Mitochondrial Disorder: Maternally Inherited Diabetes and Deafness.

Patients with maternally inherited diabetes and deafness (MIDD) have insulin-dependent diabetes with relatively low BMI; usually the onset of the diabetes is during the third or fourth decade of life and it is associated with progressive neurosensory deafness. The fundus shows circumferentially oriented but discontinuous patches of RPE and choriocapillaris (CC) atrophy around the macula, within the arcades (Figs. 31.1 and 31.2). Sometimes even hyperpigmentation can be seen, also around the optic nerve, or pattern-like dystrophy may occur. Vision is usually good, about 20/40 or better. Fundus autofluorescence (FAF) shows decreased AF in the areas of RPE atrophy, surrounded by a zone of speckled AF. No generalized retinal dysfunction is seen on full-field electroretinography (ERG), but pattern ERG or multifocal ERG shows abnormal function. Asymptomatic maternal relatives harboring the mutation may show pigmentary changes, hearing loss, and in some, diabetes. Another disorder associated with the same A3243G mitochondrial DNA (mtDNA) mutation as MIDD is Mitochondrial Encephalomyopathy with Lactic Acidosis and Stroke-like episodes (MELAS). The stroke-like episode (such as hemiplegia) occurs at about 5-15 years of age, and severe encephalopathy may cause death at a young age. Patients may also experience headache, vomiting, visual field defects, or cortical blindness.