jamaneurology | originalinvestigation ......asd, stereotypies, and hand-wringing normal at 9 mo at...
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Neurodevelopmental Disorders Caused by De Novo Variantsin KCNB1 Genotypes and PhenotypesCarolien G. F. de Kovel, PhD; Steffen Syrbe, MD, PhD; Eva H. Brilstra, MD, PhD; Nienke Verbeek, MD, PhD;Bronwyn Kerr, PhD; Holly Dubbs, MD; Allan Bayat, MD, PhD; Sonal Desai, MGC, CGC; Sakkubai Naidu, MD;Siddharth Srivastava, MD; Hande Cagaylan, MD; Uluc Yis, MD, PhD; Carol Saunders, PhD; Martin Rook, PhD;Susanna Plugge, MSc; Hiltrud Muhle, MD; Zaid Afawi, MD, PhD; Karl-Martin Klein, MD, PhD;Vijayakumar Jayaraman, MSc; Ramakrishnan Rajagopalan, PhD; Ethan Goldberg, MD, PhD; Eric Marsh, MD, PhD;Sudha Kessler, MD, MSCE; Christina Bergqvist, MD; Laura K. Conlin, PhD; Bryan L. Krok, PhD;Isabelle Thiffault, PhD; Manuela Pendziwiat, MSc; Ingo Helbig, MD; Tilman Polster, MD, PhD;Ingo Borggraefe, MD, PhD; Johannes R. Lemke, MD, PhD; Marie-José van den Boogaardt, MD, PhD;Rikke S. Møller, MSc, PhD; Bobby P. C. Koeleman, PhD
IMPORTANCE Knowing the range of symptoms seen in patients with a missense orloss-of-function variant in KCNB1 and how these symptoms correlate with the type of variantwill help clinicians with diagnosis and prognosis when treating new patients.
OBJECTIVES To investigate the clinical spectrum associated with KCNB1 variants and thegenotype-phenotype correlations.
DESIGN, SETTING, AND PARTICIPANTS This study summarized the clinical and geneticinformation of patients with a presumed pathogenic variant in KCNB1. Patients wereidentified in research projects or during clinical testing. Information on patients frompreviously published articles was collected and authors contacted if feasible. All patientswere seen at a clinic at one of the participating institutes because of presumed geneticdisorder. They were tested in a clinical setting or included in a research project.
MAIN OUTCOMES AND MEASURES The genetic variant and its inheritance and informationon the patient's symptoms and characteristics in a predefined format. All variants wereidentified with massive parallel sequencing and confirmed with Sanger sequencing in thepatient. Absence of the variant in the parents could be confirmed with Sanger sequencingin all families except one.
RESULTS Of 26 patients (10 female, 15 male, 1 unknown; mean age at inclusion, 9.8 years; agerange, 2-32 years) with developmental delay, 20 (77%) carried a missense variant in the ionchannel domain of KCNB1, with a concentration of variants in region S5 to S6. Three variantsthat led to premature stops were located in the C-terminal and 3 in the ion channel domain.Twenty-one of 25 patients (84%) had seizures, with 9 patients (36%) starting with epilepticspasms between 3 and 18 months of age. All patients had developmental delay, with 17 (65%)experiencing severe developmental delay; 14 (82%) with severe delay had behavioralproblems. The developmental delay was milder in 4 of 6 patients with stop variants and ina patient with a variant in the S2 transmembrane element rather than the S4 to S6 region.
CONCLUSIONS AND RELEVANCE De novo KCNB1 missense variants in the ion channel domainand loss-of-function variants in this domain and the C-terminal likely cause neurodevelop-mental disorders with or without seizures. Patients with presumed pathogenic variants inKCNB1 have a variable phenotype. However, the type and position of the variants in theprotein are (imperfectly) correlated with the severity of the disorder.
JAMA Neurol. 2017;74(10):1228-1236. doi:10.1001/jamaneurol.2017.1714Published online August 14, 2017.
Author Affiliations: Authoraffiliations are listed at the end of thisarticle.
Corresponding Author: Bobby P. C.Koeleman, PhD, Department ofGenetics, University Medical CenterUtrecht, PO Box 85500, 3508 GAUtrecht, the Netherlands([email protected]).
Research
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E arly infantile epileptic encephalopathies (EEs) form agroup of disorders that are characterized by epileptic sei-zures starting during the first year of life. Patients havedevelopmental delay (DD) or even regression to which the epi-leptic discharges are presumed to contribute. The seizures areoften unresponsive to treatment. Many of those epilepsies havea genetic disposition.1
In the past few years, several new genes have been iden-tified that can cause EE when mutated. One of the more re-cently discovered genes is KCNB1 (potassium voltage-gatedchannel subfamily B member 1 or delayed rectifier potassiumchannel 1 [DRK1]) (OMIM 616056), which acts in a dominantmanner. Variants are described by Torkamani et al,2 who iden-tified a de novo KCNB1 variant when exome sequencing a fam-ily with a child with EE. They subsequently found 2 other in-dependent patients with EE and KCNB1 variants. One of thosepatients had earlier been described in the Epi4K effort3 as hav-ing Lennox-Gastaut syndrome. Subsequently, more patientswith variants in KCNB1 were described.4-10
The KCNB1 gene encodes the Kv2.1 pore-forming, voltage-sensing α-subunit of a delayed rectifier potassium channel. It isexpressed in various neuronal cells in the brain.11 In Ensembl(GRCh38.p3), only 1 transcript is known (ENST00000371741).It consists of only 2 exons and contains 4 known domains(Figure): the T1 domain, which is involved in multimeriza-tion; the ion_trans domain, which contains the transmem-brane elements; and 2 intracellular Kv2 channel–specific do-mains (Pfam; http://smart.embl-heidelberg.de/).12,13 Theprotein has 6 transmembrane elements in the ion_trans do-main; the first 4 form the voltage-sensor domain, with S4 beingthe actual voltage sensor, whereas S5 and S6 form the poredomain of the protein. The extracellular loop between S5and S6 contains the selectivity filter (TVGYG amino acids;UNIPROT.org). This structure is similar to other voltage-gated potassium channels, such as KCNQ2 (OMIM 602235) and
KCNQ3 (OMIM 602232).14 The protein forms homotetramersand heterotetramers with various other voltage-gated potas-sium channel proteins, such as KCNB2 (OMIM 607738), andproteins from the KCNG (Kv6), KCNE, and KCNS (Kv9)families.15-17
MethodsIn a recent screen of 358 children with EEs, we identified 3 novelKCNB1 variants (approximately 1%), all of which were foundto be de novo.18 We subsequently collected data from 13 ad-ditional patients from research and diagnostic sources whowere reported to carry a de novo novel KCNB1 variant not pres-ent in public databases. In this article, we describe the phe-notypic and genetic characteristics of these patients. In addi-tion, we collected more information about 10 patients who weredescribed previously. For 3 of the 10 patients in previously pub-lished articles, the authors have provided updated informa-tion for the current article. We present the available informa-tion on 26 patients for a broad overview of the phenotypic andgenetic variability and similarities. Statistical tests were per-formed using χ2 2 × 2 contingency tables; the significance ofthe enrichment of de novo mutation was calculated using a
Key PointsQuestion How does the phenotype of patients with a KCNB1mutation correlate with the type of mutation?
Findings This study found that patients with a de novo mutationin KCNB1 present a variable phenotype of neurodevelopmentaldisorder.
Meaning De novo mutations in KCNB1 are associated with avariable neurodevelopmental disorder.
Figure. Distribution of Pathogenic Variants in KCNB1
Extracellular i ii iii iv v vi
Selectivity filter
Cytoplasmic
Milder
Developmental delay
No seizures
430
220
160
Pathogenic missense variantPathogenic LoF variantBTBKv2-specific domain
850
Schematic view of the Kv2.1 (KCNB1) protein in the membrane, showing pathogenic missense and loss-of-function (LoF) variants. BTB indicates broad-complex,tramtrack, and bric-brac domain.
Neurodevelopmental Disorders Caused by KCNB1 De Novo Variants Original Investigation Research
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χ2 goodness-of-fit test. A 2-sided χ2 test with P < .05 determinedstatistical significance. Collection of data procedures agreedwith the local ethics guidelines at the different institutes.
ResultsDescription of the VariantsWe identified 16 patients with KCNB1 variants who were pre-viously not described and collected information about 10 pre-viously described patients (10 female, 15 male, 1 unknown;mean age at inclusion, 9.8 years; age range, 2-32 years).2-9 Inthese 26 patients, we identified 23 different variants; 3 vari-ants were seen twice each. Twenty patients (77%) carried mis-sense variants, and 6 (23%) carried nonsense or frameshift vari-ants leading to a premature termination codon (Table 1). Allthe missense variants are located within the Pfam ion_trans do-main (ie, the 6 transmembrane regions and their extracellu-lar and intracellular connecting loops) (Figure). Two variantsin 4 patients are gating charge residues in voltage sensor S4.19
Three variants are in the selectivity filter between S5 and S6.Three of the loss-of-function (LoF) variants are in the first Kv2channel–specific domain in the intracellular C-terminus of theprotein. The other 3 LoF variants are in the S1 to S2 linker andin the S5 to S6 P-loop. The gene has 2 exons, and all variantsare in the second (last) exon. All nonsense or frameshift vari-ants are expected to result in a truncated protein rather thannonsense-mediated decay because they are located in the ter-minal part of the gene. No variants were detected in the cyto-plasmic N-terminal part of the gene. All missense variants al-ter strongly conserved amino acids and are predicted to behighly deleterious by SIFT (Sorting Intolerant From Toler-ant), Polyphen2, and Combined Annotation Dependent Deple-tion (CADD) scores.20-22 The lowest CADD score was 23.3. Inall individuals except one (patient 18), for whom parentalsamples were not available for segregation analysis, the vari-ant was confirmed to be de novo. The variant not confirmedto be de novo, R312H, was seen as de novo in another patientand was absent from the Exome Aggregation ConsortiumExAC Browser (http://exac.broadinstitute.org/)23; thus, weinterpreted it to be pathogenic and included patient 18 in ourseries. An overview of characteristics of the patients and theirvariants is given in Table 1.
Description of the PatientsThe observed phenotypes in patients are summarized in Table 2and described in detail in this section. All 26 patients pre-sented with primary DD in the first year of life, preceding on-set of epilepsy. First signs of DD were unspecific, with mus-cular hypotonia or hypertonia being recurrently reported(11 of 23 individuals [48%] with available neurologic exami-nation findings). Twenty-one of 25 patients (84%) had intrac-table epilepsy, with seizure onset in infancy or early child-hood (median age at onset, 12 months; range, 3 months to4 years). Epileptic spasms alone or as part of West syndromewere observed in 9 patients (36%), with a median onset of sei-zures of 12 months (range, 3-18 months). The only patient whodeveloped spasms before 6 months of age was patient 10, who
carried the prominent variant G381R within the selectivity fil-ter of the P-loop.7 In most patients with epilepsy, the semio-logic features developed over time into multiple seizure types,including tonic, focal-clonic, myoclonic, and atypical ab-sences. Three patients did not have epileptic seizures (pa-tients 1, 3, and 24), 1 reported only infantile spasms (patient2), and no data were available for 1 (patient 8). The patients withLoF variants in the C-terminal region had no seizures or hadinfantile spasms only; in addition, 1 patient with a variant inthe S1 to S2 linker reported no seizures. However, one patient(patient 3) with LoF variant in the C-terminus reported se-vere DD. Of the patients with LoF variants, 2 were reported tohave severe DD and 4 had moderate or moderate-severe DD(1 unspecified). In contrast, the only patient with a missensevariant for whom moderate DD was reported was patient 23,who had a missense variant in the S1 to S2 linker. In contrast,all patients with severe epilepsy harbored variants withinthe voltage sensor (S4) and the pore-forming domains (S5,P-loop, and S6) of KCNB1. These observations suggest an as-sociation between location of mutation and phenotype andseverity of disease.
In general, the epilepsy in most patients was highly re-fractory to diverse and multiple antiepileptic drugs. Anecdot-ally, partial efficacy has been reported for ketogenic diet, whichresulted in a significant decrease in seizure burden in 2 pa-tients (patients 14 and 18) but seemed ineffective in 2 others(patients 11 and 20). Improvement was also observed in 1 pa-tient who received steroid pulses (patient 17), whereas intra-muscular adrenocorticotropic hormone therapy for epilepticspasms was reported as not being of value in 3 patients (pa-tients 2, 11, and 14). Vagus nerve stimulation and corpus cal-losotomy surgery were performed in 1 patient (patient 9) with-out substantial improvement of epilepsy. Brain biopsy in thispatient revealed minimal cortical dysplasia consisting of ex-cessive but not dysplastic neurons, a finding that argues againsta role of KCNB1 in disorders of neuronal migration.
Electroencephalographic (EEG) data were reported for 21patients. The EEG displayed features of EE in 20 of 21 pa-tients (95%), including hypsarrhythmia and general slowingof background activity together with multifocal spikes andpolyspikes, and 9 of 21 patients (43%) with abnormal EEG re-sults had a combination of focal and generalized epileptic dis-charges, with 1 being mainly focal. Five patients (24%) had con-tinuous spike and wave during slow-wave sleep (CSWS) orelectrical status epilepticus during slow-wave sleep symp-toms. Patients 14, 18, and 19 had CSWS on EEG, and patients21 and 25 had a history of electrical status epilepticus duringslow-wave sleep.
For 13 patients, more detailed information on motor func-tion was available. Motor performance was poor, with lim-ited ability to walk freely and significant signs of upper motorneuron disease (brisk reflexes, contractures, clonus, and posi-tive plantar response) or ataxia in 10 patients (77%), all withmissense variants within vital channel domains (S4-S6). Theremaining 3 patients had normal neurologic examination find-ings and carried variants in S2 or the C-terminal.
For 14 of 17 patients (82%) with available data, behavioralproblems were reported. Autism spectrum disorder was
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Tabl
e1.
Clin
ical
Phen
otyp
esof
Prev
ious
lyD
escr
ibed
and
New
Patie
ntsW
ithH
eter
ozyg
ousD
eN
ovo
and
Puta
tive
De
Nov
oKC
NB1
Mut
atio
ns
Patie
ntN
o.M
utat
ion
(hg1
9;N
M_0
0497
5.2)
Chan
nel
Dom
ain
Age,
y/Se
x/Ag
eat
Seiz
ure
Ons
etEp
ileps
yDD
Beha
vior
MRI
Find
ings
EEG
Find
ings
Neu
rolo
gic
Exam
inat
ion
Find
ings
Oth
er
1ch
r20:
4799
0350
G>Ap
.Arg
583*
C-te
rmin
al11
/F/N
ANo
seiz
ures
Mod
erat
e-se
vere
(abl
eto
spea
kan
dw
alk)
Seve
rebe
havi
oral
prob
lem
s,AD
HD,a
ndAS
D
Norm
alat
age
10y
Notp
erfo
rmed
NANA
2ch
r20:
4799
0498
G>Tp
.Y53
3*C-
term
inal
32/M
/5m
oIn
fant
ilesp
asm
sUn
spec
ified
,wal
king
at2
yNA
cCT
norm
alHy
psar
rhyt
hmia
NANA
3ch
r20:
4799
0593
T>TA
p.K5
02fs
C-te
rmin
al10
/M/N
ANo
seiz
ures
Seve
reSe
vere
beha
vior
alpr
oble
ms,
ADHD
,and
ASD
Chia
ri1
mal
form
atio
nat
2y
Notd
one
NANA
4ch
r20:
4799
0849
G>Cp
.F41
6LS6
18/F
/42
mo
Toni
c,m
yocl
onic
,and
atyp
ical
abse
nces
Seve
reNA
Periv
entr
icul
arw
hite
mat
ter
abno
rmal
ities
Slow
back
grou
ndac
tivity
and
shar
p-sl
ow-w
ave
disc
harg
esat
2-2.
5Hz
alte
rnat
ing
with
rapi
ddi
scha
rges
Hype
rton
ia,
dyst
onia
Gast
rotu
befe
edin
g
5ch
r20:
4799
0849
G>Cp
.F41
6LS6
15/F
/14
mo
Toni
c-cl
onic
,sta
tus
epile
ptic
us,a
ndst
imul
usev
oked
Seve
reSt
ereo
typi
esan
dha
nd-w
ringi
ng
NAAt
14y,
mul
tifoc
alan
dge
nera
lized
ETP
Atax
iaSc
olio
sis
6ch
r20:
4799
0896
C>Tp
.G40
1RS6
4/M
/17
mo
Clon
ican
dfo
calc
loni
cSe
vere
:no
wor
dsan
dun
able
tosi
tby
4y
NANo
rmal
at9
mo
and
prog
ress
ive
brai
nat
roph
yat
1y
6m
oan
d2
y2
mo
Diff
use
poly
spik
esan
dw
aves
with
inte
rmitt
ent
mul
tifoc
alsp
ikes
at1
y6
mo
Chor
eic
mov
emen
ts,
myo
clon
ia
NA
7ch
r20:
4799
0904
C>Ap
.C39
7FS6
22/M
/10
mo
Toni
c-cl
onic
and
mul
tifoc
alSe
vere
NAAt
2y,
periv
entr
icul
arle
ukom
alac
iaan
dla
tera
lve
ntric
les
NASp
astic
tetr
apar
esis
NA
8ch
r20:
4799
0924
T>Gp
.K39
1NS5
-S6
linke
r(P
-loo
p)NA
NANA
NANA
NAAb
norm
alNA
9ch
r20:
4799
0944
C>Ap
.P38
5TS5
-S6
linke
r(P
-loo
p)17
/M/1
3m
oFo
cald
ysco
gniti
ve,d
rop
atta
cks,
toni
c,no
ctur
nal
toni
c,cl
onic
,and
myo
clon
us
Seve
re:w
alks
only
with
assi
stan
ce,a
taxi
cga
it,an
dno
nver
bal
ASD,
ster
eoty
pies
,an
dha
nd-w
ringi
ng
Norm
alat
6y
and
mild
cere
bella
rvo
lum
elo
ssat
11y
Mul
tifoc
alsh
arps
and
slow
ing
and
diso
rgan
izat
ion
ofth
eba
ckgr
ound
activ
ityat
13y
and
slow
diso
rgan
ized
back
grou
ndw
ithne
arco
ntin
uous
epile
ptifo
rmac
tivity
at16
y
Hype
rton
ia,
atax
ia,t
rem
or,
and
spas
ticity
Scol
iosi
sand
gast
rotu
befe
edin
g
10ch
r20:
4799
0956
C>Tp
.G38
1RS5
-S6
linke
r(s
elec
tivity
filte
r)
8/M
/3m
oSt
artle
epis
odes
at3
mo
evol
ving
toIS
(40/
d),
stim
ulus
-ind
uced
toni
cse
izur
es,f
ocal
dysc
ogni
tive,
and
foca
lm
otor
seiz
ures
Seve
reNA
NAAt
7y:
mul
tifoc
al,
phot
osen
sitiv
e,an
dsl
owHy
pert
onia
,sp
astic
ityPr
ogre
ssiv
em
icro
ceph
aly
(con
tinue
d)
Neurodevelopmental Disorders Caused by KCNB1 De Novo Variants Original Investigation Research
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Tabl
e1.
Clin
ical
Phen
otyp
esof
Prev
ious
lyD
escr
ibed
and
New
Patie
ntsW
ithH
eter
ozyg
ousD
eN
ovo
and
Puta
tive
De
Nov
oKC
NB1
Mut
atio
ns(c
ontin
ued)
Patie
ntN
o.M
utat
ion
(hg1
9;N
M_0
0497
5.2)
Chan
nel
Dom
ain
Age,
y/Se
x/Ag
eat
Seiz
ure
Ons
etEp
ileps
yDD
Beha
vior
MRI
Find
ings
EEG
Find
ings
Neu
rolo
gic
Exam
inat
ion
Find
ings
Oth
er
11ch
r20:
4799
0962
C>Tp
.G37
9RS5
-S6
linke
r(s
elec
tivity
filte
r)
9/M
/8m
oIS
and
late
rmul
tiple
seiz
ure
type
s,in
clud
ing
foca
ldys
cogn
itive
,at
onic
,and
gene
raliz
edto
nic-
clon
ic
Seve
re:m
otor
and
lang
uage
ASD,
ster
eoty
pies
,an
dha
nd-w
ringi
ng
Norm
alat
9m
oAt
15m
o,m
odifi
edhy
psar
rhyt
hmia
Trun
cal
hypo
toni
aan
dbr
isk
refle
xes
Stra
bism
us
12ch
r20:
4799
0964
T>Cp
.V37
8AS5
-S6
linke
r(s
elec
tivity
filte
r)
4/F/
13m
oM
yocl
onic
seiz
ure
follo
wed
bya
toni
cco
mpo
nent
,gen
eral
ized
toni
c-cl
onic
seiz
ure,
and
IS
Seve
re:n
osp
eech
,lim
ited
voca
lizat
ion;
at3
y,fu
nctio
ning
as5-
8m
o;by
3y,
able
tosi
tin
depe
nden
tlybu
tno
stan
ding
orw
alki
ng
NANo
rmal
Lack
ofa
post
erio
r-do
min
ant
rhyt
hm,g
ener
aliz
edsl
owin
g,ge
nera
lized
spik
es,p
olys
pike
sand
shar
pw
aves
,fre
quen
tbu
rsts
ofab
ortiv
efr
onta
l-do
min
ant
gene
raliz
edsp
ikes
,and
poly
spik
esan
dsh
arp
wav
edi
scha
rges
Hypo
toni
aCo
rtic
alvi
sual
impa
irmen
t
13ch
r20:
4799
0976
G>Ap
.T37
4IS5
-S6
linke
r(P
-loo
p)5/
F/6
mo
Toni
c-cl
onic
,ato
nic,
foca
ldys
cogn
itive
atyp
ical
abse
nce,
and
IS
Yes,
unsp
ecifi
edNA
Norm
alUn
spec
ified
Spas
ticity
NA
14ch
r20:
4799
0976
G>Ap
.T37
4IS5
-S6
linke
r(P
-loo
p)11
/F/1
3m
oIS
that
prog
ress
edto
Lenn
ox-G
asta
utsy
ndro
me;
curr
ently
,to
nic
and
abse
nce
seiz
ures
Seve
re:a
t7y
6m
o,co
uld
siti
ndep
ende
ntly
,wal
kw
ith2
hand
sass
iste
d,an
dco
mm
unic
ate
with
20si
gns
ASD,
ster
eoty
pies
,an
dha
nd-w
ringi
ng
T2-h
yper
inte
nsity
of periv
entr
icul
arw
hite
mat
tera
t9
mo
and
norm
alat
4y
At5
y,bi
late
ralC
SWS
with
spik
ean
dw
ave
com
plex
esw
ithsh
iftin
gas
ymm
etrie
s;at
10y,
near
lyco
ntin
uous
epile
ptifo
rmac
tivity
char
acte
rized
byin
depe
nden
tlef
t,rig
ht,o
rbi
late
rals
pike
and
wav
eac
tivity
Chor
eic
mov
emen
ts,
trun
cal
hypo
toni
a,an
dsp
astic
ity
Recu
rren
tba
cter
ial
infe
ctio
ns,l
owim
mun
oglo
bulin
leve
ls,a
ndin
com
plet
eva
ccin
atio
nre
spon
se
15ch
r20:
4799
0990
C>Tp
.W36
9*S5
-S6
linke
r(P
-loo
p)5/
M/1
8m
oHe
addr
op,b
rief
sym
met
ricax
ial,
mus
cle
cont
ract
ion,
evoc
ativ
eof
IS,l
ater
head
drop
,m
yocl
onic
,ast
atic
,ton
ic,
and
toni
c-cl
onic
Seve
re;d
evel
opm
ent
befo
reep
ileps
yon
set:
psyc
hom
otor
deve
lopm
enta
ldel
ay;
deve
lopm
enta
fter
epile
psy
onse
t:in
crea
sed
afte
rsei
zure
ssta
rted
ADHD
and
ASD
Norm
alGe
nera
lized
spik
esan
dw
aves
,foc
alsh
arp
wav
es,
and
spik
es
Trun
cal
hypo
toni
aan
dsp
astic
ity
Neon
atal
resp
irato
rydi
stre
ss
16ch
r20:
4799
1009
delG
,p.S
363f
s*13
S5-S
6lin
ker
(P-l
oop)
2/M
/14
mo
Foca
lsei
zure
sin
whi
chpa
tient
beco
mes
dist
ant
and
pale
,som
etim
esw
ithcy
anos
isof
the
lips,
eye
rolli
ng,a
ndlip
smac
king
of20
sto
2m
indu
ratio
n
Mod
erat
e:no
spee
chat
2y
None
Norm
alSh
arp
wav
esan
dsh
arp
low
wav
esin
left
fron
to-t
empo
ro-c
entr
alre
gion
Norm
alNo
rmal
17ch
r20:
4799
1056
G>Tp
.S34
7RS5
(por
e)9/
F/48
mo
Toni
c-cl
onic
;ton
ic,
aton
ic,f
ocal
,and
foca
lw
ithse
cond
ary
gene
raliz
atio
n
Seve
re:m
otor
and
lang
uage
NASu
btle
volu
me
loss
inle
fthi
ppoc
ampu
s
Mild
,diff
use
slow
ing
and
abun
dant
bihe
mis
pher
ic,
mul
tifoc
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ilept
iform
disc
harg
es
Hypo
toni
aSt
rabi
smus
and
mig
rain
e
18ch
r20:
4799
1162
C>Tp
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(VSD
)11
/M/1
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oFo
cals
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rew
ithey
ean
dm
outh
devi
atio
nto
the
right
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ally
with
seco
ndar
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nera
lizat
ion
Seve
re/r
egre
ssio
n:st
oppe
dw
alki
ngat
5y
and
neve
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elop
edla
ngua
ge
ASD
and
tem
per
tant
rum
s
Norm
alCS
WS
patt
ern
and
gene
raliz
eddi
scha
rges
ofdi
phas
icsp
ikes
and
slow
wav
esan
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Atax
iaan
dsp
astic
itySu
spec
ted
retin
opat
hy
(con
tinue
d)
Research Original Investigation Neurodevelopmental Disorders Caused by KCNB1 De Novo Variants
1232 JAMA Neurology October 2017 Volume 74, Number 10 (Reprinted) jamaneurology.com
© 2017 American Medical Association. All rights reserved.
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Tabl
e1.
Clin
ical
Phen
otyp
esof
Prev
ious
lyD
escr
ibed
and
New
Patie
ntsW
ithH
eter
ozyg
ousD
eN
ovo
and
Puta
tive
De
Nov
oKC
NB1
Mut
atio
ns(c
ontin
ued)
Patie
ntN
o.M
utat
ion
(hg1
9;N
M_0
0497
5.2)
Chan
nel
Dom
ain
Age,
y/Se
x/Ag
eat
Seiz
ure
Ons
etEp
ileps
yDD
Beha
vior
MRI
Find
ings
EEG
Find
ings
Neu
rolo
gic
Exam
inat
ion
Find
ings
Oth
er
19ch
r20:
4799
1162
C>Tp
.R31
2HS4
(VSD
)9/
M/1
0m
oIS
,myo
clon
ic,a
typi
cal
abse
nces
,and
toni
cSe
vere
:dev
elop
men
tal
dela
ysi
nce
first
year
oflif
e,no
activ
esp
eech
atag
e8
y,an
dw
alki
ngon
tipto
e
ASD
and
tem
per
tant
rum
s
Norm
alat
8y
CSW
Spa
tter
n,bi
late
ral
slow
wav
es,a
ndm
ultir
egio
nals
harp
wav
es
Atax
iaan
dsp
astic
itySl
eep
dist
urba
nce
20ch
r20:
4799
1181
G>Ap
.R30
6CS4
(VSD
)7/
M/1
2m
oIS
at1
yan
dto
nic-
clon
ic,m
yocl
onic
,an
dfo
calw
ithhe
adde
viat
ion
at2
y
Seve
re,b
utab
leto
spea
kso
me
wor
dsan
dw
alk
ASD
and
tem
per
tant
rum
s
Norm
alat
2y
3m
oGe
nera
lized
disc
harg
esof
high
-am
plitu
desp
ikes
,w
aves
,and
poly
spik
esat
2y
11m
o
NAM
acro
ceph
aly
21ch
r20:
4799
1181
G>Ap
.R30
6CS4
(VSD
)9/
M/1
yFe
w:f
ebril
eco
nvul
sion
s(a
bsen
ces/
aton
ic)
Seve
reAD
HD(s
ever
ehy
pera
ctiv
ity)
and
aggr
essi
veou
tbur
sts
Retr
ocer
ebel
lar
arac
hnoi
dalc
yst
ESES
patt
ern,
mul
tifoc
alsp
ikes
,and
diff
use
poly
spik
es
Hypo
toni
a(a
sinf
ant)
,at
axia
,and
extr
apyr
amid
alm
ovem
ent
diso
rder
NA
22ch
r20:
4799
1415
G>Ap
.Q22
8*S1
-S2
linke
r3.
5/F/
10m
oDi
alep
ticse
izur
e,au
tom
otor
seiz
ure,
and
gene
raliz
edto
nic-
clon
ic
Mod
erat
e,gl
obal
deve
lopm
enta
ldel
ay:
spee
chan
dm
otor
ADHD
Norm
alFo
cals
pike
s,ic
talp
atte
rnte
mpo
rall
eft,
and
icta
lge
nera
lized
seiz
ure
patt
ern
Norm
alNA
23ch
r20:
4799
1465
A>Gp
.L21
1PS1
-S2
linke
r7/
F/11
mo
FS,G
TCS,
and
foca
lep
ileps
yM
oder
ate
dela
yan
ddy
spra
xia
None
Norm
alPa
roxy
smal
activ
ityw
ithce
ntro
parit
alsp
ikes
and
poly
spik
es,g
ener
aliz
edan
dac
cent
uate
ddu
ring
slee
p
Hypo
toni
aNA
24ch
r20:
4799
1468
G>Ap
.T21
0MS1
-S2
linke
r4/
F/NA
Nose
izur
esUn
spec
ified
NANo
rmal
Nota
pplic
able
Norm
alGa
stro
tube
feed
ing
25ch
r20:
4799
1468
G>Tp
.T21
0KS1
-S2
linke
r7/
M/4
mo
Myo
clon
ic:g
ener
aliz
edto
nic-
clon
ic,f
ocal
dysc
ogni
tive
with
mot
orsi
gns,
aton
ic,s
ubcl
inic
alse
izur
esdu
ring
slee
p,an
dhi
stor
yof
ESES
Glob
alde
lay,
spea
ksse
nten
ces,
and
wal
king
Hype
ract
ivity
and
inat
tent
ion
Norm
alRi
ghtc
entr
alsh
arps
with
abr
oad
field
,inc
reas
ein
slee
p,an
dbi
late
ralc
entr
alsp
ike
wav
edi
scha
rges
Hypo
toni
aNA
26ch
r20:
4799
1492
G>Ap
.S20
2FS1
-S2
linke
r7/
M/2
yO
nset
:com
plex
part
ial
seiz
ures
,fev
eras
soci
ated
;rec
ent:
subc
linic
alse
izur
esdu
ring
slee
p
Glob
alde
lay,
spea
ksso
me
wor
dsan
dsh
ortp
hras
es,
and
able
tow
alk
Hype
ract
ivity
,in
atte
ntio
n,im
puls
ivity
,se
lf-in
jurio
usbe
havi
or,a
ndau
tism
Norm
alM
ultif
ocal
epile
ptifo
rmdi
scha
rges
,gen
eral
ized
burs
tsof
spik
ean
dw
aves
durin
gsl
eep
not
cons
iste
ntw
ithES
ES,a
nd2
gene
raliz
edse
izur
esat
awak
enin
g
Norm
alSh
orts
tatu
re,
wid
e-sp
aced
teet
h,in
crea
sed
droo
ling,
ingu
inal
hern
ia,
and
slee
pdy
sfun
ctio
n
Abbr
evia
tions
:AD
HD,
atte
ntio
n-de
ficit/
hype
ract
ivity
diso
rder
;ASD
,aut
ismsp
ectr
aldi
sord
er;c
CT,c
ardi
ovas
cula
rco
mpu
ted
tom
ogra
phy;
CSW
S,co
ntin
uous
spik
ean
dw
ave
durin
gslo
w-w
ave
sleep
;DD,
deve
lopm
enta
ldel
ay;
EEG,
elec
troe
ncep
halo
grap
hy;E
SES,
elec
tric
alst
atus
epile
ptic
usdu
ring
slow
-wav
esle
ep;E
TP,e
pile
psy
typi
cal
pote
ntia
l;F,
fem
ale;
FS,f
ebril
ese
izur
e;GT
CS,g
ener
aliz
edto
nic-
clon
icse
izur
e;IS
,inf
antil
esp
asm
;M,m
ale;
MRI
,mag
netic
reso
nanc
eim
agin
g;N
A,no
tapp
licab
le;V
SD,v
entr
icul
arse
ptal
defe
ct.
Neurodevelopmental Disorders Caused by KCNB1 De Novo Variants Original Investigation Research
jamaneurology.com (Reprinted) JAMA Neurology October 2017 Volume 74, Number 10 1233
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-
reported in 10 individuals, with different variants locatedthrough S4 to S6 and the C-terminus. In 4 patients, caregiversnoted specifically nonpurposeful hand-wringing stereoty-pies. In addition, attention-deficit/hyperactivity disorder orhyperactivity with inattention in 7 patients and temper tan-trums in 3 patients were mentioned.
Information on brain imaging was available from 23 of 26patients (22 with magnetic resonance imaging and 1 with com-puted tomography). Results were normal in 19 patients (83%)or revealed unspecific features after infancy, such as Arnold-Chiari malformation type 1 (patient 3), progressive supraten-torial brain atrophy (patient 6, G401R, with infantile epi-lepsy), cerebellar volume loss (patient 8, P385T, infantileepilepsy proceeding to Lennox-Gastaut syndrome), and whitematter abnormalities (patient 14, T374I, West syndrome pro-gressing to Lennox-Gastaut syndrome), corresponding to sei-zure burden in these patients.
DiscussionAll missense variants clustered within the ion_trans domain,in which few natural segregating variants are found. On theexome variants server with data from more than 6500 indi-viduals (http://evs.gs.washington.edu/EVS/), no coding variantswere found in the ion_trans domain. In the ExAC database withmore than 60 000 individuals, 9 coding variants were presentin this domain.
On the basis of the work of Samocha et al,24 we exploredthe frequency of missense variants in the ExAC database in thedifferent regions of the gene relative to the neutral expecta-tion to identify gene regions intolerant to missense variation.The ratio of missense to synonymous variants is 0.26 in the
ion_trans domain; 0.33 in the upstream region, including theT1 domain; and 2.14 in the downstream region, including theKv2 channel–specific domains. This ratio is expected to be 2.3for the whole gene after neutral expectation according toSamocha et al24; therefore, both the ion_trans domain and theupstream region of the gene are intolerant to missense vari-ants (P < 1 × 10−5). Missense variants in those regions thus havea high probability of being pathogenic.24 We assume that allmissense variants discussed in the present study are causal forthe neurodevelopmental disorder in the patient.
We also consider the LoF variants described in the presentstudy to be pathogenic. In the ExAC database, only 2 rare LoFvariants were found: p.R854* (flagged as dubious) andp.K776Qfs*23. These variants are located in the C-terminal partof the gene, closer to the terminal part than were the LoF vari-ants found in the patients and beyond the Kv2 channel–specific domains (Figure). Therefore, it can be expected thatthese variants, if they exist, do not affect normal function ofKv2.1. In contrast, the 3 C-terminal mutations observed in thepatients were in the Kv2.1-specific domain located more up-stream and therefore may be expected to have a functional ef-fect, for example, lead to differences in protein folding or affectformation of tetramers. All LoF variants in the patients were inthe last exon of the gene; thus, we expect that they will lead totruncation rather than nonsense-mediated decay.25 Because theprotein forms (hetero)tetramers, we expect that the effect of themissense and truncating variants is dominant negative unlessthe mutated protein is not incorporated in the membrane.
Because we consider all variants described in this article ascausal for the phenotype, the phenotypic range described islikely to be representative of variants in this gene. There maybe a bias, however, toward patients with epilepsy because ourinitial screen was conducted in a panel of patients with EE andmany colleagues in our network have a special interest in thisphenotype. Torkamani et al2 may also have searched only forpatients with seizures when following up their initial finding.The patients without seizures in this article were from exome-wide diagnostic screening of patients with (neuro)developmen-tal problems and from the Deciphering Developmental Disor-ders program in the United Kingdom, which also was a generalscreening of children with developmental disorders. As de-scribed in the Results section and as seen in Table 1, the rangeof symptoms in patients with variants in KCNB1 was diverse inmany aspects.
Genotype-Phenotype AssociationsMost missense variants were in the S5 to S6 linker, which formsthe pore region, particularly in or near the selectivity filter.Three patients had missense variants in one of the positivelycharged R-residues in voltage sensor S4. As described in theResults section, the distribution of variants in patients overthe domains is different from that in the general population.The variants that we found in the less constrained C-terminuswere LoF variants.
Missense variants within the voltage sensor domain or thepore region of the channel were found in patients with severeepilepsy and global DD, including intellectual disability and of-ten spasticity. Therefore, missense variants in the S4 to S6 re-
Table 2. Major Clinical Characteristics of the Patients Carryinga Presumed Pathogenic KCNB1 Mutation
PhenotypeNo. of Patients/Patients WithData Available (%)
Developmental delay 26/26 (100)
Intractable epilepsy 21/25 (84)
Epileptic spasms 9/25 (36)
EE-EEG 20/21 (95)
Focal-generalized discharges 9/21 (43)
CSWS or ESES 5/21 (24)
Poor motor function 10/13 (77)
Hypotonia 11/23 (48)
Ataxia 4/23 (17)
Abnormal behavior 14/17 (82)
ADHD 7/20 (35)
ASD 10/20 (50)
Hand-wringing 4/20 (20)
Temper tantrums 3/20 (15)
Abnormal brain imaging 4/23 (17)
Abbreviations: ADHD, attention-deficit/hyperactivity disorder; ASD, autismspectrum disorder; CSWS, continuous spike and wave during slow-wave sleep;EE, epileptic encephalopathy; EEG, electroencephalography; ESES, electricalstatus epilepticus during slow-wave sleep.
Research Original Investigation Neurodevelopmental Disorders Caused by KCNB1 De Novo Variants
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gion seem to be correlated with a more severe prognosis. AnLoF variant close to S2 and one in the C-terminus were foundin patients with milder DD, who acquired walking and were ableto communicate. Two of the 3 LoF variants in the C-terminuswere in patients without seizures (at 11 and 32 years of age),whereas a patient with a missense variant in the S1 to S2 linker,close to S1, had no seizures at 4 years of age. The degree of in-tellectual disability in this patient was unspecified.9 The LoFvariant 15 (p.W369*) in the pore region was seen in a patientwith severe DD and epilepsy at the age of 5 years, whereas theLoF variant near that in LoF variant 16 (p.S363fs*) was foundin a patient at 2 years of age with moderate DD and focal sei-zures but no additional reported problems.
No pathogenic variants have been reported thus far in thehighly constrained N-terminal region. A handful of rare mis-sense variants were described for this region in the ExACcontrol population. It remains to be determined whether mis-sense or LoF variants in this region also lead to neurodevel-opmental disorders. The strong constraints on variation in thisregion suggest that many of the possible variants are delete-rious or even fatal. Finally, patients carrying missense muta-tions more often had abnormal neurologic examination re-sults (17 of 19 available [89%]) compared with 1 of 3 LoF carriers(33%) (P = .02, χ2 test for independence). Similarly, normalmagnetic resonance imaging results were reported for all 6 pa-tients carrying an LoF mutation. Overall, patients with KCNB1mutations have a variable phenotype, a finding highlighted bythe observation that even patients carrying the same muta-tion have differences in phenotype.
Functional studies2,8,9 have been performed for several ofthe described variants. In general, the electrophysiologic char-acteristics of the different variants have a variety of func-tional aberrations, such as loss of voltage sensing (p.R306C),reduced current (p.G410R), and suppression of repetitive fir-ing (p.R306C, p.G410R). Of interest, all 3 missense mutationsin the ion-selectivity filter domain have been studied and ren-der Kv2.1, a nonselective cation channel that is not voltage ac-tivated. However, the general loss of channel function anddominant-negative effects seen in most studied variants arein support of the presumed pathogenicity and link to the EEphenotype. Finally, a Kv2.1−/− mouse model was not prone tospontaneous seizures but exhibited hypocampal hyperexcit-ability and epileptiform activity on stimulation.26 Together,these observations further support our conclusion that theKCNB1 variants described here are likely to be pathogenic.
Comparison to KCNQ2KCNB1 forms a gene family with KCNB2, with which it can formheterotetramers. To date, KCNB2 has not been implicated inmonogenic disorders. KCNB1 has a similar structure as otherpotassium channels involved in severe epilepsy, such asKCNQ2. Pathogenic mutations leading to EE in the other po-tassium channels are found in the transmembrane regions. Thisfinding is similar to the mutations in KCNB1 described in thisstudy. Furthermore, 2 of the pathogenic variants found inKCNQ227 were homologous to presumed pathogenic variantsdescribed in this article: the charged residue in the voltagesensor (p.R306C; variant 20) and missense variants 13 and14 (p.T374I) in the pore region. This finding underlines theimportance of these residues for the functioning of theproteins.
LimitationsOur study also has some limitations. Our patients may havebeen selected for certain phenotypes, in particular for epi-lepsy. Our focus on EE may have excluded cases with muchmilder phenotypes. Furthermore, the number of observa-tions remain small, and description of additional cases willfurther elucidate the full clinical spectrum associated withmutations in KCNB1.
ConclusionsMissense and LoF variants in the ion_trans domain of KCNB1 andLoF variants in the C-terminal region can cause neurodevelop-mentaldisorderwithorwithoutepilepticseizures.Missensevari-ants in the C-terminus are less likely to cause developmental dis-orders, whereas the consequences of variants in the N-terminusis not clear. The more severely affected patients consistently har-bored missense variants within vital channel domains of KCNB1and experienced late-onset epileptic spasms that evolved totreatment-refractive epilepsy and severe global DD. The effectof LoF variants was less clear, although a tendency existed to-ward less severe phenotypes. However, more outcome data onpatients with LoF variants are needed to support clinical predic-tions and counseling of such patients. There was a marked ten-dency to develop spastic paraparesis or tetraparesis and ataxiaas well as autistic spectrum disorder. Finally, patients carryingmissense mutations were more likely to have neurologic andmagnetic resonance imaging abnormalities.
ARTICLE INFORMATION
Accepted for Publication: May 18, 2017.
Published Online: August 14, 2017.doi:10.1001/jamaneurol.2017.1714
Author Affiliations: Department of Genetics,University Medical Center Utrecht, Utrecht,the Netherlands (de Kovel, Brilstra, Verbeek,van den Boogaardt, Koeleman); Department ofLanguage and Genetics, Max Planck Institute forPsycholinguistics, Nijmegen, the Netherlands(de Kovel); Division of Child Neurology andInherited Metabolic Diseases, Department ofGeneral Pediatrics, Center for Pediatrics and
Adolescent Medicine, University HospitalHeidelberg, Heidelberg, Germany (Syrbe); Instituteof Evolution, Systems and Genomics, Faculty ofMedical and Human Sciences, University ofManchester, Manchester, England (Kerr);Manchester Centre For Genomic Medicine, CentralManchester University Hospitals National HealthService Foundation Trust, Manchester, England(Kerr); Manchester Academic Health ScienceCentre, Manchester, England (Kerr); Division ofNeurology, The Children's Hospital of Philadelphia,Philadelphia, Pennsylvania (Dubbs, Goldberg,Marsh, Kessler, Bergqvist, Helbig); Department ofPediatrics, University Hospital of Hvidovre,
Copenhagen, Denmark (Bayat); Department ofNeurogenetics, Kennedy Krieger Institute,Baltimore, Maryland (Desai); Department ofNeurology and Pediatrics, Johns Hopkins School ofMedicine, Baltimore, Maryland (Naidu); HugoMoser Research Institute, Kennedy KriegerInstitute, Baltimore, Maryland (Naidu); Departmentof Neurology, Boston Children's Hospital, Boston,Massachusetts (Srivastava); Department ofMolecular Biology and Genetics, BogaziçiUniversity, Istanbul, Turkey (Cagaylan); Division ofChild Neurology, Department of Pediatrics, Schoolof Medicine, Dokuz Eylül University, İzmir, Turkey(Yis); Center for Pediatric Genomic Medicine,
Neurodevelopmental Disorders Caused by KCNB1 De Novo Variants Original Investigation Research
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Department of Pathology and Laboratory Medicine,Children's Mercy Hospital, Kansas City, Missouri(Saunders, Thiffault); Department of Pediatrics,Children's Mercy Hospital, Kansas City, Missouri(Saunders, Thiffault); Pediatric Pathology andLaboratory Medicine, University of Missouri–KansasCity School of Medicine, Kansas City (Saunders);Department of Medical Physiology, UniversityMedical Center Utrecht, Utrecht, the Netherlands.(Rook); Department of Biomedical Sciences,University Medical Center Utrecht, Utrecht,the Netherlands (Plugge); Department ofNeuropediatrics, University Medical CenterSchleswig-Holstein, Christian Albrechts University,Kiel, Germany (Muhle, Pendziwiat); Department ofPhysiology and Pharmacology, Tel Aviv UniversityMedical School, Ramat Aviv, Israel (Afawi);Department of Neurology, Epilepsy CenterFrankfurt Rhine-Main, Center of Neurology andNeurosurgery, University Hospital, Goethe-University Frankfurt, Frankfurt, Germany (Klein);Division of Genomic Diagnostics, Children’s Hospitalof Philadelphia, Philadelphia, Pennsylvania(Jayaraman, Rajagopalan, Conlin, Krok); UniversityMedical Center Schleswig-Holstein, ChristianAlbrechts University, Kiel, Germany (Helbig);Epilepsiezentrum Bethel, Krankenhaus Mara,Kinderepileptologie, Bielefeld, Germany (Polster);Department of Pediatric Neurology, DevelopmentalMedicine and Social Pediatrics Dr. von Hauner’sChildren’s Hospital, University of Munich, Munich,Germany (Borggraefe); Institute of HumanGenetics, University of Leipzig Hospitals and Clinics,Leipzig, Germany (Lemke); Danish Epilepsy Centre,Dianalund, Denmark (Møller); Institute for RegionalHealth Services, University of Southern Denmark,Odense, Denmark (Møller).
Author Contributions: Dr de Kovel had full accessto all the data in the study and takes responsibilityfor the integrity of the data and the accuracy of thedata analysis.Study concept and design: de Kovel, Syrbe, Yis,Koeleman.Acquisition, analysis, or interpretation of data:de Kovel, Syrbe, Brilstra, Verbeek, Kerr, Dubbs,Bayat, Desai, Naidu, Srivastava, Cagaylan, Saunders,Rook, Plugge, Muhle, Afawi, Klein, Rajagopalan,Jayaraman, Goldberg, Marsh, Kessler, Bergqvist,Conlin, Krok, Thiffault, Pendziwiat, Helbig, Polster,Borggraefe, Lemke, van den Boogaardt, Møller,Koeleman.Drafting of the manuscript: de Kovel, Kerr, Plugge,Afawi, Jayaraman, Helbig, Koeleman.Critical revision of the manuscript for importantintellectual content: de Kovel, Syrbe, Brilstra,Verbeek, Dubbs, Bayat, Desai, Naidu, Srivastava,Cagaylan, Yis, Saunders, Rook, Muhle, Klein,Rajagopalan, Goldberg, Marsh, Kessler, Bergqvist,Conlin, Krok, Thiffault, Pendziwiat, Helbig, Polster,Borggraefe, Lemke, van den Boogaardt, Møller,Koeleman.Statistical analysis: de Kovel, Syrbe, Afawi.Obtained funding: Helbig, Koeleman.Administrative, technical, or material support:de Kovel, Syrbe, Brilstra, Verbeek, Dubbs, Bayat,Desai, Naidu, Cagaylan, Yis, Rajagopalan, Goldberg,Kessler, Bergqvist, Conlin, Thiffault, Helbig, Lemke,van den Boogaardt, Koeleman.Study supervision: Afawi, Kessler, Helbig, Koeleman.
Conflict of Interest Disclosures: None reported.
Funding/Support: This study was funded by grantG.A.136.11.N from the Dutch Epilepsy Foundation
(Dr Koeleman) and Euroepinomics-RES (Dr Helbig).Dr Helbig was supported by grants HE 5415/5-1 andHE 5415/6-1 from the German Research Foundationand grant U01-HG006546 from the NationalHuman Genome Research Institute of the NationalInstitutes of Health. The Wellcome Trust supportedthe data generation of the Decipher project.
Role of the Funder/Sponsor: The sponsors had norole in the design and conduct of the study;collection, management, analysis, andinterpretation of the data; preparation, review, orapproval of the manuscript; and decision to submitthe manuscript for publication.
Additional Contributions: We acknowledge thecontributions of Nancy Spinner and Ian Krantz, whowere not compensated for their help. This studymakes use of data generated by the Database ofGenomic Variation and Phenotype in Humans UsingEnsembl Resources (DECIPHER) community. A fulllist of centers that contributed to the generation ofthe data is available at http://decipher.sanger.ac.ukand via email from [email protected]. Wethank the patients and their parents forcontributing to this research and all clinicians whoprovided samples from their patients. We thank theExome Aggregation Consortium and the groupsthat provided exome variant data for comparison.A full list of contributing groups can be found athttp://exac.broadinstitute.org/about.
REFERENCES
1. Deprez L, Jansen A, De Jonghe P. Genetics ofepilepsy syndromes starting in the first year of life.Neurology. 2009;72(3):273-281.
2. Torkamani A, Bersell K, Jorge BS, et al. De novoKCNB1 mutations in epileptic encephalopathy. AnnNeurol. 2014;76(4):529-540.
3. Allen AS, Berkovic SF, Cossette P, et al; Epi4KConsortium; Epilepsy Phenome/Genome Project.De novo mutations in epileptic encephalopathies.Nature. 2013;501(7466):217-221.
4. Soden SE, Saunders CJ, Willig LK, et al.Effectiveness of exome and genome sequencingguided by acuity of illness for diagnosis ofneurodevelopmental disorders. Sci Transl Med.2014;6(265):265ra168.
5. Srivastava S, Cohen JS, Vernon H, et al. Clinicalwhole exome sequencing in child neurologypractice. Ann Neurol. 2014;76(4):473-483.
6. Deciphering Developmental Disorders Study.Large-scale discovery of novel genetic causes ofdevelopmental disorders. Nature. 2015;519(7542):223-228.
7. Allen NM, Conroy J, Shahwan A, et al.Unexplained early onset epileptic encephalopathy:exome screening and phenotype expansion.Epilepsia. 2016;57(1):e12-e17.
8. Thiffault I, Speca DJ, Austin DC, et al. A novelepileptic encephalopathy mutation in KCNB1disrupts Kv2.1 ion selectivity, expression, andlocalization. J Gen Physiol. 2015;146(5):399-410.
9. Saitsu H, Akita T, Tohyama J, et al. De novoKCNB1 mutations in infantile epilepsy inhibitrepetitive neuronal firing. Sci Rep. 2015;5:15199.
10. Latypova X, Matsumoto N, Vinceslas-Muller C,Bézieau S, Isidor B, Miyake N. Novel KCNB1mutation associated with non-syndromicintellectual disability. J Hum Genet. 2017;62(5):569-573.
11. Bishop HI, Guan D, Bocksteins E, et al. Distinctcell- and layer-specific expression patterns andindependent regulation of Kv2 channel subtypes incortical pyramidal neurons. J Neurosci. 2015;35(44):14922-14942.
12. Letunic I, Doerks T, Bork P. SMART: recentupdates, new developments and status in 2015.Nucleic Acids Res. 2015;43(database issue):D257-D260.
13. Finn RD, Bateman A, Clements J, et al. Pfam:the protein families database. Nucleic Acids Res.2014;42(database issue):D222-D230.
14. Kuang Q, Purhonen P, Hebert H. Structure ofpotassium channels. Cell Mol Life Sci. 2015;72(19):3677-3693.
15. Ruppersberg JP, Schröter KH, Sakmann B,Stocker M, Sewing S, Pongs O. Heteromultimericchannels formed by rat brain potassium-channelproteins. Nature. 1990;345(6275):535-537.
16. Ottschytsch N, Raes A, Van Hoorick D,Snyders DJ. Obligatory heterotetramerization ofthree previously uncharacterized Kv channelα-subunits identified in the human genome. ProcNatl Acad Sci U S A. 2002;99(12):7986-7991.
17. Bocksteins E, Mayeur E, Van Tilborg A,Regnier G, Timmermans JP, Snyders DJ. Thesubfamily-specific interaction between Kv2.1 andKv6.4 subunits is determined by interactionsbetween the N- and C-termini. PLoS One. 2014;9(6):e98960.
18. de Kovel CG, Brilstra EH, van Kempen MJ, et al;EuroEPINOMICS RES Consortium. Targetedsequencing of 351 candidate genes for epilepticencephalopathy in a large cohort of patients. MolGenet Genomic Med. 2016;4(5):568-580.
19. Islas LD, Sigworth FJ. Voltage sensitivity andgating charge in Shaker and Shab family potassiumchannels. J Gen Physiol. 1999;114(5):723-742.
20. Ng PC, Henikoff S. Predicting the effects ofamino acid substitutions on protein function. AnnuRev Genomics Hum Genet. 2006;7:61-80.
21. Adzhubei IA, Schmidt S, Peshkin L, et al.A method and server for predicting damagingmissense mutations. Nat Methods. 2010;7(4):248-249.
22. Kircher M, Witten DM, Jain P, O’Roak BJ,Cooper GM, Shendure J. A general framework forestimating the relative pathogenicity of humangenetic variants. Nat Genet. 2014;46(3):310-315.
23. Lek M, Karczewski KJ, Minikel EV, et al;Exome Aggregation Consortium. Analysis ofprotein-coding genetic variation in 60,706 humans.Nature. 2016;536(7616):285-291.
24. Samocha KE, Robinson EB, Sanders SJ, et al.A framework for the interpretation of de novomutation in human disease. Nat Genet. 2014;46(9):944-950.
25. Baker KE, Parker R. Nonsense-mediated mRNAdecay: terminating erroneous gene expression. CurrOpin Cell Biol. 2004;16(3):293-299.
26. Speca DJ, Ogata G, Mandikian D, et al. Deletionof the Kv2.1 delayed rectifier potassium channelleads to neuronal and behavioral hyperexcitability.Genes Brain Behav. 2014;13(4):394-408.
27. Weckhuysen S, Mandelstam S, Suls A, et al.KCNQ2 encephalopathy: emerging phenotype of aneonatal epileptic encephalopathy. Ann Neurol.2012;71(1):15-25.
Research Original Investigation Neurodevelopmental Disorders Caused by KCNB1 De Novo Variants
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