A novel autosomal recessive cerebro
-
renal syndrome was identified in
consanguineous Bedouin kindred: neurological deterioration was evident as of early
age, progressing into severe intellectual disability, profound ataxia, camptocormia and
oculomotor apraxia. Brain MRI was normal. Four of t
he six affected individuals had
also early
-
onset nephropathy with features of tubulo
-
interstitial nephritis,
hypertension and tendency for hyperkalemia, though none had rapid deterioration of
renal function. Genome wide linkage analysis identified a ~
18Mbs
disease
-
associated
locus on chro
mosome 4
(
maximal
logarithm of odds
score
4.4
at
D4S2971
;
θ
=0).
Whole exome sequencing identified a single mutation
in
SLC30A9
within this locus
,
segregating
as expected within the kindred
and not found in a homozygous s
tate in
300
Bedouin controls
. We showed that
SLC30A9
(Solute Carrier Family 30
, Member
9
; ZnT
-
9) is ubiquitously expressed with high levels in cerebellum, skeletal muscle,
thymus and kidney. Confocal analysis of SH
-
SY5Y cells overexpressing
SLC30A9
fused t
o
enhanced
green fluorescent protein
demonstrated vesicular cytosolic
localization associated with the endoplasmic reticulum
, not co
-
localizing with
endosomal or Golgi markers.
SLC30A9
encodes a putative zinc transporter (by
similarity) previously associated with Wnt signaling. However, using d
ual
-
l
uciferase
r
eporter
a
ssay
in SH
-
SY5Y cells we showed that Wnt signaling was not affected by
the mutation. Based on protein modeling, the iden
tified mutation is expected to affect
SLC30A9’s
highly conserved cation efflux domain, putatively disrupting its
transmembrane
helix structure. Cytosolic Zn
2+
measurements in HEK293 cells
overexpressing wild
-
type and mutant
SLC30A9
showed lower zinc concen
tration
within
mutant
rather
than wild
-
type
SLC30A9
cells. This suggests that
SLC30A9
has
zinc transport properties
affecting
intracellular zinc homeostasis, and that the
molecular mechanism of the disease is through defective function of this novel
activi
ty of
SLC30A9
rather than by a defect in its previously described role
in
transcriptional activation of Wnt signaling.