Objective: Spinocerebellar ataxias a heterogeneous group autosomal dominant neurodegenerative diseases with the main clinical feature of ataxia. Among various types, spinocerebellar ataxia type 40 (SCA40) is extremely rare and classified as a subtype of autosomal dominant cerebellar ataxia type 1. Characteristic clinical manifestation includes adult-onset balance and gait difficulties leading to gait ataxia, dysmetria, dysdiadochokinesia with intention tremor, hyperreflexia, and dysarthria. Since it is an extremely rare phenomenon, we here reported a case of young-onset SCA40.

Background: A-32 years old man presented to our movement disorders outpatient clinic with ataxic gait, balance problems and tremor. His initial symptom was unsteady gait that started at the age of 18 years, and tremor at the upper limbs with progressive gait and balance problems became more prominent in the following years.

Method: His neurological examination revealed mild dysarthria, ocular dysmetria, bilateral severe action and intention tremor which was more prominent at the left hand with dysmetria and dysdiadochokinesia. He had hyperreflexia and a broad-based ataxic gait with mild postural instability.

Results: Cranial MRI of the patient showed mild cerebellar atrophy in T2-weighted MRI. His medical history was unremarkable and he had no family history. He had a normal developmental delay without any cognitive decline. His genetical assessment revealed an autosomal dominant mutation in the CCDC88C gene (611204) on chromosome 14q32 which was diagnosed as SCA-40.

Conclusion: This unique form of SCAs, was firstly named by Tsoi and colleagues in 2014 by defining the  coiled-coil domain containing 88c (CCDC88C) gene mutation located in 14q32.11-q32.12, Owing to the high expression of this gene in cerebellum, the initial and most prominent symptom is reported to be cerebellar ataxia accompanied by a cerebellar syndrome. Since there is limited literature data and SCA-40 is linked with an adult-onset spinocerebellar ataxia, this case is presented as a young-onset SCA-40.

References: 1. Tsoi H, Yu AC, Chen ZS, Ng NK, Chan AY, Yuen LY, et al. A novel missense mutation in CCDC88C activates the JNK pathway and causes a dominant form of spinocerebellar ataxia. J Med Genet. 2014;51:590–5. 10.1136/jmedgenet-2014-102333.
2. Han F, Su D, Qu C. Spinocerebellar ataxia type 40: A case report and literature review. Transl Neurosci. 2021 Jan 1; 12(1): 379–384. doi: 10.1515/tnsci-2020-0190

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MDS Abstracts - https://www.mdsabstracts.org/abstract/a-rare-case-of-young-onset-ataxia-spinocerebellar-ataxia-type-40/