Xmas breaks give me some time to catch up on my reading… and one paper really stood out

The quieter rhythm of the Xmas break often gives me space to step back from day-to-day clinical work and reconnect with the research. This year, one paper that particularly caught my attention is a newly published longitudinal study by Sharp and colleagues (2026) examining how self and interpersonal functioning develop across childhood—and how these trajectories may point to a core pathway toward personality pathology in late adolescence and early adulthood.

For clinicians, parents, and educators who work with young people, this study has important implications, especially when we think about early identification, prevention, and the kinds of supports that truly make a difference over time.

Why this study matters

The research is grounded in the Alternative Model for Personality Disorders (AMPD), which proposes that difficulties in:

• Self-functioning (identity, self-direction, sense of self), and

• Interpersonal functioning (empathy, intimacy, relationships)

form the core of personality pathology, rather than personality disorders being defined only by outward behaviours or symptoms.

While this idea has been influential, there has been surprisingly little long-term developmental evidence to support it—until now.

A rare long-term developmental lens

Sharp et al. drew on data from the Preschool Depression Study, following children for 17 years, from early childhood into late adolescence. This kind of prospective, multi-wave dataset is rare and incredibly valuable.

Some key features of the study:

• Self-functioning was tracked from early childhood (around age 4.5) through early adolescence.

• Interpersonal functioning was measured from around age 8 onward.

• Personality pathology in later adolescence was assessed using validated measures of borderline personality features.

• Importantly, analyses controlled for internalizing symptoms (e.g., anxiety, depression) and externalizing symptoms (e.g., impulsivity, aggression).

The central finding: self-functioning stands out

When self- and interpersonal functioning were examined separately, both showed associations with later personality pathology. However, when they were examined together in more rigorous multivariate models, a clear pattern emerged.

Trajectories of self-functioning—not interpersonal functioning—uniquely predicted later personality pathology, even after accounting for internalizing and externalizing problems.

In other words, difficulties related to:

• a coherent sense of identity

• self-understanding

• goal direction

• emotional continuity

appear to form a distinct developmental pathway toward personality disorder features.

This challenges a common assumption that problematic relationships are always the primary early warning sign. Instead, relational difficulties may often be downstream from more fundamental struggles with the self.

Clinical implications: shifting our early focus

From a child psychology and prevention perspective, these findings are significant.

They suggest that early intervention should pay closer attention to:

• how children understand themselves,

• how stable or fragmented their sense of identity feels,

• whether they experience themselves as agentic and purposeful,

• how they make sense of emotions and internal experiences.

Notably, these vulnerabilities may exist even when children do not meet criteria for anxiety, depression, or behavioural disorders. This may help explain why some young people “fly under the radar” in childhood but struggle significantly later on.

What about interpersonal functioning?

Interpersonal difficulties certainly still matter. Relationships are often where distress becomes visible—conflict, withdrawal, intense attachments, or social instability. However, this study suggests that such difficulties may not be the primary engine of personality pathology development.

Instead, they may reflect deeper challenges in self-organization that have been unfolding quietly for years.

Implications for internationals and families living abroad

There are some particularly important considerations here for international families and young people growing up outside their country of origin.

Living abroad can be enriching, but it can also place unique pressures on developing self-functioning:

• identity formation across cultures,

• navigating multiple languages, values, and social norms,

• repeated transitions, relocations, or school changes,

• feeling “in-between” cultures or not fully belonging to any one group.

For some children and adolescents, these experiences can complicate the development of a stable and coherent sense of self—especially if emotional support systems are disrupted or inconsistent.

This research highlights the importance of:

• providing continuity in emotional support during transitions,

• explicitly supporting identity development in bicultural or multicultural contexts,

• not assuming that relational competence alone indicates healthy development,

• paying attention to how internationally mobile young people describe who they are and how they see themselvesover time.

For clinicians working with expatriate or internationally mobile families, a developmental focus on self-functioning may be particularly protective.

Looking ahead: prevention and early intervention

Sharp and colleagues’ findings strengthen the argument for:

• developmentally informed models of personality,

• earlier, preventative interventions that focus on self-concept and emotional integration,

• moving beyond symptom checklists toward deeper developmental understanding.

At Baumgarten Child Psychology and More, this aligns closely with our emphasis on early, relationally attuned, and developmentally grounded work—supporting children and adolescents not just in what they do, but in how they experience themselves.

The Xmas break reading has been time well spent.

Reference

Sharp, C., Dong, F., Boone, K., Gilbert, K. E., Tillman, R., Barch, D. M., Luby, J. L., & Whalen, D. J. (2026).Do trajectories of self- and interpersonal functioning identify a core underlying developmental pathway for personality pathology in late adolescence and early adulthood?Journal of Psychopathology and Clinical Science, 135(1), 9–24.https://doi.org/10.1037/abn0001044