Antigenic alteration of an anomalous human luteinizing hormone caused by two chorionic gonadotropin-type amino-acid substitutions.

We analyzed the nucleotide sequence of the luteinizing hormone beta subunit (LH beta) in a patient with an anomalous LH. This anomalous LH showed abnormal immunogenicity, but normal bioactivity, suggesting that this variance of antigenicity was caused by amino acid substitution(s). In the anomalous LH, two single amino acid substitutions, Trp(TGG) to Arg(CGG) and Ile(ATC) to Thr(ACC), were found at the codon for the 8th and 15th residue of LH beta. These two substituted amino acid residues of the anomalous LH are identical to those of chorionic gonadotropin, but not to those of LH, although the rest of the region showed the normal sequence of human LH beta. Pedigree analysis by direct DNA sequencing revealed that the parents of the patient and the healthy sister were heterozygotes for the mutation and the patient and the healthy brother were homozygotes.