Molecular defects in a human immunoglobulin kappa chain deficiency

The molecular basis of a human immunoglobulin deficiency characterized by the complete absence of kappa chains has been investigated by nucleotide sequence analyses of a patient's kappa constant region (C kappa) genes. Both of his C kappa genes had a single point mutation, resulting in the loss of the invariant tryptophan from one allele and of an invariant cysteine from the other allele. These results indicate that neither of the patient's C kappa alleles encoded a kappa chain that could form a stable intradomain disulfide bond, although peculiarities in the expression of kappa chains in the patient's family suggest that other factors may be involved.