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.

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

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

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)