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Evaluation of an aspartame loading test for the detection of heterozygotes for classical phenylketonuria.
[classical phenylketonuria]
Classical
phenylketonuria
(
PKU
)
is
an
inborn
error
of
metabolism
of
autosomal
recessive
inheritance
characterized
by
the
accumulation
of
phenylalanine
(
Phe
)
in
tissues
due
to
Phe-
4
-
hydroxylase
deficiency
.
Several
methods
have
been
developed
for
the
detection
of
PKU
heterozygotes
based
on
the
determination
of
plasma
Phe
and
tyrosine
(
Tyr
)
levels
,
on
the
analysis
of
the
Phe
/
Tyr
and
Phe
2
/
Tyr
ratios
and
on
the
use
of
discriminant
functions
.
The
objective
of
the
present
study
was
to
test
the
value
of
loading
with
aspartame
(
a
sweetener
consisting
of
Phe
,
aspartate
and
methanol
)
for
the
identification
of
PKU
carriers
.
The
study
was
conducted
on
22
obligate
heterozygotes
and
27
controls
.
Two
blood
samples
were
collected
(
under
fasting
conditions
and
30
min
after
the
loading
)
for
fluorometric
determination
of
Phe
and
Tyr
.
Phe
,
Phe
/
Tyr
and
Phe
2
/
Tyr
values
were
higher
in
heterozygotes
,
whereas
Tyr
was
higher
in
controls
in
both
situations
investigated
.
Linear
discriminant
function
was
considered
to
be
the
best
parameter
for
differentiation
of
the
individuals
in
the
two
groups
.
Under
the
conditions
employed
in
the
present
study
,
aspartame
loading
did
not
show
any
advantages
in
discriminating
between
PKU
carriers
and
normal
individuals
when
compared
to
the
same
analysis
performed
under
fasting
conditions
.
