What causes muscular
dystrophy?
These conditions are inherited, and the
different muscular dystrophies follow
various inheritance patterns.
Duchenne Muscular Dystrophy
(DMD)
The best-known type, Duchenne
muscular dystrophy (DMD), is inherited
in an X-linked recessive pattern,
meaning that the mutated gene that
causes the disorder is located on the X
chromosome, one of the two sex
chromosomes, and is thus considered
sex-linked.
In males (who have only one X
chromosome) one altered copy of the
gene in each cell is sufficient to
cause the condition. In females (who
have two X chromosomes) a mutation must
generally be present in both copies of
the gene to cause the
disorder. Males are
therefore affected by X-linked
recessive disorders much more often
than females.
X-linked inheritance
A
characteristic of X-linked inheritance
is that fathers cannot pass X-linked
traits to their sons. In about two
thirds of DMD cases, an affected male
inherits the mutation from a mother who
carries one altered copy of the DMD
gene. The other one third of cases
probably result from new mutations in
the gene. Females who carry one copy of
a DMD mutation may have some signs and
symptoms related to the condition (such
as muscle weakness and cramping), but
these are typically milder than the
signs and symptoms seen in affected
males. Duchenne muscular dystrophy and
Becker's muscular dystrophy are caused
by mutations of the gene for the
dystrophin protein and lead to an
overabundance of the enzyme creatine
kinase. The dystrophin gene is the
second largest gene in mammals.
