Gene Therapy for Sickle Cell Disease: CRISPR Editing and Gene Addition

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.

In pregnant women who have generally done well and had infrequent pain crises up to childbearing age, hydroxyurea is usually held during pregnancy since it is not a good option for fetal development. Good hydration and avoiding any other stressful conditions are advised instead, and folic acid supplementation must continue.

As early as the disease is detected, sometimes as young as two months of age.

The best outcomes are under 16 years, 16 to 25 is still viable, and beyond 25 the risks rise and require much more detailed pre-transplant workup, including cardiac and kidney function assessment, though age is not always a fixed barrier if organ function is well preserved and the family is fully committed. A full-match sibling transplant typically costs around $24,000 to $25,000, rising for older patients closer to adult body weight, while a half-match or unrelated-donor transplant through a registry costs around $33,000 to $34,000, since registry and donor-related costs are higher even though complications are reduced.

Gene therapy uses the patient's own stem cells, modified in a laboratory using CRISPR-Cas9 editing or gene addition with a viral vector, rather than cells from a donor. This generally means faster recovery and substantially lower risk of infection or graft-versus-host disease, but it currently takes around six months and remains costly and not widely available.

Where finances are genuinely limited, an experienced allogeneic bone marrow transplant programme, with decades of proven outcomes, remains the more dependable option. Gene therapy is a reasonable choice mainly where cost is not a barrier and time is not urgent, since it currently takes about six months and a patient in acute crisis cannot wait that long.