**4. SOD1 aggregation**

Numerous experimental studies have characterized the aggregation of multiple forms of SOD1. These are described below, focussing mainly on *in vitro* studies, and their implications for disease. It is important to note, however, that it is not yet known what forms of SOD1 are involved in human disease: neither the disulfide bond status nor metal content of SOD1 in aggregates is known. Evidence supports the population of multiple forms of SOD1 *in vivo* (see section 2). Collectively, experimental findings provide support for contributions from many forms of SOD1 to toxic aggregation in ALS.
