Genetics: mitochondrial inheritance: practice question

A Anatomy question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Anatomy · Genetics: mitochondrial inheritance

Sample item

A family has a disorder with stroke-like episodes and lactic acidosis, and a muscle biopsy shows ragged-red fibres. All children of affected women are affected to variable degrees, while affected men never transmit the condition. What is the mode of inheritance?

AAutosomal recessive inheritanceBAutosomal dominant with reduced penetranceCX-linked dominant inheritanceDMitochondrial inheritance with heteroplasmy

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Mitochondrial inheritance with heteroplasmy

Mitochondria, and their DNA, are inherited almost entirely from the oocyte, so only mothers transmit mitochondrial disorders, to sons and daughters alike. Variation in the proportion of mutant mitochondria (heteroplasmy) explains variable severity. Ragged-red fibres on a Gomori trichrome stain are typical of mitochondrial myopathy, as in MELAS.

Option by option

A. Autosomal recessive inheritance
Recessive disease usually appears in siblings of unaffected parents, not in all children of an affected mother.
B. Autosomal dominant with reduced penetrance
Autosomal dominant inheritance can pass from father to children and does not give uniform maternal transmission.
C. X-linked dominant inheritance
In X-linked dominant inheritance an affected father passes the disease to all his daughters.
D. Mitochondrial inheritance with heteroplasmy (correct)
Correct. Maternal-only transmission with variable severity indicates mitochondrial DNA with heteroplasmy.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is D, Mitochondrial inheritance with heteroplasmy. Mitochondria, and their DNA, are inherited almost entirely from the oocyte, so only mothers transmit mitochondrial disorders, to sons and daughters alike.

Why is "Autosomal recessive inheritance" not the answer?

Recessive disease usually appears in siblings of unaffected parents, not in all children of an affected mother.

Why is "Autosomal dominant with reduced penetrance" not the answer?

Autosomal dominant inheritance can pass from father to children and does not give uniform maternal transmission.

Why is "X-linked dominant inheritance" not the answer?

In X-linked dominant inheritance an affected father passes the disease to all his daughters.

What concept does this question test?

It tests Genetics: mitochondrial inheritance in Anatomy. Variation in the proportion of mutant mitochondria (heteroplasmy) explains variable severity. Ragged-red fibres on a Gomori trichrome stain are typical of mitochondrial myopathy, as in MELAS.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Genetics: mitochondrial inheritance?

Learn every nerve by its route, its muscles and what a lesion looks like at the bedside. That one habit answers a large share of questions. Then use the flashcards and the other Anatomy questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.