FXN rs142133355: Understanding Carrier Status and Friedreich's Ataxia

What each genotype means

What is the rs142133355 Variant?

The variant rs142133355, also identified in scientific literature as c.2T>C or p.M1T, is a specific change in the DNA sequence of the FXN gene. Located on chromosome 9, this variant represents a single nucleotide substitution. In the context of human genetics, this specific site is monitored because it can alter the instructions the body uses to produce the frataxin protein. While most genetic variation is benign, this particular variant is classified as pathogenic, meaning it has the potential to disrupt normal biological processes if inherited in specific patterns. It is important to note that this variant is distinct from the more common GAA trinucleotide repeat expansions that account for the vast majority of Friedreich's ataxia cases.

The Role of the FXN Gene

The FXN gene provides the essential blueprint for creating a protein called frataxin. Although the full scope of its function is still being researched, frataxin is known to be critical for the health and efficiency of mitochondria, which are the energy-producing powerhouses of our cells. Specifically, frataxin is involved in the assembly of iron-sulfur clusters, which are necessary for the function of various proteins involved in energy metabolism. When the FXN gene is mutated, the production of functional frataxin is often significantly reduced. A shortage of this protein can lead to mitochondrial dysfunction, which is believed to be the underlying cause of the cellular damage observed in conditions like Friedreich's ataxia.

Research and Clinical Associations

Scientific research associates the rs142133355 variant with Friedreich's ataxia, an autosomal recessive disorder. In an autosomal recessive condition, an individual typically needs to inherit two copies of a pathogenic variant—one from each parent—to manifest the disease. Because rs142133355 is a rare sequence variant, it is most often identified in individuals who are compound heterozygotes. This means they may carry a common GAA repeat expansion on one copy of the FXN gene and this specific pathogenic sequence variant on the other. The evidence linking this variant to the disease is considered moderate to strong in clinical genetics, as it directly impacts the protein-coding sequence of the gene. However, because Friedreich's ataxia is complex, clinical diagnosis is always based on a combination of physical symptoms and comprehensive molecular genetic testing.

Population Frequency

The rs142133355 variant is classified as rare in the general population. Because it is not a common polymorphism, it is not typically found in the vast majority of individuals. Its frequency is low across most ancestral groups, which is consistent with its status as a pathogenic mutation rather than a common genetic trait. Because the variant is rare, most people will not carry it. Genetic databases like gnomAD and ClinVar serve as the primary resources for tracking the prevalence of such variants, and they consistently categorize this specific mutation as infrequent.

What This Information Means for You

If you have received information regarding your status for rs142133355, it is important to understand that this is not a medical diagnosis. Genetic testing results can be complex, and the presence of a single copy of a variant often indicates carrier status, which typically does not cause symptoms of the associated condition. If you are concerned about your genetic health or family history, the most appropriate step is to consult with a certified genetic counselor or a medical professional. They can help interpret your results in the context of your overall health and family history. Never make medical decisions based on raw genetic data alone; always discuss your findings with a clinician who can provide personalized guidance and, if necessary, recommend appropriate diagnostic follow-up.

Frequently asked questions

Sources & further reading

Related variants in FXN