Muscular dystrophies and mitochondrial myopathies: Pathology review
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Muscular dystrophies and mitochondrial myopathies: Pathology review
Musculoskeletal system
Bone disorders
Osteomyelitis
Bone tumors
Chondrosarcoma
Osteochondroma
Achondroplasia
Arthrogryposis
Cleidocranial dysplasia
Club foot
Craniosynostosis
Flat feet
Genu valgum
Genu varum
Osteogenesis imperfecta
Pectus excavatum
Pigeon toe
Lordosis, kyphosis, and scoliosis
Osteomalacia and rickets
Osteopetrosis
Osteoporosis
Osteosclerosis
Paget disease of bone
Musculoskeletal injuries and trauma
Degenerative disc disease
Sciatica
Spinal disc herniation
Spondylolisthesis
Spondylolysis
Achilles tendon rupture
Anterior cruciate ligament injury
Iliotibial band syndrome
Meniscus tear
Patellar tendon rupture
Patellofemoral pain syndrome
Sprained ankle
Unhappy triad
Compartment syndrome
Rhabdomyolysis
Carpal tunnel syndrome
Erb-Duchenne palsy
Klumpke paralysis
Sciatica
Thoracic outlet syndrome
Ulnar claw
Winged scapula
Carpal tunnel syndrome
Dislocated shoulder
Erb-Duchenne palsy
Klumpke paralysis
Radial head subluxation (Nursemaid elbow)
Rotator cuff tear
Thoracic outlet syndrome
Ulnar claw
Winged scapula
Musculoskeletal system pathology review
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Gout and pseudogout: Pathology review
Muscular dystrophies and mitochondrial myopathies: Pathology review
Myalgias and myositis: Pathology review
Neuromuscular junction disorders: Pathology review
Pediatric musculoskeletal disorders: Pathology review
Rheumatoid arthritis and osteoarthritis: Pathology review
Scleroderma: Pathology review
Seronegative and septic arthritis: Pathology review
Sjogren syndrome: Pathology review
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Muscular dystrophies and mitochondrial myopathies: Pathology review
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At the clinic, 32 year old mary comes with her 6 year old son thomas, after noticing he’s often clumsy, weak, and has trouble climbing the stairs of their house. Mary is worried because she had a brother who presented the same symptoms as a child, and developed progressive weakness, until he passed away at 23 years old due to respiratory problems. Upon physical examination, the physician notices that thomas has scoliosis and thick calves. Later that day, 29 year old sarah comes to the clinic with her 10 year old son mike because of progressive muscle weakness and fatigue, as well as vomiting and loss of appetite. In addition, she mentions that he has experienced seizures.
Based on the clinical findings, the physician concludes that both children have some form of inherited muscular disorder, and orders genetic testing to confirm the diagnosis. Now, let’s go over the two main groups: muscular dystrophies and mitochondrial myopathies.
Muscular dystrophies are a group of genetic disorders characterized by muscle degeneration and weakness. Within that group, dystrophinopathies are the most common, and this includes duchenne muscular dystrophy, or dmd for short, and becker muscular dystrophy, or bmd.
Both duchenne and becker result from mutations in the dystrophin gene, which is found on the x chromosome. For your exams, remember that these are x-linked recessive disorders, which means that all carrier males develop the disease, because they only have one x chromosome and thus one dystrophin gene available. On the other hand, females have two x chromosomes, so even if they have a defective dystrophin gene on one x chromosome, they still have another functional one. However, only one x chromosome gets expressed and the other is inactivated through a process called x-inactivation or lyonization. This inactivation is random which means that every cell could have a chance of having the mutated x chromosome be the active copy. If this is the case for more than half of the muscle cells, they will be a manifesting carrier who will develop symptoms. People with more cells with the active mutated x chromosome will have more severe symptoms and quicker disease progression. If less than half of their cells have the active mutated x chromosome, they’ll be an asymptomatic carrier and won’t develop symptoms.
Sources
- "Robbins Basic Pathology" Elsevier (2017)
- "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
- "Distal muscular dystrophies" Handbook of Clinical Neurology (2011)
- "Muscular Dystrophies" Elsevier Science Limited (2011)
- "Facioscapulohumeral Muscular Dystrophy" CONTINUUM: Lifelong Learning in Neurology (2016)
- "Cognitive Neuroscience: The Biology of the Mind (Fourth Edition)" W. W. Norton (2013)
- "Loose-leaf Version for Genetics: A Conceptual Approach" Macmillan Higher Education (2019)
- "Inheritance of most X-linked traits is not dominant or recessive, just X-linked" American Journal of Medical Genetics (2004)
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