Sickle Cell Disease

Sickle Cell Diseases

Some medical conditions, like Sickle Cell Disease and Cystic Fibrosis, are controlled by complete dominance.

A person must inherit one recessive allele from each parent to have the condition.

One recessive allele comes from their mother.

One recessive allele comes from their father.

How would two healthy biological parents produce offspring that has sickle cell disease?

If two healthy parents who are carriers (Aa × Aa) have a child, there is a 25% chance the child will have SCD (aa)

What does this mean? Both parents are healthy but carry one recessive allele (a). Each parent passes down one allele to their child. If both parents pass down a, the child gets aa and has SCD.

Carriers: People who carry one recessive allele for SCD but do not have the condition because the dominant allele masks it.

What does this mean? A carrier has Aa — one dominant allele (A) and one recessive allele (a). They usually do not have SCD, but they can pass the a allele to their children.

Sickle Cell Disease Causes

• Red blood cells are specialized cells

• They contain a protein called hemoglobin, which carries oxygen throughout the body.

• They are very flexible, allowing them to squeeze through tiny blood vessels called capillaries, even when the vessels are narrower than the cells themselves

• When someone has the homozygous recessive genotype (aa),  their red blood cells become a sickle shape when the cell is under stress and/or in low oxygen conditions.

• This makes the red blood cells stiff and less flexible, so they have trouble moving through tiny capillaries.

Sickle Cell Symptoms

The sickled red blood cells then block blood vessels throughout the body, which leads to many serious health symptoms:

Anemia (the blood doesn’t carry oxygen well)

Pain crises in the abdomen, chest and joints

Swelling in the hands and feet

Frequent infections

Vision problems

Delayed growth or puberty

Exhaustion & lethargy

SCD Medical Racism

• Rates of SCD are higher amongst populations in Western Africa, and in populations of West African descent (*more on this in the Evolution unit).

• Due to the systemic racism within health care systems, Black patients suffering from SCD symptoms continue to be ignored and left untreated.

• SCD research is also underfunded, especially when compared to conditions like Cystic Fibrosis.