Purine Nucleoside Phosphorylase Deficiency

Purine Nucleoside Phosphorylase Deficiency

OMIM number: 613179

Comments closing date: 13/08/2025

Immunodeficiency due to purine nucleoside
phosphorylase deficiency is a rare hereditary
(genetic) condition which affects the immune
system and often the brain. It is caused when a
person is born with a mutation (also called a
“pathogenic variant”) in both copies of their PNP
gene. The PNP gene produces an enzyme which
clears away waste products from cells, especially
white blood cells and brain cells. If their genes do
not work properly, these waste products
accumulate, particularly T cells and sometimes B
white blood cells as well, which can kill these cells
leading to immune deficiency. It can also damage
brain cells, causing neurological problems in some
people. Symptoms can begin in infancy or early
childhood. The main symptom is immune system
deficiency, meaning they are more likely to
develop infections, which can be life-threatening.
They also are more likely to have other
dysfunctions of the immune system, such as
autoimmune disorders. Infections are particularly
common in the sinuses and lungs, and can be
severe. Around two-thirds of people with the
condition also have developmental delay, issues
with coordination and balance, and muscular
spasticity. Sadly, some people with this condition
do not survive infancy if they develop a severe
infection. Bone marrow transplantation can
significantly help improve the quality of life and
can be curative of the immune system dysfunction,
but finding a bone marrow donor match is not
guaranteed and there is a risk to this surgery. This
is unlikely to reverse symptoms of neurological
damage. Other medications such as prophylactic
antibiotics can be helpful to avoid infection. If two
carrier parents have a child together, there is a 1
in 4 chance of having an affected pregnancy.

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