Scientists find why a debilitating genetic disorder affects only Eurasians

Scientists have discovered why Friedreich’s ataxia, a debilitating genetic disorder, predominantly affects Eurasians. The condition, also known as FRDA, causes progressive damage to nerves and the heart, leading to symptoms such as unsteadiness, impaired coordination, slowed speech, difficulty swallowing, and vision and hearing loss. Most patients die young due to heart disease, and there is no cure.

Friedreich’s ataxia is caused by a mutation in the FXN gene, which codes for a protein called frataxin. Frataxin is crucial for mitochondria, the energy-producing structures within cells. When the frataxin levels become abnormally low, mitochondria produce less ATP, the cell's energy currency, and accumulate toxic by-products. This impairs cell function, leading to the symptoms of FRDA.

A recent study published in the journal Human Molecular Genetics has shed light on the origins of FRDA. Researchers at the University of Oklahoma Health Sciences Center found that the most common disease-causing mutations occur in the intron of the FXN gene, where a repeated sequence of bases is altered. The normal variants of the FXN gene contain 5-11 or 12-33 repeats, while the expanded variants have 100-1,500 repeats.

The study revealed that 95% of these expanded variants originated from just two long-normal variants, with these mutations occurring twice in history in Eurasia. However, the researchers did not find any similar mutations in sub-Saharan Africa, which explains why FRDA is absent in this region. The presence of these protomutations in Eurasia, which arose at least 9,000 years ago, is believed to be the reason why FRDA is predominantly found in individuals of European, North African, West Asian, and South Asian descent.