Muscular Dystrophy B2.4 Flashcards
(14 cards)
What is muscular dystrophy?
A group of inherited conditions that cause gradual weakening of the muscles, leading to an increased level of disability. It is a progressive condition, some types eventually effecting the heart or the muscles used in breathing which can be life threatening.
What is the cause of muscular dystrophy?
They are caused by mutations in the genes for muscle proteins, particularly dystrophin which strengthens muscle fibres and protects them from injury as they contract and relax. This causes changes to the muscle fibres and interferes with the muscles ability to function.
Different types of muscular dystrophy can be classed as:
- dominant inherited disorders (caused by dominant alleles), where the mutation can be inherited from one parent
- recessive inherited disorders (caused by recessive alleles), where the mutations must be inherited from both parents
- sex-linked inherited disorders (caused by sex-linked alleles), which are more common and severe in males eg DMD
- spontaneous gene mutation, with no family history of the disease
What is myotonic dystrophy?
- Affects smaller muscles first eg face, neck, jaw
- Affects men and woman equally
- along with muscle wasting, can cause muscle stiffness (myotonia), cataracts, sleeping, dysphagia, learning delay, slow and irregular heartbeat
-Highly variable in symptoms, severity, age of presentation and life expectancy - Most deaths are from pneumonia, breathing difficulties or cardiac issues
What is Becker dystrophy?
- Affects mainly boys
- Similar symptoms but less severe than Duchenne muscular dystrophy
- Often able to walk unaided up to 40s or 50s
- May develop dilated cardiomyopathy or breathing difficulties
- Can have normal life expectancy
What is Duchenne muscular dystrophy?
- The most common type of MD
- In the Uk, about 100 boys are born with DMD each year
- Caused by mutations in the dystrophin gene which codes for dystrophin protein (dystrophin helps maintain muscle structure and function)
- Without dystrophin, muscle cells become damaged over time and are replaced by fat and fibrous tissue
- Leads to progressive weakness in all skeletal muscles
- DMD is an X linked recessive disorder, meaning it is caused by a mutation in a gene found on the X chromosome and in a female, 2 copies are required for the phenotype to show
What are mutations?
Changes in the base sequence of DNA
What is a gene?
A sequence of bases in DNA that codes for a polypeptide or protein
What is a dominant allele?
Forms of a gene that will have an effect even if they are inherited from only one parent
What is a recessive allele?
Forms of a gene that will only have an effect if they are inherited from both parents
What are sex linked alleles?
Forms of a gene that are carried on the X sex chromosome and are usually responsible for inherited disorders. Males have one X and one Y chromosome, but the Y is very short with only a few alleles. A male with a recessive allele on the X chromosome will have the disease. Females have two X chromosomes, so the normal allele will usually mask the mutant allele, unless they have inherited the mutant allele from both parents. For this reason, sex linked chromosomes are usually more common and severe in males.
What are the signs and symptoms of DMD?
- difficulty walking, running, jumping, standing up (gowers sign)
- learn to speak later than normal
- unable to climb stairs without support
- behavioral or learning difficulties
- unusual fatigue
How can DMD be diagnosed?
Often diagnosed around the age of three when muscle weakness or difficulty with physical activities is noticed, the GP can refer a child to a specialist for assessment
- Initial blood test- raised creatine kinase levels
- CK- enzyme released when muscles are damaged
- The liver enzymes (ALT and AST) may also be raised also indicating muscle damage and breakdown
- Genetic testing confirms diagnosis by identifying change in dystrophin gene
What are treatments for DMD?
- corticosteroids eg prednisone: can improve muscle strength and function for 6months to 2years as they have side effects long term (weight gain, excessive hair growth)
- creatine supplement: can improve muscle strength but has side effects
- ataluren: newer medicine developed to treat children 2+ who can walk
- ACE inhibitors/beta blockers: supports cardiac function
- Physiotherapy: exercise to support and maintain movement
- SALT: later stages can include difficulty swallowing
- occupational therapist: promotes independence using assistive equipment and environmental changes
- physical aids: crutches, walkers, wheelchairs, equipment to support breathing
- corrective surgery: correct some physical problems that may occur is severe cases like scoliosis
