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PubMed This is a summary of 10 peer-reviewed journal articles Updated
Metabolic Medicine

The Choice of Transplant: Protecting the Brain

At a Glance

For selected people with alpha-mannosidosis, HSCT may provide enzyme-producing cells that reach the brain and slow or stabilize neurological decline. It cannot usually reverse existing damage, and its serious risks require individualized review at a specialized center.

While enzyme replacement therapy (ERT) helps manage the physical symptoms of alpha-mannosidosis, it cannot cross the blood-brain barrier to treat the central nervous system [1]. For highly selected patients, Hematopoietic Stem Cell Transplant (HSCT)—sometimes called a bone marrow or stem cell transplant—may be considered. It is currently the only treatment option with the potential to slow or stabilize cognitive and neurological decline [2][3]. However, HSCT is not an automatic recommendation for everyone; it is a complex procedure with substantial risks that requires individualized shared decision-making.

The Goal of Transplant

The primary rationale for HSCT is to provide the brain with a permanent source of the working enzyme [3]. During the procedure, the patient’s blood-forming cells are replaced with healthy donor cells [4]. These donor cells can travel to the central nervous system, where they become specialized cells (microglia) that produce the missing alpha-mannosidase enzyme, potentially clearing the buildup of sugars [3].

  • Potential CNS Stabilization: Evidence suggests that successful HSCT may stabilize or slow cognitive decline in selected patients [2].
  • Systemic Benefits: A successful transplant may also reduce an enlarged liver (hepatomegaly), decrease the frequency of recurrent infections, and stabilize certain physical features [4][5].

Why Timing and Selection Matter

The most critical factor in considering HSCT is patient selection and timing [4][5].

  • Preserving vs. Reversing: HSCT is considered a “preservative” treatment. While it may slow future damage, it generally cannot reverse established cognitive delays or neurological injury [4][5].
  • Candidate Selection: Because the risks are high, HSCT is most often considered for younger patients or those with early, severe, or rapidly progressive disease before significant neurological deterioration has occurred [4].

Weighing the Substantial Risks

HSCT requires a prolonged hospital stay at a specialized transplant center, intensive recovery, and lifelong follow-up [4]. The potential for brain protection must be carefully weighed against significant, life-altering risks:

  1. Severe Infections: The “conditioning” process (chemotherapy) heavily suppresses the immune system. In a recent retrospective study of 21 children undergoing HSCT for this condition, 9 experienced severe post-transplant infections [4]. (Note: Complication rates depend heavily on the center, the conditioning regimen, and donor match).
  2. Graft-versus-Host Disease (GvHD): This occurs when the new donor cells attack the patient’s body. Acute GvHD can be severe (affecting roughly 24% of the children in the previously mentioned cohort), and chronic GvHD can lead to lifelong immune and organ complications [4].
  3. Graft Failure: Sometimes the donor cells do not engraft, which may require a dangerous second transplant procedure [4].
  4. Long-Term Consequences: The conditioning regimen carries risks of organ toxicity, infertility or gonadal injury, and an increased risk of secondary cancers later in life.
  5. Mortality: While modern techniques have improved survival, HSCT still carries a real risk of transplant-related mortality. Families should request individualized nonrelapse-mortality estimates from their specific transplant center [4][5].

How Treatment Decisions Are Made

Deciding between ERT, HSCT, or supportive care is complex.

Feature Enzyme Replacement (ERT) Stem Cell Transplant (HSCT)
Primary Benefit Improves physical symptoms (liver, walk tests) [6]. Potential to slow or stabilize CNS disease [2].
Brain Protection No (does not cross blood-brain barrier) [1]. Yes, variable (reaches the central nervous system) [3].
Risk Level Lower (infusion reactions, antibodies) [7]. High (infections, GvHD, graft failure, mortality) [4].
Administration Weekly, lifelong IV infusions [8]. Major procedure with prolonged recovery & lifelong monitoring [4].

Your care team will help you weigh disease severity, functional status, age, donor availability, and family goals. In some specific cases, centers may use ERT as a “bridge” to stabilize physical health prior to a transplant, though this is a highly specialized, patient-specific protocol [9][10]. Always consult with a specialized metabolic/transplant center for a thorough evaluation and second opinion.

Common questions in this guide

Why might HSCT be considered for someone with alpha-mannosidosis?
HSCT replaces a person’s blood-forming cells with healthy donor cells. These cells can become specialized enzyme-producing cells in the brain, so a successful transplant may slow or stabilize cognitive and neurological decline; it is considered only for carefully selected patients because the procedure has substantial risks.
Can a stem cell transplant reverse brain damage caused by alpha-mannosidosis?
HSCT is generally considered a preservative treatment rather than a restorative one. It may slow future neurological decline, but it usually cannot reverse established cognitive delays or neurological injury, which is why timing before major deterioration matters.
What are the major risks of HSCT for alpha-mannosidosis?
Important risks include severe infections, graft-versus-host disease, failure of the donor cells to engraft, organ toxicity, infertility or gonadal injury, secondary cancers, and transplant-related death. The procedure also involves a prolonged hospital stay, intensive recovery, and lifelong follow-up.
How does HSCT differ from enzyme replacement therapy for alpha-mannosidosis?
Enzyme replacement therapy can improve some physical and organ-related symptoms but does not cross the blood-brain barrier. HSCT may provide enzyme-producing cells that reach the central nervous system, but it carries much greater risks and requires a major procedure with prolonged recovery.
Can ERT be used before a transplant for alpha-mannosidosis?
In some highly specialized, patient-specific situations, ERT may be used as a bridge to help stabilize physical health before HSCT. ERT does not itself provide the same potential for brain protection, so the decision should be made by a metabolic and transplant team.
What should families ask a transplant center before considering HSCT?
Families should ask about the center’s experience with alpha-mannosidosis and similar disorders, donor matching, the conditioning regimen, expected benefits, and individualized risks of graft failure, graft-versus-host disease, infection, and transplant-related death. They should also ask how long-term complications and neurological function will be monitored.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Based on current cognitive function and disease trajectory, is HSCT a realistic option to potentially stabilize neurological symptoms?
  2. 2.What is this center's specific experience and success rate with HSCT for lysosomal storage disorders like alpha-mannosidosis?
  3. 3.What kind of donor match is available (e.g., matched sibling vs. unrelated donor), and how does that affect the risk of graft failure or GvHD?
  4. 4.What is the specific 'conditioning' (chemotherapy) regimen required, and what are its long-term risks for growth, organ toxicity, and fertility?
  5. 5.Should we consider using enzyme replacement therapy (ERT) as a 'bridge' to stabilize physical health before proceeding to a transplant?
  6. 6.How will we monitor for Graft-versus-Host Disease, secondary cancers, and serious infections in the months and years following the procedure?

Questions For You

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References

References (10)
  1. 1

    Diagnosis of alpha-Mannosidosis: Practical approaches to reducing diagnostic delays in this ultra-rare disease.

    Santoro L, Cefalo G, Canalini F, et al.

    Molecular genetics and metabolism 2024; (142(1)):108444 doi:10.1016/j.ymgme.2024.108444.

    PMID: 38555683
  2. 2

    Intellectual functioning in alpha-mannosidosis.

    Cathey SS, Sarasua SM, Simensen R, et al.

    JIMD reports 2019; (50(1)):44-49 doi:10.1002/jmd2.12073.

    PMID: 31741826
  3. 3

    The Role of Hematopoietic Cell Transplant in the Glycoprotein Diseases.

    Naumchik BM, Gupta A, Flanagan-Steet H, et al.

    Cells 2020; (9(6)) doi:10.3390/cells9061411.

    PMID: 32517081
  4. 4

    Outcome of Haemopoietic Stem Cell Transplantation in 21 Patients With Alpha-Mannosidosis.

    Šáhó R, Formánková R, Eisengart JB, et al.

    Journal of inherited metabolic disease 2025; (48(4)):e70047 doi:10.1002/jimd.70047.

    PMID: 40551549
  5. 5

    Clinical outcomes in alpha-mannosidosis: a systematic review of therapeutic approaches.

    Azzi A, Shlhoob RB, Al-Shehri H

    Orphanet journal of rare diseases 2026; (21(1)).

    PMID: 42482083
  6. 6

    Efficacy and safety of Velmanase alfa in the treatment of patients with alpha-mannosidosis: results from the core and extension phase analysis of a phase III multicentre, double-blind, randomised, placebo-controlled trial.

    Borgwardt L, Guffon N, Amraoui Y, et al.

    Journal of inherited metabolic disease 2018; (41(6)):1215-1223 doi:10.1007/s10545-018-0185-0.

    PMID: 29846843
  7. 7

    The SPARKLE registry: protocol for an international prospective cohort study in patients with alpha-mannosidosis.

    Hennermann JB, Guffon N, Cattaneo F, et al.

    Orphanet journal of rare diseases 2020; (15(1)):271 doi:10.1186/s13023-020-01549-8.

    PMID: 32993743
  8. 8

    Extended long-term efficacy and safety of velmanase alfa treatment up to 12 years in patients with alpha-mannosidosis.

    Guffon N, Borgwardt L, Tylki-Szymańska A, et al.

    Journal of inherited metabolic disease 2025; (48(1)):e12799 doi:10.1002/jimd.12799.

    PMID: 39381850
  9. 9

    First experience of combined enzyme replacement therapy and hematopoietic stem cell transplantation in alpha-mannosidosis.

    Santoro L, Monachesi C, Zampini L, et al.

    American journal of medical genetics. Part A 2023; (191(7)):1948-1952 doi:10.1002/ajmg.a.63210.

    PMID: 37045799
  10. 10

    Early biochemical effects of velmanase alfa in a 7-month-old infant with alpha-mannosidosis.

    Santoro L, Zampini L, Padella L, et al.

    JIMD reports 2020; (55(1)):15-21 doi:10.1002/jmd2.12144.

    PMID: 32905047

This page is for informational purposes only and does not constitute medical advice. A specialized metabolic and transplant team must assess your individual risks, donor options, and treatment goals for alpha-mannosidosis.

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