Genetic Disorders: The Early Stages; by Paige Atkins

Identical twins help to understand the beginning stages of genetic disorders

A detailed study of the first step in gene expression will help doctors and researchers better understand underlying variables that cause genetic disorders. Cancer research specialists were able to illustrate how our cells express genes inherited from our mothers and fathers and the depth at which it occurs differently, specifically in twins, to shed light on the beginning stages of a genetic disorder.

For example, identical twins share a duplicate set of DNA, but they can often appear physically different due to a genetic disorder affecting one and not the other despite both individuals carrying the disorder’s specific gene. This was previously explained by environmental conditions and life history. However, recent experimental results help us better understand how identical twins, who carry the same set of genes within their DNA, can display the effects of a genetic disorder in only one twin. This is indicated by a difference in expression of various genetic traits.

Understanding the science

As humans, we inherit two sets of genes that usually affect males and females in the same way-or autosomal genes; one copy from our mother, one from our father. Differences found in each parent’s set of autosomal genes passed on to each child do not always match up to make identical sets. This causes variation in how each set of cells are utilized in the development process and also how they vary in the outcome of genetic disease.

Chromosomes are the keepers of our individual genetic codes (DNA) and where genes, and a copy of each gene, can be found. The two copies are called alleles. Imagine a piece of string with several different coloured beads on it, two of each colour. The various colours represent different genes, such as eye colour, hair colour, freckles, and handedness to name a few. Detailed analyses and experiments conducted on alleles–represented by the coloured beads- allowed researchers to determine which ones of the same colour got fixed as being the only one expressed and which beads were dynamic enough to switch between the same two coloured beads, or alleles, over time.

We now know that random events at the cellular level affect gene expression. However, it is unknown whether the allele expressed happens while cells are dividing (during foetal development), or if it happens independently from cell to cell over the course of time. This is important because both scenarios have drastically different, physiological outcomes. The present study’s results imply that autosomal genes received from both parents are more likely to be dynamic and fluctuate in expression of the alleles -or two gene copies- while 1% or less are fixed in expressing only one gene.

This research is from the Karolinska Institute and the Ludwig Institute for Cancer Research and is published in the journal ‘Nature’ – Genetics.

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