Researchers examined a family with an interesting distri...

Question

Researchers examined a family with an interesting distribution of Leigh syndrome symptoms. In this disorder, individuals may show a progressive loss of motor function (ataxia, A) with peripheral neuropathy (PN, meaning impairment of the peripheral nerves). A mitochondrial DNA (mtDNA) mutation that reduces ATPase activity was identified in various tissues of affected individuals. The accompanying table summarizes the presence of symptoms in an extended family.

Person Condition Percent Mitochondria with
Mutation
Proband A and PN >90%
Brother A and PN >90%
Brother Asymptomatic 17%
Mother PN 86%
Maternal uncle PN 85%
Maternal cousin A and PN 90%
Maternal cousin A and PN 91%
Maternal Asymptomatic 56%
grandmother

Provide an explanation for the pattern of inheritance of the disease. What term describes this pattern?

Accepted Answer

Hello everyone. Let's look at our next question. It says Leigh syndrome can be inherited in various ways. It can be inherited when the mutated genes in mitochondrial DNA such as empty dash 80 P. Six are passed onto the offspring provided that the condition can affect both male and female offspring? What type of inheritance pattern is represented in this case? So Lee syndrome because it can be caused by mutations in so many different genes over 75 of them. It can be inherited in different ways depending on where the gene is. That has the mutation in this individual's case. So our question describes a case where the mutation on a gene in the mitochondrial D. N. A. And the saying the condition affects both males and females equally. So when we have a mutation of mitochondrial DNA, the inheritance pattern that will see is a maternal inheritance pattern because all of our mitochondrial DNA is inherited from our mother. Since that's where the organelles come from. Only the egg passes along its organelles in reproduction. So we see inheritance only from the mother. The father cannot pass the condition on to his Children even though it's inherited only from the mother. It affects male and female offspring equally. And that's because even though it's inherited only from the female parent it doesn't matter both males and females inherit that mitochondrial DNA from their solely from their mothers. So that's distinct from sex linked inheritance where you do see inheritance from mother to son most commonly. But that's of course because the son inherits the single X chromosome from the mother only um inheriting the wife and the father. Whereas females of course inherit one X from each parent. So since the male has only one X chromosome it only takes one copy to express the condition. And you see the condition much much more frequently in males. But with maternal inheritance inherited only from the mother affecting male and female offspring equally. So let's look through our answer choices noting that we have choice D. None of the options is correct. We see choice A. Is sex linked inheritance as we discussed. That's not correct. As that's not what we're seeing here. Choice B. Is paternal inheritance from the father. But that's not correct. Um Since mitochondrial DNA is never inherited from the father it doesn't matter if the father carries the condition when the mutations in the mitochondrial D. N. A. Oh I see autism. All inheritance. This is not correct. Since we see only the maternal inheritance happening, the mutation is in the mitochondrial D. N. A. Uh Leigh syndrome can be caused by a mutation on the autism's. But in this case we're told specifically in the question that the gene mutation is in the mitochondrial D. N. A. So we're left with choice D. None of the options is incorrect. And this is our answer because we're looking for maternal inheritance. So again when Leigh syndrome is inherited when the mutated mutated genes and mitochondrial DNA are passed onto the offspring um With the condition affecting both male and female offspring. What type of inheritance pattern is represented? In this case, Choice D. None of the options is correct. See you in the next video.

Key Concepts

Mitochondrial Inheritance

Leigh Syndrome

Penetrance and Expressivity

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