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.
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.


METHODS
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.
Memory Disorders Research Group, Neurogenetics Clinic, Department of Neurology, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark. troelsn@sund.ku.dk
Troels Tolstrup
TT
Nielsen
Skirmante
S
Mardosiene
Annemette
A
Løkkegaard
Jette
J
Stokholm
Susanne
S
Ehrenfels
Sara
S
Bech
Lars
L
Friberg
Jens Kellberg
JK
Nielsen
Jørgen E
JE
Nielsen
D000328:Adult; D003072:Cognition Disorders / Q000175:diagnosis* / Q000209:etiology / Q000235:genetics*; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D005810:Multigene Family; D010641:Phenotype; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics*; D020754:Spinocerebellar Ataxias / Q000150:complications / Q000175:diagnosis* / Q000235:genetics*; D035181:TATA-Box Binding Protein / Q000235:genetics*
D035181:TATA-Box Binding Protein