Impaired Hearing in MELAS.

We read with interest the article by Crundwell et al 1 about 2 patients with mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome who manifested clinically with bilateral sensorineural hearing impairment after speech development and significantly profited from unilateral implantation of a2 cochlea implant. 1 In patient 1 (53-year-old male), MELAS was found to be due to the variant m.3243A > G in MT-TL1 and in patient 2 (47-year-old male), the genetic cause of MELAS was unknown. 1 The study is appealing but has some limitations that raise concerns which need to be discussed. We disagree with the statement in the abstract that MELAS is the most common mitochondrial disorder (MID). 1 There are only few data available on the epidemiology of MIDs. 2 However, the few data reported in the literature and our own experiences suggest that non-syndromic MIDs prevail when compared with syndromic MIDs, such as MELAS. Furthermore, we do not agree with the statement in the introduction that MELAS is characterized by myelopathy and respiratory insufficiency. 1 Myelopathy is not a typical phenotypic feature of MELAS and has been only rarely reported in these patients. 3 Myelopathy is more common in leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL), a syndromic MID, in which myelopathy is a pathognomonic feature of the disease. 4 Respiratory insufficiency may develop in MELAS only in the case of affection of the respiratory muscles, the brainstem, or the lungs. It is contradictory to state that the diagnosis of MELAS was genetically confirmed and to state, at the same time, that the causative mtDNA variant