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Hyperphenylalaninemia and pterin metabolism in serum and erythrocytes.
[classical phenylketonuria]
The
relationship
between
blood
phenylalanine
concentrations
and
serum
and
erythrocyte
biopterin
and
neopterin
concentrations
was
investigated
in
20
phenylketonuric
patients
with
different
dietary
compliance
.
At
serum
phenylalanine
concentrations
ranging
from
43
to
1004
mumol
/
l
,
a
good
correlation
was
found
with
serum
biopterin
(
r
=
0
.
76
,
P
<
0
.
001
)
and
with
red
blood
cell
biopterin
(
r
=
0
.
62
,
P
<
0
.
001
)
.
A
similar
correlation
was
found
between
serum
neopterin
and
phenylalanine
(
r
=
0
.
60
,
P
<
0
.
001
)
.
The
correlation
between
red
blood
cell
neopterin
and
serum
phenylalanine
was
less
evident
,
however
(
r
=
0
.
47
,
P
<
0
.
005
)
.
After
oral
loading
with
phenylalanine
(
100
mg
/
kg
body
weight
)
,
serum
and
red
blood
cell
biopterin
concentrations
increased
in
patients
with
classical
phenylketonuria
as
well
as
in
one
patient
with
dihydropteridine
reductase
deficiency
in
response
to
the
induced
acute
hyperphenylalaninemia
.
One
patient
suffering
from
6
-
pyruvoyl
tetrahydropterin
synthase
deficiency
was
loaded
orally
with
tetrahydrobiopterin
(
20
mg
/
kg
body
weight
)
.
The
kinetics
of
administered
cofactor
confirmed
its
rapid
absorption
,
with
early
increase
of
serum
concentrations
followed
by
its
transport
into
the
red
blood
cells
.
The
half
-life
of
biopterin
was
approximately
7
h
in
serum
and
15
h
in
red
blood
cells
.
Because
both
values
are
less
than
the
half
-life
of
phenylalanine
(
20
-
30
h
)
in
serum
,
biopterin
measurement
offers
no
advantage
in
monitoring
dietary
control
in
hyperphenylalaninemic
patients
.