Duchenne Muscular Dystrophy
What is the primary cause of Duchenne muscular dystrophy?
DMD is primarily caused by mutations in the dystrophin gene located on the X chromosome. These mutations result in the absence or deficiency of the dystrophin protein.
What type of inheritance in DMD
X linked recessive
By what age should a child be walking?
18 months
How does the absence of dystrophin lead to muscle degeneration in DMD?
Dystrophin is a structural protein that plays a crucial role in maintaining the integrity of muscle cells - links intracellular actin with the extracellular matrix, which stabilises the sarcolemma (muscle cell membrane). It provides structural support to the muscle fibres and helps protect them from damage during muscle contractions.
Without dystrophin, the muscle cell membrane becomes more susceptible to damage during muscle contractions. This leads to an influx of calcium into the muscle cell, triggering a cascade of events that result in muscle cell death, fibrosis, and diminished cardiac contractile function
What type of inheritance is sickle cell disease
Autosomal recessive
At what age is it expected for babies to start smiling in response to stimuli?
6 to 8 weeks
Name some investigative tests for DMD (3)
What are some developmental milestones for a 5 year old?
Gross motor - skips and hops
Fine motor - draws squares and triangles
Speech, language, hearing - fluent speech
Social, behavioural - can dress and undress
What is calf pseudohypertrophy, and why is it a characteristic feature of DMD?
Calf pseudohypertrophy is the enlargement of the calf muscles, giving a false appearance of muscle hypertrophy. In DMD, this is due to the replacement of muscle tissue with fat and connective tissue, masking the underlying muscle wasting.
What are some developmental milestones at 18 months?
Walking
Builds a 3-block tower
10 words and can 4 identify body parts
Can hold a spoon to feed
Besides skeletal muscles, how does Duchenne muscular dystrophy affect other organ systems?
In DMD, cardiac muscles can undergo fibrosis and hypertrophy, leading to cardiomyopathy and heart failure. Respiratory muscles weaken over time (e.g. diaphragm and accessory muscles), resulting in respiratory insufficiency and the potential need for ventilatory support.
Give 5 developmental red flags
Not smiling by 10 weeks
Not sitting unsupported by 12 months
Not walking by 18 months
Showing hand preference before 12 months (normally at 18 months) - can be a sign of neurological problems
Not knowing 2-6 words before 18 months