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The nurse is reviewing the results of genetic testing of a patient with sickle cell disease, noting that HbS indicates sickle cell disease, HBAS indicates sickle cell trait and HbA indicates normal hemoglobin. The patient and her husband are at the lowest risk of having a child with sickle cell disease:

Explanation

• Sickle cell trait is autosomal recessive (2 copies of a gene must be present for the disease or trait to develop). If the father is HbA (normal hemoglobin) and the wife is HbS (sickle cell disease), then there is a 0% chance of having a child with sickle cell disease because only 1 copy of the gene is present.

• When 2 copies of the gene are present, the percentage of the chances for developing the disease or trait are dependent on whether the gene is recessive (indicates trait) or dominant (indicates disease).  HbS indicates sickle cell disease so it is dominant and HbAS indicates the trait for sickle cell disease so it is recessive.

• If both parents have sickle cell disease (HbS), there is a 100% chance of having a child with sickle cell disease.

• If one parent has the disease (HbS), but the other parent only has the trait (HbAS), then there is a 50% chance of having a child with sickle cell disease.

• If both parents have the sickle cell trait (HbAS), then there is a 25% chance of having a child with sickle cell disease.

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