Choroideremia (CHM) is a rare inherited disorder that causes progressive vision loss, ultimately leading to complete blindness.
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The first symptom is generally night-blindness, followed by vision loss in the mid-periphery. These “blind spots” appear in an irregular ring, only leaving patches of peripheral vision, while central vision is still maintained. Over time the peripheral vision loss extends in both directions leading to “tunnel vision” and eventually complete loss of sight. The disease affects the retina, which is the area at the back of the eye. CHM is considered a rare disease because it only affects an estimated 1 in 50,000 individuals. The disease is caused by a genetic defect of the X-Chromosome, and thus typically only males suffer the full effects of complete blindness, while females are carriers of the disease. CHM has a 50% chance of passing onto the children of an affected parent, although – due to the defect’s presence on the X-Chromosome affected males cannot pass the disease on to their sons.