9 Things to Know About the Inheritance of Friedreich’s Ataxia
Friedreich’s ataxia is an inherited disease that affects movement and coordination. It’s a progressive disease with symptoms including loss of strength, weakened muscles, spasticity, impaired speech, hearing and vision problems, and in some cases diabetes and scoliosis.
- The condition is due to mutations in the frataxin (FXN) gene.
- Friedreich’s ataxia is an autosomal recessive disease which means that a person inherits a copy of the mutated FXN gene from both their mother and father.
- If both the mother and father are carriers of the mutated FXN gene there is a one in four chance that any of their children will develop Friedreich’s ataxia, a one in two chance they will not develop the disease but will become a carrier, and a one in four chance they will neither develop the disease nor become a carrier.
- Part of the FXN gene contains a series of three DNA building blocks (two adenines and one guanine) called a GAA trinucleotide repeat. In people without the condition, this is repeated between five and 33 times. In those with the condition, this sequence is repeated between 66 to 1,000 times and known as a “repeat expansion.”
- The number of times this sequence is repeated is related to the age of onset, the severity of the condition, and how quickly it progresses.
- People with fewer than 300 GAA trinucleotide repeats tend to have a later onset of the disease, usually presenting symptoms after the age of 25.
- It’s estimated that one in 100 people in the U.S. is a carrier of Friedreich’s ataxia.
- People of Cajun (Acadian) descent are slightly more at risk of the disease, with one in 70 being carriers.
- More than 95 percent of people with Friedreich’s ataxia have repeated expansions on both FXN genes. The rest of cases have one FXN gene with a repeat expansion and one with a single letter alteration to the DNA code called a point mutation.
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