This mutation was identified in an ENU mutagenesis screen focused on the Del(13)39H deletion interval. A T-to-C transition at nucleotide 869 (RefSeq accession no. NM_009238) generates a Ser70Pro missense mutation. This transition introduces a proline residue into the first alpha-helix of the HMG box of the protein product. Allelic complementation suggests this is a functionally null allele. (J:101156)