The role of interruptions in polyQ in the pathology of SCA1.
At least nine dominant neurodegenerative diseases are caused by expansion of CAG repeats in coding regions of specific genes that result in abnormal elongation of polyglutamine (polyQ) tracts in the corresponding gene products. When above a threshold that is specific for each disease the expanded polyQ repeats promote protein aggregation, misfolding and neuronal cell death. The length of the polyQ tract inversely correlates with the age at disease onset. It has been observed that interruption of the CAG tract by silent (CAA) or missense (CAT) mutations may strongly modulate the effect of the expansion and delay the onset age. We have carried out an extensive study in which we have complemented DNA sequence determination with cellular and biophysical models. By sequencing cloned normal and expanded SCA1 alleles taken from our cohort of ataxia patients we have determined sequence variations not detected by allele sizing and observed for the first time that repeat instability can occur even in the presence of CAG interruptions. We show that histidine interrupted pathogenic alleles occur with relatively high frequency (11%) and that the age at onset inversely correlates linearly with the longer uninterrupted CAG stretch. This could be reproduced in a cellular model to support the hypothesis of a linear behaviour of polyQ. We clarified by in vitro studies the mechanism by which polyQ interruption slows down aggregation. Our study contributes to the understanding of the role of polyQ interruption in the SCA1 phenotype with regards to age at disease onset, prognosis and transmission.
MRC NIMR, London, United Kingdom.
Rajesh P
RP
Menon
Suran
S
Nethisinghe
Serena
S
Faggiano
Tommaso
T
Vannocci
Human
H
Rezaei
Sally
S
Pemble
Mary G
MG
Sweeney
Nicholas W
NW
Wood
Mary B
MB
Davis
Annalisa
A
Pastore
Paola
P
Giunti
D017668:Age of Onset; D000483:Alleles; D015816:Cell Adhesion Molecules, Neuronal / Q000235:genetics* / Q000378:metabolism; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation; D010375:Pedigree; D010455:Peptides / Q000235:genetics* / Q000378:metabolism; D020754:Spinocerebellar Ataxias / Q000235:genetics* / Q000473:pathology; D013132:Spinocerebellar Degenerations / Q000235:genetics* / Q000473:pathology; D019680:Trinucleotide Repeat Expansion / Q000235:genetics*
D015816:Cell Adhesion Molecules, Neuronal; D010455:Peptides; C097188:polyglutamine