
Studies have found that the burden of hypoparathyroidism negatively impacts health-related quality of
life (“QoL”), physical functioning, and psychological well-being. Compared with an age-matched general
population sample, individuals with hypoparathyroidism have reported markedly lower health-related
QoL, irrespective of serum calcium level, as measured by the physical (P<0.001) and mental (P<0.001)
component scores of the 36-Item Short Form Health Survey (SF-36) as well as the EuroQol-5
Dimensions Visual Analogue Scale. As reported in a 2021 paper, in interviews conducted on 42
individuals with hypoparathyroidism, 98% reported reduced functioning and well-being, including
anxiety (81%), feeling sad or depressed (62%), and feeling irritable or short-tempered (43%) despite
management with conventional therapy.
Hypoparathyroidism also imposes a substantial burden on the healthcare system despite the use of
conventional therapy. For example, individuals with hypoparathyroidism may require hospitalizations or
emergency department visits due to acute severe hypocalcemia (calcium crashes) and those with post-
surgical hypoparathyroidism have an increased risk of hospitalization due to infection than age- and
sex-matched controls from the general population. Individuals with hypoparathyroidism also have an
increased risk of hospitalization due to renal complications, such as chronic kidney disease and renal
failure, compared to age- and sex-matched controls. A retrospective review published in 2019 of clinical
burden and healthcare resource utilization showed that 90.7% of individuals had ≥1
hypoparathyroidism-related healthcare utilization event during a 12-month period, including 87.8% with
≥1 outpatient visit, 41% with ≥1 emergency department visit, and 19.5% with ≥1 hospitalization. The
management of hypoparathyroidism is also associated with substantial economic burdens and
consequences of hypoparathyroidism may negatively impact employment status and 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 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.
In 2015, Takeda’s NATPARA
®
(parathyroid hormone) 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 would 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. In addition, other companies and groups are developing therapies for
hypoparathyroidism at the clinical stage, including Calcilytix (a BridgeBio company), Entera Bio, Extend
Biosciences, Massachusetts General Hospital, AstraZeneca, MBX Biosciences, and Septerna.
Forteo® (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 U.S. National Institutes of Health
in subjects receiving continuous exposure to PTH (1-34), administered by an infusion pump
demonstrated simultaneous normalization of serum calcium and urinary calcium, as well as
normalization of bone turnover.
We estimate hypoparathyroidism affects over 250,000 patients in the U.S. and Europe. In the U.S., we
estimate hypoparathyroidism affects approximately 70,000 to 90,000 patients, including 4,000 to 5,000
patients who we estimate have previously been treated with PTH therapy. In Germany, we estimate
hypoparathyroidism affects approximately 70,000 patients. Outside of Germany, we estimate
hypoparathyroidism affects over 100,000 patients in the rest of Europe.