| Abstract: | We describe a new spectrin variant with a truncated beta-chain. It was discovered in a 17-year-old white boy presenting with intermittent jaundice and spleen enlargement. He also displayed numerous smooth elliptocytes. On sodium dodecyl sulfate-polyacrylamide gel, the truncated beta-chain (beta'-chain) appeared as an additional band of approximately 216 kilodaltons, migrating between spectrin beta-chain and ankyrin. It represented 30% of total beta-chain. The beta'-chain reacted with an antispectrin beta-chain monoclonal antibody. It failed to become phosphorylated when ghosts were incubated in the presence of gamma-32P] adenosine triphosphate. Whole spectrin tetramerization was defective since the amount of spectrin dimer was increased in spectrin crude extract and the association constant of the spectrin dimer self- association was decreased. Spectrin whole tetramer isolated from spectrin crude extracts contained small quantities of beta'-chain. Spectrin tryptic peptides showed an increase of the 74,000-dalton fragment at the expense of the 80,000-dalton fragment. So far, the latter abnormality has been used to characterize a number of cases of hereditary elliptocytosis or pyropoikilocytosis with no other apparent change. In the present case, we consider that the abnormality is a consequence of the beta-chain alteration. The parents seemed asymptomatic. As a result, we regard this new spectrin variant as deriving from a de novo mutation. |
