In Reference to Bilateral Sudden or Chronic Hearing Loss as an Auditory Manifestation of Mitochondrial <scp>DNA</scp> Mutations

The interesting article by Liu et al. [1] is appealing but worthy of discussion. The first point is that “sudden” hearing loss is a rather unusual phenotypic feature of MIDs [1]. Mitochondrial hearing impairment is usually a chronic, slowly or rapidly progressive process that is noticed by the patient or their relatives or caregivers long before the patient becomes deaf. Accordingly, patient-3 had a six-year history of moderate to severe hearing impairment before becoming deaf [1]. Such a course of disease should not be considered “sudden” hearing loss. Were PTA and AEP tests performed on the three included patients prior to the “sudden” hearing loss? The second point is that it is quite unusual that the cerebral MRI was normal in patient-2 [1]. Since patient-2 was diagnosed with MELAS, the medical history must be positive for stroke-like episodes (SLEs) according to the diagnostic criteria. Since SLEs often appear as white matter lesions, atrophy, cysts, laminar cortical necrosis, or toenail signs on brain imaging, it is very likely that the MRI of patient-2 also showed evidence of a previous SLE. Was the medical history of patient-2 really positive for SLEs? Was MELAS diagnosed according to the Hirano or Japanese criteria? The third point is that the family history was inadequately documented [1]. Only in patient-2 was it mentioned that the sister also had mild hypoacusis [1]. In order to assess whether the mtDNA point mutation and the single mtDNA deletion were inherited or occurred spontaneously, it is essential to compile a comprehensive family history. mtDNA point mutations are inherited through the maternal line in 75% and single mtDNA deletions in 4% of cases. Were the mothers of the three patients clinically affected by MID, and did one of them carry the variant like her daughters? Knowledge of the genetic background is important not only for predicting the course of the disease, but also for genetic counseling. The fourth point is that patient-1 should have been diagnosed with maternally inherited diabetes and deafness syndrome if there were no symptoms other than diabetes and deafness. The fifth point is that the long-term outcome was not reported [1]. Were cochlear implants still effective years after implantation? What treatment did the three patients receive for MIDs? Finally, there is a discrepancy between the statement in the discussion that the family history of hearing loss was negative and the description of the sister of patient 2 with hearing loss [1]. The author has nothing to report. The author has nothing to report. The author has nothing to report. The author declares no conflicts of interest. The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.