The mothers asks the nurse why her child’s hemoglobin was normal at birth but now the child has S hemoglobin. Which of the following responses by the nurse is most appropriate?
A. “The placenta bars passage of the hemoglobin S from the mother to the fetus.”
B. “The red bone marrow does not begin to produce hemoglobin S until several months after birth.”
C. “Antibodies transmitted from you to the fetus provide the newborn with temporary immunity.”
D. “The newborn has a high concentration of fetal hemoglobin in the blood for some time after birth.”
Correct Answer: D. “The newborn has a high concentration of fetal hemoglobin in the blood for some time after birth.”
Sickle cell disease is an inherited disease that is present at birth. However, 60% to 80% of a newborn’s hemoglobin is fetal hemoglobin, which has a structure different from that of hemoglobin S or hemoglobin A. Sickle cell symptoms usually occur about 4 months after birth, when hemoglobin S begins to replace the fetal hemoglobin.
Option A: The gene for sickle cell disease is transmitted at the time of conception, not passed through the placenta. Sickle cell disease is an autosomal recessive disorder of a gene mutation. On chromosome 11, nucleotide mutation leads to substitution of glutamic acid to valine at position six on the beta-globin subunit. This leads to changes in the physical properties of the globin chain.
Option B: Some hemoglobin S is produced by the fetus near term. The fetus produces all its own hemoglobin from the earliest production in the first trimester. Fetal hemoglobin production is switched off soon after birth although the time of switch over is not known. A replacement of glutamic acid of the beta chain by valine at the 6th position gives rise to a sickle cell disorder. This change, called hemoglobin S (HbS), is an abnormal hemoglobin
Option C: Passive immunity conferred by maternal antibodies is not related to sickle cell disease, but this transmission of antibodies is important to protect the infant from various infections during early infancy. Studies have revealed that HbF usually disappears from red blood of infants after about 6 months. However, the exact time of disappearance of HbF may vary and the signal that determines the switch from fetal to adult hemoglobin is not known.
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