Macro creatine kinase types 1 and 2: clinical significance in neonates and children as compared with adults.

We examined the case histories of seven pediatric patients (ages four days to 12 years) whose sera showed significant activities of "macro" creatine kinase (CK; EC 2.7.3.2): two cases of macro CK type 1 (CK-BB isoenzyme bound to IgG) and five cases of macro CK type 2 (polymeric complexes of mitochondrial CK). The diagnoses of the two children with macro CK type 1 were similar to those in 55 adult patients with this form of CK found earlier during screening of a population of 5000. Macro CK type 1 has generally been noted only in older women; this is the first report of it in children. In four of the five cases of macro CK type 2 we found in children, myocardial muscle damage was clinically evident. In contrast, the 26 cases of adults with macro CK type 2 found during the same screening generally had neoplasms, most with metastases to the liver. We suggest that the finding of macro CK type 2 is an indicator of cellular necrosis; in pediatric cases with myocardial damage the associated conditions may be reversible but in adults with malignancies the finding is associated with an extremely poor prognosis.