Which of the following is true for the mutated erythroid progenitors in polycythemia vera?

a. They require extremely high levels of erythropoietin for growth in vitro.
b. They are more resistant to apoptosis than normal erythroid progenitors.
c. They mature abnormally, giving rise to a marked increase in poikilocytosis in peripheral blood.
d. They are Philadelphia chromosome positive.

ANS: B
The mutated erythroid progenitors in polycythemia vera are more resistant to apoptosis than normal erythroid progenitors. Thus they do not divide more rapidly (as once believed) but accumulate abnormally because they do not die normally. This results in an increased red cell mass in peripheral blood. Maturation is normal, giving rise to essentially morphologically normal red cells. They grow in vitro with trace concentrations of erythropoietin and are Philadelphia chromosome negative.