An immunologically anomalous luteinizing hormone variant in a healthy woman.

Abstract

An investigation was undertaken to characterize an immunological LH variant in a 31-yr-old healthy woman whose serum LH was either poorly or not at all recognized by two monoclonal antibodies. The two antibodies recognize epitopes present on the intact LH dimer, but not on the free subunits. It was found that the immunologically aberrant LH of the subject was bioactive, as evidenced by an in vitro bioassay for LH. Nothing in the personal history of the subject or in the results from a number of hormone analyses revealed any endocrine abnormalities. In a GnRH stimulation test, the increase in immunoreactive LH using two reference immunometric assays for LH was less than 10% of the mean response of five control subjects. In relative terms, the maximal increase in LH in the subject was only 60-100%, in contrast to 340-560% for the control subjects. The bio/immuno ratio of the LH in the subject was high and was further increased in the GnRH stimulation test. A low proportion of acid LH isoforms in basal and stimulated samples from the subject was in agreement with the high bio/immuno ratio. Gel filtration studies showed the presence of molecular species of apparently lower molecular size than the intact LH, but different from the free beta-subunit. The results suggest the presence of fragments of the alpha-beta-dimer where at least part of the beta-subunit has been lost. A pedigree analysis involving the parents, siblings, and children of the subject strongly suggests a genetic origin of the LH variant described with an autosomal mode of inheritance. This report on an immunological variant of LH illustrates the potential dangers of using monoclonal based immunoassays where a protein hormone with fully maintained biopotency may be partially or totally missed due to the monospecificity of the immunoreagent. This possibility should be kept in mind when inappropriately low levels of gonadotropins are detected in diagnostic routine.

Impact of gene polymorphisms of gonadotropins and their receptors on human reproductive success

“…The so-called V-LH variant was discovered in Finland and is in the double R176 L Casarini and others amino acid exchange p.W8R and p.I15T of LHB (Pettersson et al 1992). V-LH shows a lower circulatory half time and bioactivity in vivo than the 'classical' LH, possibly compensated by increased transcriptional levels of the LHb subunit due to SNPs within the promoter LHB region, which are in linkage disequilibrium with p.W8R and p.I15T (Jiang et al 1999).…”

Effects of polymorphisms in gonadotropin and gonadotropin receptor genes on reproductive function

“…Concerning the LHB gene, a variant named V-LH consisting in the double amino acid change Trp8Arg and Ile15Thr in the protein [76] was discovered in Finland [76,77]. It introduces an extra glycosylation site in its aminoacidic chain [78].…”

“…It introduces an extra glycosylation site in its aminoacidic chain [78]. These characteristics change the immunological and biological properties of the molecule which, for example, can no longer be recognized by a specific antibody because the corresponding epitope present only in the LHα/β dimer is changed [77]. Moreover, the V-LH shows lower circulatory half time and bioactivity in vivo [3,79] compensated by a linkage mechanism with some SNPs in the promoter region which flattens these differences in vitro.…”

Immunoreactive LH in long‐term frozen human urine samples

“…[13,29] Validation after prolonged frozen conditions has not been evaluated by available commercial immunoassays. [17,37,38] Loss in urinary LH and hCG immunoreactivity after 7 to 70 days of storage at -20 C (unpreserved) measured with the IF immunoassay, [13,19] radioimmunoassay, [14] and immunoenzymatic assay [27] was also reported previously which was attributed to the dissociation of the heterodimeric glycoprotein into its sub-units in the presence of urinary urea in specimens. [30][31][32] This diversity reflects the metabolism of the gonadotropins which produces nicked dimers and free sub-units including the core fragment.…”