Citation: Finsterer J. Retinal nerve fiber and ganglion cell layer
thinning in hereditary and acquired mitochondrial optic neuropathies. Int J
Ophthalmol 2019;12(10):1666. DOI:10.18240/ijo.2019.10.24
·Comment·
Retinal
nerve fiber and ganglion cell layer thinning in hereditary and acquired
mitochondrial optic neuropathies
Josef Finsterer
Krankenanstalt
Rudolfstiftung, Messerli Institute, Vienna 1180, Austria
Correspondence to: Josef Finsterer. Postfach 20,
Vienna 1180, Austria. fifigs1@yahoo.de
Received:
DOI:10.18240/ijo.2019.10.24
Citation:
Finsterer J. Retinal nerve fiber and ganglion cell layer thinning in hereditary
and acquired mitochondrial optic neuropathies. Int J Ophthalmol 2019;12(10):1666
Dear Editor,
With
interest we read the article by Teng et al[1] about a
study of the retinal nerve and ganglion cell layers by means of optic coherence
tomography (OCT) in 32 patients with a mitochondrial optic neuropathy (MON).
Included were 20 patients with hereditary MON [Leber’s
hereditary optic neuropathy (LHON)], 12 patients with acquired MON [ethambutol-induced
optic neuropathy (EION)], and 41 healthy controls. Retinal nerve fiber layer
(RNFL) thickness was reduced in the nasal, superior, temporal, and inferior
quadrants in LHON patients but only in the temporal quadrant in the EION
patients. Thickness of the retinal ganglion cell layer (RGCL) was similarly
reduced in LHON and EION patients. We have the following comments and concerns.
Among the 32
patients with MON, 20 patients were diagnosed with hereditary MON (LHON) and 12
patients were diagnosed with secondary, acquired MON[1]. Surprisingly, Table 1 lists
among the 12 patients with EION, 3 patients with an OPA1 mutation and 1 patient
with an NDxx mutation.
Does it mean that 4 patients with EION also carried a mutation causing
hereditary MON? Since it was the aim of the study to compare RNFL and RGCL
thickness between primary and secondary MON patients, mixing patients with
primary and secondary MON in the EION group is confusing and not acceptable.
One patient
with human immunodeficiency virus (HIV) was included among the EION group. We should know if he
also had tuberculosis and underwent ethambutol treatment or if optic neuropathy
in this patient was attributable to other causes including anti-retroviral therapy
induced optic neuropathy[2].
Another
shortcoming of the study design is that the LHON cohort was small and not
coherent. Twelve patients carried the variant m.11778x>x, 5 patients the
variant m.14484x>x, and one patient each the variants m.3260x>x,
m.14568x>x and m.11696x>x respectively. Unfortunately, the nucleotides
being substituted were not provided.
A further
shortcoming is that heteroplasmy rates of the detected mtDNA variants was not
provided. Phenotypic expression depends at least in part on the amount of
mutated mtDNA within a mitochondrion[3]. In this respect it should be mentioned how many of the
20 LHON patients had a positive family history for LHON and in how many
patients the mutation occurred sporadically.
Another shortcoming is that tissues other than the optic
nerve were not investigated. Since
it is well appreciated that LHON is a multisystem mitochondrial disorder (MID)
already at onset of the disease or becomes a multisystem disease during the
further course[4],
it is crucial that these patients undergo prospective investigations for
multisystem disease. This is of relevance as involvement of other organs in
LHON particularly the brain and the heart may strongly influence the outcome of
these patients.
Overall,
this interesting study could be more meaningful if more profound genetic
information would have been provided, if the family history of LHON patients
would have been mentioned, and if the study groups would have been more
coherent.
ACKNOWLEDGEMENTS
Conflicts of Interest: Finsterer J, None.
REFERENCES