However, in a subsequent study of 12 mothers of infants with congenital heart block, none was homozygous for the ERV3–1 env allele with the premature stop codon (103), arguing against a mechanism whereby lack of immunological tolerance due to lack of ERV3–1 envelope expression in mothers permits the induction of a pathogenic response against this glycoprotein expressed in the fetus as a paternal alloantigen. The gene discussed is ERV3-1; the disease is congenital heart block.