With interest we read the article by Müller et al. about a
study of 36 eyes of 18 patients with genetically proven maternally
inherited diabetes mellitus and deafness (MIDD)
for outer retinal atrophy (RORA) [1]. The authors concluded
that the development and progression of RORA can
be monitored by optical coherence tomography (OCT) and
that the morphological features of RORA in MIDD patients
resemble those of age-related macular degeneration
(AMD) [1]. We have the following comments and concerns.
A shortcoming of the study is that heteroplasmy rates of
the m.3243A>G variant was not provided. It is also unclear
in which tissue the MT-TL1 variant was detected. Since
heteroplasmy rates strongly determine the phenotype, it is
crucial to know the amount of mutated mtDNA in relation
to wild-type mtDNA in the most affected tissues. Since
the phenotype in MIDD patient is also dependent on the
mtDNA copy number (mtDNA depletion) [2], it is crucial
to know if any of the 18 included patients had a reduced
amount of mtDNA copies.
A further shortcoming is that the quality of the antidiabetic
treatment was not provided. Since retinal abnormalities
in diabetes strongly depend not only on the duration
of diabetes but also on the quality of the anti-diabetic control
[3], it is crucial to know the HbA1c values of each of
the 18 included patients.
Missing are also the current medication each patient was
regularly taking. Since the medication strongly influences
the HbA1c values, we should know the drugs each patients
was taking at the time of the ophthalmologic investigation.
Additionally, it should be mentioned if the included patients
adhered to the recommended anti-diabetic diet or not.
? Corresponding author.
y Email: fifigs1@yahoo.de
Though per definition, MIDD is phenotypically characterised
by diabetes and deafness, these patients may additionally
present with a myriad of other phenotypic manifestations
[4]. Not only the ears and the pancreas may
be primarily affected but also the central nervous system,
other endocrinological organs, the heart, the gastrointestinal
tract, the kidneys, and the eyes [4]. We should know
which of these additional phenotypic features were present
in the included patients, since they may strongly determine
the prognosis and outcome of these patients.
In the eyes, MIDD patients may not only manifest
with RORA, but also with optic atrophy [5], pigmentary
retinopathy [6], macular dystrophy [7], central retinal vein
occlusion [8], or choroidal atrophy [9]. Which of these features
were additionally present in the 18 included patients?
Recently, it has been shown that autoflourescence could
be a predictive parameter to monitor retinal pigmentary
epithelium atrophy [10]. We should know if autoflourescence
was applied to assess RORA.
Overall, this interesting study has some shortcomings
which should be solved before drawing final conclusions.
The genetic background of MIDD, the multisystem involvement,
and the drug treatment may determine the phenotype,
progression, and outcome also of the ophthalmologic
abnormalities in these patients.
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