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CblE type of homocystinuria: mild clinical phenotype in two patients homozygous for a novel mutation in the MTRR gene.
[homocystinuria without methylmalonic aciduria]
Patients
with
the
cblE
type
of
homocystinuria
usually
present
with
megaloblastic
anaemia
,
feeding
difficulties
,
developmental
delay
and
cerebral
atrophy
.
We
present
a
14
-
year
-old
Spanish
girl
(
patient
1
)
and
a
10
-
year
-old
Portuguese
boy
(
patient
2
)
with
cblE
disease
and
mild
clinical
phenotype
.
The
main
clinical
feature
in
both
patients
was
persistent
megaloblastic
anaemia
observed
at
3
years
and
at
2
months
of
age
,
respectively
.
Diagnosis
was
made
at
the
ages
of
9
and
7
years
,
respectively
,
owing
to
persistent
macrocytosis
despite
cobalamin
treatment
.
Plasma
total
homocysteine
values
at
diagnosis
were
91
micromol
/
L
and
44
micromol
/
L
,
respectively
,
in
the
absence
of
methylmalonic
aciduria
.
Neurological
and
neurophysiological
examinations
were
normal
except
for
two
small
lesions
on
brain
MRI
suggestive
of
ischaemia
and
slight
abnormalities
in
somatosensitive
evoked
potentials
.
Enzymatic
analysis
,
complementation
studies
and
clearly
reduced
production
of
methylcobalamin
from
57
Co
-labelled
cyanocobalamin
indicated
functional
methionine
synthase
reductase
deficiency
due
to
the
cblE
defect
.
Genetic
analysis
confirmed
that
both
patients
are
homozygous
for
a
novel
mutation
c
.
1361
C
>
T
in
the
methionine
synthase
reductase
gene
leading
to
a
replacement
of
serine
by
leucine
(
S
454
L
)
in
a
highly
conserved
FAD-binding
domain
.
We
propose
that
homozygosity
for
this
novel
mutation
may
be
associated
with
a
mild
phenotype
,
although
its
long
-term
deleterious
neurological
consequences
remain
possible
.
Furthermore
,
we
propose
that
even
in
the
absence
of
apparent
neurological
involvement
,
total
homocysteine
should
be
investigated
in
patients
with
resistant
megaloblastic
anaemia
to
detect
possible
mild
forms
of
the
cblE
type
of
homocystinuria
.
Diseases
Validation
Diseases presenting
"a mild phenotype"
symptom
familial mediterranean fever
homocystinuria without methylmalonic aciduria
monosomy 21
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