After years of diagnostic wavering for many families, knowing the origin of disability is an essential step to move forward and not to feel alone.
The syndrome is manifested by an intellectual disability, associated or not with autistic spectrum disorders, an overall developmental delay, difficulties of language and speech, learning, hypotonia, frequent vision disorders as hyperopia and sensitivity to the sun. Can also be observed: epilepsy, balance disorders, adduction of the foot more or less severe.
The syndrome is a rare genetic disease: the prevalence is estimated at between 1.6 and 2 per 100,000 births. The "haplo-insufficiency MED13L" syndrome is due to the lack of expression of a copy of the MED13L gene, located on the long arm of chromosome 12 (12q24.2).
This gene is translated into a protein of the same name, MED13L, which is part of a vast complex called "mediator complex" whose role is to activate the expression of many other genes.
It's an autosomal dominant genetic disease
We all have 23 pairs of chromosomes, and therefore two copies of all our genes (except for the last pair in men, composed of two different chromosomes annotated X and Y). A simple abnormality in one of the two copies (allele) of the MED13L gene produces the deleterious effects on development, manifested in the syndrome. As such, it is a so-called "autosomal dominant" disease
autosomal = on a non-sexual chromosome
dominant = 1 mutation in one of the two copies of the MED13L gene is sufficient for the pathology to be declared
The mutations observed in this gene are of "de novo" origin, or a "non-hereditary" genetic disease (in the classical sense of the term). A mutation will have occurred by chance, either during the initial stages of embryo development, or even earlier in a spermatozoid or an ovocyte.Sometimes, one of the parents carries the abnormality in some of his sexual cells (germinal mosaic) that he/she will transmit to the embryo.