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Post- and prenatal diagnostic methods for the homocystinurias.
[homocystinuria without methylmalonic aciduria]
Diagnosis
of
the
homozygous
homocystinurias
can
be
performed
by
investigations
at
the
metabolite
,
enzyme
and
DNA
level
.
The
existence
of
variant
forms
due
to
the
wide
range
of
genetic
variation
may
result
in
only
small
differences
in
various
parameters
between
controls
and
affected
subjects
.
1
.
Sulphur
amino
acid
concentrations
in
plasma
,
especially
total
homocysteine
,
are
useful
in
first
line
diagnostic
investigations
.
2
.
Cystathionine-
beta
-synthase
(
CBS
)
,
methylenetetrahydrofolate
reductase
(
MTHFR
)
and
methylfolate
homocysteine
methyltransferase
(
MFMT
)
can
be
directly
assayed
in
many
tissues
including
fibroblasts
(
each
)
and
blood
cells
(
except
CBS
)
.
Indirect
whole
cell
assays
which
measure
pathway
activity
dependent
on
a
particular
enzyme
can
provide
useful
diagnostic
information
.
3
.
Direct
analysis
of
mutations
is
available
for
CBS
,
MTHFR
and
recently
also
for
MFMT
deficiencies
.
However
the
existence
of
a
larger
number
of
very
rare
,
often
private
,
mutations
limits
the
usefulness
of
this
approach
in
routine
diagnosis
.
The
above
diagnostic
approaches
can
generally
be
applied
to
prenatal
diagnosis
.
Measurement
of
methylmalonic
acid
and
other
metabolites
in
amniotic
fluid
by
stable
isotope
dilution
/
gas
chromatography-mass
spectrometry
is
well
established
for
the
methylmalonic
acidurias
.
This
method
has
also
been
applied
to
combined
homocystinuria
/
methylmalonic
aciduria
supported
by
enzyme
assays
in
cultured
cells
.
Total
homocysteine
measurement
in
cell
free
amniotic
fluid
is
also
possible
,
performed
so
far
in
14
cases
with
two
affected
fetuses
.
The
indirect
assay
of
methionine
formation
from
[
14
C
]
labelled
formate
in
intact
cultured
amniotic
fluid
cells
has
been
for
prenatal
diagnosis
of
the
remethylation
defects
.
Diseases
Validation
Diseases presenting
"useful diagnostic information"
symptom
homocystinuria without methylmalonic aciduria
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