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NBME 20 Answers

nbme20/Block 2/Question#25

A 14-year-old girl is brought to the physician ...

Mitochondrial tRNALeu

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submitted by mrmassador(4),

I think the point of the question is to recognize that this is a mitochondrial disease (mother and maternal grandmother were affected). Produces wide range of effects, but muscle weakness and some neurologic deficits stood out to me. Also this: https://ghr.nlm.nih.gov/gene/MT-TL1#conditions

sympathetikey  Yes, but doesn't that mean maternal transmission? Men can have these diseases too, they just won't pass them on. +2  




 +4  upvote downvote
submitted by sympathetikey(303),

Mutations in MT-TL1 (Mitochondrially encoded tRNA leucine 1)

A common mutation is A3243G. Can result in multiple mitochondrial deficiencies and associated disorders. It is associated with:

  • Mitochondrial encephalomyopathy
  • Lactic acidosis
  • Stroke-like episodes (MELAS)

MELAS is a rare mitochondrial disorder known to affect many parts of the body, especially the nervous system and the brain. Symptoms of MELAS include:

  • Recurrent severe headaches
  • Muscle weakness (myopathy)
  • Hearing loss
  • Stroke-like episodes with a loss of consciousness, seizures, and other problems affecting the nervous system.

Source: https://en.wikipedia.org/wiki/MT-TL1





 +2  upvote downvote
submitted by hayayah(399),

This is a presentation of mitochondrial myopathy. They often present with myopathy, lactic acidosis, and CNS disease. 2° to failure in oxidative phosphorylation. Muscle biopsy often shows “ragged red fibers”.

There is variable expression in a population or even within a family due to heteroplasmy in mitochondrial inheritance.





 +0  upvote downvote
submitted by thomas(3),

It's a mitochondrial disease. - present in successive generations, always with maternal transmission - damage to high-energy tissues - CSF lactic acidosis (due to increased anaerobic metabolism due to impaired oxidative phosphorylation)