Huntington disease like 2 (HDL-2) with parkinsonism and abnormal DAT-SPECT – A novel observation

Early Onset Parkinsonism: Differential diagnosis and what not to miss

Early Onset Parkinsonism (EOP) refers to parkinsonism occurring before the age of 50 years. The causes are diverse and include secondary and genetic causes. Secondary causes related to medications, inflammatory and infective disorders are mostly treatable and well recognized as they usually present with a relatively more rapid clinical course compared to idiopathic Parkinson's disease. Genetic causes of EOP are more challenging to diagnose especially as more of the non-PARK genes are recognized to present with typical and atypical parkinsonism. Some of the genetic disorders such as Spinocerebellar ataxia 2 (SCA2) and Spinocerebellar ataxia 3 (SCA3) may present with levodopa-responsive parkinsonism, indistinguishable from idiopathic Parkinson's disease. Additionally, some of the genetic disorders, including Wilson's disease and cerebrotendinous xanthomatosis (CTX), are potentially treatable and should not be missed. Due to the advent of next generating sequencing techniques, genetic analyses facilitate early identification and proper treatment of diverse causes of EOP. In this review, we outline the clinical approach of EOP highlighting the key clinical features of some of the non-PARK genetic causes of EOP and related investigations, which could assist in clinical diagnosis. This review also encompass genetic diagnostic approaches, emphasizing the significance of pretest counseling and the principles of bioinformatics analysis strategies.

Atypical Presentations of Huntington Disease-like 2 in South African Individuals

BACKGROUND

Huntington disease-like 2 (HDL2) is a neurodegenerative disorder, affecting only individuals of African ancestry. Full penetrance occurs in individuals with 40 repeats or more.

OBJECTIVE

To describe the phenotypic variability of HDL2 in a group of mixed ancestry individuals from South Africa.

METHODS

Eight patients were assessed with analysis of repeat size and magnetic resonance brain imaging. We applied the Unified Huntington's Disease Rating Scale (UHDRS), but in deceased patients (4), this was estimated from video material.

RESULTS

Cognitive domains were more severely affected than motor; UHDRS motor scores were notable for bradykinesia, and to a slightly lesser extent, for rigidity and dystonia; a single patient had marked chorea. Repeat lengths ranged from 45 to 63 (median, 52).

CONCLUSION

This South African group of mixed ancestry HDL2 individuals presented with severe cognitive and behavioral impairments, with lesser degrees or absence of chorea. This presentation is possibly related to large repeat sizes.

I123-FP-CIT (DaTSCAN) SPECT beyond the Most Common Causes of Parkinsonism: A Systematic Review

BACKGROUND

As the diagnosis of Parkinson's disease (PD) is fundamentally clinical, the usefulness of ioflupane (123I) single-photon emission computed tomography (SPECT) or DaTSCAN as a diagnostic tool has been a matter of debate for years. The performance of DaTSCAN is generally recommended in the follow-up of patients with a clinically uncertain diagnosis, especially in those with a suspected essential tremor, drug-induced parkinsonism, or vascular parkinsonism. However, there is a dearth of DaTSCAN findings regarding neurodegenerative parkinsonisms besides PD and atypical parkinsonisms. To date, a specific nigrostriatal dopamine uptake pattern that would help differentiate PD from the most frequent atypical parkinsonisms is yet to be described. This fact is further complicated by the possible visualization of abnormalities in the uptake pattern in patients with rarer neurodegenerative parkinsonisms.

OBJECTIVES

We aimed to summarize the current literature regarding DaTSCAN findings in patients with rare neurodegenerative parkinsonisms.

METHODS

The PubMed database was systematically screened for studies in English or Spanish up to October 15, 2023, using search terms "DaTSCAN", "ioflupane", "DaT-SPECT", "123I-FP-CIT SPECT", "dopamine transporter imaging", and "[123I] FP-CIT SPECT". Duplicated publications and studies regarding PD, atypical parkinsonisms, dystonia-parkinsonism, essential tremor, and parkinsonism due to non-degenerative causes were excluded.

RESULTS

The obtained results were reviewed and summarized, including DaTSCAN findings in fragile X-associated tremor/ataxia syndrome, prion diseases, Huntington's disease, spinocerebellar ataxia, hereditary spastic paraparesis, metabolic disorders, and other diseases (anti-IgLON5 disease, ring chromosome 20 syndrome, chorea-acanthocytosis, and neuronal ceroid lipofuscinosis).

CONCLUSIONS

This review highlights the need to determine in the future the utility and cost-effectiveness of DaTSCAN, both as a diagnostic and a prognostic tool, in patients with parkinsonian symptoms in rare neurodegenerative diseases.

Recent advances in non-Huntington's disease choreas

INTRODUCTION

Chorea is primarily due to an imbalance of basal ganglia output pathways, often due to dysfunction or degeneration of the caudate nucleus and putamen, and can be due to many causes.

METHODS

We reviewed the recent literature to identify newly-recognized causes of chorea, including auto-immune, metabolic, and genetic. We also focused upon developments in mechanisms relating to underlying pathophysiology of certain genetic choreas and advances in therapeutics.

RESULTS

Novel autoantibodies continue to be identified as causes of chorea. Both COVID-19 infection and vaccination are reported to result rarely in chorea, although in some cases causality is not clearly established. Advances in genetic testing continue to find more causes of chorea, and to expand the phenotype of known genetic disorders. Deep brain stimulation can be successful in certain circumstances.

CONCLUSION

Our understanding of mechanisms underlying this movement disorder continues to advance, however much remains to be elucidated.

Huntington disease-like 2: insight into neurodegeneration from an African disease

Huntington disease (HD)-like 2 (HDL2) is a rare genetic disease caused by an expanded trinucleotide repeat in the JPH3 gene (encoding junctophilin 3) that shows remarkable clinical similarity to HD. To date, HDL2 has been reported only in patients with definite or probable African ancestry. A single haplotype background is shared by patients with HDL2 from different populations, supporting a common African origin for the expansion mutation. Nevertheless, outside South Africa, reports of patients with HDL2 in Africa are scarce, probably owing to limited clinical services across the continent. Systematic comparisons of HDL2 and HD have revealed closely overlapping motor, cognitive and psychiatric features and similar patterns of cerebral and striatal atrophy. The pathogenesis of HDL2 remains unclear but it is proposed to occur through several mechanisms, including loss of protein function and RNA and/or protein toxicity. This Review summarizes our current knowledge of this African-specific HD phenocopy and highlights key areas of overlap between HDL2 and HD. Given the aforementioned similarities in clinical phenotype and pathology, an improved understanding of HDL2 could provide novel insights into HD and other neurodegenerative and/or trinucleotide repeat expansion disorders.