Rare genetic diseases are challenging to treat due to their complexity, the unique nature of each condition, and the – by definition – small numbers of patients affected by each one. 

Encouragingly for the rare disease community, the field is moving rapidly with a wide variety of innovative therapies being developed, including gene therapy involving editing genes in situ with tools such as CRISPR, RNA-based therapies, Enzyme Replacement Therapy (ERT) and cell therapy, amongst others. In 2023, more than half of the new drugs approved by the FDA were to prevent, diagnose or treat a rare disease or condition, for which they received an orphan-drug designation. (1)  

Given the expense, risks and timescales involved in R&D, and the small patient populations, companies developing such therapies for rare genetic diseases often target more than one condition, especially when the underlying technology can be applied across different diseases with similar genetic or biochemical pathways.  

So how are decisions made on which conditions to target? 

One key consideration is the current size of the potential patient population, and how that is expected to change in the future. Although rare diseases individually have small patient populations, collectively they represent a significant market. Companies target diseases based on the size and demographics of the affected population, as well as potential pricing and reimbursement scenarios, and the competitive landscape.  

However, determining accurate and reliable figures for rare disease patient populations is very challenging.  As outlined in our recent blog post, methods which utilise large genetic datasets can help give accurate estimates of the true patient population. These estimates can then be used in predictive modelling to quantify the future burden and determine the impact of proposed interventions.  

For early-stage R&D, data on the current and future disease burden can help inform: 

Target identification and prioritization Providing precise prevalence data helps companies identify and prioritize which rare genetic conditions to target. Knowing the exact number of potential patients can justify the investment required for developing treatments. Minimising risks by making data-driven decisions regarding portfolio management from the earliest stages of the drug development lifecycle can bring about significant benefits to pharmaceutical and biotech companies in the long-term. 

Clinical trial feasibility and optimisation Accurate prevalence figures also enable companies to conduct initial feasibility studies for the development of new therapies. Such analyses help determine whether there is a sufficiently large patient base to conduct clinical trials, which is a critical factor given the rarity of some genetic disorders. This is also essential for planning the logistics of trial recruitment and ensuring that there are enough participants to generate statistically significant data. With a clearer picture of the characteristics and demographics of a prospective new therapy’s target population, the recruitment strategies of clinical trials can be optimised so that trial studies better represent the patient population who will ultimately benefit from the therapy being developed. 

Regulatory and funding incentives Many regulatory bodies, such as the FDA and EMA, offer incentives for the development of orphan drugs. Accurate prevalence data is required in the submission process to qualify a condition as rare and thus be eligible for these incentives, which include tax credits, user fee waivers (exemptions granted from paying fees normally required when submitting regulatory filings), and extended market exclusivity upon approval. 

Strategic collaborations and investors Knowing the precise prevalence and future trajectory of a disease can help companies in their discussions on strategic partnerships and collaborations, and engaging with investors, as this is critical to informing the commercial opportunities. Reliable and credible data can support partnership discussions with academic institutions, patient advocacy groups, other commercial collaborators, and investors, with regard to sharing the financial and technological commitment required to develop treatments for rare diseases. 

Patient identification and registry creation Genetic databases facilitate the creation of patient registries, which are critical for rare disease research. Registries help in identifying patients who might benefit from new therapies and can be essential for long-term follow-up and post-marketing surveillance required by regulatory agencies. 

Patient advocacy groups Engaging with patient advocacy groups can provide insights into patient needs and help in recruiting participants for clinical trials. These groups can also be influential in advocating for drug development for specific conditions. Providing accurate data on the current and future patient population is important for supporting these advocacy programs. 


HealthLumen is committed to supporting organisations at every step of the development lifecycle from R&D through to market access, applying our innovative precision epidemiology to determine the current and future disease burden.

The next events we are attending are the RWE, Market Access, Pricing and Reimbursement Global Congress Europe and the 12th European Conference on Rare Diseases and Orphan Products.

Do reach out to us if you are planning to attend and would like to schedule a meeting, or if you would like to learn more about any of the issues covered in this article. 


  1. FDA Approves Many New Drugs in 2023 that Will Benefit Patients and Consumers

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