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Chapter 9: Problem 6

What three criteria must a human disorder fulfill to be classified as a hereditary mitochondrial disease?

Short Answer

Expert verified
Answer: A hereditary mitochondrial disease must meet the following criteria: 1) have a genetic basis in mitochondrial DNA, 2) lead to impaired mitochondrial function, and 3) present specific clinical manifestations or symptoms.

Step by step solution

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1. Genetic Basis in Mitochondrial DNA

In order for a disorder to be classified as a hereditary mitochondrial disease, it must have a genetic origin in the mitochondrial DNA. This means that the disorder should result from a mutation, deletion, or duplication in the mitochondrial DNA, which is inherited from the mother since mitochondrial DNA is maternally inherited.
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2. Impaired Mitochondrial Function

The disorder must directly affect the function of the mitochondria, either by impairing the generation of cellular energy (ATP) through oxidative phosphorylation or by disrupting other critical biochemical processes within the mitochondria. Proper mitochondrial function, including the generation of cellular energy and the maintenance of cellular health, is essential for normal cell function. A hereditary mitochondrial disease will directly or indirectly impair these processes leading to the disorder's symptoms.
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3. Clinical Manifestations

Finally, a hereditary mitochondrial disease must be associated with specific clinical manifestations or symptoms. These symptoms are often caused by dysfunction or failure in cells or tissues that have high energy demands and thus are most affected by mitochondrial dysfunction. Examples of common clinical manifestations of mitochondrial disorders include muscle weakness, neurodegeneration, cardiomyopathies, and multisystem involvement.

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Most popular questions from this chapter

Why is the rate of mutation in mitochondrial DNA higher than that in nuclear DNA but the incidence of genetic diseases caused by mutations in mitochondrial DNA relatively low?

In Drosophila subobscura, the presence of a recessive gene called grandchildless (gs) causes the offspring of homozygous females, but not those of homozygous males, to be sterile. Can you offer an explanation as to why females and not males are affected by the mutant gene?

Mutations in mitochondrial DNA appear to be responsible for a number of neurological disorders, including myoclonic epilepsy and ragged-red fiber disease, Leber's hereditary optic neuropathy, and Kearns-Sayre syndrome. In each case, the disease phenotype is expressed when the ratio of mutant to wild-type mitochondria exceeds a threshold peculiar to each disease, but usually in the 60 to 95 percent range. (a) Given that these are debilitating conditions, why has no cure been developed? Can you suggest a general approach that might be used to treat, or perhaps even cure, these disorders? (b) Compared with the vast number of mitochondria in an embryo, the number of mitochondria in an ovum is relatively small. Might such an ooplasmic mitochondrial bottleneck present an opportunity for therapy or cure? Explain.

The maternal-effect mutation bicoid ( \(b c d\) ) is recessive. In the absence of the bicoid protein product, embryogenesis is not completed. Consider a cross between a female heterozygous for the bicoid alleles \(\left(b c d^{+} / b c d^{-}\right)\) and a male homozygous for the mutation \(\left(b c d^{-} / b c d^{-}\right)\) (a) How is it possible for a male homozygous for the mutation to exist?. (b) Predict the outcome (normal vs. failed embryogenesis) in the \(\mathrm{F}_{1}\) and \(\mathrm{F}_{2}\) generations of the cross described.

Tools are now available to sequence mtDNAs from an individual's genome sequence data to accurately measure heteroplasmy and to easily recognize the most functionally important mitochondrial variants. What is the significance of these tools for the diagnosis of human mtDNA diseases? If your sibling is diagnosed with a mitochondrial degenerative neurological disorder, would you want your mtDNA to be sequenced for mutations and heteroplasmy?
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