Study design and participant selection
This study utilizes data sourced from the Recognition and Early Intervention of Prodromal Bipolar Disorders (REI-PBD) initiative (ClinicalTrials.gov Identifier: NCT01863628) (Lin et al., 2015; Lin, Shao, Geng, et al., 2018; Lin, Shao, Lu, et al., 2018; Lu et al., 2024). The Institutional Review Board of the Affiliated Brain Hospital of Guangzhou Medical University gave their ethical approval for the study. Written informed consent was acquired from all participants or their respective guardians. Recruitment included advertisements, referrals from psychiatric professionals, and word-of-mouth promotion. To balance the age and subjects number of five groups, 309 subjects selected from 392 subjects, 83 BD patients whose age were above 20 years old were excluded from further analysis. The remaining dataset included offspring of BD patients with subthreshold symptoms but without a formal BD diagnosis (OBDs, n = 48), offspring of BD patients without a BD diagnosis yet with subthreshold symptoms (OBDns, n = 63), non-BD offspring with subthreshold symptoms but without a formal BD diagnosis (nOBDs, n = 62), as well as matching BD patients (BD, n = 50) and healthy controls (HC, n = 86). The demographic and clinical characteristics of the enrolled subjects can be found in Table 1.
Table 1
Demographic and clinical characteristics of participants.
| BD (n = 50) | HC (n = 86) | nOBDs (n = 62) | OBDns (n = 63) | OBDs (n = 48) | Test Statistic (F/χ2) | P value |
Mean (SD) /n (%) |
Age(years) | 16.7 (1.46) | 16.0 (3.23) | 16.0 (3.94) | 17.5(5.55) | 17.5(5.96) | 1.865 | 0.116 |
Education (years) | 8.7 (4.2) | 9.5 (3.4) | 10.1 (2.3) | 9.6 (2.9) | | 1.379 | 0.241 |
Sex (female) | 26 (53.1%) | 30 (63.8%) | 29 (56.9%) | 40 (55.6%) | | 1.236 | 0.872 |
HAMD | 4.4 (5.3) | 0.4 (0.9) | 6.9 (7.6) | 0.6(1.0) | 7.7(8.6) | 26.42 | < 0.001 |
HAMA | 3.1 (4.8) | 0.4(1.1) | 4.9(5.5) | 0.4(0.8) | 5.8(7.5) | 20.36 | < 0.001 |
YMRS | 1.3(2.2) | 0.2(1.6) | 1.8(2.3) | 0.4(1.3) | 2.2(2.7) | 14.7 | < 0.001 |
BPRS | 20.3(2.6) | 18.3(0.8) | 21.6(5.1) | 17.7(3.3) | 23.0(5.5) | 21.85 | < 0.001 |
GAS | 79.8(10.1) | 94.2(3.5) | 93.6(13.4) | 77.2(4.2) | 75.1(11.8) | 68.03 | < 0.001 |
PBD (with/without) | 8/42 | 0/86 | 0/62 | 63/0 | 48/0 | | |
PDD | 3/47 | 1/85 | 2/60 | 3/45 | 4/59 | | |
PSP | 0/50 | 0/86 | 0/62 | 1/47 | 0/63 | | |
PSUB | 1/49 | 1/85 | 6/56 | 8/40 | 0/63 | | |
FAMDD | 2/48 | 1/85 | 5/57 | 6/42 | 4/59 | | |
FAMSP | 1/49 | 0/86 | 0/62 | 1/47 | 0/63 | | |
FAMSUB | 0/50 | 1/85 | 0/62 | 2/46 | 0/63 | | |
Note: BD, Bipolar Disorder patients; nOBDs, non-BD offspring with subthreshold symptoms; OBDs, BD offspring with subthreshold symptoms; OBDns, BD offspring without subthreshold symptoms; HAMD, Hamilton Depression Rating Scale; HAMA, Hamilton Anxiety Rating Scale; YMRS, Young Manic Rating Scale; BPRS, Brief Psychiatric Rating Scale; GAS, Global Assessment Scale; PBD, parent with bipolar disorder history; PDD, parent with depressive disorder history; PSUB, parent with substance use disorder history; PSP, parent with schizophrenia history; FAMDD, first-degree family history of depressive disorder; FAMSP, first-degree family history of schizophrenia; FAMSUB, first-degree family history of substance use disorder. The psychiatric history is indicated by with history/without history. |
Participant evaluation
We undertook systematic clinical evaluations for all participants to ascertain their symptomatology. Scales such as the Hamilton Anxiety Rating Scale (HAMA) (Hamilton, 1959), the Hamilton Depression Rating Scale (HAMD) (Hamilton, 1986), the Young Mania Rating Scale (YMRS) (Youngstrom et al., 2003), and the Brief Psychiatric Rating Scale (BPRS) (Overall & Gorham, n.d.) were implemented to evaluate the severity of anxiety, depression, mania, and psychotic symptoms. We employed semi-structured tools like the Schedule for Affective Disorders and Schizophrenia for School-Aged Children: Present and Lifetime Version (K-SADS-PL DSM-IV) (for participants under 18 years) or the Structured Clinical Interview for DSM-IV Axis I Disorders, Patient Edition (SCID-I/P) (for those 18 years and older) to validate psychiatric disorder diagnoses (Kaufman et al., 1997). The Family Interview for Genetic Studies (FIGS) was employed to validate the familial history of psychiatric conditions, entailing a broad spectrum of specific diagnoses. This encompassed PBD, indicating a parental history of bipolar disorder; PDD, representing a parental history of depressive disorder; PSUI, symbolizing parental history of substance use disorder; and PSP, reflecting a parental history of schizophrenia. In addition, first-degree family history markers were considered, namely FAMDD for depressive disorder, FAMSUI for substance use disorder, FAMSP for schizophrenia, and FAMSUB for substance use disorder. Global functionality was assessed using the Global Assessment of Functioning Scale (GAS) or the GAS for children (Endicott et al., 1976).
Criteria for participant inclusion and exclusion
In the OBDs (n = 48) and nOBDs (n = 63) groups, subthreshold symptoms were characterized as major depression or hypomania that did not fulfil the DSM-IV criteria for a major depressive episode (MDE) or hypomania due to insufficient symptom count (2–4 for MDE lasting at least seven days and 2–3 for hypomania persisting at least four days) or inadequate duration (less than two weeks for MDE or four days for hypomania). Those with subthreshold symptoms were excluded if they had any DSM-identified psychiatric disorders and/or were taking psychotropic medication. A group of OBDns (n = 62) with parents’ bipolar disorder history and without subthreshold symptoms was also recruited.
Furthermore, a cohort of BD patients (n = 50), selected from a larger sample of 133 patients aged under 20, was incorporated into the study. These patients had maintained clinical stability for a minimum of three months prior to recruitment. In addition, the HC group (n = 86) comprised individuals with no current or prior psychiatric disorders, no first- or second-degree family history of psychiatric disorders, and did not meet the criteria for the defined subthreshold syndrome. The total sample size was 309. The detailed information of demographics were collected in Table 1.
Multimodal MRI acquisition parameters
The MRI images were obtained using a 3.0 T Phillips scanner outfitted with an 8-channel SENSE head coil. Three modalities of MRI images were acquired for all participants, namely T1-weighted image, Diffusion Tensor Imaging (DTI), and resting-state functional magnetic resonance imaging (rsfMRI). The parameters for T1-weighted high-resolution anatomical images included: TR = 8.2 ms, TE = 3.7 ms, FOV = 256 × 256 mm2, voxel sizes = 1 × 1 × 1 mm3, matrix size = 256 × 256, slices = 188, slice thickness = 1 mm, slice gaps = 0 mm, and flip angle = 7 °. Whole brain DTI data was captured through the SE-EPI weighted sequence, and the established parameters included: TR = 6000 ms, TE = 70 ms, FOV = 256 × 256 mm2, Voxel size = 2 × 2 × 2 mm3, Matrix = 128 × 128, Diffusion direction = 32, slices = 75, slice gap = 0 mm, b value = 1000 s/mm2, and flip angle = 90°. The resting-state fMRI data were collected using a gradient echo planar imaging sequence, and the operational parameters were collected: TR = 2000 ms, TE = 30 ms, FOV = 220 × 220 mm2, voxel sizes = 3.44 × 3.44 mm2, matrix size = 64 × 64, slices = 33, slice thickness = 4 mm, slice gap = 0.6 mm, flip angle = 90°, and volumes = 240.
Quality assurance was maintained through rigorous protocol implementation. We excluded images that demonstrated artifacts, insufficient resolution or contrast, motion distortions, missing modalities, or inadequate registration.
Multimodal MRI data analysis
Morphometric measures calculation
The morphometric measures, obtained during the construction of Morphometric Similarity Networks (MSN), characterize the physical attributes of the brain's structures (Seidlitz et al., 2018, 2020). These measures, including volume, thickness, surface area, Gaussian curvature, mean curvature, Fractional Anisotropy (FA), and Mean Diffusivity (MD), were extracted from the structural and diffusion MRI data.
The processing of anatomical MRI data involved intricate preprocessing procedures and stringent quality assurance protocols to enable accurate morphometric analysis. T1-weighted images underwent initial correction for low-frequency bias fields and denoising (Manjón et al., 2010; Tustison et al., 2010), subsequently being processed through the Freesurfer recon-all pipeline (version 7.3) (Fischl, 2012). This protocol enables the construction of cortical surfaces, generating five morphometric features at each vertex: cortical thickness, gray matter volume, surface area, gaussian curvature, and mean curvature. After this step, native surface images were aligned with the standard Conte69-32K template (Van Essen et al., 2012) using the Workbench (https://github.com/Washington-University/workbench).
In parallel, the DTI data were subjected to a comprehensive preprocessing pipeline using the MRtrix3 (Tournier et al., 2019), which included denoising, Gibbs ringing artifacts removal, correction for distortions and head movements, and bias field correction. Following these steps, Fractional Anisotropy (FA) and Mean Diffusivity (MD) maps were derived and co-registered with the T1-weighted images as well as the Montreal Neurological Institute (MNI) template.
The cortical parcellation process was accomplished using the Schaefer 400 parcellation atlas (Schaefer et al., 2018). This atlas comprises 400 parcels, enabling effective integration of structural and functional analysis (Eickhoff et al., 2018). To capture regional morphometric features, the parcellated atlas in the template space (either Conte69 or MNI) was transformed into each participant's native surface or volumetric space, yielding 7 measures for each of the 400 parcels per subject.
Functional connectivity (FC) and structural connectivity (SC) Calculation
Calculations of FC and SC were achieved through meticulous preprocessing procedures and detailed computations (Cruces et al., 2022). The FC estimation involved the preprocessing of BOLD signals, commencing with slice timing correction to address temporal incongruities in slice acquisition times. This phase was followed by motion correction to rectify spatial distortions resulting from participant head movements. The application of ICA-FIX denoising was undertaken to minimize non-neural noise (Griffanti et al., 2014). A subsequent nuisance regression controlled for potential confounding factors such as white matter, cerebrospinal fluid, and 24 motion parameters. Band-pass filtering (0.01–0.1 Hz) was applied to focus on frequencies associated with resting-state networks. The data were then projected onto the Conte69 surface for surface-based analysis and smoothed using a 10mm kernel to improve the signal-to-noise ratio and mitigate potential effects of inter-individual anatomical variability.
SC estimation involved a comprehensive preprocessing and computation protocol for T1-weighted and DTI data (Tournier et al., 2019). T1-weighted images were processed to remove non-brain tissue and for gray matter parcellation. DTI data were subjected to denoising, Gibbs ringing artifacts removal, correction for distortions and head movements, and bias field correction. These collective preprocessing steps facilitated the extraction of whole brain masks, and the estimation of diffusion tensors at each voxel, allowing for the derivation of fractional anisotropy (FA) and axial diffusivity (AD) maps, among other measures. Anatomically constrained tractography (ACT) was employed, requiring five-tissue-type (5TT) segmented images generating from T1-weighted image for each subject. Fiber orientation distributions (FOD) were estimated from DTIs, and probabilistic tractography was performed to yield 10 million streamlines per subject. The fiber-tracking data were subsequently filtered to identify an appropriate cross-section multiplier for each streamline.
The Schaefer 400 parcellation atlas was utilized to construct FC and SC matrices. FC matrices were built from the mean time series for each region, excluding negative correlations to minimize potential spurious anticorrelations. SC matrices were derived based on the number of streamlines connecting the designated regions.
Graph measures of FC and SC
The computational exploration of complex networks involves the application of various graph-theoretic measures to encapsulate the unique properties of network nodes and their interrelations. Leveraging the BCT package (Bullmore & Sporns, 2012; Rubinov & Sporns, 2010), we computed these measures on connectivity matrices, focusing on both regional and global aspects. The collective deployment of these measures provides a robust toolkit to probe the intricate structural and functional properties of diverse networks (Hansen et al., 2022). Furthermore, they capture critical aspects of network topology, mirroring the delicate balance between segregated and integrated information processing within the brain, thereby furnishing a comprehensive depiction of functional and structural brain networks.
Regional measures predominantly concentrate on individual nodes and their immediate vicinity, encapsulating the local features of the network. They include degree centrality, which quantifies the number of direct connections a node possesses, thereby denoting its immediate influence within the network. The clustering coefficient is another such measure, assessing the extent to which a node's neighbors are interconnected, hinting at the potential for formation of closely-knit communities. Local efficiency, a complementary measure, evaluates the proficiency of information exchange within a node's immediate vicinity. Further, betweenness centrality acts as an indicator of a node's significance with respect to the shortest paths passing through it, thus underscoring its control over information flow within the network.
In contrast, global measures offer a holistic perspective of the network's characteristics. The characteristic path length, a foundational measure, calculates the average shortest path length between all pairs of nodes, signifying the network's overall navigability. Global efficiency, inversely, assesses the smoothness and swiftness of information transfer throughout the network. Modularity indicates the degree to which the network can be partitioned into distinct communities or modules. In our study, the regional and global measures were computed interhemispheric for FC and separately for each hemisphere of SC due to potential inaccuracies in estimating interhemispheric connections.
GLMNET multinomial classification
GLMNET, situated within the Generalized Linear Model (GLM) framework, excels in both regression and classification tasks (Tay et al., 2023). Its strength derives from the combined use of Lasso (L1) and Ridge (L2) regularizations, which adeptly manage the challenges of high-dimensionality and multicollinearity. This ensures that complications from interrelated predictor variables are mitigated. Particularly noteworthy is GLMNET's proficiency in multinomial classification, which models relationships between a response variable and multiple predictors, especially when outcomes exceed two. This capability facilitates the categorization of intricate, multivariate datasets. Moreover, the L1 regularization promotes robust feature selection, emphasizing only pivotal predictors. This not only streamlines interpretation but also controls model complexity, preventing overfitting.
In our study, we classified 309 subjects into five groups, subsequently all the subjects were divided into the training and testing sets at an ratio of 80:20. We harnessed grid searching and 10-fold cross-validation via Caret to optimally tune the alpha and lambda parameters. Through L1 regularization, GLMNET excels in managing a high-dimensional feature space, differentiating key predictors from unnecessary ones, enhancing both the predictive strength and model interpretability.
Understanding the efficacy of integrating MRI features with traditional diagnostic methods can revolutionize early intervention strategies for at-risk adolescents. By enhancing the diagnostic precision, this study holds potential to pave the way for timely and targeted treatments, ultimately improving the prognosis and quality of life for those afflicted with BD.
Comprehensive GLMNET model
The comprehensive model encompassed all the imaging and behavioral features. The feature selection via GLMNET aimed to identify the most predictive variables from a myriad of morphometric measures, graph measures, and behavioral attributes. These include morphometric Measures: Area, thickness, volume, mean curvature, Gaussian curvature, fractional anisotropy, and mean diffusivity. Graph Measures: Degree centrality, clustering coefficient, local efficiency, betweenness centrality, characteristic path length, global efficiency, and modularity derived from FC and SC. Behavioral Characteristics: HAMD, HAMA, YMRS, BPRS, GAS, and familial history variables (PBD, PDD, PSP, PSUB, FAMDD, FAMSP, FAMSUB), as well as age, gender, brain volume, and education years.
Clinical diagnosis GLMNET model
In clinical settings, mental disorders are often diagnosed based on clinical interviews and psychological assessments. Drawing from this, the first model was mainly focused entirely on the behavioral attributes, excluding morphometric and graph measures for the brain. This model represented the traditional diagnostic approach, enabling us to gauge how clinicians' interview-based assessments might compare with models incorporating MRI data.
MRI-based GLMNET model
The MRI-based model was exclusively focused on morphometric and graph measures from multimodal MRI data, omitting behavioral attributes and family history. These include morphometric measures: area, thickness, volume, mean curvature, Gaussian curvature, fractional anisotropy, and mean diffusivity; Graph Measures: degree centrality, clustering coefficient, local efficiency, betweenness centrality, characteristic path length, global efficiency, and modularity derived from FC and SC. This model could provide insights into the predictive power of anatomical and network features in isolation, elucidating the added value of behavioural data.
By contrasting the clinical diagnosis, MRI-based, and comprehensive models, we tried to gain a richer understanding of the relative importance of MRI and behavioral data. This deepened the interpretability and relevance of the models we craft.
Cross validation of the GLMNET models
To examine the robustness and reliability of GLMNET models, a cross-validation strategy was employed in the current study. For these three models, we used the same one-time split of subjects into an 80:20 training and testing set ratio. Recognizing the limited insights this provided, we enhanced our method by randomly splitting the subjects 100 times to perform systematic cross-validation. In each iteration, the model was trained on the selected 80% of data, and its predictive accuracy evaluated on the remaining 20%. This process was conducted for all three models, bolstering the credibility of their performance, reducing potential overfitting, and improving the reliability of our findings.
Structural equation modelling
To probe the interplay between observed variables and latent constructs, and the dynamics among the latent constructs themselves, we employed a structural equation modelling (SEM) approach using the lavaan package in R. Two distinct latent constructs were delineated: Psychiatric Symptoms and Brain Health. The manifest indicators constituting the Psychiatric Symptoms latent construct encompassed the BPRS, HAMA, HAMD, and YMRS. Meanwhile, the Brain Health latent construct was defined by the top 20 MRI features, which had been ranked according to L2-norms in the GLMNET coefficients. The regression schema was articulated as follows: the variable Clinical Diagnosis was predicated upon the Parental BD History and Psychiatric Symptoms. The Brain Health latent construct was regressed on the Psychiatric Symptoms latent construct, Clinical Diagnosis, parental BD history, and GAS. The SEM was subsequently fitted to the dataset in order to derive path coefficient estimates and to gauge the adequacy of the model fit, with the Maximum Likelihood estimation method being employed for this purpose.
Independent validation using external data
To enhance the robustness of our comprehensive GLMNET model, we performed an independent validation using an external dataset from the Affiliated Nanjing Brain Hospital of Nanjing Medical University. This external dataset was comprised exclusively of BD patients (n = 40, age = 17.6 ± 2.01) and HC (n = 34, age = 18.21 ± 1.70), reflecting a common limitation in psychiatric research where data from other conditions are less accessible. The detailed information of demographics and methodology can be found in Supplementary Materials.
The validation dataset encompassed all the measures of morphometric measures and graph measures derived from FC and SC, with the exact same processing procedures like the exploring dataset. However, education years, GAS scores and familial psychiatric history were not included in this dataset due to the limitation of the data. The validation process involved logistic regression analysis, utilizing the coefficients from the comprehensive GLMNET model to maintain consistency. This approach was critical in evaluating the model's predictive validity and generalizability to an external cohort, thereby ensuring that its performance was not an artifact of overfitting to the original dataset.