Family Tree DNA offers mitochondrial DNA (mtDNA) full sequence tests strictly for genealogy and personal ancestry information. Therefore, we do not examine or discuss medical implications of any person’s mtDNA full sequence.
In general, the medical or physiological impact of having a heteroplasmy is the same as that of having only the mutation at the same position. In other words, if you find that a mutation at this position is not known to be associated with any physiological issue, then the heteroplasmy is not either. If you find that a mutation at this position is or may be associated with a physiological issue, then the heteroplasmy may potentially produce the same issue or may produce a lesser form of it because not all of the mtDNA has the mutation.