Severe symptoms of 16q-ADCA coexisting with SCA8 repeat expansion

Spinocerebellar ataxia type 31: A clinical and radiological literature review

Spinocerebellar ataxia type 31 (SCA31) is an autosomal dominant disease, classified amongst pure cerebellar ataxias (ADCA type 3). While SCA31 is the third most prevalent autosomal dominant ataxia in Japan, it is extremely rare in other countries. A literature review was conducted on PubMed, where we included all case reports and studies describing the clinical presentation of original SCA31 cases. The clinical and radiological features of 374 patients issued from 25 studies were collected. This review revealed that the average age of onset was 59.1 ± 3.3 years, with symptoms of slowly progressing ataxia and dysarthria. Other common clinical features were oculomotor dysfunction (38.8%), dysphagia (22.1%), hypoacousia (23.3%), vibratory hypoesthesia (24.3%), and dysreflexia (41.6%). Unfrequently, abnormal movements (7.4%), extrapyramidal symptoms (4.5%) and cognitive impairment (6.9%) may be observed. Upon radiological examination, clinicians can expect a high prevalence of cerebellar atrophy (78.7%), occasionally accompanied by brainstem (9.1%) and cortical (9.1%) atrophy. Although SCA31 is described as a slowly progressive pure cerebellar syndrome characterized by cerebellar signs such as ataxia, dysarthria and oculomotor dysfunction, this study evaluated a high prevalence of extracerebellar manifestations. Extracerebellar signs were observed in 52.5% of patients, primarily consisting of dysreflexia, vibratory hypoesthesia and hypoacousia. Nonetheless, we must consider the old age and longstanding disease course of patients as a confounding factor for extracerebellar sign development, as some may not be directly attributable to SCA31. Clinicians should consider SCA31 in patients with a hereditary, pure cerebellar syndrome and in patients with extracerebellar signs.

Novel variants in SPTAN1 without epilepsy: An expansion of the phenotype

We describe two unrelated children with de novo variants in the non-erythrocytic alpha-II-spectrin (SPTAN1) gene who have hypoplastic brain structures, intellectual disability, and both fine and gross motor impairments. Using agnostic exome sequencing, we identified a nonsense variant creating a premature stop codon in exon 21 of SPTAN1, and in a second patient we identified an intronic substitution in SPTAN1 prior to exon 50 creating a new donor acceptor site. Neither of these variants has been described previously. Although some of these patients' features are consistent with the known SPTAN1 encephalopathy phenotype, these two children do not have epilepsy, in contrast to reports about nearly every other patient with heterozygous SPTAN1 variants and in all patients with a variant near the C-terminal coding region. Moreover, both children have abnormal thyroid function, which has not been previously reported in association with SPTAN1 variant. We present a detailed discussion of the clinical manifestations of these two unique SPTAN1 variants and provide evidence that both variants result in reduced mRNA expression despite different locations within the gene and clinical phenotypes. These findings expand the motor, cognitive, and behavioral spectrum of the SPTAN1-associated phenotype and invite speculation about underlying pathophysiologies.

Distinguishing spinocerebellar ataxia with pure cerebellar manifestation from multiple system atrophy (MSA-C) through saccade profiles

OBJECTIVE

Patients with spinocerebellar ataxia with pure cerebellar presentation (SCD) and multiple system atrophy (MSA-C) show similar symptoms at early stages, although cerebellofugal pathology predominates in SCD, and cerebellopetal pathology in MSA-C. We studied whether saccade velocity profiles, which reflect the accelerating and braking functions of the cerebellum, can differentiate these two disorders.

METHODS

We recorded visually guided (VGS) and memory guided saccades (MGS) in 29 MSA-C patients, 12 SCD patients, and 92 age-matched normal subjects, and compared their amplitude, peak velocity and duration (accelerating and decelerating phases).

RESULTS

Hypometria predominated in VGS and MGS of MSA-C, whereas hypometria was less marked in SCD, with hypermetria frequently noted in MGS. Peak velocity was reduced, and deteriorated with advancing disease both in SCD and MSA-C groups at smaller target eccentricities. The deceleration phase was prolonged in SCD compared to MSA-C and normal groups at larger target eccentricities, which deteriorated with advancing disease.

CONCLUSION

Saccades in MSA-C were characterized by a more prominent acceleration deficit and those in SCD by a more prominent braking defect, possibly caused by the cerebellopetal and cerebellofugal pathologies, respectively.

SIGNIFICANCE

Saccade profiles provide important information regarding the accelerating and braking signals of the cerebellum in spinocerebellar ataxia.

Ataxias with Autosomal, X-Chromosomal or Maternal Inheritance

Heredoataxias are a group of genetic disorders with a cerebellar syndrome as the leading clinical manifestation. The current classification distinguishes heredoataxias according to the trait of inheritance into autosomal dominant, autosomal recessive, X-linked, and maternally inherited heredoataxias. The autosomal dominant heredoataxias are separated into spinocerebellar ataxias (SCA1-8, 10-15, 17-23, 25-30, and dentato-rubro-pallido-luysian atrophy), episodic ataxias (EA1-7), and autosomal dominant mitochondrial heredoataxias (Leigh syndrome, MIRAS, ADOAD, and AD-CPEO). The autosomal recessive ataxias are separated into Friedreich ataxia, ataxia due to vitamin E deficiency, ataxia due to Abeta-lipoproteinemia, Refsum disease, late-onset Tay-Sachs disease, cerebrotendineous xanthomatosis, spinocerebellar ataxia with axonal neuropathy, ataxia telangiectasia, ataxia telangiectasia-like disorder, ataxia with oculomotor apraxia 1 and 2, spastic ataxia of Charlevoix-Saguenay, Cayman ataxia, Marinesco-Sjögren syndrome, and autosomal recessive mitochondrial ataxias (AR-CPEO, SANDO, SCAE, AHS, IOSCA, MEMSA, LBSL CoQ-deficiency, PDC-deficiency). Only two of the heredoataxias, fragile X/tremor/ataxia syndrome, and XLSA/A are transmitted via an X-linked trait. Maternally inherited heredoataxias are due to point mutations in genes encoding for tRNAs, rRNAs, respiratory chain subunits or single large scale deletions/duplications of the mitochondrial DNA and include MELAS, MERRF, KSS, PS, MILS, NARP, and non-syndromic mitochondrial disorders. Treatment of heredoataxias is symptomatic and supportive and may have a beneficial effect in single patients.

**Please see page 424 for abbreviation list.

The spinocerebellar ataxias: clinical aspects and molecular genetics

Spinocerebellar ataxias (SCAs) are a highly heterogeneous group of inherited neurological disorders, based on clinical characterization alone with variable degrees of cerebellar ataxia often accompanied by additional cerebellar and noncerebellar symptoms which in most cases defy differentiation. Molecular causative deficits in at least 31 genes underlie the clinical symptoms in the SCAs by triggering cerebellar and, very frequently, brain stem dysfunction. The identification of the causative molecular deficits enables the molecular diagnosis of the different SCA subtypes and facilitates genetic counselling. Recent scientific advances are shedding light into developing therapeutic strategies. The scope of this chapter is to provide updated details of the spinocerebellar ataxias with particular emphasis on those aspects aimed at facilitating the clinical and genetic diagnoses.

Autosomal dominant cerebellar ataxias: polyglutamine expansions and beyond

Cerebellar ataxias with autosomal dominant transmission are rare, but identification of the associated genes has provided insight into the mechanisms that could underlie other forms of genetic or non-genetic ataxias. In many instances, the phenotype is not restricted to cerebellar dysfunction but includes complex multisystemic neurological deficits. The designation of the loci, SCA for spinocerebellar ataxia, indicates the involvement of at least two systems: the spinal cord and the cerebellum. 11 of 18 known genes are caused by repeat expansions in the corresponding proteins, sharing the same mutational mechanism. All other SCAs are caused by either conventional mutations or large rearrangements in genes with different functions, including glutamate signalling (SCA5/SPTBN2) and calcium signalling (SCA15/16/ITPR1), channel function (SCA13/KCNC3, SCA14/PRKCG, SCA27/FGF14), tau regulation (SCA11/TTBK2), and mitochondrial activity (SCA28/AFG3L2) or RNA alteration (SCA31/BEAN-TK2). The diversity of underlying mechanisms that give rise to the dominant cerebellar ataxias need to be taken into account to identify therapeutic targets.