Infantile Onset Spinocerebellar Ataxia 2 (SCA2): A Clinical Report With Review of Previous Cases

What’s new in pontocerebellar hypoplasia? An update on genes and subtypes

Abstract: Pontocerebellar hypoplasia (PCH) describes a rare, heterogeneous group of neurodegenerative disorders mainly with a prenatal onset. Patients have severe hypoplasia or atrophy of cerebellum and pons, with variable involvement of supratentorial structures, motor and cognitive impairments. Based on distinct clinical features and genetic causes, current classification comprises 11 types of PCH. In this review we describe the clinical, neuroradiological and genetic characteristics of the different PCH subtypes, summarize the differential diagnosis and reflect on potential disease mechanisms in PCH. Seventeen PCH-related genes are now listed in the OMIM database, most of them have a function in RNA processing or translation. It is unknown why defects in these apparently ubiquitous processes result in a brain-specific phenotype. Many new PCH related genes and phenotypes have been described due to the appliance of next generation sequencing techniques. By including such a broad range of phenotypes, including non-degenerative and postnatal onset disorders, the current classification gives rise to confusion. Despite the discovery of new pathways involved in PCH, treatment is still symptomatic. However, correct diagnosis of PCH is important to provide suitable care and counseling regarding prognosis, and offer appropriate (prenatal) genetic testing to families.

A de novo missense mutation in the inositol 1,4,5-triphosphate receptor type 1 gene causing severe pontine and cerebellar hypoplasia: Expanding the phenotype of ITPR1-related spinocerebellar ataxia's.

Abstract: We report a de novo missense mutation (c.7649T>A) in the inositol, 1,4,5 triphosphate receptor type 1 (ITPR1) gene in a patient with severe pontocerebellar hypoplasia. The mutation results in an amino acid substitution of a highly conserved isoleucine by asparagine (p. I2550N) in the transmembrane domain. Mutations and deletions of the ITPR1 gene are associated with several types of autosomal dominant spinocerebellar ataxia, varying in age of onset and severity. Patients have signs of cerebellar ataxia and at most, a mild cerebellar atrophy on MRI. In contrast, the patient we report here has profound cerebellar and pontine hypoplasia. Our finding therefore further expands the spectrum of ITPR1-related ataxias. © 2016 Wiley Periodicals, Inc.

Massive CAG repeat expansion and somatic instability in maternally transmitted infantile spinocerebellar ataxia type 7.

Abstract: Importance We report the first case to date of maternally transmitted infantile spinocerebellar ataxia type 7 (SCA7), in which a tract of (CAG)45 expands to lengths as large as (CAG)92-250. Observations A 38-year-old woman with classic SCA7 (and a son, who died at age 3 years) had pronounced cerebellar atrophy and a renal biopsy specimen that showed focal segmental glomerulosclerosis with abnormal podocytes containing cytoplasmic inclusions. Polymerase chain reaction amplification across the SCA7 repeat tract assessed expansion levels in tissues of the affected son. High levels of somatic CAG instability were observed in blood, kidney, and skeletal muscle. This transmitted expansion is considerably larger than previously reported maternal transmission expansions of 5 to 10 gained repeats. Conclusions and Relevance We document the first intertissue CAG instability reported to date in patients with SCA7, similar to SCA7 mouse models. Infantile SCA7, which is often paternally transmitted, can rarely arise by maternal transmission, which has implications for diagnosis and counseling among families of patients with SCA7.

The Multiple Faces of Spinocerebellar Ataxia type 2.

Abstract: Spinocerebellar ataxia type 2 (SCA2) is among the most common forms of autosomal dominant ataxias, accounting for 15% of the total families. Occurrence is higher in specific populations such as the Cuban and Southern Italian. The disease is caused by a CAG expansion in ATXN2 gene, leading to abnormal accumulation of the mutant protein, ataxin-2, in intracellular inclusions. The clinical picture is mainly dominated by cerebellar ataxia, although a number of other neurological signs have been described, ranging from parkinsonism to motor neuron involvement, making the diagnosis frequently challenging for neurologists, particularly when information about the family history is not available. Although the functions of ataxin-2 have not been completely elucidated, the protein is involved in mRNA processing and control of translation. Recently, it has also been shown that the size of the CAG repeat in normal alleles represents a risk factor for ALS, suggesting that ataxin-2 plays a fundamental role in maintenance of neuronal homeostasis.

A clinical report of the massive CAG repeat expansion in spinocerebellar ataxia type 2: Severe onset in a Mexican child and review previous cases.

Abstract: The spinocerebellar ataxia type 2 is a neurodegenerative disease with autosomal dominant inheritance; clinically characterized by progressive cerebellar ataxia, slow ocular saccades, nystagmus, ophthalmoplegia, dysarthria, dysphagia, cognitive deterioration, mild dementia, peripheral neuropathy. Infantile onset is a rare presentation that only has been reported in four instances in the literature. In the present work a boy aged 5 years 7 months was studied due to horizontal gaze-evoked nystagmus, without saccades, ataxic gait, dysarthria, dysphagia, dysmetria, generalized spasticity mainly pelvic, bilateral Babinsky. The mother aged 27 years-old presented progressive cerebellar ataxia, dysarthria, dysmetria, dysdiadochokinesis, limb ataxia and olivopontocerebellar atrophy. The molecular analysis was made by identifying the expansion repeats in tandem by long PCR to analyze the repeats in the ATXN2 gene. We found an extreme CAG expansion repeats of ~884 repeats in the child. We describe a Mexican child affected by SCA2 with an infantile onset, associated with a high number of CAG repeats previously no reported and anticipation phenomenon.

Ataxin-2 intermediate-length polyglutamine expansions are associated with increased risk for ALS

Abstract: The causes of amyotrophic lateral sclerosis (ALS), a devastating human neurodegenerative disease, are poorly understood, although the protein TDP-43 has been suggested to have a critical role in disease pathogenesis. Here we show that ataxin 2 (ATXN2), a polyglutamine (polyQ) protein mutated in spinocerebellar ataxia type 2, is a potent modifier of TDP-43 toxicity in animal and cellular models. ATXN2 and TDP-43 associate in a complex that depends on RNA. In spinal cord neurons of ALS patients, ATXN2 is abnormally localized; likewise, TDP-43 shows mislocalization in spinocerebellar ataxia type 2. To assess the involvement of ATXN2 in ALS, we analysed the length of the polyQ repeat in the ATXN2 gene in 915 ALS patients. We found that intermediate-length polyQ expansions (27-33 glutamines) in ATXN2 were significantly associated with ALS. These data establish ATXN2 as a relatively common ALS susceptibility gene. Furthermore, these findings indicate that the TDP-43-ATXN2 interaction may be a promising target for therapeutic intervention in ALS and other TDP-43 proteinopathies.

Cloning of the gene for spinocerebellar ataxia 2 reveals a locus with high sensitivity to expanded CAG/glutamine repeats

Abstract: Two forms of the neurodegenerative disorder spinocerebellar ataxia are known to be caused by the expansion of a CAG (polyglutamine) trinucleotide repeat. By screening cDNA expression libraries, using an antibody specific for polyglutamine repeats, we identified six novel genes containing CAG stretches. One of them is mutated in patients with spinocerebellar ataxia linked to chromosome 12q (SCA2). This gene shows ubiquitous expression and encodes a protein of unknown function. Normal SCA2 alleles (17 to 29 CAG repeats) contain one to three CAAs in the repeat. Mutated alleles (37 to 50 repeats) appear particularly unstable, upon both paternal and maternal transmissions. The sequence of three of them revealed pure CAG stretches. The steep inverse correlation between age of onset and CAG number suggests a higher sensitivity to polyglutamine length than in the other polyglutamine expansion diseases.

Are interrupted SCA2 CAG repeat expansions responsible for parkinsonism

Abstract: Background: Autosomal dominant parkinsonism (ADP) is caused in a large percentage of familial and sporadic cases by mutations in the LRRK2 gene, particularly G2019S. It is also caused by mutations in genes associated with autosomal dominant cerebellar ataxia (ADCA), notably CAG/CAA repeat expansions in SCA2 . Methods: We screened 164 families with ADP for expansions in the SCA2, 3 , and 17 genes and for the G2019S mutation in LRRK2 . The SCA2 CAG/CAA repeat expansion was sequenced to determine its structure. The phenotypes of patients with ADP caused by the SCA2 , LRRK2 , and unknown mutations were compared, as well as those of SCA2 patients with interrupted or uninterrupted expansions of the same size. Results: Three French ADP families had SCA2 mutations. The expansions ranged from 37 to 39 repeats and were interrupted and stable upon transmission. All patients (n = 9) had levodopa-responsive parkinsonism without cerebellar signs. They had significantly more symmetric signs and less rigidity than ADP caused by the G2019S mutation in LRRK2 or by unknown mutations. Interestingly, two sisters carrying both the SCA2 and the G2019S LRRK2 mutations had markedly earlier onset than their mother with only SCA2 . In contrast, similar-sized but uninterrupted repeats were associated with ADCA in which cerebellar ataxia was constant and associated only rarely with one or more mild parkinsonian signs. Conclusion: These results suggest that the configuration of the SCA2 CAG/CAA repeat expansions plays an important role in phenotype variability. Uninterrupted SCA2 repeat expansions found in families with autosomal dominant cerebellar ataxia result in somatic mosaicism and produce large hairpin RNAs, which may interact with double-stranded RNA-binding proteins. These characteristics are modified by interruption of the SCA2 repeat expansion as found in families with autosomal dominant parkinsonism.

Spinocerebellar ataxia type 2 (SCA 2) in an infant with extreme CAG repeat expansion.

Abstract: Autosomal dominant cerebellar ataxias are a heterogeneous group of neurodegenerative disorders that generally present in adulthood. Spinocerebellar ataxia type 2 typically presents with progressive cerebellar symptoms, slow ocular saccades, and peripheral neuropathy. The onset of symptoms is usually between 20 and 40 years. We describe an infant who presented with neonatal hypotonia, developmental delay, and dysphagia. Ocular findings of retinitis pigmentosa were noted at 10 months. Her father had mild spinocerebellar ataxia first noted at age 22 years. Molecular studies of the SCA2 gene showed a CAG expansion of 43 repeats in the father and an extreme CAG repeat expansion of more than 200 in the baby. Our report expands the known phenotype and genotype of SCA2. Testing for dominant ataxias should be included in the evaluation of infants with nonspecific progressive neurologic symptoms and retinitis pigmentosa, especially in cases with a positive family history for spinocerebellar ataxia.