A doctor’s visit for a child is usually simple –– a few measurements, a brief conversation, and you’re done. For our family, it was never that straightforward. For years, we took our twin boys to the endocrinologist to monitor the success of their growth hormone deficiency (GHD) treatment. The standard process of measuring height and recording weight was far more complex for us. Because of their cerebral palsy (CP), a type called spastic triplegia, our boys couldn’t stand independently or fully straighten their legs, making the key measurement used to track their progress nearly impossible to capture. Managing both GHD and CP was a vivid reminder that rare diseases don’t exist in isolation. When comorbidities, or in our case true multimorbidities collide, even the most routine aspects of care can become complex challenges for families and providers to navigate.
When Multiple Conditions Intersect
Comorbidity refers to the presence of one condition in conjunction with another, typically secondary to a primary or “index” disease. Multimorbidity goes a step further, recognizing each condition equally rather than one as primary.1
In rare disease, that distinction matters. It changes how care is designed, how success is measured, and how communication is framed. When multiple conditions intersect, families aren’t managing one disease with side effects, they are navigating multiple realities that continuously influence one another.
Recognizing Complexity Early
More people are living with multiple health conditions, often due to aging, environmental factors, and accumulated risks. Research shows that those managing more than one illness face greater challenges and more complex care needs.3 While most studies focus on common chronic diseases, the same lesson applies to rare disease: planning for comorbidities and multimorbidities should be the norm, not the exception.
For families living with rare conditions, recognizing that additional diagnoses may exist is one of the hardest parts. Families often endure long diagnostic journeys, and when multiple conditions overlap, the process becomes even more complex. Shared symptoms can mask additional diagnoses, and specialists may attribute every challenge to a single “index” disease, missing signals of another condition entirely.4
Our boys’ story illustrates this challenge. Born prematurely at 27 weeks gestation and weighing about two pounds each, they faced a cascade of early complications that affected multiple systems including their lungs, heart, endocrine function, and neurological development.5 Cerebral palsy itself is a multisystem condition, affecting not only movement but also respiration, digestion, and bone health.6 Children with CP often exhibit growth abnormalities, and there’s evidence of growth hormone deficiency among the population.7 For our twins, these realities overlapped in ways that were impossible to separate. Managing one condition inevitably affected the other: growth hormone therapy improved height and bone accrual but required even greater vigilance to avoid worsening muscle tightness and contractures from spastic CP.8
Anticipating Coexisting Conditions as a Shared Responsibility
To truly address the lived reality of comorbidity and multimorbidity, healthcare systems must anticipate coexisting conditions rather than react to them. Families rarely have the resources or information to do it alone.9
Integrated care models offer a path forward by coordinating across specialties and reducing the burden of fragmented systems. Frameworks like SELFIE and the World Health Organization’s people-centered models show that anticipating complexity is not only ethical but essential for effective care.11,12
Applying this approach to rare disease means building foresight and collaboration into every stage of care. Clinicians can use shared records and cross-specialty checklists to identify comorbidities early, while hospitals and rare-disease centers develop joint care pathways that bring specialists together. Clinical trials and registries should reflect real-world complexity, capturing how overlapping conditions affect treatment and outcomes. Clear communication, education, and continuous feedback loops can ensure that insights from patients and providers inform research, care models, and support resources, making the system smarter and more responsive over time.
Turning Resistance into Opportunities for Growth
In many ways, “when growth meets resistance” isn’t just the story of my family. It reflects the reality of communicating about rare diseases. As the field grows, it still pushes against resistance: siloed thinking, limited visibility for caregivers, and a tendency to simplify what’s inherently complex. Yet growth happens at the point of resistance. When we lean into that friction by acknowledging multimorbidity, co-diagnoses, and the full picture of patients’ lives, we move closer to true partnership in care.
Recognizing comorbidities in the way we communicate is more than sharing information. It is about building trust. And in rare disease, trust is what transforms education into empowerment, and empowerment into better outcomes.
References:
1 Harrison C, Fortin M, van den Akker M, et al. Comorbidity versus multimorbidity: why it matters. J Multimorb Comorb. 2021;11:1-3.
2 Chowdhury SR, Taneja S, Mutha PK, et al. Global and regional prevalence of multimorbidity: a systematic review and meta-analysis. BMJ Open. 2023;13:e070404.
3 Shiltz NK, Koroukian SM, Warner DF. The prevalence of multimorbidity: implications for health systems and policy. BMC Public Health. 2022;22:412.
4 Briscoe K, Garside R, Lawal H, et al. Evidence of inequalities experienced by the rare-disease community: a global survey analysis. *Front Public Health.* 2025;13:1520211.
5 Zivaljevic J, Jovandaric MZ, Babic S, Raus M. Complications of Preterm Birth-The Importance of Care for the Outcome: A Narrative Review. Medicina (Kaunas). 2024;60(6):1014. Published 2024 Jun 20. doi:10.3390/medicina60061014
6 Dan B, Rosenbaum P, Carr L, Gough M, Coughlan J, Nweke N. Proposed updated description of cerebral palsy. Dev Med Child Neurol. 2025;67(6):700-709. doi:10.1111/dmcn.16274
7 Devesa J, Casteleiro N, Rodicio C, López N, Reimunde P. Growth hormone deficiency and cerebral palsy. Ther Clin Risk Manag. 2010;6:413-418. Published 2010 Sep 7. doi:10.2147/tcrm.s12312
8 Hong, J., Kim, S., Suh, J. et al. Growth hormone treatment in cerebral palsy: long-term impact on growth, outcomes, and complications. Pediatr Res (2025). https://doi.org/10.1038/s41390-025-04440-z
9 Pelentsov LJ, Laws TA, Esterman AJ. The supportive care needs of parents caring for a child with a rare disease: A scoping review. Disabil Health J. 2015;8(4):475-491. doi:10.1016/j.dhjo.2015.03.009
10 Vidic N, McGlynn A, Abdi F, et al. Integrated Care for People Living With Rare Disease: A Scoping Review on Primary Care Models in Organization for Economic Cooperation and Development Countries. Journal of Primary Care & Community Health. 2025;16. doi:10.1177/21501319241311567
11 Leijten FRM, Struckmann V, van Ginneken E, et al. The SELFIE framework for integrated care for multi-morbidity: development and description. *Health Policy.* 2018;122(1):12-22.
12 Rohwer A, Toews I, Uwimana-Nicol J, et al. Models of integrated care for multimorbidity assessed in systematic reviews: a scoping review. BMC Health Serv Res. 2023;23:894.
