Molecular heterogeneity of autosomal dominant cerebellar ataxia: analysis of flanking microsatellites of the spinocerebellar ataxia 1 locus in a northern European family unequivocally demonstrates non-linkage

Spinocerebellar ataxia type 1

Spinocerebellar ataxia type 1 (SCA1) is one out of nine polyglutamine diseases, a group of late-onset neurodegenerative diseases present only in humans. SCA1, the first autosomal dominant cerebellar ataxia (ADCA) to be genetically characterized, is caused by the expansion of a CAG triplet repeat located in the N-terminal coding region of the disease-causing gene ATX1 located on chromosome 6p23: the mutation results in the production of a mutant protein, dubbed ataxin-1, with a longer-than-normal polyglutamine stretch. The predominant effect of the mutation is thought to be a toxic gain-of-function of the aberrant protein, and longer expansions are associated with earlier onset and more severe disease in subsequent generations. The most common presentation of SCA1 is dominant ataxia 'plus', characterized by cerebellar dysfunctions variably associated with slow saccades, ophthalmoplegia, pyramidal and extrapyramidal features, mild to moderate dementia, amyotrophy, and peripheral neuropathy. Its diagnostic pathological feature is olivopontocerebellar atrophy and degeneration predominantly affects the Purkinje cells and the dentate nuclei of the cerebellum. Pathogenesis is mainly attributed to the toxic effect of mutant ataxin-1, which localizes into the nucleus and, through restricted and aberrant protein-protein interactions, causes putative dysfunctional gene transcription in target cells which leads to late-onset cell dysfunction and death.

Microsatellites in the HLA region: on overview

Microsatellites are repeats of a DNA base motif (1-6 bp, mostly CA repeats) up to 100 times; they are distributed regularly all over the genome. Many of them are polymorphic and their high polymorphism is based upon a variable number of repeats. They are widely used for genetic mapping, linkage analysis, population genetics, evolutionary studies and in forensic medicine. Such markers have also been described in the HLA region since 1991, and a growing interest in their potential applications is being expressed. The aims of this review are: 1) to outline the presently available information from literature and molecular databases concerning 53 microsatellites in the HLA region (localization, type of repeat, number of alleles, heterozygosity, primers used for amplification); 2) to address the question of technical pitfalls when using such markers; 3) to discuss specific features such as their mutation rate (10 (-3) to 10 (-6), which is higher than that reported for HLA genes, and their linkage disequilibrium with HLA alleles; 4) to present an integrated map of microsatellites and genes of this region; and 5) to provide a synopsis of their different applications in HLA-related fields (disease studies, population genetics, recombination point studies, HLA region mapping, transplantation) along with perspectives for future use. Although some HLA region microsatellites have already been applied to the analysis of more than 10 diseases, it is now evident that their use in population genetics and the determination of genomic compatibility in bone marrow transplantation represent growing areas of application.