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1.  Germ-line CAG repeat instability causes extreme CAG repeat expansion with infantile-onset spinocerebellar ataxia type 2 
The spinocerebellar ataxias (SCA) are a genetically and clinically heterogeneous group of diseases, characterized by dominant inheritance, progressive cerebellar ataxia and diverse extracerebellar symptoms. A subgroup of the ataxias is caused by unstable CAG-repeat expansions in their respective genes leading to pathogenic expansions of polyglutamine stretches in the encoded proteins. In general, unstable CAG repeats have an uninterrupted CAG repeat, whereas stable CAG repeats are either short or interrupted by CAA codons, which – like CAG codons – code for glutamine. Here we report on an infantile SCA2 patient who, due to germ-line CAG repeat instability in her father, inherited an extremely expanded CAG repeat in the SCA2 locus. Surprisingly, the expanded allele of the father was an interrupted CAG repeat sequence. Furthermore, analyses of single spermatozoa showed a high frequency of paternal germ-line repeat sequence instability of the expanded SCA2 locus.
doi:10.1038/ejhg.2012.231
PMCID: PMC3658194  PMID: 23047744
spinocerebellar ataxia type 2; ATXN2; CAG repeat instability
2.  Severe and rapidly progressing cognitive phenotype in a SCA17-family with only marginally expanded CAG/CAA repeats in the TATA-box binding protein gene: A case report 
BMC Neurology  2012;12:73.
Background
The autosomal dominant spinocerebellar ataxias (SCAs) confine a group of rare and heterogeneous disorders, which present with progressive ataxia and numerous other features e.g. peripheral neuropathy, macular degeneration and cognitive impairment, and a subset of these disorders is caused by CAG-repeat expansions in their respective genes. The diagnosing of the SCAs is often difficult due to the phenotypic overlap among several of the subtypes and with other neurodegenerative disorders e.g. Huntington’s disease.
Case presentation
We report a family in which the proband had rapidly progressing cognitive decline and only subtle cerebellar symptoms from age 42. Sequencing of the TATA-box binding protein gene revealed a modest elongation of the CAG/CAA-repeat of only two repeats above the non-pathogenic threshold of 41, confirming a diagnosis of SCA17. Normally, repeats within this range show reduced penetrance and result in a milder disease course with slower progression and later age of onset. Thus, this case presented with an unusual phenotype.
Conclusions
The current case highlights the diagnostic challenge of neurodegenerative disorders and the need for a thorough clinical and paraclinical examination of patients presenting with rapid cognitive decline to make a precise diagnosis on which further genetic counseling and initiation of treatment modalities can be based.
doi:10.1186/1471-2377-12-73
PMCID: PMC3475097  PMID: 22889412
Spinocerebellar ataxia type 17; Dementia; Short CAG repeat expansion

Results 1-2 (2)