First Report of Co-Occurring FGF14 (SCA27B) and RFC1 (CANVAS) Repeat Expansions in Two of Three Siblings with...

Cerebellar ataxia with neuropathy and vestibular areflexia syndrome (CANVAS) and spinocerebellar ataxia type 27B (SCA27B) are two increasingly recognized types of late-onset ataxia caused by biallelic RFC1 AAGGG and heterozygous FGF14 GAA repeat expansions, respectively. We describe three siblings of Greek-Cypriot origin with late-onset cerebellar ataxia. Two brothers carried biallelic pathogenic RFC1 AAGGG expansions and heterozygous FGF14 GAA expansions (338-350 repeats), establishing a dual diagnosis of CANVAS and SCA27B. Both presented with progressive gait ataxia, vestibular dysfunction, and sensory neuronopathy; one also reported episodic symptoms typical of SCA27B. Their sister, heterozygous for RFC1 and carrying a pathogenic FGF14 expansion (325 repeats), showed a pure SCA27B phenotype with episodic fluctuations, but without neuropathy or vestibular involvement. Brain MRI in all three demonstrated mild-to-moderate vermian atrophy. To our knowledge, this is the first documented report of co-occurring CANVAS and SCA27B in the same individuals. The findings expand the phenotypic spectrum of late-onset ataxia and highlight the importance of continued genetic testing, even after an initial diagnosis has been made.