Rare diseases in children can affect not only the child's health but also the well-being and relationships within the entire family. Parents often experience stress, uncertainty, and emotional strain, which may in turn influence their child's mental health and quality of life. However, little is known about how families adapt over time to living with a rare disease or how daily experiences and family interactions shape this process.

This study aims to better understand how children with rare diseases and their caregivers adjust psychologically and emotionally over time. It will examine how factors such as parental stress, uncertainty, coping strategies, and family communication are linked to the mental health and quality of life of both children and parents.

The study will include children and adolescents (ages 1-18) with a diagnosed rare disease and their caregivers. Participants will complete online questionnaires at four time points over one year. A subgroup of families will also take part in a two-week smartphone-based assessment, where parents report their daily experiences, such as stress, emotions, and worries, several times per day. Some children and adolescents will additionally participate in interviews to share their own perspectives.

The main outcomes of interest are the child's mental health and quality of life. The study will also assess parental well-being and family functioning to understand how these factors influence each other over time.

By combining long-term and daily data, this study will provide a detailed picture of how families cope with rare diseases in everyday life. The findings may help improve psychological support and guide the development of targeted interventions for families affected by rare pediatric conditions.

Rare diseases (RDs) are chronic conditions that often begin in childhood and can have lifelong consequences for affected individuals and their families. In addition to physical health challenges, families frequently face significant psychological and social burdens, including stress, uncertainty about the future, and disruptions in daily life. While prior research has mainly focused on medical aspects of rare diseases, less is known about how families adapt over time and how interactions between children and their caregivers influence psychological outcomes.

This study is based on a theoretical model of family adaptation that integrates individual, relational, and contextual factors. In particular, it focuses on cognitive and emotional processes such as intolerance of uncertainty, illness perceptions, and coping strategies, as well as family-level processes including communication, parenting, and shared experiences of illness ("we-disease"). The study adopts a systemic perspective, recognizing that the well-being of children and caregivers is interdependent and evolves over time.

The project uses a longitudinal design with four assessment waves over a 12-month period, complemented by annual follow-ups. This design allows for the investigation of both stability and change in psychological adjustment. Data will be collected using standardized, validated questionnaires assessing mental health, health-related quality of life, stress, and family functioning. To better capture the child's perspective, a subset of children and adolescents will participate in structured interviews at each time point.

In addition to the longitudinal component, a subgroup of families will participate in an Ecological Sampling Method (ESM) phase. During this two-week period, caregivers will report multiple times per day on their current emotional state, stress levels, worries, perceived uncertainty, and coping responses using a smartphone application. This intensive data collection approach enables the examination of short-term, real-life dynamics and within-person fluctuations that cannot be captured through traditional survey methods.

The study will apply advanced statistical methods to analyze both longitudinal and intensive repeated-measures data. Actor-Partner Interdependence Models (APIM) and related approaches will be used to examine reciprocal relationships between child and caregiver outcomes over time, while multilevel modeling will be used to analyze daily processes captured in the ESM phase. By integrating these approaches, the study aims to identify both long-term adaptation patterns and short-term mechanisms that contribute to psychological adjustment.

The overall goal of the project is to generate a comprehensive understanding of how families adapt to pediatric rare diseases, including identifying risk and protective factors at the individual and family level. The findings are expected to inform the development of targeted psychosocial interventions, improve clinical support for affected families, and contribute to a more holistic approach to rare disease care that addresses both medical and psychosocial needs.

Inclusion Criteria:

For children and adolescents:

• Diagnosed with an RD listed in Table 2.
• Age between 8 and 18 years.
• Sufficient knowledge of the German language.
• Declaration of informed consent must be signed by at least one legal guardian for all participants under 18; adolescents aged 14 - 17 additionally provide their own written consent.
• Lives at home (defined as sleeping inside of the home for more than four days per week, including weekends).

For parents:

• The child is affected by an RD listed in Table 2.
• The child's age is between 1 and 18 years.
• Sufficient knowledge of the German or English language.
• Availability of the signed declaration of informed consent.
• Only one child with a diagnosed RD.
• Up to two caregivers may participate per child. A stepparent may be included if they reside with the child, defined as spending at least three nights per week (including weekends) in the same household.
• Requirement ESM: Child lives at home (defined as sleeping inside of the home for more than four days per week, including weekends).

Exclusion Criteria:

For children and adolescents:

• The child is affected by an RD other than listed in Table 2.
• Age under 8 or over 18 years.
• Not sufficient knowledge of the German language.
• Lack of informed consent from at least one legal guardian (required for all participants under 18); and, for adolescents aged 14 - 17, absence of adolescent's own written consent.
• Lives outside of the home (defined as sleeping outside of the home for more than three days per week, including weekends).
• Cognitive impairment.

For parents:

• The child is affected by an RD other than listed in Table 2.
• The child's age is under 1 or over 18 years.
• Not sufficient knowledge of the German nor English language.
• Declaration of informed consent not signed.
• More than one child with a diagnosed RD.
• Requirement ESM: Child lives outside of the home (defined as sleeping outside of the home for more than three days per week, including weekends).

The study population consists of families (children/adolescents and their caregivers) affected by a pediatric rare disease. Participants are recruited through two primary sources:

• Clinical Source: Patients and their families are identified and recruited through supervising physicians at the University Children's Hospital Zurich, Switzerland.
• Community Source: Families are also reached via patient organizations dedicated to rare diseases, using their mailing lists and communication channels.

The population includes children and adolescents across various functional statuses (primarily somatic vs. primarily cognitive limitations) to capture a broad spectrum of family adaptation processes. Recruitment is focused on German-speaking families (with English as an additional option for caregivers) who reside at home, ensuring that the collected data reflects daily family life and relationship dynamics in a natural setting.

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