Spinocerebellar ataxia type 7 (SCA7): family princeps’ history, genealogy and geographical distribution

Genetic Epidemiology and Clinical Characteristics of Patients with Spinocerebellar Ataxias in an Unexplored Brazilian State, Using Strategies for Resource-Limited Settings

Spinocerebellar ataxias (SCAs) have a worldwide average prevalence of 2.7 cases per 100,000 individuals, with significant geographic variability. This study aimed to develop resource-limited strategies to detect and characterize the frequency and genetic-clinical profile of SCAs in an unexplored population from Alagoas State, a low Human Development Index state in northeastern Brazil. Active search strategies were employed to identify individuals with a diagnosis or clinical suspicion of SCAs, and a protocol for clinical and molecular evaluation was applied in collaboration with a reference center in Neurogenetics. A total of 73 individuals with SCAs were identified, with a minimum estimated prevalence of 2.17 cases per 100,000 inhabitants. SCA3 was the most common type (75.3%), followed by SCA7 (15.1%), SCA1 (6.8%), and SCA2 (2.7%). Patients with SCA3 subphenotype 2 were the most predominant. Detailed analysis of patients with SCA3 and SCA7 revealed age at onset and clinical features congruent with other studies, with gait disturbance and reduced visual capacity in SCA7 as the main initial manifestations. The study also identified many asymptomatic individuals at risk of developing SCAs. These findings demonstrate that simple and collaborative strategies can enhance the detection capacity of rare diseases such as SCAs in resource-limited settings and that Alagoas State has a minimum estimated prevalence of SCAs similar to the world average.

An update on the neurological short tandem repeat expansion disorders and the emergence of long-read sequencing diagnostics

BACKGROUND

Short tandem repeat (STR) expansion disorders are an important cause of human neurological disease. They have an established role in more than 40 different phenotypes including the myotonic dystrophies, Fragile X syndrome, Huntington's disease, the hereditary cerebellar ataxias, amyotrophic lateral sclerosis and frontotemporal dementia.

MAIN BODY

STR expansions are difficult to detect and may explain unsolved diseases, as highlighted by recent findings including: the discovery of a biallelic intronic 'AAGGG' repeat in RFC1 as the cause of cerebellar ataxia, neuropathy, and vestibular areflexia syndrome (CANVAS); and the finding of 'CGG' repeat expansions in NOTCH2NLC as the cause of neuronal intranuclear inclusion disease and a range of clinical phenotypes. However, established laboratory techniques for diagnosis of repeat expansions (repeat-primed PCR and Southern blot) are cumbersome, low-throughput and poorly suited to parallel analysis of multiple gene regions. While next generation sequencing (NGS) has been increasingly used, established short-read NGS platforms (e.g., Illumina) are unable to genotype large and/or complex repeat expansions. Long-read sequencing platforms recently developed by Oxford Nanopore Technology and Pacific Biosciences promise to overcome these limitations to deliver enhanced diagnosis of repeat expansion disorders in a rapid and cost-effective fashion.

CONCLUSION

We anticipate that long-read sequencing will rapidly transform the detection of short tandem repeat expansion disorders for both clinical diagnosis and gene discovery.

Spinocerebellar Ataxia 7: A Report of Unaffected Siblings Who Married into Different SCA 7 Families

Two families with spinocerebellar ataxia type 7 are presented. Although there are affected cousins, it is not the sibling parents that transmitted the mutation. It is assumed that the affected families share a common ancestor.

[Spinocerebellar ataxia type 7]

The aim of this study was to verify the possible alterations observed in a case of spinocerebellar ataxia type 7. The patient was referred to the Laboratory of Neurotology of Universidade Tuiuti do Paraná (Brazil), and was submitted to the following procedures: anamnesis, otoscopy, auditory and vestibular assessments. The case described is a 34-year-old woman with a genetic diagnosis of spinocerebellar ataxia type 7, who referred imbalance when walking, speech difficulties, headache, dizziness, and dysphagia. The audiological evaluation showed normal hearing thresholds and tympanometric curve type "A", with bilateral presence of stapedius reflex. In the vestibular evaluation, it was observed the presence of spontaneous and gaze nystagmus with central characteristics, altered optokinetic nystagmus and pendular tracking, and hyperreflexia during the caloric test. Labyrinth alterations were found, indicating central vestibular system affection and evidencing the importance of this evaluation. The existence of a possible relationship between the findings and the neurotological symptoms presented by the patient leads us to a new issue, that is, the importance of the applicability of rehabilitation exercises that act in central structures of neuroplasticity. These exercises accelerate and stimulate natural compensation mechanisms, which may provide the patient with ataxia a better performance of its functions.

Spinocerebellar ataxias

Spinocerebellar ataxias (SCAs) constitute a heterogeneous group of neurodegenerative diseases characterized by progressive cerebellar ataxia in association with some or all of the following conditions: ophthalmoplegia, pyramidal signs, movement disorders, pigmentary retinopathy, peripheral neuropathy, cognitive dysfunction and dementia. OBJECTIVE: To carry out a clinical and genetic review of the main types of SCA. METHOD: The review was based on a search of the PUBMED and OMIM databases. RESULTS: Thirty types of SCAs are currently known, and 16 genes associated with the disease have been identified. The most common types are SCA type 3, or Machado-Joseph disease, SCA type 10 and SCA types 7, 2, 1 and 6. SCAs are genotypically and phenotypically very heterogeneous. A clinical algorithm can be used to distinguish between the different types of SCAs. CONCLUSIONS: Detailed clinical neurological examination of SCA patients can be of great help when assessing them, and the information thus gained can be used in an algorithm to screen patients before molecular tests to investigate the correct etiology of the disease are requested.

Familial Behr syndrome-like phenotype with autosomal dominant inheritance

Behr syndrome is an autosomal recessive disease characterized by early-onset ataxia, optic atrophy and other signs such as pyramidal tract dysfunction. Autosomal dominant inheritance has also been described. In this case report we present a family pedigree of patients with an inherited autosomal dominant Behr syndrome-like phenotype emphasizing their clinical and neuroimaging features.