Hemoglobin Mizuho or beta 68 (E 12) leucine leads to proline, a new unstable variant associated with severe hemolytic anemia.

A hitherto undescribed, unstable hemoglobin was discovered in a four-year-old Japanese girl with relatively severe hemolytic anemia requiring monthly blood transfusion. Although no abnormal hemoglobin was detectable by electrophoresis at pH 8.6 and 7.0, heat denaturation and isopropanol tests gave positive results. Chemical analyses of the heat labile hemoglobin have demonstrated an amino acid substitution of a prolyl for the leucyl residue at the beta 68th (E 12) position. Remarkable clinical improvement was observed after splenectomy.