Hb Himeji or alpha 2 beta 2(140)(H18)Ala----Asp in a Portuguese family

Hemoglobin Himeji and inconsistent hemoglobin A1c values: a case report

BACKGROUND

Hemoglobin A1c is used to evaluate the glycemic control in patients with diabetes and is a risk marker for chronic complications of diabetes. Hemoglobin variants are reported to falsely lower or increase hemoglobin A1c test results. We present a case report of a patient with diabetes with discrepancy between fasting plasma glucose and hemoglobin A1c due to the presence of hemoglobin Himeji, a clinically silent and very rare hemoglobinopathy.

CASE PRESENTATION

A 76-year-old white woman, born and living in Portugal, with type 2 diabetes presented to the family physician for a routine visit. She had no active complaints, including history or symptoms of hypoglycemia, and her physical examination was unremarkable. A review of her laboratory data showed fasting plasma glucose of 190 mg/dL and a hemoglobin A1c of 4.1%. The remaining blood test results were clinically insignificant; a further review of her laboratory data over the past 4 years revealed that her fasting plasma glucose had ranged from 130 to 250 mg/dL and hemoglobin A1c was consistently lower than 5%. A study of hemoglobins detected 32.8% of abnormal hemoglobin. Genetic sequencing identified a heterozygous mutation compatible with hemoglobin Himeji (c.422C>A; p.Ala141Asp). We tracked her family (three sons, six grandchildren, and two greatgrandchildren) for the presence of this hemoglobin variant, but none had this hemoglobinopathy.

CONCLUSIONS

Despite the advantages of hemoglobin A1c in the follow-up and treatment of diabetes, the factors that interfere with its results must be known to ensure a correct estimation of the degree of glycemic control and a proper management of the disease. Therefore, health professionals should suspect the existence of hemoglobin variants when: the hemoglobin A1c value is above 15% or below the lower limit of its reference interval; there is a significant modification in its result coinciding with a change in assay methods; and there is a low correlation between plasma glucose and hemoglobin A1c. In patients with hemoglobin Himeji, alternate ways of monitoring glycemic control (fructosamine or glycated serum albumin) should be used.

Unstable hemoglobins

About 70 variants of Hb A with associated hemolytic disorders have been reported during the past 30 years. I have classified them according to four grades of severity of chronic hemolysis. Acute episodes of severe hemolysis may be seen in all classes. In addition, some 80 variants without overt hemolysis have given positive results with in vitro hemoglobin instability tests. The stereochemical bases for instability can be conjectured in most cases, although few unstable hemoglobins have actually been studied by X-ray crystallography. The mechanisms for denaturation of normal Hb A and its acceleration in unstable hemoglobins were proposed some 15 years ago. The alterations of membrane lipids and proteins leading to red cell senescence and the relevance of hemoglobin denaturation to this process are presently being investigated. Several "hyperunstable" variants are clinically silent, or equivalent to a thalassemia, probably because of very efficient degradation of the abnormal chains.