Just when I thought I know everything there is to know about identical twins, comes this new revelation. It seems that identical twins, previously thought to have 100% genetic resemblance, are anything but identical.

A group of researchers from the US, the Netherlands, and Sweden studied the genetic make up of 19 pairs of identical twins. They found that there are subtle but clear differences between the DNA of these twin pairs. These variations may be due to differences that occur during genetic copying and to mutations. In most cases, these slight differences have no observable effect in the physical and developmental make up of the twins. In some cases, however, these variations can make a world of difference health-wise. And we are not talking only about simple ailments but also serious and debilitating diseases as Parkinson`s and cancer.

Doctors were always puzzled how one twin can develop a disorder or disease and the other not. They`ve always attributed these differences to environmental factors. In the case of my twin boys, F developed eczema and asthma while R didn`t. And I`ve always asked myself, where did I do wrong? Have I somehow neglected one and favor the other? After all, I, the mom, am responsible for a lot of these so-called environmental factors, from food, to beds, to toys and baby products. It`s a relief to know that genetics, something beyond my control, plays a role in all of these.

But now, I`m at loss. With this new discovery, the the term “identical twins” has become a misnomer. Monozygotic would be a more appropriate term but who would understand that? The next time somebody asks me whether my boys are identical, how do I respond?

Source:

Bruder et al., 2008. Phenotypically Concordant and Discordant Monozygotic Twins Display Different DNA Copy- Number-Variation Profiles,

The American Journal of Human Genetics (2008), doi:10.1016/j.ajhg.2007.12.011.

Tags: DNA, genetics, identical twins, monozygotic