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Background and purpose Juvenile‐onset Huntington disease (JHD) is defined when symptoms initiate before 20 years of age. Mechanisms explaining differences between juvenile and adult onset are not fully understood. Our aim was to analyze the distribution of initial symptoms in a cohort of JHD patients and to explore its relationship with CAG expansion and relative telomere length (RTL). Methods A total of 84 JHD patients and 54 neurologically healthy age and sex matched individuals were recruited. CAG length was measured by southern blot or triplet repeat primed polymerase chain reaction. RTL was measured using the Cawthon method. Results Psychiatric symptoms were most frequent when considering the entire cohort. When divided into onset before or after 10 years, cognitive symptoms were more frequent in the youngest, whilst in the older group psychiatric symptoms prevailed. Motor symptoms were rare in the youngest and epilepsy was observed only in this group as well as a larger CAG expansion. RTL analysis revealed shorter telomeres in JHD patients compared to controls. This difference is not influenced by age, initial symptoms, time of disease or CAG expansion. Conclusions To the best of our knowledge this is the largest cohort of JHD patients reported. Psychiatric manifestations deserve special attention when JHD is suspected and epilepsy is especially important in the youngest patients. Initial symptoms seem to be influenced by CAG expansion and therefore age of onset. RTL is significantly reduced in JHD patients which can influence the characteristic neurodegeneration of JHD and contribute to the clinical discrepancy between adult and juvenile forms of Huntington disease.

Epigenetic processes have become increasingly relevant in understanding disease-modifying mechanisms. 5-Methylcytosine methylations of DNA (5mC) and RNA (m5C) have functional transcriptional and RNA translational consequences and are tightly regulated by writer, reader and eraser effector proteins. To investigate the involvement of 5mC/5hmC and m5C effector proteins contributing to the development of dementia neuropathology, RNA sequencing data of 31 effector proteins across four brain regions was examined in 56 aged non-affected and 51 Alzheimer’s disease (AD) individuals obtained from the Aging, Dementia and Traumatic Brain Injury Study. Gene expression profiles were compared between AD and controls, between neuropathological Braak and CERAD scores and in individuals with a history of traumatic brain injury (TBI). We found an increase in the DNA methylation writers DNMT1, DNMT3A and DNMT3B messenger RNA (mRNA) and a decrease in the reader UHRF1 mRNA in AD samples across three brain regions whilst the DNA erasers GADD45B and AICDA showed changes in mRNA abundance within neuropathological load groupings. RNA methylation writers NSUN6 and NSUN7 showed significant expression differences with AD and, along with the reader ALYREF, differences in expression for neuropathologic ranking. A history of TBI was associated with a significant increase in the DNA readers ZBTB4 and MeCP2 (p < 0.05) and a decrease in NSUN6 (p < 0.001) mRNA. These findings implicate regulation of protein pathways disrupted in AD and TBI via multiple pre- and post-transcriptional mechanisms including potentially acting upon transfer RNAs, enhancer RNAs as well as nuclear-cytoplasmic shuttling and cytoplasmic translational control. The targeting of such processes provides new therapeutic avenues for neurodegenerative brain conditions. Graphical abstract

Epigenetic processes have become increasingly relevant in understanding disease modifying mechanisms. 5-methylcytosine methylation of DNA (5mC) and RNA (m5C) have functional transcriptional and RNA translational consequences and are tightly regulated by writers, readers, and erasers effector proteins. To investigate the involvement of 5mC and m5C effector proteins contributing to the development of dementia neuropathology, RNA-sequencing data for 32 effector proteins across four brain regions was examined in 51 aged non-affected and 56 Alzheimer’s disease (AD) individuals obtained from the Aging, Dementia and Traumatic Brain Injury (TBI) study. Gene expression profiles were compared between AD and controls, neuropathological Braak and CERAD scores and in individuals with a history of TBI. We found an increase in DNA methylation writers DNMT1, DNMT3A, DNMT3B mRNA and reader UHRF1 mRNA in AD samples across three brain regions. While DNA methyltransferases erasers GADD45B and AICDA showed changes in mRNA abundance within neuropathological load groupings. RNA methylation writers NSUN6 and NSUN7 showed significant expression differences with AD and, along with the reader, ALYREF, differences in expression for neuropathologic ranking. A history of TBI was associated with a significant increase in ZBTB4 (p < 0.01) and decrease in NSUN6 (p < 0.005) mRNA. These findings implicate regulation of protein pathways disrupted in AD and TBI via multiple pre- and post- transcriptional mechanisms including potentially acting upon tRNAs, enhancer RNAs, as well as nuclear-cytoplasmic shuttling and cytoplasmic translational control. The targeting of such processes provide new therapeutic avenues for neurodegenerative brain conditions.