New stem cell lines may help in developing therapies for rare FA cases
Cells derived from male patient open door to studying ultra-rare mutation
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Scientists have created and validated stem cell lines derived from an adult with Friedreich’s ataxia (FA) carrying an ultra-rare disease-causing mutation, a study reports.
Because patient-derived stem cells can be transformed into any cell type — including muscle and nerve cells, which are most affected in FA, a rare inherited disease — this advancement provides researchers with tools to develop new therapies for FA patients with certain rare mutations, according to the researchers.
“Individual properties of [these types of] mutations allow for the development of personalized therapeutic approaches,” the team wrote, noting that mutations like the one found in this man “are of special interest” because of their research potential.
The study noted that the stem cell lines are now publicly available through the University of Texas Southwestern Medical Center.
Titled “Generation of Friedreich’s ataxia induced pluripotent stem cells carrying the FXN c.165 + 5G>C splicing mutation,” the study was published in the journal Stem Cell Research.
FA is caused by mutations in the FXN gene, which encodes frataxin, a protein that helps cells, particularly those of the muscles and nerves, generate energy. When frataxin levels are too low, nerve cells gradually deteriorate, leading to symptoms like muscle weakness, poor coordination, and difficulty walking.
Mutation marked by single change in the genetic code
To develop FA, a person must inherit two copies of a faulty FXN gene, one from each parent. More than 95% of FA cases involve a defect called the GAA trinucleotide repeat expansion, in which a short DNA sequence is abnormally repeated. In rarer cases, one copy carries the repeat expansion, while the other has a point mutation marked by a single change in the genetic code.
One such point mutation is c.165+5G>C, which has been reported in very few patients to date, according to the researchers. The mutation involves the substitution of one DNA building block, guanine (G), for another, cytosine (C). It’s found within an intron — a noncoding segment of the gene that is normally removed, or spliced out, before the gene’s instructions are used to build a protein.
Typically, the cell splices out introns and joins together the coding segments, called exons, to produce a blueprint for frataxin. When a mutation disrupts this process, the gene is misread and an abnormal, nonfunctional protein is produced.
ASOs, short for antisense oligonucleotides, are an emerging class of treatments designed to correct this problem. That is, a small synthetic DNA- or RNA-like fragment helps restore proper splicing, allowing the cell to produce more functional frataxin.
In a previous study, a team led by scientists at the UT Southwestern demonstrated that an ASO corrected splicing in skin cells from an FA patient who carried the c.165+5G>C mutation. This resulted in the production of functional frataxin.
Stem cell lines now available in Texas for use by researchers
Now, the team has generated a special type of stem cell — called induced pluripotent stem cells, or iPSCs — from a blood sample donated by a person living with FA who carries the rare c.165+5G>C mutation.
iPSCs are derived from ordinary adult cells, such as blood or skin cells, by reprogramming them into a stem cell-like state. Once reprogrammed, these cells become pluripotent, meaning they can develop into virtually any cell type in the body, including nerve and heart muscle cells.
“The iPSC line carrying FXN c.165+5G>C mutation in the intron 1 described in this resource will enable the testing of therapeutic strategies in disease-relevant differentiated cells and 3D cellular models of the disease,” the researchers wrote.
Two independent iPSC lines were generated from the donor’s blood, showed normal stem cell shape, and tested positive for key pluripotency markers, confirming successful reprogramming. Chromosomal analysis showed no abnormalities, and genetic fingerprinting confirmed the iPSCs matched the original donor sample, according to the researchers.
Genetic analysis confirmed that one copy of the FXN gene carried a GAA repeat expansion of approximately 700-800 repeats, well beyond the threshold of 66 or more repeats, which is considered disease-causing. The other copy carried the c.165+5G>C point mutation, which, together with the repeats, accounted for this patient’s FA diagnosis.
These iPSC lines are now stored and available to the broader research community through the FA Cell Line Repository at UT Southwestern Medical Center in Dallas, per the study.
“These cells allow for development of therapeutic approaches that target splicing defect in [FA],” the scientists wrote.
