Which of the following features is NOT typically associated with Hgb C disease?

The feature that is not typically associated with Hemoglobin C disease is the fast mobility of Hemoglobin C at pH 8.6. Hemoglobin C is known to demonstrate slower mobility on electrophoresis compared to normal hemoglobin A. This slower migration occurs because Hemoglobin C has a different charge due to its amino acid substitution, and thus it does not travel as quickly through the gel.

In contrast, Hemoglobin C crystals are commonly observed in patients with Hgb C disease and are a hallmark of the condition, serving as a diagnostic indicator. The presence of target cells, which are red blood cells that appear dimpled or have a central area of hemoglobin surrounded by a clear zone, is also a well-recognized feature of this disease and is linked to the altered red cell morphology. Furthermore, the substitution of lysine for glutamic acid at the sixth position of the β-chain is characteristic of Hemoglobin C, which leads to the distinctive properties of this hemoglobin variant.

Thus, the mobility of Hemoglobin C at alkaline pH is a key distinguishing feature that supports the identification of this condition, primarily noted for its slower rather than faster migration.