Why is autism diagnosed more often in boys than in girls?
Autism is a developmental difference that can affect communication, social interactions and the way a person responds to their environment. It manifests very differently from one person to another.
Researchers already know that many genes are involved in autism. A gene is a section of DNA that contains instructions used by our cells. Some changes to these instructions can disrupt brain development and increase the likelihood of autism.
Representation of DNA.
Pixabay
Yet changes affecting very different genes can be associated with similar characteristics. How can this common feature be explained?
A team of researchers from Boston Children's Hospital studied human cells capable of becoming nerve cells. The scientists separately reduced the activity of 18 genes associated with autism, then observed the consequences for many other genes. The result: several distinct changes triggered similar responses.
In other words, genes do not function independently of one another. Some control the activity of other genes, that is, how their instructions are used. When a gene is disrupted, this can therefore trigger chain reactions and affect the development of brain cells.
The researchers then identified one player in these interactions: the ZFX gene, located on the X chromosome. Girls have two X chromosomes in one of their chromosome pairs, while boys have one X chromosome and one Y chromosome.
In cells with two X chromosomes, most genes present on one of the two chromosomes are deactivated. But ZFX escapes this rule: it can remain active on both chromosomes. Its activity is therefore generally higher in girls.
ZFX helps stimulate the activity of many genes associated with autism. This may seem paradoxical: why would higher activity of these genes reduce the likelihood of autism? Because “associated with autism” does not mean that they cause autism when functioning normally. On the contrary, some are important for brain development, and it is their disrupted functioning that can increase the likelihood.
The researchers therefore believe that the additional activity of ZFX in girls could compensate for certain genetic disruptions. This protective effect remains a hypothesis to be confirmed, notably through experiments on female cells.