For most of their lives, people born with autosomal dominant hypocalcemia type 1 (ADH1) have had exactly one option: swallow calcium pills and vitamin D supplements every day and hope the numbers stay close enough to normal. The supplements never fix the underlying genetic defect. They just push calcium into the bloodstream while often driving too much of it into the urine, raising the risk of kidney stones and long-term kidney damage. There has been no approved drug for ADH1, and no controlled trial had ever shown that a targeted therapy could reliably normalize calcium in these patients.
That gap started to close in October 2025, when BridgeBio Pharma disclosed results from its Phase 3 CALIBRATE trial showing that an experimental oral drug called encaleret restored normal blood calcium levels in 76 percent of adults with ADH1 after 24 weeks of treatment. Now, as of June 2026, the rare-disease community is watching to see whether those results translate into a regulatory filing and, eventually, the first approved therapy for the condition.
What the trial showed
CALIBRATE (NCT05680818) was a randomized, open-label study that compared encaleret to standard-of-care calcium and vitamin D supplementation in adults with genetically confirmed ADH1. According to BridgeBio’s SEC Form 8-K filing dated October 29, 2025, 34 of 45 patients on encaleret hit the primary endpoint: serum calcium within a target range of 8.3 to 10.7 mg/dL alongside acceptable urine calcium levels. None of the patients on standard of care met the same threshold, a contrast that underscores how poorly conventional management controls the disease.
The biology behind the result matters. ADH1 is caused by gain-of-function mutations in the calcium-sensing receptor gene (CASR). Those mutations make the receptor behave as if calcium is too high even when it is dangerously low, suppressing parathyroid hormone and forcing the kidneys to dump calcium into the urine. Encaleret is a calcilytic, a small molecule that turns down the volume on that overactive receptor so the body’s own calcium-regulating machinery can work closer to the way it should. Earlier Phase 2b data, published in the New England Journal of Medicine under trial identifier NCT04581629, had already demonstrated that encaleret could shift both serum and urinary calcium in the right direction. CALIBRATE confirmed that effect in a larger, controlled setting.
A broader shift in rare calcium disorders
Encaleret’s progress does not exist in isolation. In August 2024, the FDA approved YORVIPATH (palopegteriparatide), a long-acting parathyroid hormone analog developed by Ascendis Pharma, as the first approved treatment for chronic hypoparathyroidism in adults. Hypoparathyroidism is a separate condition from ADH1, most often caused by surgical damage to the parathyroid glands rather than a genetic mutation, but it shares the central problem of chronically low blood calcium and reliance on the same inadequate supplement regimen.
YORVIPATH’s approval rested on the PaTHway Phase 3 trial (NCT04701203), a 26-week randomized, double-blind, placebo-controlled study. Its composite primary endpoint required patients to normalize calcium while becoming independent from active vitamin D and high-dose calcium supplements. Peer-reviewed results published in the Journal of Bone and Mineral Research documented that efficacy, and a subsequent 52-week analysis in the Journal of Clinical Endocrinology and Metabolism showed the benefit held over a longer period with a well-characterized safety profile.
Together, these two programs represent something new: the first time targeted therapies for distinct rare calcium disorders have produced strong controlled-trial evidence within a roughly two-year span. For a patient community that spent decades with nothing beyond supplements, the pace is striking.
What is still missing
Promising as the CALIBRATE numbers are, several important pieces remain incomplete as of mid-2026.
No peer-reviewed publication yet. The 76 percent response rate comes from a company securities filing, not a full manuscript with detailed efficacy tables, adverse-event breakdowns, or subgroup analyses. The ClinicalTrials.gov record lists additional endpoints, including patient-reported outcome scores and data on hospitalizations and fractures, but those results have not been posted or published. Until independent reviewers and journal editors scrutinize the complete dataset, the headline number stands on BridgeBio’s own accounting.
Open-label design. Unlike PaTHway, which used placebo control and double-blinding, CALIBRATE compared encaleret to standard of care without blinding investigators or patients. Open-label designs are common and often ethically necessary in ultra-rare diseases, and the FDA has accepted them as the basis for approval in other rare conditions such as enzyme replacement therapies. Still, they can inflate perceived benefit. Doctors may titrate doses more aggressively when they know a patient is on the experimental drug, and patients may report symptoms differently when they know what they are taking. The objective lab-based primary endpoint (serum and urine calcium) mitigates some of that concern, but subjective outcomes will need closer scrutiny.
Safety details are thin. Phase 2b data suggested encaleret was generally well tolerated, but longer-term effects on bone density, kidney function, and cardiovascular markers will only become clear with more complete reporting. YORVIPATH’s published data, by contrast, already include detailed safety tables covering rates of hypercalcemia and injection-site reactions across a full year of follow-up.
Prevalence is hard to pin down. ADH1 is recognized as rare, but published registry or claims-based analyses confirming exact patient counts are limited. Estimates in the medical literature range widely, and company-cited figures in investor materials have not been independently verified. That uncertainty matters because it shapes how payers and regulators assess the drug’s public health significance, influencing pricing, coverage decisions, and the willingness to fund post-approval safety registries.
What comes next for patients
BridgeBio has indicated it intends to seek FDA approval for encaleret, though the company had not disclosed a specific submission date as of its most recent public filings. Several questions will determine how quickly the drug reaches patients if it is approved.
Regulatory pathway is one. The FDA granted encaleret Breakthrough Therapy designation, which provides more intensive agency guidance and can accelerate review timelines. Whether BridgeBio files a standard New Drug Application or pursues an accelerated pathway will depend in part on how the agency views the open-label data and whether it requests additional information.
Cost and access are another. YORVIPATH’s launch offered a preview of the pricing dynamics in rare calcium disorders: specialty therapies for small patient populations typically carry high list prices, and insurance coverage can be uneven, particularly in the early months after approval. For ADH1 patients, many of whom have managed their condition with inexpensive over-the-counter supplements for years, the transition to a branded specialty drug will raise practical questions about copays, prior authorization, and long-term affordability.
Pediatric data are also on the horizon. ADH1 is a genetic condition present from birth, and children with the disorder face the same risks of kidney damage and poor calcium control. Whether encaleret is safe and effective in younger patients is a question that clinical development will need to answer.
How to weigh the evidence right now
Readers comparing these two programs should keep the evidence gap in perspective. YORVIPATH’s data have passed through multiple layers of independent review: a peer-reviewed pivotal publication, a peer-reviewed extension study, an FDA review package, and posted results on ClinicalTrials.gov. Encaleret’s Phase 3 data have not yet cleared any of those checkpoints beyond the company’s own SEC disclosure and the earlier Phase 2b journal publication.
That asymmetry does not mean encaleret’s results are unreliable. Securities filings are legally constrained documents, and companies face penalties for materially misleading statements. But topline disclosures are curated by nature: they spotlight primary endpoints and favorable measures while less flattering details may surface only in full manuscripts or regulatory review documents. The prudent read is to treat the 76 percent normalization rate as genuinely promising but provisional until the full dataset is published and independently reviewed.
For patients with ADH1, the practical signal is clear even with those caveats. A therapy designed to correct the specific molecular defect driving their disease has, for the first time, shown robust benefit in a Phase 3 trial. For those with hypoparathyroidism, YORVIPATH already supports a shift away from lifelong high-dose supplements toward a hormone replacement that more closely mimics normal physiology. And for the rare disease field as a whole, the near-parallel progress of these two programs is a concrete example of what genetically informed drug design and sustained clinical investment can accomplish for conditions that were, until very recently, considered untreatable.
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*This article was researched with the help of AI, with human editors creating the final content.
