The genetic anomaly responsible for Type
1 Myotonic Dystrophy was identified in 1992. It is
located on chromosome 19, a chromosome that is not
implicated in the determination of the sex of the
individual. This gene was identified as the gene for
myotonin-protein kinase. This name comes from the fact
that the gene carries the information to produce an
enzyme that is part of the protein kinase family.
Each gene is made up
of three parts. The promoting area (blue) is
responsible for gene expression in tissues as well as
gene regulation. This means that this area will make it
possible for gene to be expressed in the muscle but not
in the brain, for example. This area also controls the
level of expression of the gene which determines whether
it can be activated or inhibited depending on its
environment. The second area holds the information for
protein production (green) and the third area at the
extremity of the gene (grey) plays a little known role.
The genetic anomaly responsible for Myotonic Dystrophy
is located in this third area.
The gene for Type 1 Myotonic Dystrophy. The gene
contains an area that is responsible for its expression
and regulation (blue), an area containing the information
for protein synthesis (green) and a non coding 3’ area
whose role is not well known (grey).
To understand the genetic anomaly, we
must go over gene composition. Genes can be compared to
the letters of the alphabet i.e. they are composed of letters. The gene alphabet has 4 letters A, T, C,
G that are repeated in varying order. These letters are
used to form words. In genetics, all words are composed
of 3 letters (for example: ATC). In Myotonic Dystrophy,
the word is CTG. In the normal population, this word is
repeated several times within the Myotonic Dystrophy
gene but always less than 40 times (CTG-CTG-CTG-CTG-etc.).
For reasons still unknown, the number of repetitions can
be up to 3000 to 5000 times. This is the anomaly
responsible for Type 1 Myotonic Dystrophy.