Background: Attention-deficit/hyperactivity disorder (ADHD) is a common neuro-developmental disorder that often persists into adulthood. Moreover, it is frequently accompanied by bipolar disorder (BD) as well as borderline personality disorder (BPD). It is unclear whether these disorders share underlying pathomechanisms, given that all three are characterized by alterations in affective states, either long or short-term. BD is characterized by infrequent but intense mood shifts, while ADHD and BPD involve more dynamic emotional fluctuations. It is yet to be determined whether these disorders represent distinct phenomena or different points on a spectrum of affective dysregulation.

Methods: This study seeks to distinguish the emotional dysregulation of BPD, ADHD, and BD by using digital phenotyping, a measurement burst electronic-diary method with different sampling rates, and accelerometry to measure participants' activity. Our study will include 480 participants aged 14 to 50 (120 each from BPD, ADHD, BD, and healthy control groups) from five European sites. Participants' smartphones will provide continuous data on their digital phenotypes, i.e., by indicators of physical activity and communication, for one year, along with daily evening ratings of mood and sleep. Moreover, five intensive measurement periods of five days each, called measurement bursts, will occur throughout the year, with electronic diaries asking participants to report on mood, self-esteem, impulsivity, life events, social interactions, and dysfunctional behaviors ten times a day. Moreover, participants will wear activity sensors during the five measurement bursts. Statistical analysis aims to identify whether affective dysregulation aspects share or differ across disorders. Specifically, data analysis aims to investigate the differences in parameters of affect fluctuation such as attractor strength and variability between disorders and to test the association of genetic risk factors for psychiatric disorders and resilience factors with critical parameters of affect modulation.

Discussion: The results of this study offer the potential to link patients' external exposures with their affective state, reduce misdiagnosis, and determine the best timing for therapeutic interventions. Potential limitations of the study include insufficient recruitment of patients and drop-outs due to various protocol violations.

Trial registration: Study code: DRKS00028917, registered 27.07.2022, https://drks.de/search/de/trial/DRKS00028917 .