Dentatorubropallidoluysian atrophy in Chinese

Atrophin-1 Function and Dysfunction in Dentatorubral-Pallidoluysian Atrophy

Dentatorubral-pallidoluysian atrophy (DRPLA) is a rare, incurable genetic disease that belongs to the group of polyglutamine (polyQ) diseases. DRPLA is the most common in the Japanese population; however, its global prevalence is also increasing due to better clinical recognition. It is characterized by cerebellar ataxia, myoclonus, epilepsy, dementia, and chorea. DRPLA is caused by dynamic mutation of CAG repeat expansion in ATN1 gene encoding the atrophin-1 protein. In the cascade of molecular disturbances, the pathological form of atrophin-1 is the initial factor, which has not been precisely characterized so far. Reports indicate that DRPLA is associated with disrupted protein-protein interactions (in which an expanded polyQ tract plays a crucial role), as well as gene expression deregulation. There is a great need to design efficient therapy that would address the underlying neurodegenerative process and thus prevent or alleviate DRPLA symptoms. An in-depth understanding of the normal atrophin-1 function and mutant atrophin-1 dysfunction is crucial for this purpose. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

DRPLA: understanding the natural history and developing biomarkers to accelerate therapeutic trials in a globally rare repeat expansion disorder

Dentatorubral–pallidoluysian atrophy (DRPLA) is a rare neurodegenerative disorder caused by CAG repeat expansions in the atrophin-1 gene and is inherited in an autosomal dominant fashion. There are currently no disease-modifying treatments available. The broad development of therapies for DRPLA, as well as other similar rare diseases, has hit a roadblock due to the rarity of the condition and the wide global distribution of patients and families, consequently inhibiting biomarker development and therapeutic research. Considering the shifting focus towards diverse populations, widespread genetic testing, rapid advancements in the development of clinical and wet biomarkers for Huntington’s disease (HD), and the ongoing clinical trials for antisense oligonucleotide (ASO) therapies, the prospect of developing effective treatments in rare disorders has completely changed. The awareness of the HD ASO program has prompted global collaboration for rare disorders in natural history studies and the development of biomarkers, with the eventual goal of undergoing treatment trials. Here, we discuss DRPLA, which shares similarities with HD, and how in this and other repeat expansion disorders, neurogenetics groups like ours at UCL are gearing up for forthcoming natural history studies to accelerate future ASO treatment trials to hopefully emulate the progress seen in HD.

Report of progressive myoclonus ataxia (PMA) in two Chinese pedigrees

OBJECTIVE

To describe the clinical characteristics of patients diagnosed with progressive myoclonus ataxia (PMA) from two Chinese pedigrees.

METHODS

An analysis of clinical data is presented and inferences drawn.

RESULTS

The propositus from pedigree-I (9-year-old female) could not walk stably and had a history of frequent falls. The symptoms aggravated over time until she lost the ability to take care of herself. Her physical and mental development (including cognitive ability) was normal. She had an ataxic gait, ataxic dysarthria, bilateral horizontal nystagmus and visible limb myoclonus. She failed the bilateral finger-to-nose and heel-knee-tibia tests and could not walk in a straight line. Babinski signs were not observed. EEG tracing during sleep showed low-amplitude spikes and spike-and-slow waves in the bilateral frontal and mid-frontal areas. Her magnetic resonance imaging scan was normal. In pedigree-II, the propositus (a 54-year-old male) could not walk stably and had a history of occasional falls for the past 34 years. The symptoms aggravated gradually until he lost the ability to perform routine daily activities. There was no history of convulsions. His physical and mental faculties, as well as the neurological findings were similar to those of the pedigree-I. Both proposituses did not respond well to symptomatic treatment. A novel mutation has been identified in SGCE gene (NM_003919:exon3:c.360delT:p.A120fs) using exome sequencing.

CONCLUSION

PMA patients from the two pedigrees had autosomal dominant mode of inheritance, with variability in the age of onset and disease severity. The cardinal symptoms were myoclonic seizures and ataxia without mental retardation.

Polyglutamine (PolyQ) diseases: genetics to treatments

The polyglutamine (polyQ) diseases are a group of neurodegenerative disorders caused by expanded cytosine-adenine-guanine (CAG) repeats encoding a long polyQ tract in the respective proteins. To date, a total of nine polyQ disorders have been described: six spinocerebellar ataxias (SCA) types 1, 2, 6, 7, 17; Machado-Joseph disease (MJD/SCA3); Huntington's disease (HD); dentatorubral pallidoluysian atrophy (DRPLA); and spinal and bulbar muscular atrophy, X-linked 1 (SMAX1/SBMA). PolyQ diseases are characterized by the pathological expansion of CAG trinucleotide repeat in the translated region of unrelated genes. The translated polyQ is aggregated in the degenerated neurons leading to the dysfunction and degeneration of specific neuronal subpopulations. Although animal models of polyQ disease for understanding human pathology and accessing disease-modifying therapies in neurodegenerative diseases are available, there is neither a cure nor prevention for these diseases, and only symptomatic treatments for polyQ diseases currently exist. Long-term pharmacological treatment is so far disappointing, probably due to unwanted complications and decreasing drug efficacy. Cellular transplantation of stem cells may provide promising therapeutic avenues for restoration of the functions of degenerative and/or damaged neurons in polyQ diseases.

Dentatorubral-pallidoluysian atrophy

Dentatorubral-pallidoluysian atrophy (DRPLA) is a rare autosomal dominant neurodegenerative disorder clinically characterized by various combinations of cerebellar ataxia, choreoathetosis, myoclonus, epilepsy, dementia, and psychiatric symptoms. The most striking clinical features of DRPLA are the considerable heterogeneity in clinical presentation, depending on the age of onset, and the prominent genetic anticipation. DRPLA is caused by unstable expansion of CAG repeats coding for polyglutamine stretches located in exon 5 of the DRPLA gene. DRPLA is characterized by prominent anticipation, with paternal transmission resulting in more prominent anticipation than does maternal transmission, which is now understood based on the intergenerational stability of the CAG repeats. DRPLA protein (also called atrophin-1) is localized in the nucleus and functions as a transcription co-regulator. Recent immunohistochemical studies on autopsied tissues of patients with DRPLA have demonstrated that diffuse accumulation of mutant DRPLA protein (atrophin-1) in the neuronal nuclei, rather than the formation of neuronal intranuclear inclusions (NIIs), is the predominant pathologic condition and involves a wide range of central nervous system regions far beyond the systems previously reported to be affected. Thus, age-dependent and CAG repeat-dependent intranuclear accumulation of mutant DRPLA leading to nuclear dysfunctions are suggested to be the essential pathophysiologic mechanisms in DRPLA.

The Huntington's disease-like syndromes: what to consider in patients with a negative Huntington's disease gene test

Huntington's disease (HD), which is caused by a triplet-repeat expansion in the IT15 gene (also known as huntingtin or HD), accounts for about 90% of cases of chorea of genetic etiology. In recent years, several other distinct genetic disorders have been identified that can present with a clinical picture indistinguishable from that of HD. These disorders are termed Huntington's disease-like (HDL) syndromes. So far, four such conditions have been recognized, namely disorders attributable to mutations in the prion protein gene (HDL1), the junctophilin 3 gene (HDL2), and the gene encoding the TATA box-binding protein (HDL4/SCA17), and a recessively inherited HD phenocopy in a single family (HDL3), the genetic basis of which is currently poorly understood. These disorders, however, account for only a small proportion of cases with the HD phenotype but a negative genetic test for HD, and the list of HDL genes and conditions is set to grow. In this article, we review the most important HD phenocopy disorders identified to date and discuss the clinical clues that guide further investigation. We will concentrate on the four so-called HDL syndromes mentioned above, as well as other genetic disorders such as dentatorubral-pallidoluysian atrophy, neuroferritinopathy, pantothenate-kinase-associated neurodegeneration and chorea-acanthocytosis.