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Steroidogenesis of the testis -- new genes and pathways.
[congenital adrenal hyperplasia]
Defects
of
androgen
biosynthesis
cause
46
,
XY
disorder
of
sexual
development
(
DSD
)
.
All
steroids
are
produced
from
cholesterol
and
the
early
steps
of
steroidogenesis
are
common
to
mineralocorticoid
,
glucocorticoid
and
sex
steroid
production
.
Genetic
mutations
in
enzymes
and
proteins
supporting
the
early
biosynthesis
pathways
cause
adrenal
insufficiency
(
AI
)
,
DSD
and
gonadal
insufficiency
.
The
classic
androgen
biosynthesis
defects
with
AI
are
lipoid
CAH
,
CYP
11
A
1
and
HSD
3
B
2
deficiencies
.
Deficiency
of
CYP
17
A
1
rarely
causes
AI
,
and
HSD
17
B
3
or
SRD
5
A
2
deficiencies
only
cause
46
,
XY
DSD
and
gonadal
insufficiency
.
All
androgen
biosynthesis
depends
on
17
,
20
lyase
activity
of
CYP
17
A
1
which
is
supported
by
P
450
oxidoreductase
(
POR
)
and
cytochrome
b
5
(
CYB
5
)
.
Therefore
46
,
XY
DSD
with
apparent
17
,
20
lyase
deficiency
may
be
due
to
mutations
in
CYP
17
A
1
,
POR
or
CYB
5
.
Illustrated
by
patients
harboring
mutations
in
SRD
5
A
2
,
normal
development
of
the
male
external
genitalia
depends
largely
on
dihydrotestosterone
(
DHT
)
which
is
converted
from
circulating
testicular
testosterone
(
T
)
through
SRD
5
A
2
in
the
genital
skin
.
In
the
classic
androgen
biosynthetic
pathway
,
T
is
produced
from
DHEA
and
androstenedione
/
-
diol
in
the
testis
.
However
,
recently
found
mutations
in
AKR
1
C
2
/
4
genes
in
undervirilized
46
,
XY
individuals
have
established
a
role
for
a
novel
,
alternative
,
backdoor
pathway
for
fetal
testicular
DHT
synthesis
.
In
this
pathway
,
which
has
been
first
elucidated
for
the
tammar
wallaby
pouch
young
,
17
-
hydroxyprogesterone
is
converted
directly
to
DHT
by
5
α-
3
α
reductive
steps
without
going
through
the
androgens
of
the
classic
pathway
.
Enzymes
AKR
1
C
2
/
4
catalyse
the
critical
3
αHSD
reductive
reaction
which
feeds
17
OH
-DHP
into
the
backdoor
pathway
.
In
conclusion
,
androgen
production
in
the
fetal
testis
seems
to
utilize
two
pathways
but
their
exact
interplay
remains
to
be
elucidated
.
Diseases
Validation
Diseases presenting
"fetal testis"
symptom
congenital adrenal hyperplasia
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