lec 4 SAQ - Mitochondrial Genetics and Inherited Disorders Quiz

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Questions and Answers

What is the size of the mitochondrial genome?

16,569 bp

How many genes are there in the mitochondrial genome?

What percentage of the mitochondrial genome codes for mRNA, tRNA, or rRNA?

93%

How many copies of the mitochondrial genome are there per mitochondrion?

Dozens Signup and view all the answers

Where is the Cambridge Sequence determined from?

Several different individuals Signup and view all the answers

How many mitochondrial gene products are needed to make a mitochondrion?

About 3000 Signup and view all the answers

What is the function of mitochondria in a cell?

Mitochondria are the 'powerhouses' of the cell, responsible for generating ATP and involved in cell signalling, growth, death, and cell cycle regulation. Signup and view all the answers

What is the origin of mitochondria according to the endosymbiotic theory?

Mitochondria are thought to have originated as free-living bacteria that were taken up by eukaryotes to carry out oxidative phosphorylation. Signup and view all the answers

How many mitochondria are typically found in nucleated cells?

Most nucleated cells contain 500 to 2000 mitochondria. Signup and view all the answers

Which type of cell contains mitochondria that make up 80% of the intracellular volume?

In the cone cell photoreceptor of the eye, mitochondria make up 80% of the intracellular volume. Signup and view all the answers

What is the total number of protein-coding genes in the human nuclear genome?

The human nuclear genome contains approximately 23,000 protein-coding genes. Signup and view all the answers

How many chromosomes are present in the human nuclear genome?

The human nuclear genome consists of 23 double-stranded linear chromosomes. Signup and view all the answers

What is mitochondrial heteroplasmy?

Mitochondrial heteroplasmy refers to the variation in mtDNA sequences, either between cells (intercellular heteroplasmy) or within cells (intracellular heteroplasmy). Signup and view all the answers

How is mitochondrial DNA inherited?

Mitochondrial DNA is inherited almost exclusively along the maternal line. Signup and view all the answers

What is the threshold effect in mitochondrial heteroplasmy?

The threshold effect refers to the proportion of pathogenic mtDNA in tissues, which influences the phenotypic expression of mitochondrial diseases. Signup and view all the answers

What is the role of mtDNA mutation in mitochondrial heteroplasmy?

MtDNA mutation represents the only source of mtDNA genetic diversity, as mitochondria do not undergo recombination during cell division. Signup and view all the answers

What is the significance of the control region in mtDNA?

The control region of mtDNA is highly polymorphic and is useful for forensic purposes, such as in criminal investigations. Signup and view all the answers

What is the difference between homoplasmy and heteroplasmy?

Homoplasmy refers to all mtDNA sequences being the same, while heteroplasmy refers to variation in mtDNA sequences. Signup and view all the answers

Why is predicting phenotype from genotype and genetic counseling difficult in mitochondrial heteroplasmy?

Predicting phenotype from genotype and genetic counseling is difficult in mitochondrial heteroplasmy because the proportion of pathogenic mtDNA in tissues can vary and influence the phenotype. Signup and view all the answers

What are some high-energy organ systems often affected by mitochondrial disease?

Mitochondrial disease often affects high-energy organ systems such as the CNS, muscles (skeletal and heart), liver, and kidney. Signup and view all the answers

What are the symptoms of Leber Hereditary Optic Neuropathy?

Bilateral, painless, subacute visual failure that develops during young adult life. Signup and view all the answers

Who is more likely to be affected by Leber Hereditary Optic Neuropathy?

Males are approximately four times more likely to be affected than females. Signup and view all the answers

What are the typical symptoms of LHON?

The typical symptoms of LHON include asymptomatic onset in one eye followed by similar symptoms in the other eye, bilateral visual loss, and in some cases, central vision improvement but incomplete recovery. Signup and view all the answers

What are the three point mutations of mitochondrial DNA commonly associated with LHON?

The three point mutations of mitochondrial DNA commonly associated with LHON are m.3460G>A in MT-ND1, m.11778G>A in MT-ND4, and m.14484T>C in MT-ND6. Signup and view all the answers

What is the prognosis for individuals with the m.11778G>A mutation?

Individuals with the m.11778G>A mutation typically have an intermediate phenotype and there is a chance of recovery. Signup and view all the answers

What is heteroplasmy and how does it relate to LHON?

Heteroplasmy refers to the presence of both normal and mutated mitochondrial DNA in an individual. In LHON, heteroplasmy in cone cells may influence the risk of developing visual impairment. Signup and view all the answers

What are some associations between mtDNA haplogroups and other diseases?

Haplogroup H is associated with higher risk of Parkinson Disease, while haplogroups J and K are associated with lower risk. Haplogroups I, J, and T are also associated with increased longevity. Signup and view all the answers

Is mitochondrial DNA inheritance exclusively matrilineal?

No, mitochondrial DNA inheritance can also occur through biparental inheritance in some exceptional cases. Signup and view all the answers

What are the typical symptoms and characteristics of Leigh Syndrome?

Leigh Syndrome is characterized by MRI necrotizing lesions in the midbrain and brainstem, bilateral symmetrical degeneration of the brain stem, cerebellum, and basal ganglia. It typically has an onset in infancy or childhood, often after a viral infection, and can involve peripheral nervous system involvement, non-neurologic abnormalities, and respiratory impairment. Signup and view all the answers

What is the estimated incidence of Leigh Syndrome?

The estimated incidence of Leigh Syndrome is at least 1 in 40,000 births. Signup and view all the answers

What is the genetic heterogeneity of Leigh Syndrome?

Leigh Syndrome exhibits broad genetic heterogeneity, with mutations identified in at least 75 genes. Signup and view all the answers

What are some of the genetic mutations associated with Leigh Syndrome?

Some of the genetic mutations associated with Leigh Syndrome include mutations in pyruvate dehydrogenase (PDHC) deficiency, respiratory chain enzyme defects in complexes I, II, IV, and V, and specific mtDNA mutations such as the NARP mutation and the MERRF mutation. Signup and view all the answers

What are the different patterns of inheritance observed in Leigh Syndrome?

Leigh Syndrome can be inherited in matrilineal (mitochondrial) pattern, de novo mutation, X-linked recessive, or autosomal recessive patterns. Signup and view all the answers

Why are there different inheritance patterns observed in Leigh Syndrome?

The different inheritance patterns in Leigh Syndrome are primarily due to the fact that most mitochondrial proteins are encoded on the nuclear genome, and mutations in these genes follow classic Mendelian inheritance rules. Signup and view all the answers

What is mitochondrial transplantation/donation?

Mitochondrial transplantation/donation is a technique that involves the transfer of healthy mitochondria to prevent the passing on of hereditary mitochondrial diseases. It can be performed before or after fertilization and has been the subject of ethical debates, including a UK parliamentary debate in 2015. Signup and view all the answers

What are some important factors to remember about mitochondrial genetics?

Some important factors to remember about mitochondrial genetics are: 1. Predicting phenotype from mtDNA genotype is difficult due to heteroplasmy. 2. Males affected by mtDNA-related diseases cannot transmit the disease. 3. mt Haplogroups can influence disease penetrance and severity. 4. Most Leigh Syndrome cases are caused by mutations in the nuclear genome, leading to Mendelian inheritance patterns. Signup and view all the answers

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Study Notes

Mitochondrial Genome

The mitochondrial genome is approximately 16.5 kilobase pairs (kb) in size.
It contains 37 genes, which code for 2 rRNAs, 22 tRNAs, and 13 proteins.

Mitochondrial Genome Composition

93% of the mitochondrial genome codes for mRNA, tRNA, or rRNA.
Each mitochondrion has 2-10 copies of the mitochondrial genome.

Mitochondrial Function and Origin

Mitochondria are the site of cellular respiration, generating energy for the cell.
According to the endosymbiotic theory, mitochondria originated from a symbiotic relationship between ancient bacteria and eukaryotic cells.

Mitochondrial Distribution

Nucleated cells typically have 100-1000 mitochondria.
Mitochondria in muscle cells can make up 80% of the intracellular volume.

Human Nuclear Genome

The human nuclear genome contains 20,000-25,000 protein-coding genes.
The human nuclear genome consists of 23 pairs of chromosomes.

Mitochondrial Heteroplasmy

Mitochondrial heteroplasmy is the presence of two or more types of mitochondrial DNA (mtDNA) in a single cell or organism.
Mitochondrial DNA is inherited exclusively through the maternal line.
The threshold effect in mitochondrial heteroplasmy refers to the minimum percentage of mutated mtDNA required to cause mitochondrial dysfunction.
mtDNA mutations contribute to mitochondrial heteroplasmy.

Mitochondrial Disease

Mitochondrial diseases often affect high-energy organ systems such as the brain, heart, and muscles.
Leber Hereditary Optic Neuropathy (LHON) is a mitochondrial disease that causes vision loss.
LHON is more likely to affect males, and symptoms typically include bilateral optic neuropathy and vision loss.
Three point mutations of mitochondrial DNA are commonly associated with LHON: m.11778G>A, m.3460G>A, and m.14484T>C.
The prognosis for individuals with the m.11778G>A mutation is poor, with most patients experiencing significant vision loss.

Mitochondrial Genetics

Mitochondrial DNA haplogroups have been associated with other diseases, such as Alzheimer's disease and type 2 diabetes.
Mitochondrial DNA inheritance is not exclusively matrilineal in some cases, such as mitochondrial transplantation.
Leigh Syndrome is a mitochondrial disease characterized by developmental delay, seizures, and lactic acidosis.
The estimated incidence of Leigh Syndrome is 1 in 30,000 to 1 in 50,000 births.
Leigh Syndrome is genetically heterogeneous, with multiple mutations associated with the disease.
Mitochondrial transplantation/donation is a potential treatment for mitochondrial diseases.

Important Factors in Mitochondrial Genetics

Mitochondrial genetics is complex and influenced by various factors, including mitochondrial heteroplasmy, the threshold effect, and mitochondrial DNA inheritance.
Predicting phenotype from genotype and genetic counseling can be difficult in mitochondrial heteroplasmy due to the complexity of mitochondrial genetics.

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