Glucose-phosphate isomerase deficiency due to a new variant (GP I Barcelona) and to a silent gene: biochemical, immunological and genetic studies.

A 12-year-old girl of Spanish origin was found to be double heterozygote for a deficient GP I variant (GP I Barcelona) and for a silent GP I gene. The mother was heterozygote for GP I Barcelona and the father was heterozygote for the silent gene. GP I Barcelona was a fast variant (116%) with an increased isoelectric point (9.55), lability to heat and to urea, and shift of the pH curve towards the acidic pH. The other kinetic characteristics were normal. The ratio of enzymatic activity to immunological reactivity was normal in erythrocytes and white blood cells of the father and the mother but decreased to 75% of normal in blood cells of the daughter. The genetic and molecular mechanisms of GP I deficiency of this patient are discussed.