RESUMO
<p><b>OBJECTIVE</b>To analyse the heritabilities of serum luteinizing hormone(LH), follicle-stimulating hormone (FSH), testosterone (T) and estradiol (E2) in twin boys, and to study the genetic contributions to gonadotropin-gonadal axis.</p><p><b>METHODS</b>A total of 51 pairs of male twins, 35 monozygotic (MZ) and 16 dizygotic(DZ) aged 5 to 11 years, were investigated. Serum gonadotropin and sex hormone were measured by radioimmunoassay. The twin zygosity was verified by determination of short tandem repeat amplified fragment length polymorphism systems. The genetic analysis was performed using intraclass correlation coefficient method.</p><p><b>RESULTS</b>The intraclass correlation coefficient was greater in the MZ twins than in the DZ twins. The estimated heritabilities were respectively LH 0.51, FSH 0.32, T 0.81, E2 0.41.</p><p><b>CONCLUSION</b>Genetic factors are major determinants of gonadotropin-gonadal axis in boys.</p>