TransCon PTH
Market Opportunity in Hypoparathyroidism
Hypoparathyroidism is a rare endocrine disease characterized by insufficient levels of parathyroid hormone
(“PTH”). Most patients with hypoparathyroidism develop the condition following damage to or accidental
removal of the parathyroid glands during thyroid surgery. Post-surgical hypoparathyroidism accounts for the
majority of cases (70-80%); other etiologies include autoimmune disorders, genetic disorders such as
autosomal dominant hypocalcemia type 1 (“ADH1”), and idiopathic causes. Conventional therapy with oral
calcium and active vitamin D (also called calcitriol) does not effectively address the short-term symptoms, long-
term complications, or quality-of-life impacts of hypoparathyroidism.
Short-term symptoms include weakness, severe muscle cramps (tetany), abnormal sensations such as
tingling, burning and numbness (paresthesia), memory loss, impaired judgment, and headache. Patients often
experience decreased quality of life, and, over the long term, prolonged use of conventional therapy may
increase risk of major complications, such as calcium deposits in the brain, blood vessels, eye, and other soft
tissues. According to a recent systematic literature review, chronic hypoparathyroidism treated with
conventional therapy is associated with higher rates of renal complications compared to the general
population, such as nephrolithiasis (up to 36%), nephrocalcinosis (up to 38%), and chronic kidney disease (up
to 41%). Hypoparathyroidism remains among the few hormonal insufficiency states without a replacement
therapy that restores the missing hormone at physiologic levels.
Hypoparathyroidism also poses a high burden on the healthcare system despite current conventional therapy.
For example, one survey of 374 patients showed that 72% experienced more than ten symptoms in the
preceding twelve months, with symptoms experienced for a mean of 13 ± 9 hours a day. Other studies showed
that 79% of hypoparathyroidism cases require hospitalizations and that patients with the disease have a four-
fold increase in the risk of renal disease compared to healthy controls. Patients often experience decreased
quality of life. We conducted a survey of 42 patients which found that 100% of patients reported negative
psychological impacts, interference with daily life and impact on physical functioning from HP, and that 76%
were either no longer able to work or experienced interference with work productivity.
The 2022 Guidelines from the Second International Workshop addressing the prevention, diagnosis, and
management of hypoparathyroidism was published in September 2022 in the Journal of Bone and Mineral
Research and authored by leading clinicians from North America, Europe, and Asia. The authors suggest
consideration of PTH replacement therapy in patients whose hypoparathyroidism is inadequately controlled
with conventional therapy. Inadequate control is considered to be any one of the following: symptomatic
hypocalcemia, hyperphosphatemia, renal insufficiency, hypercalciuria, or poor quality of life. In addition, the
guideline indicates that individuals with poor compliance, malabsorption or who are intolerant of large doses
of calcium and active vitamin D may also benefit from PTH replacement therapy. Based on this current
guideline, we believe PTH replacement therapy could be applicable to most patients with hypoparathyroidism.
Currently, an effective PTH replacement therapy that fully addresses the condition is not widely available to
patients with hypoparathyroidism. In 2015, NATPARA
®
(parathyroid hormone) for injection was approved in
the U.S. for once-daily subcutaneous injection as an adjunct to vitamin D and calcium in patients with
hypoparathyroidism. NATPARA was voluntarily recalled in September 2019 in the U.S. and is now only
available to a limited number of patients through a Special Use Program offered by its manufacturer, Takeda.
In October 2022, Takeda announced that it will discontinue manufacturing NATPARA/NATPAR globally by the
end of 2024.
We are also aware of several academic groups and companies working on making longer-acting agonists of
the PTH receptor (“PTH1R”). In addition, other companies and groups are developing or commercializing
therapies for hypoparathyroidism, including Calcilytix (a BridgeBio company), Entera Bio, Extend Biosciences,
Massachusetts General Hospital, Amolyt Pharma, and MBX Biosciences.
Teriparatide, PTH (1-34), approved since 2002 for the treatment of osteoporosis, has sometimes been used
for treatment of hypoparathyroidism using multiple daily injections, despite not being approved for this
indication. Clinical research conducted by the National Institutes of Health (“NIH”) in subjects receiving
continuous exposure to PTH (1-34), administered by an infusion pump, demonstrated simultaneous
normalization of sCa and urinary calcium, as well as normalization of bone turnover.