Bone Marrow Transplant for Sickle Cell Disease: Indications and Process

If finances are genuinely not a barrier, gene therapy is worth choosing once it is better established, since it avoids the donor-related risks. But where finances are a limiting factor, an experienced allogeneic bone marrow transplant programme should still be trusted: it has decades of mature outcome data behind it, and families should not exhaust all their resources chasing a gene therapy process that could stall partway through. If a patient is having an acute crisis such as a recent stroke, there is also often not enough time to wait the six to eight months gene therapy currently requires, and transplant should be pursued instead.

Parents are usually a half match by default, provided they are not sicklers themselves and have no disqualifying condition such as HIV or organ damage. A full-match sibling occurs in about 25% of cases, and a half-matched sibling is actually a better donor than a half-matched parent, since sibling cells are better tolerated with fewer pre-existing antibody reactions. Beyond parents and siblings, more distant relatives such as aunts, uncles or cousins are rarely even a half match, so realistic donor availability is mostly limited to the immediate family.

Dactylitis, swelling of the fingers from small vessel blockage in the hands, is more commonly seen in children because they have not yet developed collateral blood vessels the way adults have. In adults, the vessels involved are relatively larger and better able to develop collaterals, so dactylitis is much less common in that age group.

Patients carrying both sickle cell genes typically have a haemoglobin S level above 60%, and below that the manifestations are usually milder, seen more in sickle cell trait or a combination haemoglobinopathy such as HbSC or HbSE. There is a general tendency for higher HbS to mean more symptoms, but the correlation is not exact and cannot be relied on mathematically for any individual patient.

The middle and posterior cerebral artery territories are affected most commonly, similar to the pattern seen in adults, though the anterior territory can occasionally be involved too. Regular transcranial Doppler screening from two years of age is the key prevention tool: it uses ultrasound to measure blood flow velocity in the cerebral vessels and identifies children at higher risk of stroke early, so that preventive medication and closer monitoring can begin before a stroke actually happens.

A history of stroke, two or more episodes of acute chest syndrome, transfusion dependence, more than three hospital visits for painful crises in a year, and evidence of cardiomyopathy or tricuspid valve regurgitation on screening.

Engraftment is when the donor's stem cells reach the patient's bone marrow and begin producing healthy blood cells, usually within two to three weeks. It is the step transplant physicians watch most closely, since the steps before it rarely cause complications.