Kyoto University researchers found SLF2 and SMC5 variants activate p53 and prematurely age haematopoietic stem cells — then corrected the variants in patient-derived stem cells and watched the defects reverse.

Inherited bone marrow failure syndromes are a group of conditions in which a person’s blood-forming system fails early in life because of a genetic defect. Many have known causes — Fanconi anaemia, Diamond-Blackfan anaemia, dyskeratosis congenita — and a substantial fraction do not, leaving patients with a failing marrow and no explanation. Some of those patients also develop myelodysplastic syndromes, a pre-leukaemic marrow disorder, at ages where it is otherwise rare.

A study in Leukemia from Kyoto University identifies a cause for some of them, in two genes previously associated with something else entirely.

The first author is Sho Shibata and the corresponding author Kazuhisa Chonabayashi, both of Kyoto University.

Starting from the wrong disease

The entry point was Atelis Syndrome, a condition linked to variants in SLF2 and SMC5 and described as a neurodevelopmental disorder. Some patients with it developed myelodysplastic syndrome at a young age and showed the clinical features of inherited bone marrow failure.

The team’s conclusion is that SLF2 and SMC5 dysfunction causes both inherited bone marrow failure and a predisposition to MDS — that is, the haematological features are not a complication of the neurodevelopmental syndrome but a direct consequence of the same genetic defect.

“We were intrigued to find that genes originally linked to a neurodevelopmental disorder also play a critical role in maintaining hematopoietic stem cell function,” Shibata said, “and that their disruption predisposes individuals to MDS.”

That a gene can do unrelated-looking jobs in brain development and in blood is less surprising than it first appears, and the functions of these two explain why. SMC5 is part of the SMC5/6 complex, which maintains chromosome integrity and resolves problems that arise when DNA is replicated; SLF2 helps recruit it to damaged DNA. Tissues that suffer most when DNA repair fails are the ones that divide most — and the neural progenitors of a developing brain and the stem cells of a marrow are both in that category.

The mechanism

The pathway identified runs through p53. The mutations activate the p53 protein and cause premature aging of haematopoietic stem cells.

p53 is the cell’s damage sentinel: it accumulates when DNA is broken or replication stalls, and it responds by arresting the cell cycle, driving the cell into senescence, or killing the cell outright. That response is protective against cancer and expensive for a stem cell pool, because a stem cell arrested or senescent is a stem cell no longer replenishing anything.

This produces the paradox that makes these syndromes coherent. Faulty DNA repair causes persistent damage signals; p53 responds by shutting down the affected stem cells; the marrow is progressively depleted of them, which is bone marrow failure. Then any stem cell that acquires a way to ignore p53 has an enormous competitive advantage in a depleted marrow — and expands. That is the standard account of why DNA-repair-deficiency syndromes cause both marrow failure and a raised leukaemia risk, and it fits what was found here.

The experiment that settles causation

The strongest evidence in the paper is a correction experiment. The team made induced pluripotent stem cell lines from a patient carrying SLF2 variants, used CRISPR-Cas9 to create genetically corrected versions of those lines, and tested both in vitro and in vivo. Correcting the variants reversed the cellular abnormalities.

“It is particularly exciting to see that correcting the SLF2 variants in patient-derived iPSCs reversed the cellular abnormalities,” Chonabayashi said, “providing direct evidence that these variants cause bone marrow failure.”

The claim to direct evidence is justified, and the reason is the design. An isogenic pair — two cell lines identical except at the edited position — removes the objection that always attends patient-derived cells, which is that a patient’s cells differ from a healthy donor’s in countless ways besides the variant of interest. When the only difference is the variant and the phenotype follows it, the variant is the cause.

This is also, in principle, the logic of a therapy. Gene correction in a patient’s own haematopoietic stem cells is an established approach that has reached clinical use in other inherited blood disorders, and a demonstration that correction restores function in patient-derived cells is the first step on that path. The release does not claim a treatment, and the distance between an edited iPSC line and an edited marrow graft is considerable.

What it is useful for now

The immediate application is diagnostic. The authors say the results may help identify causes of unexplained inherited bone marrow failure and MDS in young patients.

For a family with an undiagnosed marrow failure syndrome, a named gene changes several things at once: it ends the diagnostic search, it allows relatives to be tested, it informs surveillance for MDS in someone known to be predisposed, and it bears on decisions about transplantation — since marrow from an affected sibling would carry the same defect.

The limitations are those of a study built on one patient’s cells. The iPSC work used a single patient with SLF2 variants, so how the phenotype varies between different variants in the same gene, or between SLF2 and SMC5, is not addressed. The release gives no figure for how many Atelis Syndrome patients were examined, how many had haematological features, or at what ages, which leaves the central clinical claim — that these patients get MDS young — without a number attached to it.

Nor does an iPSC-derived haematopoietic cell fully reproduce a real haematopoietic stem cell, a known limitation of the model; and premature aging in culture, while measurable, is not the same process as decades of marrow decline in a person.

The paper appeared on 7 August 2026. Funding came from the Japan Society for the Promotion of Science, the Japan Agency for Medical Research and Development, and a long list of Japanese medical foundations including Takeda Science Foundation, the Kobayashi Foundation for Cancer Research and the Daiichi Sankyo Foundation of Life Science, as well as Fondation Leducq. The release includes no conflicts of interest statement.

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Notes

1. Shibata, S., et al. “SLF2 and SMC5 dysfunction drives HSC aging and predisposes to MDS, defining a new inherited bone marrow failure syndrome.” Leukemia, 2026. DOI: 10.1038/s41375-026-03061-7.
2. Kyoto University. “The gene mutations behind serious bone marrow conditions.” EurekAlert!, 6 August 2026. https://www.eurekalert.org/news-releases/1138537.

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