It has been shown that heterozygous mice, generated by exon 2–6 replacement, do not display any characteristics of cerebellar ataxia [33], in common with heterozygous dogs in the Beagle population, suggesting that SCA5 in heterozygous humans is caused by dominant negative effects of mutant β-III spectrin, rather than haploinsufficiency. The gene discussed is SPTBN2; the disease is aceruloplasminemia.