Sickle Cell Trait: Could it be a Risk Factor for Severe Coronavirus?
Sickle Cell Trait affects 8–10% of African Americans. Could it increase risk of death from Coronavirus?
Sickle Cell Disease and Sickle Cell Trait
Sickle Cell Disease is a group of inherited disorders that cause a haemoglobin abnormality. Haemoglobin is the molecule found inside red blood cells that carries oxygen around the body. This abnormality causes the haemoglobin molecules to stick to each other, bending the red blood cells into an abnormal “sickle”-shape. Sickled cells can block capillaries and venules, causing acute pain, starving body tissues of oxygen and damaging vital organs. Sickle cell disease is also associated with other complications, including Acute Chest Syndrome, a severe lung injury with similar presentation to the Acute Respiratory Distress Syndrome (ARDS) seen in critically ill Coronavirus patients.
Sickle Cell Disease is a genetic disorder. Affected individuals inherit two mutant copies of the β-globin gene, one from each parent. Individuals with just one mutant β-globin gene have Sickle Cell Trait. Having Sickle Cell Trait provides some protection against malaria, so it is highly prevalent in places where malaria is endemic: approximately 300 million people worldwide, including 30% of people from West Africa and 20% of people from eastern Saudi Arabia have Sickle Cell Trait. Moreover, in the United States, 8% of African Americans have Sickle Cell Trait, compared with 0.05% of White Americans.
Although Sickle Cell Trait has no population-level impact on life expectancy, it is not completely harmless. Among other risks, people with Sickle Cell Trait have a 28-fold higher risk of sudden exercise-related death; and are at risk of developing illness at high altitude. There are also cases of individuals with Sickle Cell Trait developing Acute Chest Syndrome. Although these complications are rare, they are associated with conditions where the body doesn’t get enough oxygen. In these conditions, people with Sickle Cell Trait can experience the haemoglobin polymerisation and red blood cell sickling that is so dangerous in Sickle Cell Disease.
Coronavirus and Sickle Cell Trait
Coronavirus Covid-19 is an acute infection of the respiratory tract. Although many patients experience only mild or asymptomatic disease, approximately 13% of patients require hospitalisation, with hypoxaemia and respiratory failure the main causes of hospitalisation. One of the main symptoms of severe Coronavirus is severe hypoxemia (lack of oxygen in the blood), including an atypical “silent” hypoxaemia, likened to altitude sickness , in which the patient displays severely reduced blood oxygen saturation, but without the reduced lung compliance and respiratory distress typical of severe ARDS. Acute Chest Syndrome and Vaso-occlusive crises have also been observed in Coronavirus-positive people with homozygous Sickle Cell Disease, even in the absence of respiratory complaints.
Sickle Cell carriers are at risk of death or serious illness under conditions of physiological stress that can induce sickling. It is possible that Coronavirus infection and Coronavirus pneumonia, which cause hypoxaemia and resultant tissue hypoxia, could induce these conditions. This strongly suggests that people with Sickle Cell Trait may be at considerably enhanced risk of death or severe disease from Coronavirus infection.
Furthermore, African American individuals are hugely over-represented among Coronavirus hospitalisations and fatalities in America. In Louisiana, approximately 70% of Coronavirus fatalities are in people of African American heritage, despite making up only one third of the population. There are likely to be many intersecting reasons for this discrepancy, including structural racism, reduced access to medical care, a higher risk of co-morbidities and potentially an increased likelihood of Coronavirus exposure during essential work duties.
However, considering that 8% of African Americans have Sickle Cell Trait, we can’t ignore its possible contribution to Coronavirus-related hospitalisations and fatalities. To do so would be to compound the existing systematic disadvantages faced by African Americans needing medical care.
Screening for Sickle Cell is performed routinely in America, but the relationship between Sickle Cell Trait and death from Coronavirus is currently completely unknown. This data must exist. So why hasn’t anyone tried to answer this question?
If Sickle Cell Trait doesn’t increase the risk of severe disease and death, we’re in the same position that we’re in now. But if it does, that’s something we can act on to save lives:
- Individuals with Sickle Cell Trait should fully self-isolate to avoid exposure to the Coronavirus, even if otherwise healthy;
- Hospital admission thresholds could be lowered for symptomatic individuals with Sickle Cell Trait to enable rapid intervention if required.
- The high prevalence of Sickle Cell trait in many regions of the developing world could be a major public health concern.
Right now, we just don’t know. But this must be something worth finding out.
