“…The two MZ twins concordant for GID described by Sadeghi and Fakhrai [14] and Knoblauch et al [15], respectively, shared certain common features: they both had troublesome childhoods, a difficult relationship with their parents (particularly with the mother), cross-gender behavior since early childhood on, and a good relationship with each other. In contrast, the MZ twins evaluated at our gender clinic in Ghent mentioned no specific problems with their parents, although the communication was rather superficial and the father was often absent.…”