Expanded CAG Repeat Size Research Articles

Variants in Genes of Calpain System as Modifiers of Spinocerebellar Ataxia Type 3 Phenotype

Calpain-mediated proteolysis has been proposed to modulate the pathogenesis of spinocerebellar ataxia type 3, also known as Machado-Joseph disease (SCA3/MJD), a disorder due to a CAG repeat expansion (CAGexp) at ATXN3. We aimedto investigate if single-nucleotide polymorphisms (SNPs) at calpain gene CAPN2 and at calpastatin gene CAST modulate the age at onset (AO) and disease progression in SCA3/MJD. A total of 287 SCA3/MJD symptomatic subjects (151 families) were included. AO was analyzed and controlled by the CAG repeat length of expanded allele and family. Candidate polymorphisms were chosen based on the literature and on a priori criteria. The CAG repeat length and SNPs were genotyped according to standard methods. AO of carriers of AA and AG + GGrs1559085 genotypes in CAST and with the median value of 75 repeats at the expanded allele were 34.23 (33.07-35.38) and 36.42years (34.50-38.34), respectively (p = 0.049, mixed model treating the expanded CAG repeat size as fixed effect and family as random effect). Carriers of haplotype Crs27852/Grs1559085 had mean AO of 37.23 (12.76) and 33.42years (12.20) (p = 0.047, Student's t test). Our data suggest an association between allele Grs1559085 and haplotype Crs27852/Grs1559085 at CAST and variations in the AO of SCA3/MJD subjects, independent from the effects of the CAGexp and family. The present results support the potential role of calpain cleavage pathway over modulation of SCA3/MJD phenotype.

Extending the Phenotypic Spectrum of Huntington Disease: Hypothermia

Huntington disease (HD) is an autosomal dominant progressive neurodegenerative disorder associated with expanded CAG repeat size in the huntingtin gene and usually presenting with movement disorder, psychiatric symptoms, and cognitive decline. Sleep problems, weight loss, and cachexia are also common. Here, we report a patient presenting with hypothermia in late-stage HD. Although thermoregulatory defects were documented in animal models, this is the first report describing HD with hypothermia in humans.

Novel allele-specific quantification methods reveal no effects of adult onset CAG repeats on HTT mRNA and protein levels.

Huntington's disease (HD) reflects dominant consequences of a CAG repeat expansion mutation in HTT. Expanded CAG repeat size is the primary determinant of age at onset and age at death in HD. Although HD pathogenesis is driven by the expanded CAG repeat, whether the mutation influences the expression levels of mRNA and protein from the disease allele is not clear due to the lack of sensitive allele-specific quantification methods and the presence of confounding factors. To determine the impact of CAG expansion at the molecular level, we have developed novel allele-specific HTT mRNA and protein quantification methods based on principles of multiplex ligation-dependent probe amplification and targeted MS/MS parallel reaction monitoring, respectively. These assays, exhibiting high levels of specificity and sensitivity, were designed to distinguish allelic products based upon expressed polymorphic variants in HTT, including rs149109767. To control for other cis-haplotype variations, we applied allele-specific quantification assays to a panel of HD lymphoblastoid cell lines, each carrying the major European disease haplotype (i.e. hap.01) on the mutant chromosome. We found that steady state levels of HTT mRNA and protein were not associated with expanded CAG repeat length. Rather, the products of mutant and normal alleles, both mRNA and protein, were balanced, thereby arguing that a cis-regulatory effect of the expanded CAG repeat is not a critical component of the underlying mechanism of HD. These robust allele-specific assays could prove valuable for monitoring the impact of allele-specific gene silencing strategies currently being explored as therapeutic interventions in HD.

Preliminary analysis of Huntington's Disease in South Korea.

There have been epidemiological studies of Huntington's disease (HD) in various populations and nations. Only a few studies describing clinical characteristics have been reported in Asia. To conduct preliminary analyses of demographic, clinical and genetic characteristics of HD in South Korea. From 1994 to 2011, thirty six subjects were diagnosed as HD in Seoul National University Hospital. Demographic, clinical and genetic data were carefully analyzed in all subjects. Mean age of onset was 46.5 ± 12.7 years and mean expanded CAG repeat size was 45.4 ± 4.7. Twenty-eight subjects (80%) had a family history of HD. Chorea was the most frequent symptom at first visit (89%). Proportion of cognitive decline (36%) and psychiatric symptom (28%) at first visit were lower than proportion of previous reports. A negative correlation (Pearson correlation coefficient -0.757, p = 0.001) was found between expanded CAG repeat size and age of onset. Seven subjects without family history of HD had higher mean age of onset (54.0 ± 8.1) and smaller expanded CAG repeat size (42.4 ± 2.7). Cognitive problems at first visit of subjects without family history were more prominent than those with family history (86% vs. 25%). This study is the first demographic, clinical and genetic analyses in South Korea. These results will be helpful to stimulate more large-scale research in South Korea and other Asian nations.

Localization of sequence variations in PGC-1α influence their modifying effect in Huntington disease

BackgroundHuntington disease (HD) is caused by a polyglutamine expansion of more than 35 units in the huntingtin protein. This expanded repeat length inversely correlates with the age-at-onset (AAO), however, additional genetic factors apart from the expanded CAG repeat size are thought to influence the course and the AAO in HD. Until now, among others, the gene encoding PCG-1α (PPARGC1A) was shown to modify the AAO in two independent, however small, populations. PGC-1α is involved in the induction of various mechanisms regulating mitochondrial biogenesis and oxidative stress defence. Furthermore, several studies have linked impairment of its function and/or its expression to HD pathogenesis. As the identification of distinct modifiers in association studies is largely dependent on the size of the observed population, we investigated nine different single nucleotide polymorphisms (SNPs) in PPARGC1A in order to replicate the disease modifying effect in more than 800 European HD patients and to identify an association with AAO in HD.ResultsTwo SNPs, one in the promoter and one in the transcribed region of the gene, showed a significant effect on the AAO. While the minor allele of SNP rs7665116 (g.38570C), located in the transcribed gene region, was associated with a delay in disease onset, especially in HD patients with Italian ancestry, the minor allele of SNP rs2970870 (g.-1437C) in the promoter region leads to an earlier onset of HD in its homozygous state. Additionally, global testing of haplotype block 2, which covers the main part of the transcribed region of the gene, revealed an association between block 2 haplotypes and the disease onset.ConclusionTherefore, our results indicate opposing modifying influences of two SNPs within one gene on AAO and support the idea that PGC-1α dysfunction is involved in HD pathology.

C04 The effects of GRIN gene variations on age at onset of Turkish Huntington's disease patients

BackgroundThe length of the CAG repeats is the major determinant in defining the age of onset (AO) of Huntington's disease (HD). However, there remains a significant variance in AO when...

X-linked recessive bulbospinal neuronopathy (SBMA).

X-linked recessive bulbospinal neuronopathy (SBMA) is an adult onset motor neuronopathy with androgen receptor (AR) gene mutation of expanded CAG repeat size in the first exon. The size of CAG repeats in the AR gene is one of the determinant factors of the severity and progression rate of SBMA phenotypes, but the meiotic and somatic instability of CAG repeats is far more stable as compared with other diseases caused by trinucleotide repeat expansions such as HD, DRPLA, MJD and SCA1. Several evidences suggest that aberrant transcriptional activity of androgen through mutant AR is related to the pathogenic mechanism of this disease.