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Diagnostic yield of various genetic approaches in patients with unexplained developmental delay or mental retardation.
[cohen syndrome]
The
underlying
cause
of
mental
retardation
remains
unknown
in
up
to
80
%
of
patients
.
As
chromosomal
aberrations
are
the
most
common
known
cause
of
mental
retardation
,
several
new
methods
based
on
FISH
,
PCR
,
and
array
techniques
have
been
developed
over
recent
years
to
increase
detection
rate
of
subtle
aneusomies
initially
of
the
gene
rich
subtelomeric
regions
,
but
nowadays
also
genome
wide
.
As
the
reported
detection
rates
vary
widely
between
different
reports
and
in
order
to
compare
the
diagnostic
yield
of
various
investigations
,
we
analyzed
the
diagnostic
yield
of
conventional
karyotyping
,
subtelomeric
screening
,
molecular
karyotyping
,
X-
inactivation
studies
,
and
dysmorphological
evaluation
with
targeted
laboratory
testing
in
unselected
patients
referred
for
developmental
delay
or
mental
retardation
to
our
cytogenetic
laboratory
(
n
=
600
)
and
to
our
genetic
clinic
(
n
=
570
)
.
In
the
cytogenetic
group
,
15
%
of
patients
showed
a
disease-related
aberration
,
while
various
targeted
analyses
after
dysmorphological
investigation
led
to
a
diagnosis
in
about
20
%
in
the
genetic
clinic
group
.
When
adding
the
patients
with
a
cytogenetic
aberration
to
the
patient
group
seen
in
genetic
clinic
,
an
etiological
diagnosis
was
established
in
about
40
%
of
the
combined
study
group
.
A
conventional
cytogenetic
diagnosis
was
present
in
16
%
of
combined
patients
and
a
microdeletion
syndrome
was
diagnosed
in
5
.
3
%
,
while
subtelomeric
screening
revealed
only
1
.
3
%
of
causes
.
Molecular
karyotyping
with
a
10
K
SNP
array
in
addition
revealed
5
%
of
underlying
causes
,
but
29
%
of
all
diagnoses
would
have
been
detectable
by
molecular
karyotyping
.
In
those
patients
without
a
clear
diagnosis
,
5
.
6
%
of
mothers
of
affected
boys
showed
significant
(
>
95
%
)
skewing
of
X-
inactivation
suggesting
X-
linked
mental
retardation
.
The
most
common
diagnoses
with
a
frequency
of
more
than
0
.
5
%
were
Down
syndrome
(
9
.
2
%
)
,
common
microdeletion
22
q
11
.
2
(
2
.
4
%
)
,
Williams-
Beuren
syndrome
(
1
.
3
%
)
,
Fragile-
X
syndrome
(
1
.
2
%
)
,
Cohen
syndrome
(
0
.
7
%
)
,
and
monosomy
1
p
36
.
3
(
0
.
6
%
)
.
From
our
data
,
we
suggest
the
following
diagnostic
procedure
in
patients
with
unexplained
developmental
delay
or
mental
retardation
:
(
1
)
Clinical
/
dysmorphological
investigation
with
respective
targeted
analyses
;
(
2
)
In
the
remaining
patients
without
an
etiological
diagnosis
,
we
suggest
conventional
karyotyping
,
X-
inactivation
screening
in
mothers
of
boys
,
and
molecular
karyotyping
,
if
available
.
If
molecular
karyotyping
is
not
available
,
subtelomeric
screening
should
be
performed
.
Diseases
Validation
Diseases presenting
"common diagnoses with a frequency"
symptom
cohen syndrome
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