There are 153 mutations in the SOD1 gene that have been claimed to be associated with MND in an autosomal dominant or autosomal recessive pattern.
Research that has come out of Umea, Sweden has cast some doubt on two of the 153 reported mutations. The authors report on four MND pedigrees from Finland, France, Germany and Sweden that had been reported to have either the D90A or E100K SOD1 mutation. They found that some members of the families were affected by MND but did not carry the SOD1 mutation. This may mean that these reported mutations do not cause MND. So just as the changing definition of a planet meant that Pluto was crossed off the planet list, the D90A and E100K SOD1 mutations may have to be re-evaluated as a cause for MND.
Source: International MND research update - June 2010, Dr Justin Yerbury for MNDRIA