Nigrostriatal involvement in ataxia with oculomotor apraxia type 1

Heterozygous APTX mutation associated with atypical multiple system atrophy-like phenotype: A case report

We describe here a 73-year-old patient presenting with atypical MSA-P-like phenotype carrying a monoallelic p. W279X mutation in the APTX gene, which causes ataxia with oculomotor apraxia type 1 (AOA1) when in homozygous state. We hypothesize that rare monoallelic APTX variants could modulate MSA risk and phenotype.

Autosomal Recessive Cerebellar Ataxias With Elevated Alpha-Fetoprotein: Uncommon Diseases, Common Biomarker

alpha-Fetoprotein (AFP) is a biomarker of several autosomal recessive cerebellar ataxias (ARCAs), especially ataxia telangiectasia (AT) and ataxia with oculomotor apraxia (AOA) type 2 (AOA2). More recently, slightly elevated AFP has been reported in AOA1 and AOA4. Interestingly, AOA1, AOA2, AOA4, and AT are overlapping ARCAs characterized by oculomotor apraxia, with oculocephalic dissociation, choreo-dystonia, and/or axonal sensorimotor neuropathy, in addition to cerebellar ataxia with cerebellar atrophy. The genetic backgrounds in these disorders play central roles in nuclear maintenance through DNA repair [ATM (AT), APTX (AOA1), or PNKP (AOA4)] or RNA termination [SETX (AOA2)]. Partially discriminating thresholds of AFP have been proposed as a way to distinguish between ARCAs with elevated AFP. In these entities, elevated AFP may be an epiphenomenon as a result of liver transcriptional dysregulation. AFP is a simple and reliable biomarker for the diagnosis of ARCA in performance and interpretation of next-generation sequencing. Here, we evaluated clinical, laboratory, imaging, and molecular data of the group of ARCAs that share elevated AFP serum levels that have been described in the past two decades. © 2020 International Parkinson and Movement Disorder Society.

Recent advances in genetics of chorea

PURPOSE OF REVIEW

Chorea presenting in childhood and adulthood encompasses several neurological disorders, both degenerative and nonprogressive, often with a genetic basis. In this review, we discuss how modern genomic technologies are expanding our knowledge of monogenic choreic syndromes and advancing our insight into the molecular mechanisms responsible for chorea.

RECENT FINDINGS

A genome-wide association study in Huntington's disease identified genetic disease modifiers involved in controlling DNA repair mechanisms and stability of the HTT trinucleotide repeat expansion. Chorea is the cardinal feature of newly recognized genetic entities, ADCY5 and PDE10A-related choreas, with onset in infancy and childhood. A phenotypic overlap between chorea, ataxia, epilepsy, and neurodevelopmental disorders is becoming increasingly evident.

SUMMARY

The differential diagnosis of genetic conditions presenting with chorea has considerably widened, permitting a molecular diagnosis and an improved prognostic definition in an expanding number of cases. The identification of Huntington's disease genetic modifiers and new chorea-causing gene mutations has allowed the initial recognition of converging molecular pathways underlying medium spiny neurons degeneration and dysregulation of normal development and activity of basal ganglia circuits. Signalling downstream of dopamine receptors and control of cAMP levels represent a very promising target for the development of new aetiology-based treatments for chorea and other hyperkinetic disorders.

The Response to Oxidative DNA Damage in Neurons: Mechanisms and Disease

There is a growing body of evidence indicating that the mechanisms that control genome stability are of key importance in the development and function of the nervous system. The major threat for neurons is oxidative DNA damage, which is repaired by the base excision repair (BER) pathway. Functional mutations of enzymes that are involved in the processing of single-strand breaks (SSB) that are generated during BER have been causally associated with syndromes that present important neurological alterations and cognitive decline. In this review, the plasticity of BER during neurogenesis and the importance of an efficient BER for correct brain function will be specifically addressed paying particular attention to the brain region and neuron-selectivity in SSB repair-associated neurological syndromes and age-related neurodegenerative diseases.

Movement disorder in ataxia-telangiectasia: treatment with amantadine sulfate

Ataxia-telangiectasia is a cerebellar neurodegenerative disorder presenting with ataxia, chorea, myoclonus, and bradykinesia. Literature on treatment of movement disorders is scarce. We treated 17 children (aged 11.2 ± 3.9 years) for 8 weeks with the dopaminergic and anti-N-methyl-d-aspartate (NMDA) agent amantadine sulfate 6.3 ± 0.87 mg/kg/d. Ataxia was assessed by using the International Cooperative Ataxia Scale, parkinsonism by the Unified Parkinson Disease Rating Scale, and chorea/myoclonus by the Abnormal Involuntary Movement Scale. Responders were considered those patients who had at least 20% improvement in the summation of the 3 scales. Overall, 76.5% of patients were responders, with a mean 29.3% improvement. Ataxia, involuntary movements, and parkinsonism improved significantly (25.3%, 32.5%, and 29.5%, respectively); (P < .001, t test). Side effects were mild and transient, and they did not lead to drug discontinuation. Amantadine is a well-tolerated and effective treatment for motor symptoms in ataxia telangiectasia. Assessment of long-term effects and a double-blind study should follow.

Aprataxin localizes to mitochondria and preserves mitochondrial function

Ataxia with oculomotor apraxia 1 is caused by mutation in the APTX gene, which encodes the DNA strand-break repair protein aprataxin. Aprataxin exhibits homology to the histidine triad superfamily of nucleotide hydrolases and transferases and removes 5'-adenylate groups from DNA that arise from aborted ligation reactions. We report herein that aprataxin localizes to mitochondria in human cells and we identify an N-terminal amino acid sequence that targets certain isoforms of the protein to this intracellular compartment. We also show that transcripts encoding this unique N-terminal stretch are expressed in the human brain, with highest production in the cerebellum. Depletion of aprataxin in human SH-SY5Y neuroblastoma cells and primary skeletal muscle myoblasts results in mitochondrial dysfunction, which is revealed by reduced citrate synthase activity and mtDNA copy number. Moreover, mtDNA, not nuclear DNA, was found to have higher levels of background DNA damage on aprataxin knockdown, suggesting a direct role for the enzyme in mtDNA processing.