To determine (1) detailed retinal and audiological features of probands harboring the A3243G mitochondrial DNA mutation (m.3243A>G) and their asymptomatic maternal relatives, (2) intrafamilial and interfamilial phenotypic variability, and (3) the presence of other systemic features.
Seven probands harboring the A3243G mitochondrial DNA mutation and 36 asymptomatic maternal relatives were ascertained. Participants underwent ophthalmologic examination, fundus photography, autofluorescence imaging, and audiological evaluation and completed a questionnaire. Blood samples were taken to test for diabetes, determine renal function, and screen relatives for the A3243G mutation.
The A3243G mutation was associated with both intrafamilial and interfamilial variable expressivity regarding retinal appearance, hearing loss, diabetes, and other systemic features. The most common macular appearance in maternal relatives (one-third of those positive for the mutation) was mild abnormalities of the retinal pigment epithelium (more clearly identified using autofluorescence), which may therefore be a useful clinical indicator suggesting positive mutation status. Four probands and 13 mutation-positive relatives were found to have evidence of significant bilateral, cochlear, symmetrical age-adjusted hearing loss, predominantly affecting high frequencies.
Hearing loss and macular disturbance were the most frequent findings in mutation-positive participants, with 95% of mutation-positive relatives having hearing loss. Diabetes was the least frequent finding. Patients with progressive hearing loss may merit ophthalmologic assessment to detect retinal abnormalities consistent with the A3243G mutation. Conversely, patients with macular features in keeping with the A3243G mutation should have audiological testing, even in the absence of diabetes or a positive family history.