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Mendelian genetics and punnett squares
Independent assortment of genes and linkage
Evolution and natural selection
Down syndrome (Trisomy 21)
Edwards syndrome (Trisomy 18)
Patau syndrome (Trisomy 13)
Fragile X syndrome
Cri du chat syndrome
Alagille syndrome (NORD)
Polycystic kidney disease
Familial adenomatous polyposis
Multiple endocrine neoplasia
Treacher Collins syndrome
von Hippel-Lindau disease
Polycystic kidney disease
Gaucher disease (NORD)
Glycogen storage disease type I
Glycogen storage disease type II (NORD)
Glycogen storage disease type III
Glycogen storage disease type IV
Glycogen storage disease type V
Mucopolysaccharide storage disease type 1 (Hurler syndrome) (NORD)
Niemann-Pick disease types A and B (NORD)
Niemann-Pick disease type C
Primary ciliary dyskinesia
Sickle cell disease (NORD)
Tay-Sachs disease (NORD)
Fragile X syndrome
Fabry disease (NORD)
Glucose-6-phosphate dehydrogenase (G6PD) deficiency
Mucopolysaccharide storage disease type 2 (Hunter syndrome) (NORD)
Ornithine transcarbamylase deficiency
Autosomal trisomies: Pathology review
Muscular dystrophies and mitochondrial myopathies: Pathology review
Miscellaneous genetic disorders: Pathology review
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Evan Debevec-McKenneySalma Ladhani, MD
Jahnavi Narayanan, MBBS
Primary mitochondrial myopathy is a rare genetic disorder that occurs when there are mutated mitochondria in muscle cells, especially skeletal muscle cells.
These mitochondria are unable to generate adenosine triphosphate, or ATP, which is a form of energy used by our cells.
As a result, muscle cells, which require a lot of energy to function, stop functioning properly.
The mitochondria are the main energy producing factories of a cell, and they do so with the help of the electron transport chain, and the enzyme ATP synthase.
The electron transport chain is made up of complexes of proteins or lipids, called electron carriers, embedded within the inner mitochondrial membrane which pass electrons along like the baton in a relay race.
This movement of electrons helps establish a proton gradient that drives ATP synthase to phosphorylate adenosine diphosphate or ADP into ATP.
Primary mitochondrial myopathy is caused by a mutation either in the mitochondrial DNA or nuclear DNA, which results in the abnormal production of mitochondrial proteins, impairing the function of the electron transport chain.
Mutations in the nuclear DNA are commonly inherited in an autosomal dominant fashion, which means one mutated gene is enough to cause the disease; or autosomal recessive fashion, which means two mutated genes, one from each parent, are needed to cause the disease.
Mutations in the mitochondrial DNA follow maternal inheritance , meaning that only an affected woman can pass on the disease to her children.
This is because, typically during fertilization, the father's mitochondria are left behind while the sperm’s nucleus alone enters the egg.
The exception is the mitochondrial DNA single deletion, a common cause of primary mitochondrial myopathy, which is always sporadic and cannot be transmitted to the offspring.
In primary mitochondrial myopathy, muscle cells are unable to generate ATP, which results in muscle weakness and fatigue.
Sometimes there may also be muscle pain, cramping, stiffness, or even paralysis of the muscle.
Individuals typically develop exercise intolerance, which is a reduced ability to perform physical activity.
Mitochondrial myopathies refers to a group of neuromuscular disorders caused by damage to the mitochondria, which are the energy-producing organelles in cells. This damage can disrupt the normal function of muscles and organs. Symptoms may include body weakness, exercise intolerance, loss of muscle mass, and problems with breathing, seizures, ophthalmoplegia (paralysis of eye muscles), and hypotonia (abnormally reduced muscle tone).
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