On the pedigree, it clearly shows maternal inheritance, this is what distinguishes it from literally all other options. Mitochondrial myopathies show MATERNAL inheritance (on a pedigree chart the circle aka female is affected and only the female can pass it on to her kids, an affected male can NEVER pass it on to his kids), why? Because sperm cells lose their mitochondrial DNA before fertilization, so in all of your cells, your mitochondrial DNA is from mom. Now, when mom passes down her mitochondrial DNA, she can be passing down her mutated mitochondrial DNA and a portion of normal mitochondrial DNA this mixture is called heteroplasy, it means that a person with a mitchondrial myopathy can show variability in the clinical symptoms they present with.

This means, they can be more severe in their presentation or less severe. In the vignette it states that mom has 50% mutated mitochondrial DNA versus her offspring who have 100% mutated mitochondrial DNA. Her kids presented more severely, than she did, aka variable clinical presentation in a mitchondrial myopathy = heteroplasmy.

Contrast this with variable expressivity, which occur in autosomal dominant disorders, not mitochondrial myopathies.

Heteroplasmy:Presence of both normal and mutated mtDNA, resulting in variable expression in mitochondrially inherited disease.

Anticipation: Increased severity or earlier onset of disease in succeeding generations (Examples are tri-nucleotide repeats such as Huntingtons and Fragile X)