The inherited leukoencephalopathy is a heterogeneous group of rare white matter diseases (Kohler, Curiel, & Vanderver, 2018) which affects only 1 in 50,000(Kohler et al., 2018) people. Compared to those young-onset ones, it is even rarer for adult-onset phenotypes such as CSF1R-related leukoencephalopathy, making it difficult to collect large samples for relative clinical studies, thus largely limiting the exploration on their mechanisms, diagnosis and treatment. Despite its rarity, studies on CSF1R-related leukoencephalopathy are urgently needed, since it mainly affects adults of around 40 years old(Tian et al., 2019) who are usually the main supporters for family, and is associated with high morbidity and mortality that most patients will get bedridden, severe dementia or dying within 4–6 years after diagnosis(Konno et al., 2017; Sundal et al., 2015).
For CSF1R-related leukoencephalopathy, early diagnosis is of great significance, because the progression of this fatal disease might be controlled or even slightly reversed if patients receive bone marrow transplantation at the early stage(Eichler et al., 2016; Gelfand et al., 2020; Mochel et al., 2019). However, the incomplete penetrance, which means some carriers may not develop the disease for life, has suggested that CSF1R deficiency is not the only factor that determines the early onset of the disease. On the other hand, current diagnosis, which combines genetic analysis with brain structural magnetic resonance imaging (MRI), featured with asymmetrical periventricular white matters abnormalities on diffusion weighted imaging (DWI) and fluid attenuated inversion recovery (FLAIR) sequence(Bender et al., 2014), is not sensitive enough to detect pre-clinical onset and easily confuse the disease with other disorders with leukoencephalopathy, such as Alzheimer’s disease (AD), multiple sclerosis (MS), frontotemporal dementia and cerebral small vessel diseases(Kohler et al., 2018). Therefore, new techniques need to be introduced to improve the early diagnosis of the disease.
Recent studies have shown that the application of single photon emission computered tomography (SPECT)(Daida et al., 2017; Kitani-Morii et al., 2014; Terasawa et al., 2013) and [18F]-fluorodeoxyglucose positron emission tomography (PET)(Kim et al., 2015; Nicholson et al., 2013) has already demonstrated diffuse cortical hypometabolism predominantly in fronto-parietal areas in several cases, indicating the relationship between brain function and CSF1R-related leukoencephalopathy. Considering the radioactivity and expensiveness of SPECT and PET, our previous study based on an alternative technique, resting-state functional MRI (rsfMRI), has also revealed some functional abnormalities among patients(Zhan et al., 2020), implying the potential of brain function changes as a contributive biomarker for the early diagnosis of CSF1R-related leukoencephalopathy.
In recent years, rsfMRI, as a non-invasive functional imaging technique, has shown its enormous potential in detecting functional abnormalities at an early stage before objective deficits are detectable(Hohenfeld, Werner, & Reetz, 2018), and studying neural mechanisms of neurological dysfunctions (Biswal, 2012), with high acceptance to patients and good reproductivity(Zou et al., 2015). In rsfMRI data analysis, the amplitude of low-frequency fluctuations (ALFF) and regional homogeneity (ReHo) are two commonly calculated local indices(Disner, Marquardt, Mueller, Burton, & Sponheim, 2018; Pan et al., 2017). ALFF is calculated as the mean square root of power spectrum in a low-frequency range (0.01-0.08Hz) at each voxel based on blood oxygenation level-dependent (BOLD) signals(Y. F. Zang et al., 2007). As a promising method for detecting the regional intensity of spontaneous activity, ALFF has been applied in a wide range of brain disorders including AD(X. Liu et al., 2014; Yang et al., 2018), Parkinson’s disease (PD)(Hou, Wu, Hallett, Chan, & Wu, 2014; Wang et al., 2020; Yue et al., 2020), MS(Liu et al., 2011), cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL)(Su, Wang, et al., 2019), subcortical ischemic vascular dementia (SIVD)(C. Liu et al., 2014) and moyamoya disease(Lei et al., 2014). On the other hand, ReHo is a measurement for the similarity of the time series of a given cluster. It could reflect local synchronization of spontaneous brain activity and indicate the changes of temporal neuronal activity in specific regional areas. The ReHo method has also been widely used for the investigation of neural activity changes in neurologic diseases, such as AD(Tu et al., 2020; Zhang et al., 2012), PD(Liu et al., 2019; Yue et al., 2020), MS(Wu et al., 2016; Zhu et al., 2020), CADASIL(Orsolini et al., 2020; Su, Ban, et al., 2019) and SIVD(Tu et al., 2020). The combination of ALFF and ReHo might offer us a comprehensive view of regional spontaneous activities in patients with CSF1R-related leukoencephalopathy from different dimensions, and provide potential regions of interest for further functional analysis. However, so far, no study has been conducted to explore the characteristics of local brain activity for this disease.
We hypothesize that patients with CSF1R-related leukoencephalopathy would exhibit abnormal temporal variability of brain activity compared to healthy controls. 2 resting state methods, ALFF and ReHo were employed to evaluate the variability of intrinsic brain activities. These might provide early clues for disease onset and enhance our understanding of the disease.