Mohr-Tranebjærg syndrome

Mohr-Tranebjærg syndrome, also called deafness-dystonia-optic neuronopathy syndrome or DDON syndrome, is a rare inherited disorder that affects hearing, movement, vision and behavior, and it occurs almost exclusively in males. The first sign is sensorineural hearing loss caused by nerve damage in the inner ear, which begins in early childhood and usually becomes profound by about age 10. Movement problems, such as involuntary tensing of the muscles (dystonia) or difficulty coordinating movements (ataxia), typically begin in the teenage years and tend to worsen. Vision is normal in childhood, but breakdown of the nerves that carry signals from the eyes to the brain (optic atrophy) can bring light sensitivity and falling visual acuity, often ending in legal blindness in mid-adulthood. Behavior problems such as personality change, aggression or paranoia can occur, and a gradual decline in thinking and reasoning (dementia) usually develops in the forties. The condition is caused by mutations in the TIMM8A gene on the X chromosome, whose protein works with TIMM13 to move other proteins within the mitochondria, and it is inherited in an X-linked recessive pattern. It has been reported in fewer than 70 people worldwide. Lifespan depends on severity: severe cases have survived into the teenage years, while milder cases have lived into the sixties.