Determination of a common genetic variant of luteinizing hormone using DNA hybridization and immunoassays.

OBJECTIVE

An immunologically anomalous form of LH, due to two point mutations in codons 8 and 15 of the LH beta gene, has previously been described. LH status, i.e. the discrimination between wild-type (WT) and variant (V) LH, is usually determined by immunoassays, which can be unreliable at low serum concentrations of LH. A DNA hybridization assay was therefore developed to score the LH genotype in all subjects, independent of their serum LH concentrations. To evaluate the performance of the hybridization method, and to expand our observations of the worldwide occurrence of the V-LH, we determined its frequency in additional populations. To confirm the connection between the anomalous immunoreactivity and the V-LH beta gene, we also sequenced the LH beta subunit gene of a homozygous person.

DESIGN

According to the ratio of two immunoassays, one detecting only WT-LH and the other detecting equally WT and V-LH, individuals can be classified as homozygotes for the V-LH beta allele, heterozygotes or WT. DNA samples from persons with known LH status, according to the immunoassays, were used for the development and evaluation of a new allele-specific DNA hybridization assay. This assay, and PCR and restriction fragment length polymorphism analysis, were used to determine the frequency of the V-LH beta allele in DNA samples obtained from eight populations.

PATIENTS

Ambulatory adult men and women, apparently healthy and with no endocrine disorders.

RESULTS

The LH genotyping by immunoassays and by the new hybridization method gave identical results with all samples analysed (n = 25). The V-LH beta subunit was observed to always have the two point mutations, and to be identical with the ones previously reported. The V-LH beta carrier frequency in the DNA samples collected from various populations varied between 0 and 53.5%.

CONCLUSIONS

The immunoassay technique and the hybridization assay can be used as alternatives to determine the LH status. A great variation in carrier frequency of the V-LH beta allele is observed in different populations.