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Genetic testing for adult-onset neurodegenerative diseases: A clinical perspective.

Adult-onset neurodegenerative diseases (AOND), such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and frontotemporal dementia, severely affect patients' quality of life. Pathogenic single-nucleotide variations (SNVs) and small insertions and deletions (indels) can disrupt genes involving ANOD, and expansion of short tandem repeats such as trinucleotide repeats is an important etiology of hereditary ataxia. Variations in more than one gene combined to create polygenic risk scores (PRS) for multifactorial types of AOND. Recently, genome structural variations (SVs) l

Molecular diagnosis of Huntington's disease in Trinidadian families via triplet repeat primed PCR, fragment analysis, and nanopore sequencing.

BackgroundHuntington's disease (HD) is a neurodegenerative disorder caused by CAG expansions in the Huntingtin (HTT) gene. Due to its non-specific and variable phenotype, diagnosis requires clinical assessments and genetic testing. In the Caribbean, the genetic etiology of HD is underexplored due to the unavailability of genetic testing.ObjectiveWe investigated whether 32 participants from four multigenerational families from Trinidad and Tobago (T&T) presenting with Huntington-like symptoms carried HTT CAG expansions, and whether CAG length was related to decreasing age of onset with each gen

Suppression of Huntington's Disease Somatic Instability by Transcriptional Repression and Direct CAG Repeat Binding.

Huntington's disease arises from a CAG expansion in the huntingtin gene beyond a critical threshold. Current therapeutics primarily aim to reduce toxicity by lowering levels of mutant HTT mRNA and protein. Genetic data support a role for somatic instability in HTT's CAG repeat as a driver of age of motor dysfunction onset, but currently, the relationship between instability and HTT lowering remains unexplored. Here, we investigate various HTT-lowering modalities to establish the relationship between HTT lowering and instability in Huntington's disease knock-in mice. We find that repressing tra

Low and High-Normal FMR1 Triplet Cytosine, Guanine Guanine Repeats Affect Ovarian Reserve and Fertility in Women Who Underwent In Vitro Fertilization Treatment? Results from a Cross-Sectional Study.

Dynamic mutations in the 5' untranslated region of FMR1 are associated with infertility. Premutation alleles interfere with prenatal development and increase infertility risks. The number of CGG repeats that causes the highest decrease in ovarian reserves remains unclear. We evaluated the effect of FMR1 CGG repeat lengths on ovarian reserves and in vitro fertilization (IVF) treatment outcomes in 272 women with alleles within the normal range. FMR1 CGG repeat length was investigated via PCR and capillary electrophoresis. Alleles were classified as low-normal, normal, and high-normal. Serum leve

Instability of CAG-trinucleotide repeats in chronic lymphocytic leukemia.

Anticipation--earlier onset and more severe disease in the offspring generation--is a well documented feature of familial chronic lymphocytic leukaemia (CLL). In a number of Mendelian diseases, anticipation is caused by expansion of contiguous triplets of nucleotides. The severity of disease expression and penetrance is related to the extent of the triplet expansion. To investigate whether repeat nucleotide repeat expansion is a feature of CLL, the repeat expansion detection (RED) technique was applied to samples from 17 patients with familial disease and 32 patients with early-onset CLL disea

Increased transmission of intermediate alleles of the FMR1 gene compared with normal alleles among female heterozygotes.

Fragile X syndrome (Fra X) is the most common heritable disease accounting for mental retardation and is caused by an expanded CGG repeat in the first exon of the FMR1gene. Previous studies have shown an increased fertility rate among fragile X carrier mothers and a preponderance of mentally retarded boys among the male offspring. In this study, we examined the transmission of the intermediate allele in the lower range of CGG repeats in carrier mothers found randomly in a screening program of the normal population. We tested 10,587 healthy women with no family history of mental retardation and

Polymorphic CGG repeats in gene regulation and disease.

Polymorphic CGG repeats, present at thousands of loci across the human genome, represent a distinctive class of regulatory DNA elements with dual roles in gene regulation and disease. Once regarded primarily as pathogenic triggers, CGG repeats are now recognized as modulators of transcription, chromatin state, and RNA metabolism. When expanded beyond normal thresholds, these repeats can drive neurodevelopmental and neurodegenerative disorders through transcriptional silencing, RNA toxicity, and repeat-associated non-AUG (RAN) translation. Recent advances in long-read sequencing have enabled co

ASO therapy rescues NOTCH2NLC GGC repeat expansion-induced genomic damage, 3D chromatin structural abnormalities, and senescence.

Neuronal intranuclear inclusion disease is caused by abnormal GGC repeat expansion in the NOTCH2NLC gene, though its pathogenic mechanism remains incompletely understood. This study shows that the abnormally expanded polyG-uN2C protein, encoded by the repeat sequence, contains intrinsically disordered regions and forms aggregates, leading to mislocalization of nucleophosmin and downregulation of fibrillarin. PolyG aggregates interact with nucleophosmin and rRNA, disrupting ribosomal homeostasis. Furthermore, polyG facilitates the downregulation of chromatin structural proteins CTCF and RAD21,

Two new cases of fragile X syndrome without CGG triplet expansion. Clinical-molecular characterization and review of the literature.

Fragile X syndrome (FXS) is classically caused by CGG repeat expansion in the FMR1 gene leading to gene silencing. We describe two unrelated patients with clinical features consistent with FXS but harbouring distinct molecular mechanisms. The first patient had a pathogenic intronic variant in FMR1, predicted to impair protein function, and no repeat expansion. The second patient carried a complete deletion of the FMR1 gene, resulting in loss of gene expression. Both individuals presented with developmental delay, intellectual disability, and behavioural manifestations typical of FXS. These cas

Rare but Instructive: Pediatric-Onset Spinocerebellar Ataxia Type 2 and Its Clinical and Genetic Insights.

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant neurodegenerative disorder caused by CAG trinucleotide repeat expansion in the ATXN2 gene. While typically adult-onset, pediatric cases are rare and exhibit distinct clinical features. Here, we report two pediatric-onset SCA2 cases. A 7-year-old boy with involuntary movements, developmental delay, and 58 CAG repeats, and a 16-year-old boy with tremors and gait instability carrying 44 repeats. Both showed cerebellar atrophy on MRI. A literature review of 22 genetically confirmed pediatric SCA2 cases revealed a strong inverse correlat…

На основе CRISPR-Cas9 лечение болезни Хантингтона и атаксии Фридрейха: механизмы, достижения и будущие перспективы.

Болезнь Хантингтона (HD) и атаксия Фридрейха (FRDA) являются прогрессивными унаследованными нейродегенеративными расстройствами, вызванными повторной экспансией тринуклеотида, но характеризующимися различными патогенными механизмами. HD возникает в результате расширения региона кодирования CAG в гене HTT, что вызывает токсичное повышение функциональности охотничьего мутанта (mHTT), в то время как FRDA является главным образом результатом интронического расширения GAA в FXN, что приводит к эпигенетическим репрессиям и фратаксиновому дефициту. Появление инженерии генома на основе CRISPR открыло

Совпадение в аннотации оригинала
Huntington's disease (HD) and Friedreich's ataxia (FRDA) are progressive inherited neurodegenerative disorders caused by trinucleotide repeat expansions but characterized by distinct pathogenic mechanisms. HD arises from a coding-region CAG expansion in the HTT gene that produces toxic gain-of-function effects of mutant huntingtin (mHTT), whereas FRDA result…

DNA extrusion size determines pathway choice during CAG repeat expansion.

DNA triplet repeat expansion causes several primarly neurological disorders like Huntington's disease, myotonic dystrophy type 1, and fragile-X related disorders. There is general consensus that recognition of extrahelical extrusions or hairpin-loop structures (formed by strand slippage) by the DNA mismatch repair protein MutSβ leads to repeat expansion by a mutagenic process. By contrast, the FAN1 nuclease attenuates triplet repeat expansion, the molecular basis of which was explained by our recent finding that FAN1 nuclease cleaves and initiates removal of extrahelical extrusions. Here we sh

A Family with Patients Manifesting Different Phenotypes of Neuromuscular Disease Depending on the CGG Repeat Number in LRP12.

This study describes a family of patients with distal muscle atrophy and oculopharyngodistal myopathy (OPDM). Patients with distal muscle atrophy exhibited slowly progressive distal-predominant muscle weakness without ptosis, ophthalmoplegia, or facial weakness. Long-read sequencing confirmed the presence of intermediate and pathogenic CGG repeat expansions in LRP12 in the patients with distal muscle atrophy and OPDM, respectively. This family demonstrated a similar phenotype-genotype correlation dependent on the LRP12 repeat length, as in a previous study, but the case with intermediate repea

Huntingtin reduction results in altered nuclear structure and heterochromatic instability.

Huntington's disease (HD), a fatal neurodegenerative disease, arises due to a CAG repeat expansion in the huntingtin (HTT) gene. Non-pathogenic wild type HTT (wtHTT) is essential for neurodevelopment as well as many vital cellular functions within the adult brain; however, the consequences of wtHTT reduction in adulthood and particularly in extrastriatal regions of the brain have not been well characterized. Understanding the implications of wtHTT loss is essential as numerous genetic therapies for HD non-specifically reduce the expression levels of both mutant and wtHTT. The aim of the curren

Intersecting impact of CAG repeat and huntingtin knockout in stem cell-derived cortical neurons.

Huntington's Disease (HD) is caused by a CAG repeat expansion in the gene encoding huntingtin (HTT). While normal HTT function appears impacted by the mutation, the specific pathways unique to CAG repeat expansion versus loss of normal function are unclear. To understand the impact of the CAG repeat expansion, we evaluated biological signatures of HTT knockout (HTT KO) versus those that occur from the CAG repeat expansion by applying multi-omics, live cell imaging, survival analysis and a novel feature-based pipeline to study cortical neurons (eCNs) derived from an isogenic human embryonic ste

Myotonic dystrophy type 1 testing, 2024 revision: A technical standard of the American College of Medical Genetics and Genomics (ACMG).

Myotonic dystrophy type 1 (DM1) is a form of muscular dystrophy causing progressive muscle loss and weakness. Although clinical features can manifest at any age, it is the most common form of muscular dystrophy with onset in adulthood. DM1 is an autosomal dominant condition, resulting from an unstable CTG expansion in the 3'-untranslated region of the myotonic dystrophy protein kinase (DMPK) gene. The age of onset and the severity of the phenotype are roughly correlated with the size of the CTG expansion. Multiple methodologies can be used to diagnose affected individuals with DM1, including p

Role of Bβ1 overexpression in the pathogenesis of SCA12.

BACKGROUND: Spinocerebellar ataxia type 12 (SCA12) is a neurodegenerative disease caused by a CAG/CTG repeat expansion at the PPP2R2B locus. OBJECTIVE: We investigated how the CAG repeat expansion within the PPP2R2B 7B7D transcript influences the expression of Bβ1 and a potential protein containing a long polyserine tract. METHODS: Transcript and protein expression were measured using quantitative PCR (qPCR) and Western blot, respectively, in an SK-N-MC cell model that overexpresses the full-length PPP2R2B 7B7D transcript. The apoptotic effect of a protein containing a long polyserine tract

The genetic landscape and phenotypic spectrum of GAA-FGF14 ataxia in China: a large cohort study.

BACKGROUND: An intronic GAA repeat expansion in FGF14 was recently identified as a cause of GAA-FGF14 ataxia. We aimed to characterise the frequency and phenotypic profile of GAA-FGF14 ataxia in a large Chinese ataxia cohort. METHODS: A total of 1216 patients that included 399 typical late-onset cerebellar ataxia (LOCA), 290 early-onset cerebellar ataxia (EOCA), and 527 multiple system atrophy with predominant cerebellar ataxia (MSA-c) were enrolled. Long-range and repeat-primed PCR were performed to screen for GAA expansions in FGF14. Targeted long-read and whole-genome sequencing were perfo

Glial dysregulation in the human brain in fragile X-associated tremor/ataxia syndrome.

Short trinucleotide expansions at the FMR1 locus are associated with the late-onset condition fragile X-associated tremor/ataxia syndrome (FXTAS), which shows very different clinical and pathological features from fragile X syndrome (associated with longer expansions), with no clear molecular explanation for these marked differences. One prevailing theory posits that the shorter, premutation expansion uniquely causes extreme neurotoxic increases in FMR1 mRNA (i.e., four to eightfold increases), but evidence to support this hypothesis is largely derived from analysis of peripheral blood. We app

The CGG repeat expansion in RILPL1 is associated with oculopharyngodistal myopathy type 4.

Recent studies indicate that CGG repeat expansions in LRP12, GIPC1, and NOTCH2NLC are associated with oculopharyngodistal myopathy (OPDM) types 1, 2, and 3, respectively. However, some clinicopathologically confirmed OPDM cases continue to have unknown genetic causes. Here, through a combination of long-read whole-genome sequencing (LRS), repeat-primed polymerase chain reaction (RP-PCR), and fluorescence amplicon length analysis PCR (AL-PCR), we found that a CGG repeat expansion in the 5' UTR of RILPL1 is associated with familial and simplex OPDM type 4 (OPDM4). The number of repeats ranged fr