MJD has even been found among aboriginal natives of Australia. The mutation most likely originated in mainland Portugal, and was concentrated in the Azores in the 15th and 16th century. We believe it was disseminated along Portuguese routes of trade, coming to New England in the 19th century with the whaling business. In general terms, all patients with MJD have an affected parent. There appears to be a relationship between the clinical presentation, the age of onset, and the rate of progression.
Balance is impaired, and stumbling is an early and typical feature.
In some of the affected patients lid retraction produces characteristic staring expression. Some experience double vision. There is a great deal of variability in other features of the illness. They usually esperience onset of symptoms before age 25. For others, the illness begins later in life and is associated with muscle atrophy and sensory loss in the legs, with depressed reflexes.