There is no clear evidence yet for the implication of hereditary factors in a genetic contribution to having monozygotic twins. However, based on work by Prof Bruno Reversade (IMB Singapore & AMC/VUMC The Netherlands) in some rare cases MZ twinning seems to be segregating in families. Although this is likely a rare allele with substantial effect Mendelian trait, given the enrichment that twin studies have in their data for MZ twins as well as DZ twins this might be the right sample to look for these specific mutations.
