About 100 people in the U.S. experience onset of LHON vision loss each year, joining the 4,000 or so in the U.S. who are already legally blind due to LHON. Thousands more are unaffected carriers of an LHON genetic mutation, and could suddenly become affected by LHON vision loss at any time. It’s estimated that about 35,000 people worldwide have LHON vision. About 25% of those affected are female; 75% are male. Onset of vision loss can happen at any age. Females have no peak onset age. Males have a peak onset at ages 12-26. Individuals carrying an LHON mutation are never “too young” or “too old” to become affected. Prior to the era of genetic testing, it was estimated that 50% of males who carry an LHON mutation will become affected and that figure is still commonly quoted. However, recent studies indicate that less than 20% is a better estimate among families with someone affected by vision loss, and even lower when families with no one yet affected are included.