Mitochondrial Inheritance

Mitochondrial DNA and Inheritance Pattern

Mitochondrial DNA Mitochondrial DNA Double-stranded DNA of mitochondria. In eukaryotes, the mitochondrial genome is circular and codes for ribosomal rnas, transfer rnas, and about 10 proteins. DNA Types and Structure ( mtDNA mtDNA Double-stranded DNA of mitochondria. In eukaryotes, the mitochondrial genome is circular and codes for ribosomal rnas, transfer rnas, and about 10 proteins. DNA Types and Structure)

• Circular and double-stranded DNA DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA Types and Structure
• 37 genes Genes A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. DNA Types and Structure encoding 13 proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis
• All proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis are part of the oxidative phosphorylation Phosphorylation The introduction of a phosphoryl group into a compound through the formation of an ester bond between the compound and a phosphorus moiety. Post-translational Protein Processing system ( mitochondria Mitochondria Semiautonomous, self-reproducing organelles that occur in the cytoplasm of all cells of most, but not all, eukaryotes. Each mitochondrion is surrounded by a double limiting membrane. The inner membrane is highly invaginated, and its projections are called cristae. Mitochondria are the sites of the reactions of oxidative phosphorylation, which result in the formation of ATP. They contain distinctive ribosomes, transfer RNAs; amino Acyl tRNA synthetases; and elongation and termination factors. Mitochondria depend upon genes within the nucleus of the cells in which they reside for many essential messenger RNAs. Mitochondria are believed to have arisen from aerobic bacteria that established a symbiotic relationship with primitive protoeukaryotes. The Cell: Organelles = powerhouses of the cell).
• Located within the mitochondria Mitochondria Semiautonomous, self-reproducing organelles that occur in the cytoplasm of all cells of most, but not all, eukaryotes. Each mitochondrion is surrounded by a double limiting membrane. The inner membrane is highly invaginated, and its projections are called cristae. Mitochondria are the sites of the reactions of oxidative phosphorylation, which result in the formation of ATP. They contain distinctive ribosomes, transfer RNAs; amino Acyl tRNA synthetases; and elongation and termination factors. Mitochondria depend upon genes within the nucleus of the cells in which they reside for many essential messenger RNAs. Mitochondria are believed to have arisen from aerobic bacteria that established a symbiotic relationship with primitive protoeukaryotes. The Cell: Organelles, therefore separate from a cell’s nuclear genome Genome The complete genetic complement contained in the DNA of a set of chromosomes in a human. The length of the human genome is about 3 billion base pairs. Basic Terms of Genetics
• Replication is not dependent on the cell cycle Cell cycle The phases of the cell cycle include interphase (G1, S, and G2) and mitosis (prophase, metaphase, anaphase, and telophase). The cell’s progression through these phases is punctuated by checkpoints regulated by cyclins, cyclin-dependent kinases, tumor suppressors, and their antagonists. Cell Cycle.
• Each mitochondrion contains several copies of its genome Genome The complete genetic complement contained in the DNA of a set of chromosomes in a human. The length of the human genome is about 3 billion base pairs. Basic Terms of Genetics:
  • Homoplasmy Homoplasmy Mitochondrial Myopathies: all copies of mtDNA mtDNA Double-stranded DNA of mitochondria. In eukaryotes, the mitochondrial genome is circular and codes for ribosomal rnas, transfer rnas, and about 10 proteins. DNA Types and Structure in a eukaryotic Eukaryotic Eukaryotes can be single-celled or multicellular organisms and include plants, animals, fungi, and protozoa. Eukaryotic cells contain a well-organized nucleus contained by a membrane, along with other membrane-bound organelles. Cell Types: Eukaryotic versus Prokaryotic cell identical
  • Heteroplasmy Heteroplasmy The occurrence of more than one organellar genome in the organelle population of a cell, tissue, or individual organism. It is due to the accumulation of different mutations that occur within the population of individual organelles of a cell. Mitochondrial Myopathies: copies of mtDNA mtDNA Double-stranded DNA of mitochondria. In eukaryotes, the mitochondrial genome is circular and codes for ribosomal rnas, transfer rnas, and about 10 proteins. DNA Types and Structure in eukaryotic Eukaryotic Eukaryotes can be single-celled or multicellular organisms and include plants, animals, fungi, and protozoa. Eukaryotic cells contain a well-organized nucleus contained by a membrane, along with other membrane-bound organelles. Cell Types: Eukaryotic versus Prokaryotic cells differ from each other → most cases of mutated mtDNA mtDNA Double-stranded DNA of mitochondria. In eukaryotes, the mitochondrial genome is circular and codes for ribosomal rnas, transfer rnas, and about 10 proteins. DNA Types and Structure are heteroplasmic (only some mtDNA mtDNA Double-stranded DNA of mitochondria. In eukaryotes, the mitochondrial genome is circular and codes for ribosomal rnas, transfer rnas, and about 10 proteins. DNA Types and Structure copies carry the mutation Mutation Genetic mutations are errors in DNA that can cause protein misfolding and dysfunction. There are various types of mutations, including chromosomal, point, frameshift, and expansion mutations. Types of Mutations).

Inheritance pattern

• Mitochondrial inheritance is a form of extranuclear, and therefore nonmendelian, inheritance.
• mtDNA mtDNA Double-stranded DNA of mitochondria. In eukaryotes, the mitochondrial genome is circular and codes for ribosomal rnas, transfer rnas, and about 10 proteins. DNA Types and Structure maternally inherited:
  • Most paternal mitochondria Mitochondria Semiautonomous, self-reproducing organelles that occur in the cytoplasm of all cells of most, but not all, eukaryotes. Each mitochondrion is surrounded by a double limiting membrane. The inner membrane is highly invaginated, and its projections are called cristae. Mitochondria are the sites of the reactions of oxidative phosphorylation, which result in the formation of ATP. They contain distinctive ribosomes, transfer RNAs; amino Acyl tRNA synthetases; and elongation and termination factors. Mitochondria depend upon genes within the nucleus of the cells in which they reside for many essential messenger RNAs. Mitochondria are believed to have arisen from aerobic bacteria that established a symbiotic relationship with primitive protoeukaryotes. The Cell: Organelles are found at the base of the sperm’s tail, which is used for propelling sperm cells.
  • In sexual reproduction, the mitochondria Mitochondria Semiautonomous, self-reproducing organelles that occur in the cytoplasm of all cells of most, but not all, eukaryotes. Each mitochondrion is surrounded by a double limiting membrane. The inner membrane is highly invaginated, and its projections are called cristae. Mitochondria are the sites of the reactions of oxidative phosphorylation, which result in the formation of ATP. They contain distinctive ribosomes, transfer RNAs; amino Acyl tRNA synthetases; and elongation and termination factors. Mitochondria depend upon genes within the nucleus of the cells in which they reside for many essential messenger RNAs. Mitochondria are believed to have arisen from aerobic bacteria that established a symbiotic relationship with primitive protoeukaryotes. The Cell: Organelles in mammalian sperm are destroyed by the egg cell (oocyte) following fertilization Fertilization To undergo fertilization, the sperm enters the uterus, travels towards the ampulla of the fallopian tube, and encounters the oocyte. The zona pellucida (the outer layer of the oocyte) deteriorates along with the zygote, which travels towards the uterus and eventually forms a blastocyst, allowing for implantation to occur. Fertilization and First Week. 
• Role of heteroplasmy Heteroplasmy The occurrence of more than one organellar genome in the organelle population of a cell, tissue, or individual organism. It is due to the accumulation of different mutations that occur within the population of individual organelles of a cell. Mitochondrial Myopathies:
  • Severity of disease depends on the proportion of mutated versus nonmutated alleles that are inherited.
  • Because of heteroplasmy Heteroplasmy The occurrence of more than one organellar genome in the organelle population of a cell, tissue, or individual organism. It is due to the accumulation of different mutations that occur within the population of individual organelles of a cell. Mitochondrial Myopathies, mitochondrial disorders have a variable Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables presentation within a family.

Mitochondrial Disorders

Mitochondrial disorders are extremely variable Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables and may range from mild to severe clinical presentation within the same family owing to heteroplasmy Heteroplasmy The occurrence of more than one organellar genome in the organelle population of a cell, tissue, or individual organism. It is due to the accumulation of different mutations that occur within the population of individual organelles of a cell. Mitochondrial Myopathies. 

• Leber hereditary optic neuropathy Neuropathy Leprosy ( LHON LHON A maternally linked genetic disorder that presents in mid-life as acute or subacute central vision loss leading to central scotoma and blindness. The disease has been associated with missense mutations in the mtDNA, in genes for complex I, III, and IV polypeptides, that can act autonomously or in association with each other to cause the disease. Mitochondrial Myopathies):
  • Degeneration of retinal ganglion cells Ganglion Cells The Visual Pathway and Related Disorders and optic nerves
  • Typical age at onset: young adulthood
  • Acute or subacute bilateral vision Bilateral Vision Macular Degeneration loss
  • Causes permanent vision Vision Ophthalmic Exam loss, predominantly in young men
• Mitochondrial myopathy Myopathy Dermatomyositis, encephalopathy Encephalopathy Hyper-IgM Syndrome, lactic acidosis Lactic Acidosis Oxazolidinones, and stroke-like episodes (MELAS):
  • Typical age at onset: 2–10 years
  • Lactic acidosis Lactic Acidosis Oxazolidinones leads to vomiting Vomiting The forcible expulsion of the contents of the stomach through the mouth. Hypokalemia, abdominal pain Abdominal Pain Acute Abdomen, fatigue Fatigue The state of weariness following a period of exertion, mental or physical, characterized by a decreased capacity for work and reduced efficiency to respond to stimuli. Fibromyalgia, and muscle weakness.
  • Less common symptoms: stroke-like episodes, blindness Blindness The inability to see or the loss or absence of perception of visual stimuli. This condition may be the result of eye diseases; optic nerve diseases; optic chiasm diseases; or brain diseases affecting the visual pathways or occipital lobe. Retinopathy of Prematurity, and seizure activity
• Myoclonic epilepsy Epilepsy Epilepsy is a chronic brain disorder marked by recurrent and unprovoked seizures. These seizures can be classified as focal or generalized and idiopathic or secondary to another condition. Clinical presentation correlates to the classification of the epileptic disorder. Epilepsy with ragged red fibers (MERRF):
  • Manifests in childhood after previously normal development
  • Symptoms: myoclonus Myoclonus Involuntary shock-like contractions, irregular in rhythm and amplitude, followed by relaxation, of a muscle or a group of muscles. This condition may be a feature of some central nervous system diseases; (e.g., epilepsy-myoclonic). Nocturnal myoclonus is the principal feature of the nocturnal myoclonus syndrome. Neurological Examination, seizures Seizures A seizure is abnormal electrical activity of the neurons in the cerebral cortex that can manifest in numerous ways depending on the region of the brain affected. Seizures consist of a sudden imbalance that occurs between the excitatory and inhibitory signals in cortical neurons, creating a net excitation. The 2 major classes of seizures are focal and generalized. Seizures, ataxia Ataxia Impairment of the ability to perform smoothly coordinated voluntary movements. This condition may affect the limbs, trunk, eyes, pharynx, larynx, and other structures. Ataxia may result from impaired sensory or motor function. Sensory ataxia may result from posterior column injury or peripheral nerve diseases. Motor ataxia may be associated with cerebellar diseases; cerebral cortex diseases; thalamic diseases; basal ganglia diseases; injury to the red nucleus; and other conditions. Ataxia-telangiectasia, and myopathy Myopathy Dermatomyositis
  • Ragged red fibers (RRFs) can be seen in muscle biopsy Muscle Biopsy Trichinella/Trichinellosis.
• Leigh syndrome Leigh syndrome A group of metabolic disorders primarily of infancy characterized by the subacute onset of psychomotor retardation, hypotonia, ataxia, weakness, vision loss, eye movement abnormalities, seizures, dysphagia, and lactic acidosis. Pathological features include spongy degeneration of the neuropile of the basal ganglia, thalamus, brain stem, and spinal cord. Patterns of inheritance include X-linked recessive, autosomal recessive, and mitochondrial. Leigh disease has been associated with mutations in genes for the pyruvate dehydrogenase complex; cytochrome-c oxidase; ATP synthase subunit 6; and subunits of mitochondrial complex I. Mitochondrial Myopathies:
  • Subacute necrotizing encephalopathy Encephalopathy Hyper-IgM Syndrome
  • Leads to focal lesions in the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification stem, basal ganglia Basal Ganglia Basal ganglia are a group of subcortical nuclear agglomerations involved in movement, and are located deep to the cerebral hemispheres. Basal ganglia include the striatum (caudate nucleus and putamen), globus pallidus, substantia nigra, and subthalamic nucleus. Basal Ganglia: Anatomy, and cerebellum Cerebellum The cerebellum, Latin for “little brain,” is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Cerebellum: Anatomy
  • Can be caused by mutations in mtDNA mtDNA Double-stranded DNA of mitochondria. In eukaryotes, the mitochondrial genome is circular and codes for ribosomal rnas, transfer rnas, and about 10 proteins. DNA Types and Structure or nuclear DNA Nuclear DNA Mitochondrial Myopathies
  • ↓ Levels of thiamine Thiamine Also known as thiamine or thiamin, it is a vitamin C12H17N4OSCl of the vitamin B complex that is essential to normal metabolism and nerve function and is widespread in plants and animals Water-soluble Vitamins and their Deficiencies triphosphate
  • Symptoms:
    • Typically begin in infancy, but can appear at any age
    • Diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, vomiting Vomiting The forcible expulsion of the contents of the stomach through the mouth. Hypokalemia, dysphagia Dysphagia Dysphagia is the subjective sensation of difficulty swallowing. Symptoms can range from a complete inability to swallow, to the sensation of solids or liquids becoming “stuck.” Dysphagia is classified as either oropharyngeal or esophageal, with esophageal dysphagia having 2 sub-types: functional and mechanical. Dysphagia, seizures Seizures A seizure is abnormal electrical activity of the neurons in the cerebral cortex that can manifest in numerous ways depending on the region of the brain affected. Seizures consist of a sudden imbalance that occurs between the excitatory and inhibitory signals in cortical neurons, creating a net excitation. The 2 major classes of seizures are focal and generalized. Seizures 
  • Generally lethal within a few years after symptom onset