Ultragenyx Announces the Presentation of Data From a Single Dose Phase 1 Study, Conducted by Kyowa Hakko Kirin Co. Ltd. (KHK),

Ultragenyx Announces the Presentation of Data From a Single Dose Phase 1
Study, Conducted by Kyowa Hakko Kirin Co. Ltd. (KHK), of KRN23 in X-linked
Hypophosphatemia (XLH) in Adults

KRN23 Increased Phosphate Levels and Was Safe and Well Tolerated

NOVATO, Calif., Oct. 6, 2013 (GLOBE NEWSWIRE) -- Ultragenyx Pharmaceutical
Inc., a biotechnology company, announced the release of data from a
first-in-human, randomized, double-blind, placebo-controlled, single dose
study of a human monoclonal anti-FGF23 antibody (KRN23) in X-linked
hypophosphatemia in adults. X-linked hypophosphatemia (XLH) is an inherited
metabolic bone disease characterized by short stature and skeletal
deformities. A Phase I study (US-02) was conducted by KHK with KRN23 to assess
its safety and tolerability and to measure changes in biochemical markers in
adult patients with XLH. Thirty-eight adults with XLH were randomized to
receive single doses of KRN23 or placebo via intravenous (IV) (0.003 to 0.3
mg/kg) or subcutaneous (SC) (0.1 to 1.0 mg/kg) routes.

Data were presented by Thomas Carpenter, MD, Yale University at the American
Society of Bone Mineralization Research (ASBMR) 2013 Annual Meeting on October
6, 2013. The study showed single doses of either IV or SC KRN23 increased
serum phosphate level, renal absorption of phosphate and 1,25 dihydroxy
Vitamin D compared to placebo (p < 0.01) for higher doses. Peak serum
phosphate effects occurred later with SC (8-15 days) than with IV dosing
(0.5-4 days). Duration of effect on phosphate was dose-related, greater with
SC than IV, and persisted beyond 29 days with SC. No meaningful changes in
serum calcium, serum parathyroid hormone, and urinary calcium excretion
occurred. There were no SAEs, no discontinuations due to AEs and no changes in
safety biochemistries, ECGs, or renal sonograms.AEs considered related to the
study drug occurred in 6patients (4in IV dose groups [24%] and 2in SC
groups [17%]).Single dose administration of KRN23 was safe and
well-tolerated; no patient developed anti-KRN23 antibodies.

"The study results suggest the potential to change the paradigm for treatment
in XLH and we thank the investigators, patients and Kyowa Hakko Kirin for the
successful conduct of the study," Emil D. Kakkis, M.D., Ph.D., Ultragenyx's
Chief Executive Officer commented.

Ultragenyx and KHK plan to continue the development of KRN23 in adult XLH
patients while planning to initiate a pediatric XLH program in 2014.

About X-linked Hypophosphatemia (XLH)

XLH is a disorder of phosphate metabolism caused by phosphate wasting in the
urine leading to severe hypophosphatemia.XLH is the most common heritable
form of rickets that is inherited as an X-linked dominant trait affecting both
males and females, though some reports indicate that the disease may be more
severe in males.XLH is a distinctive bone disease characterized by inadequate
mineralization of bone that leads to a spectrum of abnormalities, including
progressive bowing of the leg, osteomalacia, bone pain, waddling gait, short
stature, gross motor impairment, muscle weakness, osteopenia, frequent/poorly
healing microfractures, spinal stenosis and osteoarthritis.

Most patients are managed using oral phosphate replacement and vitamin D
(calcitriol) therapy, which is poorly tolerated and only partially effective
at restoring bone physiology and growth.Current treatment with oral phosphate
requires close monitoring and can result in complications such as secondary
hyperparathyroidism, hypercalciuria, hypercalcemia and nephrocalcinosis. XLH
was originally called vitamin D-resistant rickets because doses of vitamin D
effective for the treatment of vitamin D-deficient nutritional rickets did not
have an impact on phosphate levels in these patients.

About KRN23 and FGF23

KRN23 is a recombinant fully human monoclonal IgG[1] antibody discovered by
KHK and being developed to treat X-linked hypophosphatemia (XLH).KRN23 is
designed to bind to and thereby reduce the biologic activity of fibroblast
growth factor 23 (FGF23).FGF23 is a hormone that promotes phosphate excretion
by the kidney and suppresses vitamin D production.FGF23 also reduces the
expression of the enzyme that is required to synthesize a hormone that
normally increases renal tubular absorption of both phosphate and
calcium.Therefore, FGF23 induces profound reductions in serum phosphate
levels.Phosphate wasting in XLH is caused by excessive levels and activity of
FGF23.

About Ultragenyx

Ultragenyx is a privately held, clinical-stage biotechnology company committed
to bringing to market novel products for the treatment of rare and ultra-rare
diseases, with an initial focus on serious, debilitating metabolic genetic
diseases. Founded in 2010, the company has rapidly built a diverse portfolio
of product candidates with the potential to address diseases for which the
unmet medical need is high, the biology for treatment is clear, and for which
there are no approved therapies.

The company is led by a management team experienced in the development and
commercialization of rare disease therapeutics. Ultragenyx's strategy is
predicated upon time and cost-efficient drug development, with the goal of
delivering safe and effective therapies to patients with the utmost urgency.

For more information on Ultragenyx, please visit the company's website at
www.ultragenyx.com.

About Kyowa Hakko Kirin

Kyowa Hakko Kirin is a leading biopharmaceutical company in Japan focusing on
its core business areas of nephrology, oncology and immunology/allergy.Kyowa
Hakko Kirin leverages antibody-related leading-edge technologies to discover
and develop innovative new drugs aiming to become a global specialty
pharmaceutical company contributing to the health and well-being of people
around the world.

For more information, please visit the company's website at
www.kyowa-kirin.com.

CONTACT: Ultragenyx Pharmaceutical Inc.
         415-483-8800
         For Media, Bee Nguyen
         bnguyen@ultragenyx.com
         For Investors, Shalini Sharp
         ssharp@ultragenyx.com
 
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