Maternal inheritance was historically the primary explanation for mitochondrial diseases due to early mtDNA sequencing.

“you know when I was going through residency probably when you're also going through your clinical training the answer to almost every single question about mitochondrial disease was maternal inheritance mm-hmm and that's because the nuclear genome was sequenced in draft format in 2001 but the mitochondrial DNA was sequenced in 1981 so those almost exactly 20 years earlier and it's small and so as soon as you saw patients that had a particular clinical phenotype that could be a mitochondrial disease it was easy to sequence the mitochondrial DNA”