Human chorionic gonadotropin beta genes and recurrent miscarriage: expression and variation study

Abstract

The study focuses on the expression and variation of the genes encoding beta-subunit of human chorionic gonadotropin (HCG) in the pathogensis of recurrent miscarriage. HCG, one of the first proteins produced by conceptus, is essential for the normal course of human pregnancy. Critical for hCG function is the beta-subunit of the hormone that is coded by four genes (CGB, CGB5, CGB7, CGB) sharing a common gene cluster with highly homologous luteinizing hormone beta-subunit and two beta-subunit non-coding CGB genes. The aim of the study was to (1) determine the expression profile of all CGB genes in trophoblastic tissue during the normal and complicated pregnancy (extrauterine pregnancy, recurrent miscarriage, molar pregnancy) and (2) find variants of HCG beta genes that are related to recurrent miscarriage by resequencing two most actively expressed genes in 284 patients and 195 fertile controls. The results of the study showed that the reduced hormone level in maternal serum in cases of recurrent miscarriages is associated to low transcriptional activity of CGB genes in trophoblastic tissue. The minor allele variants of six polymorphisms in promoter and intronic region of CGB5 and CGB8 reduce the risk of recurrent miscarriage up to 1.8 fold. All these variants occur more frequently in fertile women compared to the patients. Additionally, three non-synonymous amino acid substitutions in CGB5 and CGB8 were identified only in patients with recurrent miscarriage as possible risk variants. The high genetic variation in HCG beta genes may explain large interindividual differences in HCG level during the pregnancy. The results of this study could be applied in development of diagnostic methods for improving early and preventive treatment of recurrent miscarriage.Doktoritöö keskendub inimese koorion gonadotropiini (HCG) beeta alaühiku geenide ekspressiooni ja varieeruvuse rolli selgitamisele korduva raseduse katkemise patogeneesis. HCG on üks esimesi hormoone, mida loode toodab raseduse ajal ning selle piisav hulk on vajalik raseduse normaalseks kuluks. Hormooni spetsiifilist toimet määravat beeta alaühikut kodeerib neli CGB geeni, mis paiknevad samas geeniklastris koos luteiniseeriva hormooni beeta alaühiku geeni ning kahe HCG mittekodeeriva CGB geeniga. Töö eesmärgiks oli määrata (1) CGB geenide transkriptsioonimuster normaalse ja tüsistunud (emakaväline rasedus, raseduse katkemine, moolrasedus) raseduse ajal trofoblasti koes ning (2) leida korduva raseduse katkemisega seonduvad HCG beeta geenide variandid kasutades kahe enim hormooni tootva CGB geeni sekveneerimist 185 patsiendil ning 195 kontrollindiviidil. Töö tulemusena selgus, et korduva raseduse katkemise korral on madal hormooni tase ema seerumis tingitud CGB geenide madalast ekspressioonitasemest trofoblasti koes. CGB8 ja CGB5 promootorpiirkonnas ning intronis paikneb 6 polümorfismi, mille minoorse geenivariant seondub kuni 1,8 korda alanenud riskiga raseduse katkemiseks. Töös on kirjeldatud kolme aminohappe muutust põhjustavat polümorfismi, mis esinesid vaid korduva raseduse katkemisega patsientidel. CGB geenide suur varieeruvus võib olla põhjuseks, miks HCG tase on samas raseduse suurusega indiviididel erinev ning põhjustab raskusi HCG diagnostilist kasutamist. Doktoritöö tulemused aitavad välja selgitada raseduse katkemiset soodustavaid tegureid ning paremini valida sobivaimat ravimeetodit.