India’s Eyes Breakthrough Against Sickle Cell.
What is Sickle Cell ?
Sickle cell disease (SCD) is a genetic blood disorder that affects hemoglobin, the protein in red blood cells that carries oxygen throughout the body. This disorder is inherited in an autosomal recessive pattern, meaning that a person must inherit two copies of the mutated gene (one from each parent) to have the disease.
How is it inherited?
Sickle cell disease (SCD) is passed down through families in a way that requires two copies of the mutated gene, one from each parent, for the disease to develop. Here’s a detailed look at how this happens:
- The Genetic Foundation:
1. Mutation in Hemoglobin Gene: SCD is caused by a change in the gene that makes hemoglobin, a protein in red blood cells that carries oxygen around the body. Normally, hemoglobin is made up of two alpha-globin and two beta-globin chains. The mutation in SCD affects the beta-globin chain of hemoglobin.
2. Different Types of Hemoglobin**: The most common type of SCD is due to a specific mutation where the amino acid glutamic acid is swapped for valine at the sixth position of the beta-globin chain, leading to the formation of hemoglobin S (HbS). This abnormal hemoglobin causes red blood cells to become stiff and adopt a sickle shape under certain conditions.
- How It’s Passed Down:
1. Autosomal Recessive: Sickle cell disease follows an autosomal recessive pattern of inheritance, meaning a person needs to get two copies of the mutated gene (one from each parent) to have the disease.
2. Different Genotypes:
-Homozygous HbS (SS): A person with two copies of the HbS mutation (one from each parent) has sickle cell anemia (SS genotype). This is the most severe form of SCD.
Heterozygous HbS (AS): A person with one copy of the HbS mutation and one normal beta-globin gene (from the other parent) is a carrier of the sickle cell trait (AS genotype). Carriers usually don’t show symptoms of SCD but can pass the gene on to their children.
Other Forms: Besides HbS, other types of hemoglobin can mix with HbS to create various forms of SCD, such as HbSC disease (inheriting HbS from one parent and HbC from the other) or combinations with other abnormal hemoglobin variants.
3. Risk Factors
– When both parents are carriers (AS genotype), each child has a:
– 25% chance of getting two normal hemoglobin genes (AA, unaffected),
– 50% chance of getting one normal gene and one sickle cell gene (AS, carrier like the parents),
– 25% chance of getting two sickle cell genes (SS, affected with sickle cell disease).
Genetic Counseling and Testing:
Genetic Counseling: People with a family history of sickle cell disease or those at risk of being carriers of the sickle cell trait can benefit from genetic counseling. This service helps individuals understand their risk of passing on the gene and what it means for their children’s health.
Prenatal Testing: Prenatal testing can be done to check if a fetus has inherited the sickle cell gene mutations. This information helps families make informed choices about their pregnancy and prepare for the potential medical needs of the baby.
Understanding how sickle cell disease is inherited is key for individuals and families dealing with the condition to make educated decisions about their health and family planning.
