Muscle biopsy findings can suggest the presence of an mtDNA disorder, revealing the pathognomonic ragged red fibers
caused by proliferation of abnormal mitochondria.
7) Ragged red fibers and cytochrome c oxidase--negative muscle fibers, reflective of mitochondrial DNA alterations, are frequent but not diagnostic findings.
8) In addition, most of the vacuolated muscle fibers in h-IBM do not stain positively for Congo red and do not contain ragged red fibers or cytochrome c oxidase-negative fibers.
An example of a mitochondrial disorder is myoclonus epilepsy with ragged red fibers
(MERRF), in which the children have myoclonic and generalized tonic clonic seizures, dementia, ataxia, and weakness.
The most common point mutations are A3243G, accounting for 80% of patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS); A8344G, which underlies myoclonic epilepsy, ragged red fibers (MERRF); T8993G/C, leading to neuropathy, ataxia, retinitis pigmentosa (NARP); and G11778A, found in >50% of patients with Leber hereditary optic neuropathy (LHON).
The clinical phenotype of patients with A3243G overlaps with that of patients with A8344G in that they may both have ragged red fibers and lactic acidosis.
The presence of ragged red fibers
or a partial absence of cytochrome C oxidase staining, suggestive of mitochondrial defects, was also documented.
What they had done was test for several markers, like ragged red fibers
in the muscle tissue, and known mitochondrial DNA mutations.