Dados do Trabalho

Título

SPINOCEREBELLAR ATAXIA TYPE 7 WITH EARLY ONSET AND ABSENCE OF FAMILY HISTORY

Apresentação do caso único

A 10-year-old male presented with progressive imbalance since age 6. He developed progressive upper limb tremors and bilateral visual impairment due to retinitis pigmentosa, besides learning difficulties characterized by inattention and restlessness. He was born to non-consanguineous parents with no family past medical history of neurological diseases. Neurological examination revealed dysarthria, dysphonia, mydriatic pupils, visual acuity of 20/135 in the right eye and 20/155 in the left eye, optic disc pallor, gaze apraxia, signs of cerebellar dysfunction and tongue fasciculations. Global muscle strength was grade III with distal muscle atrophy, and Achilles tendon retraction was noted bilaterally. Cranial MRI showed cerebellar atrophy. Cerebrospinal fluid analysis was normal. Expanded panel genetic testing identified an abnormal CAG repeat expansion (75 repeats) in the ATXN7 gene, confirming the diagnosis of spinocerebellar ataxia type 7 (SCA7). The patient's father, though asymptomatic, also carried an expanded allele (41 repeats), underscoring the variable expressivity and anticipation seen in SCA7.

Discussão

SCA 7 is characterized by progressive cerebellar ataxia and blindness. Its prevalence is of less than 1/300000 in the general population and it corresponds to 2% of all SCAs and is classified as a rare disease.This condition is inherited in autosomal dominant manner and anticipation. In molecular genetic testing, 34-36 CAG trinucleotide repeat in ATXN7 confirms a pathogenic condition, but only from 37 the penetrance is complete. The anticipation phenomenon, characterized by earlier onset and increased severity in successive generations, was observed as the patient's father, although asymptomatic at the time of assessment, also carried an expanded allele (41 repeats). This highlights the importance of genetic testing in establishing a diagnosis, even in the absence of symptomatic family members, as seen in this case.

Comentários finais

This case underscores the phenotypic variability and challenges in diagnosing SCA7. Despite the rarity of the condition, early recognition based on clinical presentation and genetic testing is crucial for appropriate management and genetic counseling, even in the absence of a family history of neurological symptoms.

Referências

1. LA SPADA, Antonio R. Spinocerebellar Ataxia Type 7. GeneReviews. Seattle (WA): University of Washington, Seattle; p. 1-20. July, 2020.
2. GOSWAMI, Rituparna, et al. The Molecular Basis of Spinocerebellar Ataxia type 7. Frontiers in Neuroscience. United Sattes: Duke University; v. 16; p. 1-15. March, 2022.

Palavras Chave

Spinocerebellar Ataxia Type 7; Anticipation Genetic; ATXN7