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Early-onset combined methylmalonic aciduria and homocystinuria: neuroradiologic findings.
[homocystinuria without methylmalonic aciduria]
Combined
methylmalonic
aciduria
and
homocystinuria
(
MMA-HC
)
is
caused
by
impaired
hepatic
conversion
of
dietary
cobalamin
to
methylcobalamin
and
adenosylcobalamin
,
resulting
in
decreased
activity
of
methylmalonyl-
CoA
mutase
and
methionine
synthase
.
Patients
with
the
early
-onset
variety
present
within
12
months
of
age
with
severe
neurologic
,
hematologic
,
and
gastrointestinal
abnormalities
.
We
describe
the
neuroradiologic
features
of
early
-onset
MMA-HC
and
discuss
related
pathophysiological
mechanisms
.
Twelve
infants
with
hypotonia
,
failure
to
thrive
,
poor
feeding
,
and
hematologic
abnormalities
were
diagnosed
with
MMA-HC
on
the
basis
of
a
typical
plasmatic
and
urinary
metabolic
profile
and
enzyme
activity
in
fibroblastic
cultures
.
Complementation
studies
were
performed
in
two
cases
,
and
yielded
a
CblC
result
.
MR
imaging
was
performed
at
presentation
in
four
cases
and
later
in
the
others
.
All
patients
showed
prompt
biochemical
improvement
with
intramuscular
hydroxocobalamin
administration
,
and
most
had
moderate
neurologic
improvement
.
Diffuse
supratentorial
white
matter
edema
and
dysmyelination
was
the
typical
MR
picture
at
presentation
,
whereas
white
matter
bulk
loss
characterized
later
stages
of
the
disease
.
Nucleocapsular
areas
of
gliosis
were
an
additional
finding
in
one
case
.
One
patient
had
tetraventricular
hydrocephalus
at
presentation
.
White
matter
damage
is
probably
caused
by
reduced
methyl
group
availability
and
nonphysiological
fatty
acids
toxicity
,
whereas
focal
gliosis
results
from
homocysteine-induced
toxicity
to
the
endothelium
.
Hydrocephalus
may
result
from
diffuse
intracranial
extracerebral
arterial
stiffness
,
known
as
reduced
arterial
pulsation
hydrocephalus
.
MR
imaging
features
at
presentation
and
at
follow-up
are
nonspecific
.
Diseases
Validation
Diseases presenting
"white matter edema"
symptom
homocystinuria without methylmalonic aciduria
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