Genetic analysis of the GRIK2 modifier effect in Huntington's disease.
BACKGROUND
In Huntington's disease (HD), age at neurological onset is inversely correlated with the length of the CAG trinucleotide repeat mutation, but can be modified by genetic factors beyond the HD gene. Association of a relatively infrequent 16 TAA allele of a trinucleotide repeat polymorphism in the GRIK2 3'UTR with earlier than expected age at neurological onset has been suggested to reflect linkage disequilibrium with a functional polymorphism in GRIK2 or an adjacent gene.


RESULTS
We have tested this hypothesis by sequencing all GRIK2 exons, the exon-flanking sequences and 3'UTR in several individuals who were crucial to demonstrating the modifier effect, as they showed much earlier age at neurological onset than would be expected from the length of their HD CAG mutation. Though ten known SNPs were detected, no sequence variants were found in coding or adjacent sequence that could explain the modifier effect by linkage disequilibrium with the 16 TAA allele. Haplotype analysis using microsatellites, known SNPs and new variants discovered in the 3'UTR argues against a common ancestral origin for the 16 TAA repeat alleles in these individuals.


CONCLUSIONS
These data suggest that the modifier effect is actually due to the TAA repeat itself, possibly via a functional consequence on the GRIK2 mRNA.
Zeng
Wenqi
W
Molecular Neurogenetics Unit, Center for Human Genetic Research, Massachusetts General Hospital, 185 Cambridge Street, Boston, MA 02114, USA. wzeng@coh.org
Gillis
Tammy
T
Hakky
Michael
M
Djoussé
Luc
L
Myers
Richard H
RH
MacDonald
Marcy E
ME
Gusella
James F
JF
D020413:3' Untranslated Regions / Q000235:genetics*; D000225:Adenine; D017668:Age of Onset; D000483:Alleles; D003596:Cytosine; D005091:Exons / Q000235:genetics; D014644:Genetic Variation; D006147:Guanine; D006801:Humans; D006816:Huntington Disease / Q000453:epidemiology / Q000235:genetics*; D018092:Kainic Acid Receptors / Q000235:genetics*; D018911:Trinucleotide Repeats; D000097806:GluK2 Kainate Receptor
D020413:3' Untranslated Regions; D000225:Adenine; D003596:Cytosine; D006147:Guanine; D018092:Kainic Acid Receptors; D000097806:GluK2 Kainate Receptor