Choreiform movements in spinocerebellar ataxia type 1

Huntington's disease-like disorders in Latin America and the Caribbean

Diseases with a choreic phenotype can be due to a variety of genetic etiologies. As testing for Huntington's disease (HD) becomes more available in previously resource-limited regions, it is becoming apparent that there are patients in these areas with other rare genetic conditions which cause an HD-like phenotype. Documentation of the presence of these conditions is important in order to provide appropriate diagnostic and clinical care for these populations. Information for this article was gathered in two ways; the literature was surveyed for publications reporting a variety of genetic choreic disorders, and movement disorders specialists from countries in Latin America and the Caribbean were contacted regarding their experiences with chorea of genetic etiology. Here we discuss the availability of molecular diagnostics for HD and for other choreic disorders, along with a summary of the published reports of affected subjects, and authors' personal experiences from the regions. While rare, patients affected by non-HD genetic choreas are evidently present in Latin America and the Caribbean. HD-like 2 is particularly prevalent in countries where the population has African ancestry. The incidence of other conditions is likely determined by other variations in ethnic background and settlement patterns. As genetic resources and awareness of these disorders improve, more patients are likely to be identified, and have the potential to benefit from education, support, and ultimately molecular therapies.

Chorea

PURPOSE OF REVIEW

This article reviews the clinical approach to the diagnosis of adult patients presenting with chorea, using Huntington disease (HD) as a point of reference, and presents the clinical elements that help in the diagnostic workup. Principles of management for chorea and some of the associated features of other choreic syndromes are also described.

RECENT FINDINGS

Mutations in the C9orf72 gene, previously identified in families with a history of frontotemporal dementia, amyotrophic lateral sclerosis, or both, have been recognized as one of the most prevalent causes of HD phenocopies in the white population.

SUMMARY

The diagnosis of chorea in adult patients is challenging. A varied number of associated causes require a physician to prioritize the investigations, and a detailed history of chorea and associated findings will help. For chorea presenting as part of a neurodegenerative syndrome, the consideration of a mutation in the C9orf72 gene is a new recommendation after excluding HD. There are no new treatment options for chorea, aside from dopamine blockers and tetrabenazine. There are no disease-modifying treatments for HD or other neurodegenerative choreic syndromes.

Genetics of Huntington's disease and related disorders

Huntington's disease is the most frequent form of the hereditary choreas and has a multifaceted phenotype including cognitive and psychiatric impairment. The disorder is due to a dynamic mutation, which also influences the onset age of the disorder. Other genetic modifiers of the HD phenotypes have been suggested but often not confirmed by independent studies. Several syndromes with similar presentation have different genetic backgrounds, including the neuroacanthocytoses, mainly choreoacanthocytosis and MacLeod syndrome as a result of mutations in chorein and Kell protein, respectively, but also benign hereditary chorea, owing to mutations in NKX-2-1, and paroxysmal kinesigenic dyskinesia, as a result of recently found mutations in the proline-rich transmembrane protein 2, PRRT2. Chorea can also be a major feature in other neurogenetic disorders, including the spinocerebellar ataxias and also in neurometabolic disorders.

The differential diagnosis of Huntington's disease-like syndromes: 'red flags' for the clinician

A growing number of progressive heredodegenerative conditions mimic the presentation of Huntington's disease (HD). Differentiating among these HD-like syndromes is necessary when a patient with a combination of movement disorders, cognitive decline, behavioural abnormalities and progressive disease course proves negative to the genetic testing for HD causative mutations, that is, IT15 gene trinucleotide-repeat expansion. The differential diagnosis of HD-like syndromes is complex and may lead to unnecessary and costly investigations. We propose here a guide to this differential diagnosis focusing on a limited number of clinical features ('red flags') that can be identified through accurate clinical examination, collection of historical data and a few routine ancillary investigations. These features include the ethnic background of the patient, the involvement of the facio-bucco-lingual and cervical district by the movement disorder, the co-occurrence of cerebellar features and seizures, the presence of peculiar gait patterns and eye movement abnormalities, and an atypical progression of illness. Additional help may derive from the cognitive-behavioural presentation of the patient, as well as by a restricted number of ancillary investigations, mainly MRI and routine blood tests. These red flags should be constantly updated as the phenotypic characterisation and identification of more reliable diagnostic markers for HD-like syndromes progress over the following years.

Spinocerebellar ataxia type 31 exists in northeast China

Spinocerebellar ataxia type 31 (SCA31), is a recently defined subtype of autosomal dominant cerebellar ataxia (ADCA) characterized by late-onset pure cerebellar ataxia. SCA31 is common in Japan but whether or not it exists in other countries is still unclear. In this study, the authors describe a sporadic Chinese patient with SCA31. Although the cardinal clinical features, i.e., late-onset cerebellar ataxia and hearing impairment in our sporadic patient were similar to those described previously in Japan, mild axonal sensorimotor neuropathy was identified in our SCA31 patient, which is somewhat distinct from most prior reports of the disease. This is the first report of SCA31 in China; thus, extending the ethnic association beyond families of Japanese origin. In addition, our study suggests that the clinical features of SCA31 might be broader than previously thought.

Update on the Non-Huntington's Disease Choreas with Comments on the Current Nomenclature

CHOREA CAN BE CAUSED BY A MULTITUDE OF ETIOLOGIES: neurodegenerative, pharmacological, structural, metabolic, and others. In absence of other apparent causes, exclusion of Huntington's disease is often a first step in the diagnostic process. There are a number of neurodegenerative disorders whose genetic etiology has been identified in the past decade. Molecular diagnosis has enabled genetic identification of disorder subtypes which were previously grouped together, such as the neurodegeneration with brain iron accumulation disorders and the neuroacanthocytosis syndromes, as well as identification of phenotypic outliers for recognized disorders. Correct molecular diagnosis is essential for genetic counseling and, hopefully, ultimately genetic therapies. In addition, there has recently been recognition of other disorders which can mimic neurodegenerative disorders, including paraneoplastic and prion disorders. This article focuses upon recent developments in the field but is not intended to provide an exhaustive review of all causes of chorea, which is available elsewhere. I also discuss the nomenclature of these disorders which has become somewhat unwieldy, but may ultimately be refined by association with the causative gene.

Differential diagnosis of chorea

Chorea is a common movement disorder that can be caused by a large variety of structural, neurochemical (including pharmacologic), or metabolic disturbances to basal ganglia function, indicating the vulnerability of this brain region. The diagnosis is rarely indicated by the simple phenotypic appearance of chorea, and can be challenging, with many patients remaining undiagnosed. Clues to diagnosis may be found in the patient's family or medical history, on neurologic examination, or upon laboratory testing and neuroimaging. Increasingly, advances in genetic medicine are identifying new disorders and expanding the phenotype of recognized conditions. Although most therapies at present are supportive, correct diagnosis is essential for appropriate genetic counseling, and ultimately, for future molecular therapies.

Movement disorders in spinocerebellar ataxias

Autosomal dominant spinocerebellar ataxias (SCAs) can present with a large variety of noncerebellar symptoms, including movement disorders. In fact, movement disorders are frequent in many of the various SCA subtypes, and they can be the presenting, dominant, or even isolated disease feature. When combined with cerebellar ataxia, the occurrence of a specific movement disorder can provide a clue toward the underlying genotype. There are reasons to believe that for some coexisting movement disorders, the cerebellar pathology itself is the culprit, for example, in the case of cortical myoclonus and perhaps dystonia. However, movement disorders in SCAs are more likely related to extracerebellar pathology, and imaging and neuropathological data indeed show involvement of other parts of the motor system (substantia nigra, striatum, pallidum, motor cortex) in some SCA subtypes. When confronted with a patient with an isolated movement disorder, that is, without ataxia, there is currently no reason to routinely screen for SCA gene mutations, the only exceptions being SCA2 in autosomal dominant parkinsonism (particularly in Asian patients) and SCA17 in the case of a Huntington's disease-like presentation without an HTT mutation.

Huntington's disease look-alikes

Huntington's disease (HD) is caused by a triplet repeat expansion in the IT15 gene on chromosome 4 encoding huntingtin. Gene mutations are found in about 99% of cases, with symptoms and signs suggestive of HD. This implies the existence of other causes of this syndrome, and, in recent years, several other distinct genetic disorders have been identified that can present with a clinical picture indistinguishable from HD, termed HD-like (HDL) syndromes. So far, four genes associated with HDL syndromes have been identified, including the prion protein gene (HDL1), the junctophilin 3 gene (HDL2) and, the gene encoding the TATA box-binding protein (HDL4). In addition, a single family with a recessively inherited HD phenocopy, the exact genetic basis of which is currently unknown (HDL3), has been described. These disorders, however, account for only a small proportion of HDL cases, and the list of HDL genes and conditions is set to grow. In this article, we review the currently identified HD phenocopy disorders and discuss clinical clues to facilitate further investigations. We will concentrate on the four so-called HDL syndromes mentioned above. Other genetic choreatic syndromes such as dentatorubral-pallidoluysian atrophy, neuroferritinopathy, pantothenate kinase-associated neurodegeneration, and chorea-acanthocytosis are also briefly discussed.

Developments in neuroacanthocytosis: Expanding the spectrum of choreatic syndromes

As with other neurodegenerative disorders, research into the group of diseases known under the umbrella term of "neuroacanthocytosis" has greatly benefited from the identification of causative genes. The distinct and unifying aspect of these disorders is the presence of thorny deformations of circulating erythrocytes. This may be due to abnormal properties of red cell membranes, which could lead to insights into mechanisms of neurodegeneration. Research approaches in this field, in addition to examining functions and protein interactions of the affected proteins with particular respect to neurons, have also drawn upon the expertise of hematologists and red cell membrane biologists. In this article, recent developments in the field are presented.

16q-linked autosomal dominant cerebellar ataxia: a clinical and genetic study

The autosomal dominant cerebellar ataxias (ADCAs) comprise a genetically and clinically heterogenous group of neurodegenerative disorders. Very recently, a C-to-T single nucleotide substitution in the puratrophin-1 gene was found to be strongly associated with a form of ADCA linked to chromosome 16q22.1 (16q-linked ADCA; OMIM 600223). We found the C-to-T substitution in the puratrophin-1 gene in 20 patients with ataxia (16 heterozygotes and four homozygotes) and four asymptomatic carriers in 9 of 24 families with an unknown type of ADCA. We also found two cases with 16q-linked ADCA among 43 sporadic patients with late-onset cortical cerebellar atrophy (LCCA). The mean age at onset in the 22 patients was 61.8 years, and that of homozygous patients was lower than that of heterozygous ones in one family. Neurological examination revealed that the majority of our patients showed exaggerated deep tendon reflexes in addition to the cardinal symptom of cerebellar ataxia (100%), and 37.5% of them had sensorineural hearing impairment, whereas sensory axonal neuropathy was absent. The frequency of 16q-linked ADCA was about 1/10 of our series of 110 ADCA families, making it the third most frequent ADCA in Japan.