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Newborn screening and early biochemical follow-up in combined methylmalonic aciduria and homocystinuria, cblC type, and utility of methionine as a secondary screening analyte.
[homocystinuria without methylmalonic aciduria]
Combined
methylmalonic
aciduria
and
homocystinuria
,
cobalamin
C
(
cblC
)
type
,
is
an
inherited
disorder
of
vitamin
B
(
12
)
metabolism
caused
by
mutations
in
MMACHC
.
CblC
typically
presents
in
the
neonatal
period
with
neurological
deterioration
,
failure
to
thrive
,
cytopenias
,
and
multisystem
pathology
including
renal
and
hepatic
dysfunction
.
Rarely
,
affected
individuals
present
in
adulthood
with
gait
ataxia
and
cognitive
decline
.
Treatment
with
hydroxocobalamin
may
ameliorate
the
clinical
features
of
early
-onset
disease
and
prevent
clinical
late-onset
disease
.
Propionic
acidemia
(
PA
)
,
methylmalonic
acidemia
(
MMA
)
,
and
various
disorders
of
cobalamin
metabolism
are
characterized
by
elevated
propionylcarnitine
(
C
3
)
on
newborn
screening
(
NBS
)
.
Distinctions
can
be
made
between
these
disorders
with
secondary
analyte
testing
.
Elevated
methionine
is
already
routinely
used
as
a
NBS
marker
for
cystathionine
beta
-synthase
deficiency
.
We
propose
that
low
methionine
may
be
useful
as
a
secondary
analyte
for
specific
detection
of
cbl
disorders
among
a
larger
pool
of
infants
with
elevated
C
3
on
NBS
.
Retrospective
analysis
of
dried
blood
spot
(
DBS
)
data
in
patients
with
molecularly
confirmed
cblC
disease
.
Nine
out
of
ten
patients
with
confirmed
cblC
born
in
New
York
between
2005
and
2008
had
methionine
below
13
.
4
mumol
/
L
on
NBS
.
Elevated
C
3
,
elevated
C
3
:
C
2
ratio
,
and
low
methionine
were
incorporated
into
a
simple
screening
algorithm
that
can
be
used
to
improve
the
specificity
of
newborn
screening
programs
and
provide
a
specific
and
novel
method
of
distinguishing
cblC
from
other
disorders
of
propionate
metabolism
prior
to
recall
for
confirmatory
testing
.
It
is
anticipated
that
this
algorithm
will
aid
in
early
and
specific
detection
of
cobalamin
C
,
D
,
and
F
diseases
,
with
no
additional
expense
to
NBS
laboratories
screening
for
organic
acidemias
and
classical
homocystinuria
.
Diseases
Validation
Diseases presenting
"inherited disorder of vitamin"
symptom
homocystinuria without methylmalonic aciduria
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