Prothrombin "Mexico City," an asymptomatic autosomal dominant prothrombin variant.

A functionally normal but structurally abnormal prothrombin variant was found in a Mexican family. Immunoisoelectricfocusing studies revealed that this variant has a more acidic isoelectric point (4.01) than normal prothrombin (4.29), but it proved to have a normal molecular weight as assessed by sodium-dodecyl-sulphate polyacrylamide gel electrophoresis. Two-dimensional immunoelectrophoresis studies showed an abnormal cleavage of the prothrombin molecule by factor Xa and Echis carinatus venom as well, despite the fact that both yield functionally normal thrombin molecules. Finally, the ability of the molecule to bind calcium ions as well as its overall antigenic structure were investigated and found to be normal. These results taken together suggest a simple (substitution or translocation) mutation at the fragment 2 level. Since this prothrombin variant is different from others described previously, the name "Mexico City" is proposed to identify it.

'Incomplete' pyroglobulin-gamma disease in a patient with osteosclerotic myeloma.

A 50-year-old female, heterozygous for beta-thalassaemia was found to have a lytic lesion surrounded by osteosclerotic tissue in the 1st lumbar vertebra. Aspiration of the lesion showed 100% atypical plasma cells. The bone marrow contained 17% myeloma cells. Despite normal electrophoresis and immunoelectrophoresis of serum and urine, 'rouleaux' formation was pronounced. Treatment of the serum sample with 2-mercaptoethanol and heat (56 degrees C) disclosed an uncommon pyroglobulin. Analysis of the ammonium sulphate precipitate of the serum by sodium-dodecyl-sulphate polyacrylamide gel electrophoresis revealed a 43 kD component with higher anodic mobility than normal gamma chains. Ultrafiltration column chromatography of the serum revealed a narrow spike of approximately 4 S that contained gamma heavy chain antigenic determinants in addition to normal 7 S IgG.