Polyendocrinopathy and multisystem involvement are common phenotypic features of Kearns-Sayre syndrome.

Dear Editor, We were interested to read the article by Amergoolov et al. on two patients with Kearns-Sayre Syndrome (KSS) due to single mtDNA deletions who had phenotypic endocrine disorders among other features.1 Patient 1, a 20-year-old female, was diagnosed with hypogonadism, diabetes and osteoporosis, and patient 2, a 22-year-old male, was diagnosed with impaired glucose tolerance and osteoporosis.1 It was found that the severity of clinical manifestations increases with the size of the mtDNA deletion, but that other factors such as heteroplasmy, mtDNA duplications or pleioplasmia can also determine the severity of the disease.1 The study is impressive, but some points should be discussed. [...].