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When you look at major depressive disorder (MDD) over time, it does not always show up the same way at every stage of life, and that is where heterotypic and homotypic continuity come into play. Homotypic continuity is when the same symptoms persist over time, while heterotypic continuity is when the core issue persists but manifests differently as a person grows and changes (Speranza et al., 2023). With MDD, homotypic continuity might look like someone experiencing persistent low mood, loss of interest, and fatigue across different stages of life, since depression is characterized by symptoms like tiredness, weight loss, and appetite loss, along with a lack of motivation and emotional distress (Cui et al., 2024). These core symptoms can remain relatively stable over time. For example, a kid might come off as irritable, but as they get older, it might shift into things like pulling away from others or losing motivation.  

Personality also plays a role in how these patterns continue. Certain traits can increase vulnerability to depression, especially when combined with stress. Environmental influences such as adverse life events and high stress levels have been shown to contribute to the development of MDD (Cui et al., 2024). For instance, someone who is more emotionally reactive may be more likely to carry depressive symptoms over time, reinforcing homotypic continuity. Developmental processes also interact with personality and life experiences. As people move through different stages, factors like increased pressure or social stress can influence how depression appears, especially since MDD has been linked to increased life pressure and social stressors that can trigger symptoms (Cui et al., 2024). Research shows that depression can both remain stable over time and change in how it presents across development, reflecting both homotypic and heterotypic continuity (Speranza et al., 2023). Overall, considering both types of continuity makes it easier to understand how MDD can remain consistent in some ways while still changing across the lifespan, depending on personality and development.