Histiocytic disorders
Familial hemophagocytic lymphohistiocytosis
Also called: FHL · FHLH · primary HLH · familial HLH · HLH · hemophagocytic lymphohistiocytosis · Primary familial hemophagocytic lymphohistiocytosis · Familial erythrophagocytic lymphohistiocytosis
What a donor has to do with this
For some people with this condition, a transplant using blood stem cells from an unrelated donor is part of the treatment guidelines. When a transplant is the right route and no one in the family matches, that donor comes from a registry. Not everyone with this condition has a transplant, and many never need one.
This is our reading of published transplant guidelines for this condition, not a measurement of how many people need a donor. Where a source actually counted donors, the figure and the people it counted are shown further down. Where none did, we say so rather than estimate.
What the evidence says
- Who it affects
- Typical onset/diagnosis: disease is usually apparent during infancy, although later childhood or adolescent presentation occurs. Evidence: U.S. NIH GARD synthesis (updated 2026); no markedly enriched population was identified.
- Treatments other than a transplant
- HLH-directed immune-chemotherapy or cytokine blockade — bridge to curative HCT — multiple regions — Disease control before transplant is essential; these therapies are not definitive for germline FHL.
- If a transplant is used, the cells come from
- bone marrow: used in opened IEI transplant guidance; disease-specific share was not reported; mobilized peripheral blood stem cells: used in opened IEI transplant guidance; disease-specific share was not reported; umbilical cord blood: used as an alternative in opened IEI transplant guidance; disease-specific share was not reported; dominance: no dominant graft source was reported in the opened disease-specific sources
- How often the donor was unrelated
- Not reported. No source we could read states this for this condition, so we do not give a number. An estimate here would be a guess dressed as evidence.
Where this gets complicated
This row excludes secondary HLH and macrophage activation syndrome, which are not inherited transplant indications by default.; Reduced-intensity conditioning can reduce toxicity but mixed chimerism may permit relapse; acceptable donor chimerism thresholds vary.
People with this condition need donors
Joining a registry is a cheek swab and a short health form. You are contacted only if you turn out to be a possible match for someone, and you can ask questions and decline before anything else happens.
Related conditions
Others in histiocytic disorders. They are genuinely different diseases with different treatments — the group name is not a diagnosis.
Where this came from
- Familial hemophagocytic lymphohistiocytosis — NIH NCATS GARD, updated 2026-06
- Guidelines for hematopoietic stem cell transplantation for inborn errors of immunity — EBMT/ESID Inborn Errors Working Party, 2021
- EBMT Handbook, Chapter 90: Inborn Errors of Immunity — EBMT/Springer, 2024-04-11