Assignment of the calcium channel, voltage-dependent, P/Q type, alpha 1A subunit gene <i>(CACNA1A)</i>, and the ataxin 7 gene <i>(ATXN7)</i> to canine chromosome 20 by fluorescence in situ hybridization and confirmation by radiation hybrid mapping

CACNA1A (SCA6, Spinocerebellar ataxia type 6), and ATXN7 (SCA7, Spinocerebellar ataxia type 7) belong to a group of genes involved in autosomal dominant cerebellar ataxia in humans. The autosomal dominant cerebellar ataxias are a heterogeneous group of neurodegenerative disorders characterized by progressive degeneration of the cerebellum, brain stem and spinal cord. The pathogenetic mechanism is the same in all SCA genes and is based on the inheritance of an unstable, expanded CAG trinucleotide repeat in the coding region, resulting in an extended polyglutamine sequence within the protein. The function of the proteins (ataxin 6 and 7) is not known (Klockgether and Evert, 1998; Lebre and Brice, 2003). The human CACNA1A gene maps at 13.47 Mb on HSA19p13.2→p13.1 and contains 47 exons spanning 39 kb, whereas the human ATXN7 gene maps at 64.63 Mb on HSA3p14 and consists of 14 exons spanning 136 kb (NCBI map viewer, human genome build 35.1). The mapping of these two genes in the dog is the first step for further investigations in inherited ataxia in the dog which is a well known problem in several dog breeds (Wessmann et al., 2004). Materials and methods