The recent study on Major Depressive Disorder (MDD) has revealed a fascinating insight into the biological distinctions between its subtypes. The research, which has yet to undergo peer review, introduces an immunometabolic framework to address the diagnostic discrepancy in MDD. This framework highlights the existence of two distinct forms of MDD, each with its own unique set of energy-related symptoms (AERS).
One subtype, AERS+, is characterized by hypersomnia (excessive sleepiness) and weight gain. Interestingly, this subtype is not solely defined by BMI, but also exhibits higher recurrence, more severe functional impairments, earlier onset, and a higher prevalence of comorbidities. The genetic analysis revealed 27 genome-wide loci associated with AERS+, including a gene linked to BMI and MDD, as well as a non-coding RNA associated with cortical inhibitory neurons.
In contrast, AERS- is associated with insomnia and weight loss. This subtype is linked to 'favorable' metabolic traits, such as a gene variant associated with smaller waist circumference. Interestingly, AERS- is also associated with a reduced risk of type 2 diabetes and a possible link to schizophrenia, suggesting a shared mechanism via gene regulation. The genetic analysis identified 10 loci associated with AERS-.
The Uncategorized MDD subtype, which represents a mix of AERS+ and AERS-, was also analyzed. This subtype exhibited a partially distinct genetic architecture, with 13 loci identified. The study further revealed a positive genetic correlation between AERS+ and metabolic markers, including BMI, waist circumference, metabolic syndrome, type 2 diabetes, and blood glucose. Conversely, these traits are negatively correlated with AERS-.
The researchers also found correlations between AERS- and anorexia nervosa, as well as between AERS+ and ADHD, hypertension, and coronary heart disease. AERS+ was also negatively correlated with 'good' HDL cholesterol and positively correlated with C-reactive protein, an inflammatory marker associated with MDD. These findings suggest that AERS+ may be linked to impaired cholesterol transport, insulin resistance, and a pro-inflammatory state, increasing the risk of cardiovascular diseases.
In summary, this study highlights the meaningful differences in genetic architecture between MDD subtypes. It also emphasizes the role of immunometabolic factors in modifying MDD subtypes without directly causing them. The findings suggest that disruptions in homeostasis may impair energy management, leading to symptoms such as appetite, weight, and sleep issues. This research provides valuable insights into the inconsistent symptoms and comorbidities associated with MDD, offering new perspectives on its study and treatment.
