Which of the following disorders has an increase in osmotic fragility?

Hereditary spherocytosis is characterized by an increase in osmotic fragility of red blood cells. In this disorder, the red blood cells have an abnormal shape, becoming more spherical instead of the typical biconcave disc shape. This alteration in shape is a result of defects in the proteins that maintain the cell membrane's integrity, which can include spectrin, ankyrin, and band 3.

When these spherically-shaped cells are placed in a hypotonic solution, they take in more water than normal cells, leading to their rupture more readily than healthy red blood cells. This property is measured through the osmotic fragility test, where spherocytes demonstrate increased sensitivity to hemolysis under low osmotic conditions.

The other disorders mentioned do not share this specific feature of increased osmotic fragility. For example, iron deficiency anemia generally affects red blood cell size and hemoglobin content but does not cause changes to the cell's shape that influence their fragility in this manner. Hereditary elliptocytosis involves elongated red blood cells that are more resilient under osmotic stress. Lastly, hereditary stomatocytosis may exhibit increased permeability but is not primarily characterized by osmotic fragility in the same way as hereditary s