Ultragenyx Announces Collaboration With Kyowa Hakko Kirin to Develop and Commercialize Phase 2-Stage KRN23 for X-Linked

Ultragenyx Announces Collaboration With Kyowa Hakko Kirin to Develop and
Commercialize Phase 2-Stage KRN23 for X-Linked Hypophosphatemia

Exclusive Partnership Will Advance Global Clinical Development of KRN23, an
Antibody for a Rare Bone Disease

NOVATO, Calif., Sept. 3, 2013 (GLOBE NEWSWIRE) -- Ultragenyx Pharmaceutical
Inc. today announced it has entered into a collaboration and license agreement
with Kyowa Hakko Kirin Co., Ltd. (KHK), to develop and commercialize KRN23.
KRN23 is a recombinant fully human monoclonal IgG[1] antibody intended to
treat X-linked hypophosphatemia (XLH). KHK is currently completing a Phase 1/2
study in adults with XLH in the US and Canada. The two companies plan to
initiate a pediatric XLH program in 2014.

XLH is a rare metabolic bone disorder caused by excessive loss of phosphate in
the urine leading to severe hypophosphatemia and poor bone growth and
mineralization.XLH patients have low serum phosphate levels due to high
levels of FGF23, a hormone that represses the reabsorption of phosphate from
the urine.KRN23 is intended to bind to and render FGF23 inactive, leading to
an increase in kidney tubular absorption of phosphate and increased serum
phosphate levels. KRN23 is potentially the first specific treatment that
addresses the underlying problem of excess FGF23 production in XLH.

Under the terms of the agreement, Ultragenyx and KHK will collaborate on the
development of KRN23 for the US, Canada and European Union (EU), with
Ultragenyx leading development efforts in the XLH indication and the parties
sharing development costs.If KRN23 is approved, Ultragenyx and KHK will share
commercial responsibilities and profits in the US and Canada, KHK will
commercialize KRN23 in the EU and Ultragenyx will develop and commercialize
KRN23 in Mexico, Central and South America.KHK will manufacture and supply
KRN23 for clinical and commercial use globally.

"We are excited to enter into this collaboration with KHK on KRN23, a
promising clinical-stage product to treat a rare and debilitating bone
disease," said Emil D. Kakkis, MD, PhD, Chief Executive Officer of Ultragenyx.
"The collaboration combines KHK's broad antibody-based discovery,
manufacturing and development capabilities with our expertise in the clinical
development of novel therapeutics for rare genetic diseases.We look forward
to working closely with the KHK team, investigators, and patients on
continuing development of KRN23, a much needed new therapy for XLH patients."

KHK has successfully completed a Phase 1 (US-02) and a Phase 1/2 (INT-001)
study with a Phase 1/2 extension (INT-002) study ongoing in adults with
XLH.Data from the Phase 1 (US-02) study will be presented at an upcoming
scientific meeting.Under the collaboration, Ultragenyx and KHK plan to
continue the development of KRN23 in adult XLH patients while initiating a
pediatric XLH program in 2014.

"KRN23 is a strategically important product for Kyowa Hakko Kirin to expand
its business into global markets," commented Yoichi Sato, Executive Managing
Officer, Vice President, Head, Development Division at KHK."We believe that
the collaboration with Ultragenyx will accelerate the development and
commercialization of KRN23 and maximize its value in global markets.Through
the collaboration, Kyowa Hakko Kirin will continue to use its best efforts to
bring KRN23 to XLH patients who need the new therapy the most."

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 the disease in males by some reports may be more
severe.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 extremely 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 life-transforming therapeutics for patients with rare
and ultra-rare metabolic genetic diseases. Founded in 2010, the company is
rapidly building 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 effective treatments.

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: For Media inquiries:
         Susan Kinkead, Kinkead Communications
         susan@kinkeadcomm.com
        
         For Investor inquiries:
         Shalini Sharp, Ultragenyx Pharmaceutical Inc.
         ssharp@ultragenyx.com
 
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