MGI:1891692 Mice homozygous for a knock-out allele in which expression of the full-length isoform is abolished while expression of the N-terminally truncated isoform is retained are viable and survive to adulthood with no overt phenotypic defects. In culture, primary motoneurons from these mice do not exhibit axonal growth defects but show increased accumulation of double strand breaks and an impaired DNA damage response upon exposure to genotoxic agents.