BACKGROUND: Hydatidiform moles are associated with an excess of paternal genome set(s) or abnormal imprinting of multiple imprinted genes. However, it appears unlikely that all imprinted genes are relevant for the pathogenesis of a hydatidiform mole.

CASES: We studied two rare cases of triploid, diandric moles that were tetrasomic for chromosome 6. DNA-marker analysis showed that in one mole the fourth chromosome 6 originated in the father, and in the other mole the fourth chromosome 6 originated in the mother. Histopathologic revision disclosed that both moles were partial moles with no significant difference in the phenotypes.

CONCLUSION: It is unlikely that a major gene involved in the pathogenesis of hydatidiform mole, or a major gene involved in determining the severity of the molar phenotype, is located on chromosome 6.