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Behavioral Variant Frontotemporal Dementia With C9orf72 Intermediate Repeat Expansion
Sufen Huang, Yuzhang Bei, Qingxiang Zhang, Haitian Nan, Junjie Li. Alzheimer Disease & Associated Disorders, 2026-01-01
Topic: Brain proteins, microglia and lab models
Hexanucleotide repeat expansion in the chromosome 9 open reading frame 72 ( C9orf72 ) gene has been identified as the most common genetic cause of both frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). While large pathogenic expansions can reach hundreds to thousands of repeats, the lower limit for the number of pathogenic repeats remains controversial. Pathogenic threshold ranges from 30 to >60 repeats. Here, we report a rare case of behavioral variant frontotemporal dementia (bvFTD) associated with a C9orf72 repeat expansion of 49 units, a size that falls within the intermediate-length range. The patient presented with progressive neuropsychiatric decline, which progressed to include emotional blunting and memory impairment. Neuroimaging demonstrated bilateral temporal and hippocampal atrophy, with a reduction in glucose metabolism observed in the left fronto-parieto-temporal cortex and thalamus. This study may provide crucial clinical evidence for the ongoing debate on the pathogenicity of intermediate-length alleles in C9orf72 .
Key findings
- Here, we report a rare case of behavioral variant frontotemporal dementia (bvFTD) associated with a C9orf72 repeat expansion of 49 units, a size that falls within the intermediate-length range.
- Neuroimaging demonstrated bilateral temporal and hippocampal atrophy, with a reduction in glucose metabolism observed in the left fronto-parieto-temporal cortex and thalamus.
Why it matters
This single case report describes a patient with behavioral variant frontotemporal dementia carrying a C9orf72 repeat expansion of 49 units, within the intermediate-length range. It adds clinical evidence to the debate about which repeat lengths are pathogenic, but it is one case and offers no treatment, cure, or prevention.
Study details
- Evidence strengthLow
How this study scored 33/100
Published in a peer-reviewed journal. Scored zero for study design, sample size, effect reported, studied in people and randomised / blinded because the record does not state it.
| Component | Points | Why |
|---|---|---|
| Journal tier | 7 / 10 | Tier 3 — peer-reviewed journal (Alzheimer Disease & Associated Disorders) |
| Journal's citation record | 1 / 4 | Alzheimer Disease & Associated Disorders: journal h-index 131 (OpenAlex, 2026-10-29) |
| Study design | 0 / 12 | No study design recorded — scores zero, not guessed (not stated in the record — scored 0) |
| Strength of evidence | 1 / 5 | Rated “low” in our summary |
| Peer-review validation | 10 / 10 | Peer-reviewed. Published as an article in a named peer-reviewed journal. |
| How recent | 5 / 5 | 2026 — within 1 year(s) of the newest study here |
| Sample size | 0 / 4 | Participant count not stated — scores zero (not stated in the record — scored 0) |
| Effect reported | 0 / 3 | No effect size reported — scores zero (not stated in the record — scored 0) |
| Studied in people | 0 / 3 | Not stated whether this was studied in people — scores zero (not stated in the record — scored 0) |
| Randomised / blinded | 0 / 2 | No randomisation or blinding stated — scores zero (not stated in the record — scored 0) |
| Times cited | 1 / 7 | Cited 1 times (OpenAlex, 2026-10-10) |
| Citations per year | 0 / 5 | 0.5 citations a year over 2 year(s) since 2026 |
| Impact for its field and year | 3 / 6 | Cited 4.3× the average for papers of its field and year (OpenAlex FWCI) |
| Cited by studies here | 0 / 6 | No other study in this library cites it |
| Still being cited | 0 / 4 | Cited 1 times in 2024–2026 (2026 still in progress; OpenAlex) |
| Senior author's track record | 2 / 4 | Last-listed author Junjie Li: h-index 41 (OpenAlex, whole career) |
| Institution's track record | 0 / 3 | Capital Medical University: institution h-index 643 (OpenAlex) |
| Multi-centre collaboration | 1 / 3 | OpenAlex lists 2 institution(s) in 1 country |
| Indexed in PubMed | 2 / 2 | Indexed in PubMed (PMID 41665027) |
| Free to read | 0 / 2 | Behind a paywall — scores zero |
| Total | 33 / 100 | — |
What each of these 20 components measures, and what this score is not →
Read the original
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Cite this study APA, Vancouver, BibTeX · download .bib or .ris
Built from the record alzhub holds for this paper, not looked up. Volume, issue and page numbers are not held in the record. Check the citation against the original before you use it.
APA 7th
Huang, S., Bei, Y., Zhang, Q., Nan, H., & Li, J. (2026). Behavioral Variant Frontotemporal Dementia With C9orf72 Intermediate Repeat Expansion. Alzheimer Disease & Associated Disorders. https://doi.org/10.1097/wad.0000000000000718
Vancouver
Huang S, Bei Y, Zhang Q, Nan H, Li J. Behavioral Variant Frontotemporal Dementia With C9orf72 Intermediate Repeat Expansion. Alzheimer Disease & Associated Disorders. 2026. doi:10.1097/wad.0000000000000718. PMID: 41665027.
BibTeX
@article{huang2026-41665027,
author = {Huang, Sufen and Bei, Yuzhang and Zhang, Qingxiang and Nan, Haitian and Li, Junjie},
title = {{Behavioral Variant Frontotemporal Dementia With C9orf72 Intermediate Repeat Expansion}},
journal = {Alzheimer Disease \& Associated Disorders},
year = {2026},
doi = {10.1097/wad.0000000000000718},
pmid = {41665027},
url = {https://doi.org/10.1097/wad.0000000000000718}
}
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