Mutational Analysis Of Glutamate Receptor Delta 2 Gene (GluR δ2) In Patients With Cerebellar Ataxia

Baekground: Cerebellar ataxia is a group of neurodegenerative disease which shares high clinieal and genetic heterogeneity. It mainly involves the cerebellum,the brain stem and the spinal cord. The phenotype of the disease is complex and diverse, and there are familial and sporadic cases, both of which have been identified to be relevant with gene. Recently, glutamate receptor delta2 gene (GluRδ2), has been proved to play a crucial role in the cerebellar function. One prominent feature of GluRδ2 is its predominant expression in Purkinje cell in the cerebellum. GluRδ2 deficiency or mutations cause ataxia which is very similar to cerebellar ataxias. The human glutamate receptorδ2 gene has been mapped to chromosome 4 q22, which has 97.0% and 90.0% identity in amino acid and nucleotide sequence, respectively, to the mouse glutamate receptorδ2. However, it is no report about the mutations in human, though it is highly homologous to the mouse counterpart. Neither has been report as to its relation to human cerebellar ataxia. The current study aimed to examine whether similar mutations within the human GluRδ2 gene occurred in human cerebellar ataxias.Objective: To detect mutations within the human glutamate receptor delta2 gene (GluRδ2) among patients with cerebellar ataxias. Methods: Subjects included in the study were 17 patients with hereditary cerebellarataxias and 16 family members from 4 families,7 unrelated sporadic cerebellar ataxias patients, and 36 normal controls. Polymerase chain reaction(PCR), agarose gel electrophoresis(AGE), Denaturing High Performance Liquid Chromatography(DHPLC)and direct sequencing analysis were performed to detect mutations within the human GluRδ2 gene.Results: (1) Frenquencies of 4 bp deletion within intron 4 of the human GluRδ2 gene were 5.88%,71.43%,17.65% and 11.11% in patients with hereditary cerebellar ataxias,sporadic cerebellar ataxias patients,family members and normal controls. Patients with hereditary cerebellar ataxias and sporadic cerebellar ataxiaspatients were classified as case group, family members and normal controls were classified as control group.No significant difference was found in the frequeney of 4bp deletion within intron 4 between two groups(χ2=0.85,P?0.05).(2) Frenquencies of T allele in 1590 single-nucleotide site within exon 9 of the human GluRδ2 gene were 26.08% and 18.18% between case group and control group, frenquencies of G allele in the same site were 73.91% and 81.81% between case group and control group. No significant difference was found in the frequeney distribution of T/G allele between two groups(χ2=1.28,P>0.05).(3) Frenquencies of C allele within intron 13(63 bp upstream of exon 14) of the human GluRδ2 gene were 71.74% and 75% between case group and control group, frenquencies of G allele in the same site were 28.26% and 25% between case group and control group. No significant difference was found in the frequency distribution of C/G allele between two groups(χ2=0.007,P>0.05).Conclusion: (1) The size of the GluRδ2 gene is relatively large,so many spontaneous mutations in the mouse occur in this gene,but the structure of GluRδ2 gene is relatively stable in human and spontaneous deletion within exons 1-16 was not detected in the human GluRδ2 gene.(2) A small fragment deletion in intron,polymorphism in the human GluRδ2 gene were detected in patients with cerebellar ataxia (whether it is familial or sporadic), and the changes in GluRδ2 gene may be the common genetic foundation between familial and sporadic cerebellar ataxia patients.