Rare Endocrine System Disorders: What the Last Five Years Have Taught Us

By Mila Grieg, MD, PhD (Vice President, Medical Affairs, ACE Therapeutic Strategy Head, Cardiometabolic)

A Field in Motion: Growing Opportunity for Therapeutic Innovation

For biopharma sponsors, scientific clarity, measurable outcomes, and ease of regulatory validation are important factors to consider when developing new therapies. As the industry focus on precision medicine and orphan drug innovation continues to grow, rare endocrine system disorders emerge as a strategically important area for clinical development.

For decades, drug development in rare endocrinology felt like a quiet corner of the industry: small populations, slow timelines, modest pipelines, and a heavy reliance on therapies that had been on the market for thirty years or more. That has changed remarkably quickly.

Between 2020 and 2025, four first-in-class agents reached approval across four different rare endocrine indications:

• Osilodrostat (Isturisa®): a potent oral 11β-hydroxylase inhibitor became the first agent specifically developed for Cushing’s disease and was approved by the FDA in March 2020 and EMA in January 2020, for endogenous Cushing’s syndrome.
• Palopegteriparatide/TransCon PTH (Yorvipath®): a long-acting prodrug of Parathyroid hormone (PTH) became the first true PTH replacement therapy for adults with chronic hypoparathyroidism, with EMA approval in 2023 and FDA approval in August 2024.
• Crinecerfont (Crenessity®): a selective oral corticotropin-releasing factor type 1 (CRF1) receptor antagonist was approved by the FDA in December 2024 as the first new treatment for classic congenital adrenal hyperplasia (CAH) in approximately 70 years.
• Paltusotine (Palsonify®): a once-daily oral non-peptide somatostatin receptor type 2 agonist became the first oral therapy for acromegaly when the FDA approved it in 2025 and EMA in 2026.

High Unmet Need Meets Strong Development Potential: Defined Mechanistic Pathways, Biomarker-Driven Monitoring, and Protocol Considerations

Although rare endocrine system disorders individually affect a relatively small population, they are an area of significant unmet need, chronic health impact, and growing opportunity. With identifiable pathways of action and quantifiable biomarkers to determine composite endpoints, as well as regulatory incentivization of rare diseases, these disorders are a potentially high-impact area for research.

Endocrine disorders generally follow well-defined, identifiable physiological pathways. Unlike other disease areas where there are more complex or poorly understood mechanistic pathways, these disorders are often associated with specific hormone/biomarker imbalances, well-understood physiological pathways, receptor dysfunction, or single-gene mutations. In these diseases, the underlying mechanism is recognizable, making it easier to identify the therapeutic interventions that might be most effective. However, pure biochemical endpoints (an isolated hormone level, for example) are increasingly viewed by regulators as insufficient evidence of clinical benefit; they want to see that biochemistry translates into something the patient can feel.

Acromegaly

Acromegaly is a rare endocrine disorder usually caused by excess production of growth hormone (GH) from a pituitary adenoma, resulting in elevated levels of insulin-like growth factor-1 (IGF-1). The disease is diagnosed by the elevated level of GH and IGF-1 and has an estimated prevalence of 50-70 persons per million. Despite this, acromegaly is still grossly underdiagnosed because onset symptoms such as fatigue, soft tissue enlargement, and joint pain can also be attributed to aging and other factors.

Protocol Design Considerations: When developing therapies for acromegaly, several protocol design considerations must be carefully addressed. Protocols should incorporate thoughtful patient stratification, balance complex GH sampling requirements with visit duration and site burden, ensure consistent tumour volume assessment via centralized blinded MRI core labs, and plan for large, multinational study designs to support effective patient recruitment.

Cushing’s Disease

Cushing’s disease is characterized by increased adrenocorticotropic hormone (ACTH) production from the anterior pituitary gland, resulting in excess cortisol secretion. It is commonly caused by benign pituitary adenomas and/or the excessive production of corticotropin-releasing hormone (CRH) from the hypothalamus and diagnosed through elevated cortisol levels measured via urinary, salivary, or serum testing alongside ACTH measurements and pituitary MRI.

Cushing’s disease is rarer still, with an annual incidence around 0.2-5 per million. Endogenous Cushing’s syndrome remains a heterogeneous category including pituitary, adrenal, and ectopic causes, making careful eligibility criteria essential. Historically managed through surgery and broad hormonal suppression, development is increasingly shifting toward selective inhibitors and targeted pathway modulation.

Protocol Design Considerations: There are certain operational and patient safety aspects to be considered when designing study protocols for Cushing’s disease. Protocols for Cushing’s disease should incorporate clear washout and biochemical stabilization criteria, balance operationally intensive cortisol sampling strategies with feasibility considerations, ensure accurate biomarker quantification through appropriate patient training and centralized labs, include robust cardiac safety monitoring, and proactively manage hypocortisolism risk through defined stopping rules and specialized oversight.

Hypoparathyroidism

Hypoparathyroidism is caused by a deficiency or absence of parathyroid hormone (PTH) secretion leading to an impaired regulation of calcium and phosphate and a severe imbalance. The diagnosis is typically confirmed with low or undetectable PTH levels along with co-existing hypocalcemia and supported by other biomarker tests, including serum phosphate and magnesium.

Historically, management involved calcium and active vitamin D supplementation, which corrected hypocalcemia but did not correct the underlying PTH deficiency and could contribute to renal complications. This approach was more centered around minimizing symptoms rather than overall disease management. PTH replacement approaches that aim to restore physiologic regulation are increasingly being developed.

Protocol Design Considerations: For hypoparathyroidism, study protocol design must address the complexity of dose titration with appropriate clinical oversight and rapid lab support, incorporate validated disease-specific PRO measures from the outset, account for long-term renal outcomes as key endpoints, and include etiology-based stratification to manage variability in response and retention.

Congenital Adrenal Hyperplasia

Congenital adrenal hyperplasia (CAH) is a group of autosomal recessive inherited disorders resulting from mutations affecting the pathways of adrenal steroid biosynthesis. Classic CAH due to 21-hydroxylase deficiency was previously treated with supraphysiologic doses of glucocorticoids to suppress ACTH and the excess production of adrenal androgens, often at the cost of growth suppression, obesity, hypertension, and osteoporosis.

CAH is quantified through elevated adrenal steroid precursors such as androstenedione and 17-hydroxyprogesterone. Because the mechanistic pathway is well understood, newer therapies increasingly focus on reducing excess androgen production while minimizing glucocorticoid exposure.

Protocol Design Considerations: CAH studies should account for the added complexity and duration of the two-question design, ensure rigorous multiplicity control across endpoints, standardize diurnal-sensitive biomarker sampling through centralized labs, and incorporate comprehensive adrenal crisis risk mitigation and patient safety measures.

Other Rare Endocrine System Disorders

Several additional rare endocrine disorders share similar protocol-design challenges, including X-linked hypophosphatemia (XLH), tumor-induced osteomalacia (TIO), multiple endocrine neoplasia syndromes (MEN1, MEN2, MEN4), Carney complex, primary aldosteronism, pediatric growth disorders, and adrenal insufficiency/Addison’s disease.

Across these indications, common themes include biomarker-guided dosing, centralized adjudication, long-term safety monitoring, incorporation of natural history data, and increasing use of patient-centered endpoints within clinical development programs.

Evolving Expectations in Rare Endocrine Protocol Design

• Disease-specific patient-reported outcomes (PROs) are no longer optional: These are increasingly becoming essential components of rare endocrine clinical development rather than optional additions. Tools such as the Hypoparathyroidism Patient Experience Scale (HPES) for hypoparathyroidism and the Acromegaly Symptom Diary (ASD) for acromegaly represent years of psychometric validation work. Protocols that rely solely on generic instruments, such as the Short Form-36 Health Survey (SF-36), or attempt to introduce ad hoc symptom scales are now at a significant disadvantage from both regulatory and clinical relevance perspectives.
• Centralized assays are non-negotiable: Inter-laboratory variability for biomarkers such as IGF-1, cortisol, androstenedione, 17-hydroxyprogesterone, PTH, and intact GH can be substantial enough to obscure genuine treatment effects. As a result, the use of a single central laboratory with documented assay performance characteristics, harmonized reference ranges, and pre-validated transport logistics is increasingly considered standard practice.
• Plan for the open-label extension (OLE) as part of the original protocol: OLE studies should now be planned as part of the original protocol design rather than after primary readout. Many rare endocrine therapies reach the market supported by multi-year OLE data, and regulators increasingly expect longitudinal evidence demonstrating long-term safety, durability of biochemical response, and sustained physiologic dosing, particularly for therapies designed to reduce glucocorticoid exposure.

Transitioning from Symptom Control to Precision Therapies

As focus on precision medicine increases, treatment options for rare endocrine system disorders are shifting from broad hormonal treatments and chronic symptom control to precise, mechanism-based therapies that target the root cause. This shift is important because, while traditional approaches have undoubtedly been crucial in managing patient outcomes so far, they can also lead to additional complications due to off-target effects and overcorrection.

This change reflects how drug development for endocrine disease is evolving from symptom management toward disease modification and restoration of hormonal balance. This enables biopharma companies to develop new therapies that are of stronger clinical value.

Regulatory Incentives Enhance Commercial Viability

In terms of regulatory and commercial considerations, many of these disorders qualify for orphan drug incentives, market exclusivity benefits, designated regulatory support as well as fee reductions depending on the location. These frameworks are in place to encourage development for rare diseases in smaller patient populations.

Additionally, patients with these disorders are usually diagnosed and managed by specialist doctors or expert health centers/hospitals. This means that patient care is often concentrated within a small network of experienced healthcare providers. This can improve with patient identification and access during commercial launch, enabling smoother introduction of new therapies to the patients who would benefit most from them.

Future Scope

The drug development landscape for rare endocrine system disorders has shifted, in less than a decade, from a quiet specialty to one of the most scientifically interesting corners of late-stage development. The protocol-design lessons from those four landmark programs are now reusable templates: composite endpoints that pair biochemistry with patient experience, dual-question designs that capture the full value of the mechanism, disease-specific PROs that have done their psychometric homework, and centralized everything: labs, imaging, ECG, and adjudication.

For a CRO that has been running rare endocrine disease trials over multiple years, this trajectory is not abstract. It tells us where sponsors are heading, where regulators have settled on acceptable endpoint structures, and, perhaps most importantly, where protocol design choices make the difference between a study that delivers and one that drags. The question is whether the protocol is designed to walk it efficiently, and whether the operational partner has lived through enough of the indication-specific edge cases to spot them before database lock.

Allucent’s Center of Expertise (ACE) for Cardiometabolic has a dedicated team of cross-functional experts who provide comprehensive support to biopharma sponsors developing therapies for cardiovascular, metabolic, and endocrine conditions. This expertise is further strengthened by Allucent’s broader strategic focus on rare diseases and a team specializing in this, supported through dedicated subject matter experts and operational solutions developed for rare disease clinical trials. From early-phase design to global execution, we help bring first-in-class and best-in-class treatments to patients with speed, precision, and regulatory confidence.

Contact us to speak with Allucent’s team of experts to learn how we can support your rare endocrine disease studies.