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Maternally-inherited diabetes and deafness
Maternally inherited diabetes and deafness (MIDD) is a mitochondrial disorder characterized by maternally transmitted diabetes and sensorineural deafness.
The prevalence is unknown, but MIDD accounts for 0.2-3% of all cases of diabetes.
The first manifestations may occur at any age, but the disease is usually diagnosed in early adulthood. In most cases, the onset of deafness precedes that of diabetes. The severity of the hearing loss is variable but it is sensorineural, bilateral and progressive, and is more profound at higher frequencies. In most cases, patients present pseudo-type 2 diabetes, with a normal or low body mass index. Pseudo-type 1 diabetes, sometimes with ketoacidosis, is observed in 20% of cases. Diabetic retinopathy is less common in MIDD patients than in those with classic forms of diabetes. In more than 80% of cases, patients develop specific macular pattern dystrophy lesions that are only seen in MIDD patients and are asymptomatic in most cases. Organs with high metabolic activity (muscles, myocardium, kidney, and brain) are frequently affected potentially leading to muscle pain, gastrointestinal tract symptoms, nephropathy, cardiomyopathy, and neuropsychiatric symptoms.
In most cases, MIDD is caused by a point mutation in the mitochondrial gene MT-TL1, encoding the mitochondrial tRNA for leucine, and in rare cases in MT-TE and MT-TK genes, encoding the mitochondrial tRNAs for glutamic acid, and lysine, respectively.
Diagnosis is based on the clinical picture and patient history. Measurements of fasting plasma glucose levels allow diagnosis of the diabetes. Ophthalmologic examination reveals the disease-specific macular pattern dystrophy. The diagnoses of standard type 2 and type 1 diabetes are excluded by the presence of the deafness, low body weight and the specific macular pattern dystrophy, and by evidence of maternal transmission.
The disease is maternally transmitted.
Management and treatment
Management is symptomatic. Oral antidiabetic agentsand/or insulin therapy are used to treat the diabetes. Hearing aids or cochlear implants are recommended for the hearing loss. Administration of Co-enzyme Q10 supplements has been proposed for treatment of the mitochondrial defect. Treatment of MIDD should be initiated at an early stage, since complications may lead to renal disease or MELAS syndrome (myocardial complications, mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes; see this term).
The prognosis for MIDD is better than that for MELAS syndrome (which occurs mainly in children and has a generally poor prognosis) and for other subtypes of mitochondrial diseases with diabetes.