Hereditary chorea - what else to consider when the Huntington's disease genetics test is negative?

Diagnostic Uncertainties: Chorea

Chorea is a hyperkinetic movement disorder with a multitude of potential etiologies, both acquired and inherited. Although the differential diagnosis for new-onset chorea is extensive, there are often clues in the history, exam, and basic testing that can help to narrow the options. Evaluation for treatable or reversible causes should take priority, as rapid diagnosis can lead to more favorable outcomes. While Huntington's disease is most common genetic cause of chorea, multiple phenocopies also exist and should be considered if Huntington gene testing is negative. The decision of what additional genetic testing to pursue should be based on both clinical and epidemiological factors. The following review provides an overview of the many possible etiologies as well as a practical approach for a patient presenting with new-onset chorea.

Combining Literature Review With a Ground Truth Approach for Diagnosing Huntington's Disease Phenocopy

One percent of patients with a Huntington's disease (HD) phenotype do not have the Huntington (HTT) gene mutation. These are known as HD phenocopies. Their diagnosis is still a challenge. Our objective is to provide a diagnostic approach to HD phenocopies based on medical expertise and a review of the literature. We employed two complementary approaches sequentially: a review of the literature and two surveys analyzing the daily clinical practice of physicians who are experts in movement disorders. The review of the literature was conducted from 1993 to 2020, by extracting articles about chorea or HD-like disorders from the database Pubmed, yielding 51 articles, and analyzing 20 articles in depth to establish the surveys. Twenty-eight physicians responded to the first survey exploring the red flags suggestive of specific disease entities. Thirty-three physicians completed the second survey which asked for the classification of paraclinical tests according to their diagnostic significance. The analysis of the results of the second survey used four different clustering algorithms and the density-based clustering algorithm DBSCAN to classify the paraclinical tests into 1st, 2nd, and 3rd-line recommendations. In addition, we included suggestions from members of the European Reference Network-Rare Neurological Diseases (ERN-RND Chorea & Huntington disease group). Finally, we propose guidance that integrate the detection of clinical red flags with a classification of paraclinical testing options to improve the diagnosis of HD phenocopies.

Neurodegenerative disorders and gut-brain interactions

Neurodegenerative disorders (NDs) affect essential functions not only in the CNS, but also cause persistent gut dysfunctions, suggesting that they have an impact on both CNS and gut-innervating neurons. Although the CNS biology of NDs continues to be well studied, how gut-innervating neurons, including those that connect the gut to the brain, are affected by or involved in the etiology of these debilitating and progressive disorders has been understudied. Studies in recent years have shown how CNS and gut biology, aided by the gut-brain connecting neurons, modulate each other's functions. These studies underscore the importance of exploring the gut-innervating and gut-brain connecting neurons of the CNS and gut function in health, as well as the etiology and progression of dysfunction in NDs. In this Review, we discuss our current understanding of how the various gut-innervating neurons and gut physiology are involved in the etiology of NDs, including Parkinson's disease, Alzheimer's disease, Huntington's disease, and amyotrophic lateral sclerosis, to cause progressive CNS and persistent gut dysfunction.

Disorders of the enteric nervous system - a holistic view

The enteric nervous system (ENS) is the largest division of the peripheral nervous system and closely resembles components and functions of the central nervous system. Although the central role of the ENS in congenital enteric neuropathic disorders, including Hirschsprung disease and inflammatory and functional bowel diseases, is well acknowledged, its role in systemic diseases is less understood. Evidence of a disordered ENS has accumulated in neurodegenerative diseases ranging from amyotrophic lateral sclerosis, Alzheimer disease and multiple sclerosis to Parkinson disease as well as neurodevelopmental disorders such as autism. The ENS is a key modulator of gut barrier function and a regulator of enteric homeostasis. A 'leaky gut' represents the gateway for bacterial and toxin translocation that might initiate downstream processes. Data indicate that changes in the gut microbiome acting in concert with the individual genetic background can modify the ENS, central nervous system and the immune system, impair barrier function, and contribute to various disorders such as irritable bowel syndrome, inflammatory bowel disease or neurodegeneration. Here, we summarize the current knowledge on the role of the ENS in gastrointestinal and systemic diseases, highlighting its interaction with various key players involved in shaping the phenotypes. Finally, current flaws and pitfalls related to ENS research in addition to future perspectives are also addressed.

Review of Hereditary and Acquired Rare Choreas

Background:

Movement disorders are often a prominent part of the phenotype of many neurologic rare diseases. In order to promote awareness and diagnosis of these rare diseases, the International Parkinson’s and Movement Disorders Society Rare Movement Disorders Study Group provides updates on rare movement disorders.

Methods:

In this narrative review, we discuss the differential diagnosis of the rare disorders that can cause chorea.

Results:

Although the most common causes of chorea are hereditary, it is critical to identify acquired or symptomatic choreas since these are potentially treatable conditions. Disorders of metabolism and mitochondrial cytopathies can also be associated with chorea.

Discussion:

The present review discusses clues to the diagnosis of chorea of various etiologies. Authors propose algorithms to help the clinician in the diagnosis of these rare disorders.

Genetics of Movement Disorders and the Practicing Clinician; Who and What to Test for?

PURPOSE OF REVIEW

This review aims to provide the basic knowledge on the genetics of hypokinetic and hyperkinetic movement disorders to guide clinicians in the decision of "who and what to test for?"

RECENT FINDINGS

In recent years, the identification of various genetic causes of hypokinetic and hyperkinetic movement disorders has had a great impact on a better definition of different clinical syndromes. Indeed, the advent of next-generation sequencing (NGS) techniques has provided an impressive step forward in the easy identification of genetic forms. However, this increased availability of genetic testing has challenges, including the ethical issue of genetic testing in unaffected family members, "commercially" available home testing kits and the increasing number and relevance of "variants of unknown significance." The emergent role of genetic factors has important implications on clinical practice and counseling. As a consequence, it is fundamental that practicing neurologists have a proper knowledge of the genetic background of the diseases and perform an accurate selection of who has to be tested and for which gene mutations.

Clinical spectrum of C9orf72 expansion in a cohort of Huntington's disease phenocopies

The expansion in the C9orf72 gene has been recently reported as a genetic cause of Huntington's disease (HD) phenocopies. We aim to assess the frequency of the C9orf72 gene expansion in a Portuguese HD phenocopies cohort. Twenty HD phenotype-like patients without diagnosis were identified in our institutional database. C9orf72 gene expansion was detected using repeat-primed PCR. Clinical files were reviewed to characterize the phenotype of expansion-positive cases. One patient (5%) was positive for the C9orf72 expansion. A second patient presented 27 repeats-within the intermediate size interval. Both had familial neuropsychiatric disease characterized by diverse movement disorders, dementia, and psychiatric dysfunction that was distinct in severity and clinical expression. C9orf72 disease is clinically heterogeneous and without evident imaging markers. The definition of the role of intermediate alleles and of the pathological threshold for C9orf72 repeat expansions may have diagnostic implications.

Discrepancy in prevalence of Huntington's disease in two Swedish regions

BACKGROUND

Huntington's disease (HD) is a neurodegenerative disease with an autosomal dominant pattern of inheritance. The prevalence varies between different geographical regions with an estimated average in Europe of about 6/100 000. Parts of northern Sweden are known to have an accumulation of HD, but no prevalence studies have been undertaken for 50 years.

OBJECT

The aim of this study was to estimate the prevalence of HD in the two different Swedish counties of Jämtland and Uppsala and compare them with the reported prevalence in Europe.

METHOD

Patients registered with the diagnosis of HD were identified through medical records in each county. Presymptomatic patients were excluded. We also compared the annual number of individuals with HD registered in the database of the National Board of Health and Welfare in these regions, with all of Sweden.

RESULTS

The prevalence of HD was found to be 22.1/100 000 in Jämtland and 4.9/100 000 in Uppsala county. The mean age was 62.2 years and 61.8 years, respectively. The annual average of patients with HD registered at inpatient care was 1.5/100 000 in Jämtland, 0.44/100 000 in Uppsala county, and 0.56/100 000 in all of Sweden.

CONCLUSION

The prevalence of patients with the diagnosis of HD is four times higher in the county of Jämtland than in the county of Uppsala, where the prevalence is more similar to the average in Europe. Our results support earlier findings of regional variations of HD prevalence with an accumulation in certain parts of northern Sweden.

Myoclonic Disorders

Few movement disorders seem to make a straightforward approach to diagnosis and treatment more difficult and frustrating than myoclonus, due to its plethora of causes and its variable classifications. Nevertheless, in recent years, exciting advances have been made in the elucidation of the pathophysiology and genetic basis of many disorders presenting with myoclonus. Here, we provide a review of all of the important types of myoclonus encountered in pediatric and adult neurology, with an emphasis on the recent developments that have led to a deeper understanding of this intriguing phenomenon. An up-to-date list of the genetic basis of all major myoclonic disorders is presented. Randomized studies are scarce in myoclonus therapy, but helpful pragmatic approaches at diagnosis as well as treatment have been recently suggested.