We describe a 56-year-old woman hospitalized under a diagnosis of acute myocardial infarction without an increase in serum creatine kinase(CK) activity during the clinical course. The patient had had no previous muscular symptoms. CK-M protein in the myocardial tissue of the patient was substantially lower(103±7ng/mg protein) than that in control myocardial tissue(35800±2860ng/mg protein). Immunoreactive CK-M in the patient tissue sample was 0.3% of the value for the control sample. CK-M mRNA was 53-fold less in the patient sample compared with the control. This very low expression of CK-M mRNA was considered to be the primary reason for CK-M deficiency. Direct sequencing demonstrated a point mutation at residue 54 in exon2, which was specific for the patient.
There were no other abnormalities found in the CK-M gene of the patient. This report identifies a molecular abnormality in human CK deficiency and discusses the physiologic relevance of CK-M.


*1Clinical Laboratory Medicine, West Kobe Medical Center, Kobe 651-2273

【Key Words】CK isoenzyme, genetic, CK-M deficiency, a point mutation, mRNA suppression