Frequency of FGF14 intronic GAA repeat expansion in patients with multiple system atrophy and undiagnosed ataxia in the Japanese population

Abstract

Multiple system atrophy (MSA) is a neurodegenerative disorder characterized by autonomic nervous system dysfunction and cerebellar ataxia or parkinsonism. Recently, expanded GAA repeats (≥250 repeat units) in intron 1 of FGF14 have been shown to be responsible for spinocerebellar ataxia type 27B (SCA27B), a late-onset ataxia with an autosomal dominant inheritance. Patients with SCA27B may also exhibit autonomic nervous system dysfunction, potentially overlapping with the clinical presentations of MSA patients. In this study, to explore the possible involvement of expanded GAA repeats in MSA, we investigated the frequencies of expanded GAA repeats in FGF14 in 548 patients with MSA, 476 patients with undiagnosed ataxia, and 455 healthy individuals. To fully characterize the structures of the expanded GAA repeats, long-range PCR products suggesting the expansion of GAA repeats were further analyzed using a long-read sequencer. Of the 548 Japanese MSA patients, we identified one MSA patient (0.2%) carrying an expanded repeat with (GAA)_≥250. Among the 476 individuals with undiagnosed ataxia, (GAA)_≥250 was observed in six (1.3%); this frequency was higher than that in healthy individuals (0.2%). The clinical characteristics of the MSA patient with (GAA)_≥250 were consistent with those of MSA, but not with SCA27B. Further research is warranted to explore the possibility of the potential association of expanded GAA repeats in FGF14 with MSA.

Fig. 1. Analysis of expanded GAA repeats in the intron 1 of FGF14.

A Flowchart of analysis of repeat configurations. B Representative waterfall plot of a patient with MSA who had an expanded repeat consisting of pure GAA repeats. Pure GAA repeats are shown in green. Note that a substantial number of mismatched nucleotides are observed in the reads derived from pure expanded GAA repeats possibly reflecting errors in the LR-PCR or in the long-read sequence analysis, which are more numerous than those observed in (C) or (D). C Waterfall plot of a patient with ataxia who had a complex configuration containing GAA repeats with 100–200 repeat units. D Waterfall plot of a patient with ataxia who had a complex configuration with GAA repeat units less than 100 repeat units. E–G Fragment analysis of the RP-PCR products of the same patients as shown in Fig. 1B–D. The result of the RP-PCR was interpreted as positive (E), inconclusive (F), and negative (G). RP-PCR, repeat-primed PCR.

Fig. 2. Size distribution and frequency of expanded GAA repeats in the patients with ataxia, patients with MSA, and healthy individuals.

A Swarm plots showing the number of the GAA repeat units for each read in patients with ataxia (n = 9), a patient with MSA (n = 1), and healthy individuals (n = 2) who had expanded repeats consisting of pure GAA repeats. Short black line in each individual showed median of the repeat units. The horizontal bold black line indicates the 300 GAA repeat units. The GAA repeat units exceeding 300 are considered to have full penetrance. The dashed black line indicates the 250 GAA repeat units, indicating that GAA repeats ranging from 250 to 299 repeat units are considered to have incomplete penetrance. B An inverse correlation between age at onset of SCA27B and the number of GAA repeat units of FGF14 (n = 6). The dashed line shows the linear regression.

Fig. 3. Brain MRI of the patients with MSA or undiagnosed ataxia with expanded GAA repeats.

Axial T2-weighted image (A) and sagittal T1-weighted image (B) of the patient with undiagnosed ataxia who had (GAA)₃₁₂. MRI was performed at the age of 84, twelve years after the symptom onset. Atrophic changes in the upper part of the cerebellar hemisphere and the vermis were observed. The brainstem was not atrophic. Axial T2-weighted image (C) and sagittal T1-weighted image (D) of the patient with MSA who had (GAA)₂₆₉ seven years after the symptom onset. Atrophic changes in the cerebellum, middle cerebellar peduncles, and basis pontis were observed. The hot cross bun sign was observed in (C).