Spectrin, the predominant component of the membrane skeleton of the red cell, is essential in determining the properties of the membrane including its shape and deformability. It consists of 2 nonidentical subunits, alpha and beta. Spectrin is present in the red cell membrane in a tetrameric or possibly higher polymeric form through head-to-head self-association of heterodimers that are linked by actin polymers and protein 4.1 to form a 2-dimensional network. Non-erythroid spectrin gene is mapped to human chromosome 2. Spectrin mutations cause spinocerebellar ataxia type 5.