TMEM106B Variant Delays FTD Onset in GRN Mutation Carriers

Navigating Genetic Complexity in Frontotemporal Dementia

Frontotemporal dementia (FTD) presents a significant clinical challenge due to its marked heterogeneity in presentation and progression, even among individuals with a shared genetic cause [1, 2]. While mutations in genes like GRN, MAPT, and C9orf72 are established drivers of hereditary FTD, the wide variability in age at onset suggests that the primary mutation is not the sole determinant of an individual's clinical course [3, 4]. This unpredictability complicates patient counseling and prognosis. Consequently, identifying genetic or environmental factors that modify disease expression is a critical step toward improving risk stratification and developing more precise therapeutic strategies for patients and their families [5, 6, 7, 8].

Understanding GRN and TMEM106B in FTD Pathogenesis

Mutations in the Granulin (GRN) gene, which encodes the progranulin (PGRN) protein, are a major cause of FTD. However, clinicians are familiar with the wide spectrum of outcomes in GRN mutation carriers, where age at onset and pathological features can differ substantially even within the same family. This variability strongly implies the existence of other genetic factors that modify the disease's trajectory. Previous genome-wide association studies pointed to the Transmembrane protein 106B (TMEM106B) gene locus as a key player. Specifically, a non-coding variant, rs1990622, was identified where the major allele (T) was associated with increased FTD risk, while the minor allele (C) appeared to confer protection.

Investigating a Protective TMEM106B Variant in GRN Carriers

Building on this knowledge, a recent study focused on a specific coding variant, TMEM106B-rs3173615, within a large Italian cohort of GRN mutation carriers. This variant was selected because it is in linkage disequilibrium with the previously identified risk variant rs1990622, a genetic state where two alleles at separate locations are inherited together more often than expected by chance, making rs3173615 a functional proxy. The investigation aimed to quantify how this variant modulates age at onset, survival, and PGRN levels. The study's design is notable for including the largest sample to date of individuals who are homozygous for the protective allele, providing greater statistical power to assess its effects. The genetic screening encompassed a total of 187 GRN mutation carriers, a cohort composed of 131 symptomatic FTD patients and 56 pre-symptomatic carriers, allowing for a comprehensive analysis across the disease spectrum.

Significant Delay in FTD Onset with Protective Genotype

The analysis yielded a clinically significant finding regarding the influence of TMEM106B on FTD presentation in GRN carriers. The researchers found that individuals with the protective genotype (GG) for the rs3173615 variant had a risk of developing FTD that was reduced by 80%. This dramatic risk reduction translated into a substantial delay in the typical disease timeline. Specifically, the median age at onset for carriers of the protective GG genotype was 77 years. This stands in stark contrast to the median age at onset of 63 years for individuals in the cohort who did not carry the protective genotype. The data demonstrate a 14-year difference in median onset, establishing TMEM106B-rs3173615 as a potent genetic modifier that helps explain the long-observed clinical heterogeneity in this patient population.

Clinical Implications for Risk Stratification

These findings have direct relevance for the clinical management of individuals carrying GRN mutations. The powerful modifying effect of the TMEM106B-rs3173615 variant provides a concrete biomarker for refining patient prognosis. For a patient with a known GRN mutation, knowledge of their TMEM106B genotype could substantially alter counseling about their lifetime risk and expected age at onset. An individual with the protective GG genotype, for example, could be counseled about a significantly later potential onset compared to a carrier without it. The study's authors suggest that testing for this variant could be integrated into clinical practice to optimize risk stratification. This more granular risk assessment could also inform decisions regarding the timing of surveillance, enrollment in preventative clinical trials, and long-term care planning, moving the field toward a more personalized approach for managing FTD risk.

References

1. Magee RG, Ohm DT, Rhodes E, et al. Clinical Manifestations.. Alzheimer's & Dementia. 2024. doi:10.1002/alz.089185

2. Rohrer JD, Nicholas J, Cash DM, et al. Presymptomatic cognitive and neuroanatomical changes in genetic frontotemporal dementia in the Genetic Frontotemporal dementia Initiative (GENFI) study: a cross-sectional analysis. The Lancet Neurology. 2015. doi:10.1016/s1474-4422(14)70324-2

3. Swift IJ, Esteve A, Heller C, Zetterberg H, Rohrer J. A systematic review of progranulin concentrations in biofluids in over 7,000 people: Assessing the pathogenicity of GRN mutations and other influencing factors. Alzheimer's & Dementia. 2021. doi:10.1002/alz.051609

4. Greaves C, Rohrer JD. An update on genetic frontotemporal dementia. Journal of Neurology. 2019. doi:10.1007/s00415-019-09363-4

5. Poos JM, Berg EVD, Boer LD, et al. Neuropsychological Profiles in Genetic Frontotemporal Dementia: A Meta-Analysis and Systematic Review.. Aging and disease. 2024. doi:10.14336/AD.2024.0183

6. Pagano L, Saraceno C, Geviti A, et al. Protective TMEM106B-rs3173615 delays age at onset in GRN mutation carriers.. Molecular psychiatry. 2026. doi:10.1038/s41380-026-03653-w

7. Pottier C, Zhou X, Perkerson RB, et al. Potential genetic modifiers of disease risk and age at onset in patients with frontotemporal lobar degeneration and GRN mutations: a genome-wide association study. The Lancet Neurology. 2018. doi:10.1016/s1474-4422(18)30126-1

8. Tsai R, Boxer AL. Therapy and clinical trials in frontotemporal dementia: past, present, and future. Journal of Neurochemistry. 2016. doi:10.1111/jnc.13640