Lack of differences in serum binding of calcium in cystic fibrosis, carriers and controls.

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Attempts have been made to detect carriers for cystic fibrosis (CF) by some means other than genetic inference from affected children to their otherwise normal parents1. The ability to detect CF carriers would result in substantial advances in genetic counselling. Moreover, an assay by which heterozygotes are identifiable must involve a parameter close to the elusive primary gene abnormality. Accordingly the paper by Fitz-patrick et al.2 in which serum binding of tracer amounts of calcium (determined by equilibrium dialysis) of CF > heterozygotes > controls was a potentially significant report. We were, however, sceptical about data in which healthy carrier individuals demonstrated so great a difference from normal (an increase in serum binding of 45Ca in heterozygotes over controls of 65 ± 11%) for a clearly nonspecific characteristic. As we have substantial serum and salivary electrophoretic data3 in which no consistent protein differences were apparent in carriers and because we wondered about the biological explanation of the findings of Fitzpatrick et al.2, we decided to repeat their serum binding of calcium experiments. We repeated the reported procedures as closely as possible. We also assayed calcium binding with the additional buffer and salt concentration conditions described below. Sera from different individuals [N (controls = 30; N (heterozygotes) = 31; N (CF) = 33] were used in 4 experiments.