Question

A 10-year old black male child named Michael Jones was admitted to the hospital because he was experiencing severe chest pain. He had been hospitalized on several previous occasions for vaso-occlusive episodes that caused him to experience severe pain that could not be managed with non-prescription drugs such as ibuprofen. He was slightly jaundiced, short of breath and easily tired, and feverish. A chest x-ray was taken and was abnormal. An arterial blood sample showed a P_O2 value of 6 kPa (normal is 10 – 13 kPa).

As Michael’s blood sample was waiting for processing a lab technician noticed that the red blood cells at the bottom of the tube had a strange, elongated shape. When the technician mixed the blood the red blood cells returned to their normal shape.Furthermore, the cells were lysed, run on a non-denaturing (ie. simple) electrophoresis gel to separate the proteins, and stained for hemoglobin. Lanes 1 – 3 are standards, lane 4 is from Michael’s blood, and lane 5 is a reference sample of “normal” blood.

Question 1:

What is the most likely diagnosis for Michael?

A.            Carbon monoxide poisoning

B.            Dietary anemia (low intake of iron)

C.            Pernicious anemia (due to a vitamin B12 deficiency)

D.            Sickle cell anemia

Question 2:

Why does the hemoglobin from Michael’s blood not run as far on the electrophoresis gel as the normal sample?

A.            Sickle hemoglobin (HbS) is a longer protein than normal hemoglobin (HbA) so does not travel as

                far in the gel.

B.            HbS aggregate together and since this was a non-denaturing gel there are multiple copies of HbS

                trying to run together through the gel.

C.            HbS has been cleaved as compared to HbA so runs differently.

D.            HbS has a different overall net charge than HbA, which causes it to run differently through the

                gel.

Question 3:

What is the best explanation for the observation of abnormally shaped red blood cells at the bottom of Michael’s blood sample that appear to correct themselves when the sample was mixed?

A.            The sickle shape is more pronounced when the hemoglobin is in the T state, which would be

                more likely at the bottom of the tube due to lower oxygen availability.

B.            The sickle shape is more pronounced when the hemoglobin is in the R state, which would be

                more likely at the bottom of the tube due to lower oxygen availability.

C.            The sickle cells are more dense than normal shaped cells so they settle to the bottom of the

                tube.

D.            The lab technician was seeing things, there were no differences in the cells at the bottom of the

                tube.

Question 4:

In the gel, which lane would look the most similar to what would be obtained if Michael’s parents had their blood sampled?

A.            Lane 1

B.            Lane 2

C.            Lane 3

The doctors treated Michael in part by administering 100% oxygen (normal air is ~20% oxygen), which alleviated some of his symptoms.

Question 5:

Why would 100% oxygen be an effective treatment for Michael?

A.            HbS can only bind 1 oxygen per Hb molecule so more oxygen is required to allow for effective     transport to the rest of the body.

B.            HbS has a lower affinity for oxygen so more oxygen is required to get HbS fully saturated with

                oxygen.

C.            High oxygen will activate the release of BPG to result in more oxygen being delivered to the

                tissues.

D.            High oxygen will cause other oxygen carriers to be activated.

Answer 1

1.- d) Sickle cell anemia.

The sickle form is a specific feature of this condition

2.- d) HbS has a different overall net charge than HbA, which causes it to run differently through the gel

Some glutamic acids are substituted by valines in HbS, this changes the overall net charge

3.- a) The sickle shape is more pronounced when the hemoglobin is in the T state, which woud be more likely at the bottom of the tube due to lower oxygen availability

The sickle shape only occurs in T state, because the R state conformation covers the valine patch mutation

4.- We need the picture of the gel to know that. But have in mind that their parents are carriers, that means they are heterozygous, so they are going to show both bands corresponding for both HbS and HbA

5.- b) HbS has a lower affinity to oxygen so more oxygen is required to get BhS fully saturated with oxygen