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Kinetics of phenylalanine transport at the human blood-brain barrier investigated in vivo.
[classical phenylketonuria]
In
vivo
proton
magnetic
resonance
spectroscopy
was
used
to
investigate
intracerebral
phenylalanine
(
Phe
)
concentrations
in
nine
patients
with
classical
phenylketonuria
(
PKU
)
.
The
study
included
serial
examinations
(
n
=
31
;
plasma
Phe
levels
:
0
.
47
-
2
.
24
mmol
/
l
)
of
patients
either
receiving
a
Phe-
restricted
diet
(
200
mg
Phe
per
day
;
four
patients
)
or
a
diet
rich
in
Phe
(
1000
mg
Phe
per
day
;
three
patients
)
.
No
spectrum
showed
metabolic
abnormalities
besides
elevated
Phe
.
Difference
spectroscopy
yielded
intracerebral
Phe
concentrations
between
0
.
20
and
0
.
76
mmol
/
l
.
Regional
variations
between
parieto-
occipital
periventricular
brain
,
frontal
brain
,
and
cerebellum
were
not
statistically
significant
.
Data
could
be
fitted
assuming
saturable
Phe
transport
into
the
brain
,
based
on
a
symmetric
Michaelis-
Menten
model
(
characterized
by
an
apparent
Michaelis
transport
constant
,
K
(
t
,
app
)
,
and
a
maximum
transport
velocity
,
Tmax
)
and
constant
Phe
consumption
in
the
brain
cells
(
described
by
a
velocity
Vmax
)
.
Non-linear
least-squares
fitting
of
the
combined
data
from
all
patients
yielded
K
(
t
,
app
)
=
0
.
16
+
/
-
0
.
11
mmol
/
l
and
(
Tmax
/
Vmax
)
=
9
.
0
+
/
-
4
.
1
.
Carrier
saturation
and
competitive
inhibition
of
the
influx
of
other
large
neutral
amino
acids
can
be
expected
at
plasma
Phe
levels
usually
found
in
PKU
patients
.
Diseases
Validation
Diseases presenting
"brain cells"
symptom
classical phenylketonuria
gm1 gangliosidosis
kallmann syndrome
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