF) however,
there are small numbers of CF patients having Delta F508/F311L. In the present study, the authors report a
2 year-old Thai boy, originating from North India, presenting with recurrent episodes of febrile illness,
hyponatremia, hypokalemia, and metabolic alkalosis since 4 months of age. He was transferred to our hospital
for further investigation. Blood chemistry revealed the following serum electrolytes, sodium 122, potassium
3.69, chloride 79.7, and bicarbonate 33.8 mEq/L, and the following urine electrolytes, sodium < 10, potassium
45.7 and chloride < 10 mEq/L. After intravenous fluid administration, hyponatremia and metabolic alkalosis
improved. DNA sequencing analysis of his blood demonstrates compound mutation for Delta F508 and F311L
in CFTR gene. In conclusion, the authors report a rare case of CF with Delta F508/ F311L genotype presented
with recurrent hyponatremia and metabolic alkalosis. Awareness of electrolyte abnormalities during febrile
illness, proper genetic counseling, and long-term follow up are necessary in this patient.

Keywords: Alkalosis, Cystic fibrosis, Cystic fibrosis transmembrane conductance regulator, Hyponatremia,
Mutation