Tandem cytosine-adenine-guanine (CAG) repeat sizes of 36 or more in the huntingtin gene (HTT) cause Huntington's disease (HD). Apart from neuropsychiatric complications, the disease is also... Show moreTandem cytosine-adenine-guanine (CAG) repeat sizes of 36 or more in the huntingtin gene (HTT) cause Huntington's disease (HD). Apart from neuropsychiatric complications, the disease is also accompanied by metabolic dysregulation and weight loss, which contribute to a progressive functional decline. Recent studies also reported an association between repeats below the pathogenic threshold (<36) for HD and body mass index (BMI), suggesting that HTT repeat sizes in the non-pathogenic range are associated with metabolic dysregulation. In this study, we hypothesized that HTT repeat sizes < 36 are associated with metabolite levels, possibly mediated through reduced BMI. We pooled data from three European cohorts (n = 10 228) with genotyped HTT CAG repeat size and metabolomic measurements. All 145 metabolites were measured on the same targeted platform in all studies. Multilevel mixed-effects analysis using the CAG repeat size in HTT identified 67 repeat size metabolite associations. Overall, the metabolomic profile associated with larger CAG repeat sizes in HTT were unfavorable-similar to those of higher risk of coronary artery disease and type 2 diabetes-and included elevated levels of amino acids, fatty acids, low-density lipoprotein (LDL)-, very low-density lipoprotein- and intermediate density lipoprotein (IDL)-related metabolites while with decreased levels of very large high-density lipoprotein (HDL)-related metabolites. Furthermore, the associations of 50 metabolites, in particular, specific very large HDL-related metabolites, were mediated by lower BMI. However, no mediation effect was found for 17 metabolites related to LDL and IDL. In conclusion, our findings indicate that large non-pathogenic CAG repeat sizes in HTT are associated with an unfavorable metabolomic profile despite their association with a lower BMI. Show less
Many common disorders, including depression, dementia and obesity are for a large part heritable. Despite the fact that genome-wide association studies (GWAS) have contributed substantially to... Show moreMany common disorders, including depression, dementia and obesity are for a large part heritable. Despite the fact that genome-wide association studies (GWAS) have contributed substantially to unraveling the genetic architecture of these polygenetic disorders, a large amount of ‘missing heritability’ remains. A possible explanation is that GWAS, aside single-nucleotide polymorphisms cannot assess the contribution of other important genetic polymorphisms, especially tandem repeats. Tandem repeats constitute 3% of the human genome. Nine hereditary neurodegenerative diseases, known as polyglutamine diseases, including Huntington disease (HD), are the most prevalent disorders associated with tandem repeat variations. These diseases are caused by an elongated cytosine-adenine-guanine (CAG) repeat sequence in the respective polyglutamine disease-associated gene (PDAG). In this dissertation, we provide ample evidence that CAG repeat variations within the ‘normal’ range in PDAGs can affect various aspects of disease, including the age of onset in HD, cognitive function, depression and body mass index. Finally, we found a relatively large prevalence of intermediate and pathological PDAG alleles in the general population. Therefore, we provided support for the role of repetitive DNA polymorphisms in elucidating the ‘missing heritability’ of polygenetic disorders and emphasized the necessity to include these variations in future genetic research. Show less
Autosomal dominant cerebellar ataxias (ADCAs) are a group of neurodegenerative disorders characterized by degeneration of the cerebellum and its connections. All ADCAs have progressive ataxia as... Show moreAutosomal dominant cerebellar ataxias (ADCAs) are a group of neurodegenerative disorders characterized by degeneration of the cerebellum and its connections. All ADCAs have progressive ataxia as their main clinical feature, frequently accompanied by dysarthria and oculomotor deficits. The most common spinocerebellar ataxias (SCAs) are 6 polyglutamine (polyQ) SCAs. These diseases are all caused by a CAG repeat expansion in the coding region of a gene. Currently, no curative treatment is available for any of the polyQ SCAs, but increasing knowledge on the genetics and the pathological mechanisms of these polyQ SCAs has provided promising therapeutic targets to potentially slow disease progression. Potential treatments can be divided into pharmacological and gene therapies that target the toxic downstream effects, gene therapies that target the polyQ SCA genes, and stem cell replacement therapies. Here, we will provide a review on the genetics, mechanisms, and therapeutic progress in polyglutamine spinocerebellar ataxias. Show less
