Sickle Cell Risk in a Wayanad Family
A couple from a tribal hamlet near Mananthavady, Wayanad, have a 4-year-old daughter with sickle cell anaemia. Both parents are healthy and have never had a blood transfusion. Haemoglobin electrophoresis shows the father and mother both have HbAS; the daughter has HbSS. The mother is now 10 weeks pregnant. The nearest government hospital is 45 km away, and the family is worried because a local healer has advised them that 'since the first child is affected, the next child will certainly be a boy with the same disease' and that a special herbal oil will 'turn the blood normal'. The couple wants to know the chance that the next child will be affected, and whether anything can be checked during pregnancy. They have one other child, a 7-year-old son, who is healthy but has not been tested.
1. Use the parents' genotypes to calculate the chance that the next child will be affected, a carrier, or unaffected. Correct the healer's two claims.
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- Both parents are HbAS, so each can pass either HbA or HbS.
- A Punnett square gives: HbAA 25%, HbAS 50%, HbSS 25%.
- HbSS is the affected genotype, so the chance for the next child is 1 in 4, or 25%.
- The chance of a carrier is 2 in 4, or 50%. The chance of being unaffected and not a carrier is 1 in 4, or 25%.
- The sex of the child is determined separately by sex chromosomes, so having an affected daughter does not make the next child 'certainly a boy'. Each pregnancy is an independent event; the previous child's result does not change the 25% risk.
- No herbal oil can change a child's haemoglobin genotype. The couple needs genetic counselling, not a promise of a cure.
2. Explain why both parents are healthy although their daughter has sickle cell anaemia.
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- Sickle cell anaemia is an autosomal recessive condition. The HbS allele produces an abnormal form of beta-globin.
- HbAS parents have one HbA allele and one HbS allele. They make both normal HbA and sickle HbS, but the normal haemoglobin is usually enough to prevent severe sickling. They are carriers and are generally healthy.
- The daughter has HbSS: she inherited HbS from both parents. With little or no normal HbA, her red cells can become sickle-shaped under low oxygen conditions. This causes anaemia, pain episodes and other complications.
- The parents being healthy is therefore expected in a recessive condition; it does not mean the allele has disappeared.
3. If the family asks about checking the fetus during pregnancy, what test could be offered and what ethical point must be discussed?
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- Fetal genotype can be checked by obtaining fetal cells, for example by chorionic villus sampling in early pregnancy or amniocentesis later, followed by DNA testing for the HbS mutation. The exact timing and choice must be decided by a qualified clinician.
- These are invasive tests and carry a small risk of miscarriage, so the family must understand the risk as well as the benefit.
- Counselling must be non-directive, confidential and free from pressure. The test should be for information and medical planning, not for sex selection or for discriminating against a child with sickle cell disease.
- The couple should also be told that a test result can reduce uncertainty but cannot change the condition; supportive care and early treatment remain important.