ORIGINAL ARTICLE

KCNQ2 Encephalopathy: EmergingPhenotype of a Neonatal Epileptic

Encephalopathy

Sarah Weckhuysen, MD,1,2,3 Simone Mandelstam, MB ChB,4,5 Arvid Suls, PhD,1,2

Dominique Audenaert, PhD,1,2,6 Tine Deconinck, MSc,1,2 Lieve R.F. Claes, PhD,1,2 Liesbet

Deprez, PhD,1,2 Katrien Smets, MD,1,2,7 Dimitrina Hristova, MD,8

Iglika Yordanova, MSc,9 Albena Jordanova, PhD,1,2 Berten Ceulemans, MD, PhD,2,10

An Jansen, MD, PhD,11,12 Daniele Hasaerts, MD,11 Filip Roelens, MD,13

Lieven Lagae, MD, PhD,14 Simone Yendle, BSc (Hons),15 Thorsten Stanley, MD,16

Sarah E. Heron, PhD,17 John C. Mulley, PhD,18,19 Samuel F. Berkovic, MD, FRS,15

Ingrid E. Scheffer, MBBS, PhD,4,15,20 and Peter de Jonghe, MD, PhD1,2,7

Objective: KCNQ2 and KCNQ3 mutations are known to be responsible for benign familial neonatal seizures (BFNS).A few reports on patients with a KCNQ2 mutation with a more severe outcome exist, but a definite relationship hasnot been established. In this study we investigated whether KCNQ2/3 mutations are a frequent cause of epilepticencephalopathies with an early onset and whether a recognizable phenotype exists.Methods: We analyzed 80 patients with unexplained neonatal or early-infantile seizures and associated psychomotorretardation for KCNQ2 and KCNQ3 mutations. Clinical and imaging data were reviewed in detail.Results: We found 7 different heterozygous KCNQ2 mutations in 8 patients (8/80; 10%); 6 mutations arose de novo.One parent with a milder phenotype was mosaic for the mutation. No KCNQ3 mutations were found. The 8 patientshad onset of intractable seizures in the first week of life with a prominent tonic component. Seizures generallyresolved by age 3 years but the children had profound, or less frequently severe, intellectual disability with motorimpairment. Electroencephalography (EEG) at onset showed a burst-suppression pattern or multifocal epileptiformactivity. Early magnetic resonance imaging (MRI) of the brain showed characteristic hyperintensities in the basalganglia and thalamus that later resolved.Interpretation: KCNQ2 mutations are found in a substantial proportion of patients with a neonatal epilepticencephalopathy with a potentially recognizable electroclinical and radiological phenotype. This suggests that KCNQ2screening should be included in the diagnostic workup of refractory neonatal seizures of unknown origin.

ANN NEUROL 2012;71:15–25

View this article online at wileyonlinelibrary.com. DOI: 10.1002/ana.22644

Received Apr 19, 2011, and in revised form Sep 25, 2011. Accepted for publication Sep 30, 2011.

Address correspondence to Dr Peter de Jonghe, VIB-Department of Molecular Genetics, Neurogenetics Group, University of Antwerp, Campus CDE,

Parking P4, Building V, Universiteitsplein 1, 2610 Antwerp, Belgium. E-mail: peter.dejonghe@molgen.vib-ua.be

From the 1Neurogenetics Group, VIB-Department of Molecular Genetics, 2Laboratory of Neurogenetics, Institute Born-Bunge, University of Antwerp,

Antwerp, Belgium, 7Department of Neurology, University Hospital of Antwerp, and 10Pediatric Neurology, Department of Neurology, University Hospital of

Antwerp, Antwerp, Belgium; 3Epilepsy Centre Kempenhaeghe, Oosterhout, the Netherlands; 4Florey Neurosciences Institutes, Austin Health, Melbourne,

Australia; 5Department of Radiology, Royal Children’s Hospital, Melbourne, Australia; 6Department of Plant Systems Biology, VIB, Ghent University, Ghent,

Belgium; 8Children Neurology Unit, Pediatrics Clinic, Tokuda Hospital-Sofia, Sofia, Bulgaria; 9National Genetics Laboratory, Medical University-Sofia, Sofia,

Bulgaria; 11Pediatric Neurology Unit, Department of Pediatrics, UZ Brussel and 12Department of Public Health, Vrije Universiteit Brussel, Brussels, Belgium;13Department of Pediatrics, Heilig Hart Ziekenhuis, Roeselare, Belgium; 14Department of Pediatric Neurology, University Hospital Gasthuisberg, Leuven,

Belgium; 15Epilepsy Research Centre, Department of Medicine, University of Melbourne, Austin Health and 20Department of Paediatrics, Royal Children’s

Hospital, University of Melbourne, Melbourne, Australia; 16Department of Paediatrics, University of Otago, Wellington, New Zealand; and 17Epilepsy

Research Program, School of Pharmacy and Medical Sciences, The University of South Australia, 18Epilepsy Research Program, SA Pathology at Women’s

and Children’s Hospital, and 19School of Molecular and Biomedical Sciences and School of Paediatrics and Reproductive Health, University of Adelaide,

Adelaide, Australia.

Additional Supporting Information can be found in the online version of this article.

VC 2012 American Neurological Association 15

Benign familial neonatal seizures (BFNS) is an autoso-

mal dominant epilepsy syndrome with a favorable

prognosis. Seizures typically begin between day 2 to 8 of

life, and remit by 16 months. Seizures often begin with a

tonic component followed by a range of autonomic and

motor changes, which may be uni- or bilateral, and may

be symmetrical. They are often accompanied by apnea.

Seizures are brief but can occur up to 30 times a day or

even evolve into status epilepticus.1–4 Development is

usually normal. Although BFNS is considered a benign

condition, patients have a slightly increased risk of

epilepsy later in life.5,6

Mutations in KCNQ2 and KCNQ3, which encode

the voltage-gated potassium channels Kv7.2 and Kv7.3

have been identified in 60% to 70% of families with

BFNS.7–10 Both genes are expressed in the central nerv-

ous system, where their gene products form heteromulti-

meric channels that mediate the M-current (IKM), a

slowly activating, noninactivating potassium conductance

that inhibits neuronal excitability. KCNQ2 is the main

gene for BFNS, being mutated in more than 90% of the

patients in which the genetic cause has been found.

Rare sporadic and familial cases with neonatal onset

seizures and poor outcome attributed to KCNQ2 muta-

tions have been described. Four reported BFNS families

with KCNQ2 mutations contain some family members

showing a more severe outcome including variable

degrees of intellectual disability.11–13 An additional

sporadic patient with neonatal tonic seizures and mental

impairment had a de novo KCNQ2 mutation.14 The in

vitro electrophysiological characteristics of these muta-

tions were similar to other KCNQ2 mutations associated

with BFNS. Therefore, it is difficult to assess the causal-

ity between these KCNQ2 mutations and the severe

outcome, and authors suggested that other genetic or

environmental factors must influence the more severe

phenotypic outcome of these mutations.

In order to clarify whether particular KCNQ2 and

KCNQ3 mutations are associated with a recognizable

severe epilepsy phenotype, we performed a mutational

analysis of KCNQ2 and KCNQ3 in a cohort of 80

patients with epileptic encephalopathies where they had

refractory seizures with neonatal or early infantile onset

and intellectual disability of unknown origin.

Patients and Methods

PatientsWe selected from our patient database 80 patients with an

unexplained neonatal or early infantile epileptic encephalopathy.

Patients were referred mainly by collaborating child neurologists

from Western Europe and from the Australian infantile epilep-

tic encephalopathy study. All patients had onset of seizures

within the first 3 months of life followed by slowing of psycho-

motor development with or without additional neurological

deficits such as spasticity. Since patients were referred from

multiple clinical centers no uniform predetermined etiological

screening protocol was used. However, all children were fol-

lowed by experienced child neurologists and thus in all patients

the routine diagnostic process including metabolic screening

(at least amino acids in blood and urine, organic acids in urine

and lactate) and chromosomal analysis was negative. Mutations

in genes such as STXBP1, CDKL5, and SCN1A, were excluded

when the treating physician thought the phenotype had features

suggestive of the respective associated syndromes. In addition,

magnetic resonance imaging (MRI) of the brain did not reveal

causal abnormalities. Parents or the legal representative of each

patient signed an informed consent for participation. The study

was approved by the Commission for Medical Ethics of the

University of Antwerp and the Human Research Ethic

Committee of Austin Health.

Mutation AnalysisGenomic DNA was extracted from peripheral blood using

standard methods. We Polymerase chain reaction (PCR) ampli-

fied the complete coding regions of KCNQ2 and KCNQ3,

including exon–intron boundaries, and 50- and 30-untranslatedregions (UTRs). PCR products were sequenced using the Big-

Dye Terminator Cycle Sequencing kit from Applied Biosystems

(Foster City, CA). Sequences were analyzed on an ABI 3730

automated sequencer. To assess for the presence of each muta-

tion in a healthy control population, we sequenced genomic

DNA of 276 Belgian controls. Each mutation was numbered

relative to the ATG initiation codon and described according

to the Mutation Database Initiative (MDI)/Human Genome

Variation Society (HGVS) Mutation Nomenclature Recommen-

dations (http://www.hgvs. org/mutnomen). For numbering

mutations in KCNQ2, which has several splice variants, we

used the longest mRNA transcript (isoform a; NM_172107.2),

encoding a protein containing 872 amino acids. To confirm

paternity, we genotyped 15 short tandem repeat (STR) markers

located on 10 different chromosomes. To determine the approx-

imate level of parental mosaicism for 1 mutation, we performed

a MspI (New England Biolabs, Ipswich, MA) digest (since the

mutation destroys an MspI site) and compared the intensity of

the bands after gel electrophoresis of the patient, the mosaic

father, and normal controls.

ImagingAll MRIs of the brain were reexamined by a single neuroradiol-

ogist (S.M.).

Results

Mutation AnalysisHeterozygous missense mutations in KCNQ2 were iden-

tified in 8 of 80 (10%) patients (Table 1). Six mutations

arose de novo. One mutation was inherited from a less

ANNALS of Neurology

16 Volume 71, No. 1

TABLE1:ClinicalFeaturesofPatients

withaKCNQ2Mutation

Patient1

Patient2

Patient3

Patient4

Patient5

Patient6

Patient7

Patient8

Mutation

c.638G

>A;

p.Arg213G

lnc.821C

>T;

p.Thr274Met

c.613A

>G;

p.Ile205Val

c.1678C>T;

p.Arg560T

rpc.793G

>C;

p.Ala265P

roc.1636A>G;

p.Met546V

alc.869G

>A;

p.Gly290A

spc.869G

>A;

p.Gly290A

sp

Inheritance

Father

mosaic

Mutationabsentin

mother.DNA

father

unavailable.

Denovo

Denovo

Denovo

Denovo

Denovo

Denovo

Sex/age

atstudy

F/2

years10

mon

ths

F/7

years

M/8

years

F/5

years6mon

ths

F/7

years

M/9

years

F/3

years11

mon

ths

F/4

years1mon

th

Family

history

ofseizures

Yes;father

mosaicfor

KCNQ2mutation

had

benignneonatal

seizureswithseizures

from

4days

to11

weeks;6tonic-

clon

icseizuresbetween4

years

and32

years,remains

onCBZ.Myokymia.

No

Paternalauntwith

seizuresfrom

day

7to

4years.

Twouncles

offather

withfebrileseizures.

No

Cousinof

father

withepilepsy.

Nofurther

details.

Maternalgrandmother

fewepilepticseizures

asolder

child.Sister

with1febrile

seizure.

Paternalgrandfather

withepilepsy

since

age30

years.

Clinical

exam

ination

atbirth

Macrocephaly

(HC

40.5

cm)

atterm

(fam

ilial

macrocephalyin

father).

Normal.Extreme

irritability

innew

born

period.

Normal

Normal

Normal

Hypospadias

Normal

Normal

Seizure

onset

Day

2.Tremor

noted

inutero

over

last

2mon

ths:jerking

ofalimbfor4sec

everyfewdays.

Day

3Day

2.Last

2mon

ths

ofpregnancy

rhythm

ical

jerkingsimilar

toseizures.

Day

3Day

7Day

3Day

2Day

2

Initial

seizure

type

Apnea,generalized

stiffeningwith

facialsuffusion

,followed

bypallorand

cyanosis.Duration

3sec.Multiple

seizuresdaily.

Stiffening,

head

andeyedeviation

andtonicposturing.

Multipleseizures

daily.

Generalized

tonic

withclon

iccompon

ents,

lipsm

acking,

back

arching,

apnea.Multiple

seizuresdaily.

Ton

icseizure,

followed

bymyoclon

icjerks

andnystagm

us.

Multipleseizures

daily.

Ton

icflexion

spasms.Multiple

seizuresdaily.

Ton

icextension

with

clon

icmovem

entsleft

hem

icorpusandeyelid

myoclon

ia.Multiple

seizuresdaily.

Ton

icextension

,highpitchcry,

cyanosisand

bradypnea.

Sometim

eswith

myoclon

iasof

arms.

Multipleseizuresdaily.

Ton

icseizureswith

versionof

theheadto

1sidefollowed

bycyanosisandeyelid

myoclon

ias.Clonic

movem

entsleft

morethan

right

hem

icorpus.Multiple

seizures

daily.

EEG

aton

set

(age)

Con

tinuousmultifocal

andbilaterally

synchronous

epileptiform

activity.In

sleep,

discontinuitywith

markedattenuation

betweenbu

rsts

ofepileptiform

discharges.(10days)

BS.

Threeseizures

withheadand

eyedeviation

toright,trunk

toleft,generalized

stiffening,

facial

twitching.

Centroparietalictal

rhythm

evolvingto

highvoltageslow

ing;

rightsided

in2and

leftsided

in1seizure.

(5days)

Multifocalepileptic

activity

most

frequentlyseen

inlefttemporal

andrightfron

tal

region

s.Oneseizure

withnystagm

usand

interm

ittentbilateral

clon

icjerks.Ictal

changesshow

eddiffuse

attenuation

withmultifocalspikes.

(7days)

BS.

(3days)

Multifocal

epileptic

activity.

(2mon

ths)

BS.

(3days)

BS.

(5days)

Multifocalepileptic

activity

most

frequentlyseen

inrightfron

tal

region

s.(4

weeks)

TABLE1(Continued)

Patient1

Patient2

Patient3

Patient4

Patient5

Patient6

Patient7

Patient8

EEG

evolution

(age)

Significant

improvement

withslow

background

andoccasion

alsharp

transientsover

both

temporalregion

s.(5

weeks)

BS.

(15days)

Multifocalspikes,

SWandsharp

waves.(2

mon

ths)

Bilateraltemporal

sharpwaves.

(4mon

ths)

Multifocalepileptic

activity.(3

weeks)

Multifocalepileptic

activity.(9

days)

LastEEG

(age)

Normal.(1

year)

Alm

ostcontinuous

multifocalslow

ing

andepilepticactivity.

Ton

icseizureswith

variableon

setfrom

rightor

left

fron

totemporalregion

.(3

years6mon

ths).

NoEEG

available

afterseizurefreedom

.

Normal.(9

mon

ths)

Multifocalspikes

andSW

,increasing

duringsleep.

(4years)

Slow

background;

noepilepticactivity.

(3years)

Normal.(8

years)

Normal.(3

years

11mon

ths)

Slow

background;

noepilepticactivity.

(4mon

ths)

Treatment

received

PB,PHT

PB,PHT,VGB,

TPM,OXC,CNZ

PB,midazolam

infusion

,folinic

acid,betamethason

e,VPA,pyridoxine,

VGB,TPM,

dexam

ethason

e

VGB,PB,VPA,

TPM,PHT,CNZ,

ETX,LV

T,CBZ

VGB,VPA,TPM

PB,CNZ,PHT,

VPA,CBZ,VGB

PBþ

LVT.PBstop

at15

mon

ths.VPA

startat

3years.

PB,VPA,CNZ

Respon

seto

treatm

ent,

evolution

ofseizure

type

Norespon

seto

PB;

PHTstartedat

3w

eventually

controlled

seizures.One

hem

iclonicseizure

at14

m,nofurther

seizures.

Norespon

seto

PB,

PHT,VGB,CNZ.

Someim

provement

withTPM.OXC

very

effective.Run

of8seizures

after

varicella

immunization

at2years,then

seizure

free

until

4years,associated

withAED

reduction.

Norespon

seto

PB,

temporaryrespon

seto

midazolam

infusion

.VGBinitially

reducedseizures

andnormalized

EEG

(7weeks

seizure

freedom

).Com

bination

TPM,VGB,and

pyridoxine

controlledseizures;

episodeof

SEat

3mon

ths;

seizure-freefrom

9mon

thsuntil

8years.

Daily

tonic

seizuresdespite

multidrug

regimen.

Tem

porary

respon

seto

VGB.Recurrence

ofextension

spasms

withnystagm

uslater

infirstyear.Gradual

dim

inishingof

seizure

frequency

afterthat.

Daily

tonicseizures,

oftenlateralizedto

theleft.After

2mon

thssporadic

tonicseizureswith

CBZþ

VGB.

Mon

thly

tonicor

tonicclon

icseizures,

oftenwithfever.

Seizure-free

between

11mon

thsand

3years2mon

ths.

At3years2mon

ths

TC

seizure.

Norespon

seto

PB;

VPAandCNZ

startedat

4weeks

controlledseizures.

Current

seizure

type

Seizure-freesince

age14

mon

ths

Seizure

free

since

age4years

Seizure

free

from

9mon

thsto

8yearswith

2recenttonic

seizures

Frequent

tonic

seizures

Seizure-freesince

age2years6mon

ths

Seizure-free

since

age3years

Seizure-free

since

age3years

2mon

ths

Seizure-freebetween

2mon

thsand2years

11mon

ths.Then

1nocturnaltonicclon

icseizure.Seizure-free

since

then.

TABLE1(Continued)

Patient1

Patient2

Patient3

Patient4

Patient5

Patient6

Patient7

Patient8

Current

treatm

ent

PHT

OXC,GBP

TPM

TPM

þLV

Tþ

VPA

VGBþ

TPM

CBZ

LVTþ

VPA

VPA

Other

genetic

testing

don

e

Karyotype,PCDH19,

CDKL5,

array

CGH

Karyotype,

SCN1A

,PCDH19,

POLG,

STXBP1,

CDKL5

Karyotype,SC

N1A

Karyotype,

SCN2A

,ST

XBP1

Array-C

GH,

MECP2,

CDKL5,

STXBP1

Karyotype,SC

N1A

,SC

N2A

,ST

XBP1,

Angelm

an

Karyotype

SCN1A

,ST

XBP1

Karyotype,

Angelm

anmitochon

drial

DNA.

arylsulfataseA,

b-galactosidase

Cognition

PMR.Never

normal:

poorhead

control,s

miled

6to

8weeks.

Not

sitting

unsupported

andnot

transferring

objects.Can

lifthead

from

pronebu

tnot

ableto

supporton

forearmsor

roll

over.Non

verbal

PMR.

Non

verbal

MMR.Regression

withSE

.Not

rolling

at6mon

ths.Walked

at16

mon

ths;30

singlewords

at4years.At8years:

follows2commands,

readssm

allwords.

Nouseof

toys

PMR.

Non

verbal

PMR.

Non

verbal

PMR.Non

verbal

PMR.

Non

verbal

PMR.Non

verbal

Neurological

exam

ination

Macrocephaly.

Severe

asym

metric

spasticqu

adriplegia.

Visually

attentive

andsm

iles

respon

sively

Severe

asym

metric

spastic

quadriplegia

Normalexam

ination.

Poor

finemotor

skills

Spastic

quadriplegia.

Novisual

contact

Severe

spastic

quadriplegia.

Axialhypoton

ia

Widely-spaced

gait,

mildspasticity

Axialhypoton

ia.

Walks

with

assistance.

Widely-spaced

gait

Moderate

asym

metric

spastic

quadriparesis

Additional

features

Frontalbossing,

scaphocephaly,

upturned

nares,

shortph

iltrum,

widemouth,full

lower

lip.HC

above98th

percentile

HC

on3rd

percentile

at21

mon

ths

(25thpercentile

forheightand

weight)

CTscan

(2days):

Subd

uralhemorrhage.

Generalized

hypodense

cerebralparenchym

asuggestive

ofhypoxia

(but

not

confirm

edon

MRIat

11days).HC

justabove50th

percentile(4

years)

HC

on75th

percentile

firstyears

oflife

HC

on50th

percentile

at6years

Plagiocephaly,large

forehead,large

mouth,and

widely-spaced

teeth.Hypospadias.

Autism

.Stereotypic

handmovem

ents.

HC

on90th

percentile

at2years

Non

epileptic

aggressive

spells.

HC

on75th

percentileat

3years

MRIreported

toshow

thin

corpuscallosum.

HC

on3rd

percentileat

4years

BS¼

burstsuppression;CBZ¼

carbam

azepine;CNZ¼

clon

azepam

;CT¼

compu

tedtomography;

EEG

¼electroencephalography;

ETX¼

ethosuximide;F¼

female;GBP¼

gabapentin;HC

¼headcircumference;HS¼

hypsarrhythmia;LV

T¼

levetiracetam;LT

G¼

lamotrigine;M

¼male;MRI¼

magneticresonance

imaging;

MMR¼

moderatementalretardation;NTZ¼

nitraze-

pam

;OXC

¼oxcarbazepine;PB¼

phenobarbital;PHT¼

phenytoin;PMR¼

profoundmentalretardation;SE

¼statusepilepticus;SW

¼spike-waves;TPM

¼topiram

ate;VGB¼

vigabatrin;

VPA¼

valproicacid.

severely affected father who was mosaic for the mutation.

A low level of mosaicism was observed in the sequencing

trace. The level of mosaicism was determined for lym-

phocyte-derived DNA and the mutation was found to be

present in approximately 30% of lymphocytes. The

inheritance pattern of the remaining mutation was

unknown; the mutation was not present in maternal

DNA, but paternal DNA was unavailable. None of the 7

different mutations were observed in 276 ethnically

matched control individuals, or were previously pub-

lished in association with BFNS. Interestingly a mutation

of the same codon as Patient 1 but with a different sub-

stitution (p.Arg213Trp) has been reported in a sibling

pair with BFNS.15 All substituted amino acids were evo-

lutionary highly conserved in mammals. Five mutations

(c.613A>G, c.638G>A, c.793G>C, c.821C>T, and

c.869G>A) were located in the part of the gene encod-

ing the transmembrane domain; the first 2 in transmem-

brane segment S4, the next 2 in the pore-loop between

S5 and S6, and the fifth mutation (occurring in 2

patients) was located in S6. Mutations c.1636A>G and

c.1678C>T were located in 1 of 2 calmodulin binding

domains in the C-terminal region. For the c.821C>T

mutation, where paternal DNA was unavailable, the

prediction program PolyPhen showed a very high proba-

bility of a damaging effect, further supporting the patho-

genic nature of this mutation. No KCNQ3 mutations

were identified in the 80 patients.

Clinical Features of KCNQ2 EncephalopathySeizure onset occurred in the first week of life for all

patients. Interestingly, 2 mothers retrospectively recog-

nized that rhythmical jerking or jerking of a limb

occurred during the last 2 months of pregnancy suggest-

ing possible prenatal seizure onset. All patients presented

with tonic seizures accompanied by motor and auto-

nomic features, similar to seizures in BFNS. One patient

(Patient 5) presented with flexion spasms with an

obvious tonic component. All patients had multiple daily

seizures at onset and continued to have frequent therapy-

resistant seizures in the first few months to the first year

of life. Thereafter, seizure frequency gradually diminished

in 7 patients to sporadic tonic or tonic-clonic seizures

with seizure offset between 9 months and 4 years of life.

One patient (Patient 4) still had frequent tonic seizures

at 5.5 years despite treatment with a multiple antiepilep-

tic drug regimen. Another (Patient 3) had a recurrence of

tonic seizures at 8 years following 7 years of seizure free-

dom. (See Table 1.)

Seven patients were profoundly intellectually

impaired and had axial hypotonia and/or spastic quadri-

plegia. Patient 3 had a somewhat milder phenotype.

He had moderate intellectual disability. Gross motor

function was considerably better than in other patients

although his fine motor skills were very poor.

Electroencephalograms (EEGs) recorded in the first

week of life typically showed a burst suppression pattern.

Later in the course of the disorder, multifocal epilepti-

form activity was seen in all patients. In parallel with the

diminishing seizure frequency the epileptiform activity

became less frequent and EEGs performed after seizure

freedom were normal or had a mildly slow background.

All EEGs were evaluated by child neurologists experi-

enced with neonatal EEG.

One patient (Patient 1) inherited the mutation

from a mosaic parent with a milder phenotype. Before

inclusion of this patient in the study, the epilepsy of the

father and the severe clinical picture of the son were con-

sidered unrelated. The father had not received a specific

syndrome diagnosis and genetic testing for KCNQ2 was

not considered. Critical review showed he had an appro-

priate phenotype with seizures from 4 days to 11 weeks.

He is now 35 years old and had 6 seizures from 4 to 32

years, is of normal intellect and remains on carbamaze-

pine. Remarkably he also has a history of mild myoky-

mia, a feature described in rare BFNS families.16

Imaging FindingsImaging was initially reported to be normal in most

patients, but closer reexamination by an experienced

pediatric neuroradiologist revealed consistent changes

(Table 2). An early MRI of Patients 6 and 8 could not be

retrieved, but in all other patients in whom an early MRI

was available, variable T1 and T2 hyperintensities of

the basal ganglia and sometimes thalamus were seen. These

were usually bilateral but in some cases asymmetrical.

These changes were mostly apparent in the neonatal

period, becoming less obvious with increasing age (Fig A,

B; Supplementary Fig 1). Basal ganglia hyperintensities

resolved by 3 years 6 months in one child while 3 patients

have minor residual increased T2 signal at 18 months, 2

years 7 months, and 6 years. These subtle hyperintensities

did not necessarily involve the same basal ganglia

structures that were involved on the initial MRI. Other

common findings were small frontal lobes with increased

adjacent extra-axial spaces, a thin corpus callosum and

decreased posterior white matter volume (see Fig B–D;

Supplementary Fig 1). For Patient 8 a thin corpus

callosum was reported to be present, but the actual

images were not available for review. A selection of images

of all patients can be found in the Supplementary

Material.

ANNALS of Neurology

20 Volume 71, No. 1

TABLE2:Im

agingFindingsin

Patients

withaKCNQ2Mutation

Patient1:CG

Patient2:HMH

Patient3:JM

Patient4:

120.1

(KC)

Patient5:

1552.03(FJ)

Patient6:

EP201.1

(TvE

)

Patient7:

302.1

(AV)

10days

11months

3months

6years

11days

3years

6months

4months

3years

5month

2weeks

2years

7months

2weeks

Basal

ganglia

:T1putamina,

globuspallidi;

NormalT2

T1normal;:T

2

globuspallidi

:T2globuspallidi

(bilateral);:T

2

rightputamen

only

Patchy:T

2in

both

lentiform

nuclei

:T2globus

pallidi

Normal

:T1:T

2

globus

pallidi

Normal

:T1caudate,

lentiform

nuclei

Subtle:F

LAIR/T

2

globuspallidi

þþArtifact;

possible:T

1:T

2

medialglobus

pallidi

Thalam

us

Leftthalam

us

has

:T2sm

all

focus

Normal

Rightthalam

us

withpatchy

inhom

ogeneous

:T2signal,

normalvolume

Rightthalam

us

smallerand

irregularwith:T

2

andFLAIR

signal

:T2signal

Normal

Normal

Normal

Normal

Normal

Normal

Frontal

lobe

Relativelysm

all

Normal

Relativelysm

all

Small

Normal

Normal

Relatively

small

Verysm

all

Normal

Small

Normal

Tem

poral

lobe

Normal

Normal

Smallerleft

temporallobe

Normal

Normal

Normal

Normal

Verysm

all

Normal

Small

Normal

Myelination/

whitematter

;Posterior

white

mattervolume

;Posterior

white

mattervolume;

:T2periventricular

whitematter;

borderlinedelayed

myelination

Normal

;Whitematter

volume;:T

2/

FLAIR

signal

intheright

perirolandic

subcorticalwhite

matterand

parallelto

the

PLIC

bilaterally;

abnormal

subcortical

myelination,right

posterior

>left

Normalwhite

mattervolume;

:T2;T

1signalin

periventricular

whitematter;:T

2

signalparalleling

thePLIC

Normal

Normal

Normal

Normal

Borderlinedelayed

myelination

Normal

Corpus

callosum

Normal

Thin

Thin

Verythin

Normal

Normal

Thin

Thin

Normal

Thin

posteriorly

Normal

Cerebellum

Normal

Normal

Normal

Normal

Normal

Normal

Normal

:T2;T

1Normal

Normal

Normal

Ventricles

Ventriculomegaly

withreported

macrocephaly

Ventriculomegaly

withreported

macrocephaly

Normal

Normal

Normal

Normal

Prominent

ventriclesand

extra-axialCSF

spaces

Mildfron

tal

ventriculomegaly;

bilateralchoroid

plexuscysts

Normal

Ventriculomegaly,

especially

fron

tal

horns

Normal

Other

Nil

Thickcranial

vault

Giantperivascular

spaces,left>

right;

hippocam

pi

under-rotated

Persistentgiant

perivascular

spaces;

hippocam

pal

rotation

normal

Nil

Bilateral

hippocam

pal

enlargem

ent(L>R)

with:T

2left

hippocam

pus

Cavum

vergae

:Frontotemporal

extra-axialCSF

spaces;bilateral

anterior

temporal

arachnoidcysts;

underopercularized

sylvianfissures

Nil

:Frontotemporal

extra-axial

CSF

spaces

þþArtifact

FLAIR

¼fluid

attenuated

inversionrecovery;PLIC

¼posterior

limbs

oftheinternalcapsules;L¼

left;R¼

right;CSF

¼cerebrospinalfluid.

Discussion

KCNQ2 mutations are associated with several phenotypes

including typical BFNS,9,17 myokymia associated with

neonatal or early infantile epilepsy,16,18 and peripheral

nerve excitability without known epilepsy.19 All these

entities share a self-limited seizure disorder or even ab-

sence of seizures in the latter phenotype. Outcome is

good. Interestingly, patients with prolonged neonatal seiz-

ures and a poor outcome with severe intellectual disabil-

ity have been observed in 4 small BFNS families11–13

and 1 isolated patient,14 each carrying a different

KCNQ2 mutation. The familial cases were detected fol-

lowing assessment of BFNS families referred for KCNQ2

testing, and the de novo case was identified from a group

of 6 patients with neonatal seizures. The significance of

KCNQ2 mutations in the group of patients with neona-

tal onset epileptic encephalopathies is not known. Impor-

tantly, in standard clinical practice KCNQ2 mutation

screening is not generally included as part of the diagnos-

tic workup of neonatal epileptic encephalopathies.

In this study we analyzed 80 patients with unex-

plained neonatal or early-infantile seizures and associated

developmental retardation for KCNQ2 and KCNQ3

mutations. No KCNQ3 mutations were found, but we

did find novel KCNQ2 mutations in 8 of 80 (10%)

patients (7 mutations, because 1 mutation occurred in 2

FIGURE: Brain MRI of subjects with KCNQ2 encephalopathy. (A,B) T1-weighted axial images of Patient 6, demonstratingincreased T1 signal intensity within both lentiform nuclei (arrows) at 14 days in A, which has normalized by 2 years 7 months inB. Note the small frontal lobes, thinned splenium of corpus callosum (arrowhead) and increased CSF spaces compared to theneonatal scan in A. (C) T2-wieghted axial image of Patient 5 at 3 years 5 months showing small frontal lobes (arrowhead) andunderopercularized sylvian fissures bilaterally (asterisks). (D) Midline sagittal T1-weighted image of Patient 2 at 6 years showingmarked thinning of all components of the corpus callosum (arrowhead) with increased frontal interhemispheric CSF spaces.

22 Volume 71, No. 1

ANNALS of Neurology

individuals) who shared an electroclinical and radiologi-

cal phenotype.

We found that KCNQ2 encephalopathy is charac-

terized by onset of intractable epileptic seizures in the

first week of life; the seizures had a prominent tonic

component. Although age of seizure onset and seizure

type was similar to BFNS, seizures were extremely ther-

apy resistant. Patients had several seizures a day during

the first few months despite multiple antiepileptic drug

treatment. In contrast to most infantile onset epileptic

encephalopathies, seizure frequency gradually diminished

over the first few years of life. Most patients were

seizure-free by the age of 3 years. As 6 patients are still

younger than 8 years, and 1 patient had seizure recur-

rence at 8 years, the long-term course of the epilepsy in

this disorder may not be fully delineated.

EEG showed a typical age-dependent evolution

with a burst-suppression pattern in the first few days of

life, followed by multifocal epileptiform activity. With

seizure remission EEG studies no longer showed epilepti-

form activity.

Most patients were profoundly intellectually dis-

abled, nonverbal, and had axial hypotonia and/or spastic

quadriplegia. In some cases the initial electroclinical his-

tory resembled Ohtahara syndrome, but the evolution

with diminishing seizure frequency easily distinguishes

KCNQ2 encephalopathy from most patients with Ohta-

hara syndrome.

MRI showed a characteristic and evolving picture.

MRIs performed during the acute seizure phase revealed

hyperintensities of the basal ganglia and thalamus that

had been previously overlooked or attributed to hypoxia.

These lesions became more subtle or disappeared later in

life. Other common findings were small frontal lobes, a

thin corpus callosum and reduced posterior white matter

volume. MRI findings have only been previously pub-

lished for 1 patient with a KCNQ2 mutation and severe

outcome.12 Interestingly, a thin corpus callosum was also

seen in this patient on the MRI at 2 and at 7 years. A

neonatal MRI was not reported for this patient.

The basal ganglia are known to be highly vulnera-

ble to different stressors, and the neonatal brain is even

more sensitive to this.20,21 Lesions in basal ganglia are

often present in severe neonatal hypoxic-ischemic ence-

phalopathy (HIE), and are correlated with a more severe

outcome.22,23 Nevertheless, in cases of HIE findings tend

to be in a more characteristic distribution and the nor-

malization of initial signal changes with the later appear-

ance of signal abnormalities in different basal ganglia

regions is not seen in HIE. Several reports also describe

the vulnerability of basal ganglia to excitotoxicity.24 Exci-

totoxic stress caused by frequent neonatal seizures might

explain the lesions seen in our patients, but they have

never been reported in other severe neonatal epileptic

syndromes such as Ohtahara syndrome, early myoclonic

encephalopathy, or pyridoxine-dependent epilepsy. The

exact nature of the imaging findings remains elusive, but

the presence of this characteristic radiological pattern

together with a history of unexplained neonatal refractory

seizures is a clue to search for KCNQ2 mutations.

Follow-up studies are needed to determine the specificity

of these findings, but we believe an electroclinical and

radiological phenotype associated with KCNQ2 encephal-

opathy is emerging.

In our cohort, 6 out of 8 mutations arose de novo,

but 1 mutation was inherited from a parent with a

milder phenotype. This parent had 30% mosaicism for

the KCNQ2 mutation in lymphocytes. Mosaicism is well

known to be associated with a milder phenotype than

would otherwise be expected based on the mutation. In

infantile onset epileptic encephalopathies a recent study

demonstrated that mosaicism is a major cause of inher-

ited SCN1A mutations causing Dravet syndrome with

mosaic parents varying in affection status from unaffected

to more severely affected correlating with the level of

SCN1A mosaicism.25 The mosaic father had a BFNS

phenotype but had ongoing seizures into adult life and

myokymia in the setting of normal intellect. The finding

of mosaicism in this family carries significant genetic

counseling implications.

We hypothesize that particular KCNQ2 mutations

as observed in this study directly give rise to a KCNQ2encephalopathy based on the following arguments: (1)

none of these mutations has been observed in classical

BFNS patients; (2) 1 of these mutations occurred twice

de novo in 2 unrelated patients making it difficult to

explain the severe phenotype by invoking additional

genetic and environmental background factors; and (3)

the mutations are associated with a well-delineated,

potentially recognizable electroclinical and radiological

phenotype in the 8 patients.

The hypothesis of a strict genotype-phenotype cor-

relation is challenged, however, by the observation of

severely affected patients in a few multigenerational

BFNS families. While in 2-generation pedigrees mosai-

cism can still be invoked as the underling mechanism,

this fails to explain some reported families: 2 of the pre-

viously reported families included siblings with different

disease severity, which cannot be explained by mosai-

cism.12,13 Genetic modifiers may account for this differ-

ence in phenotype. Indeed, in a mouse model where

mutations in 2 genes that each cause mild epilepsy,

KCNQ2 and SCN2A, were co-expressed, a severe pheno-

type resulted with early onset and juvenile lethality.26

Weckhuysen et al: KCNQ2 Encephalopathy

January 2012 23

Interestingly, the mutation seen in the father-

daughter pair (c.638G>A/p.Arg213Gln) affects the same

codon as that described in a small Japanese family with 2

affected siblings, but causes a different amino acid substi-

tution.15 In the Japanese family, seizures settled by

25 days of age and development was normal; as neither

parent had the mutation, parental germline mosaicism

was inferred. Possibly the different amino acid substitu-

tions have different functional effects, explaining the

difference in phenotype. Nevertheless, genetic modifiers

or environmental factors might also play a role.

The same diversity in phenotype is seen for muta-

tions in the sodium channel gene SCN1A. Loss-of-

function mutations invariably cause Dravet syndrome, but

some missense mutations can give rise to either the benign

fever sensitive epilepsy forms of the generalized epilepsy

with febrile seizure plus (GEFSþ) syndrome or to Dravet

syndrome at the most severe end of the spectrum. KCNQ2mutations now seem to give rise to neonatal epilepsy

syndromes with a similarly diverse outcome.

A diagnosis of a KCNQ2 mutation in patients with

such a severe disease course may well have therapeutic

consequences, as drugs like retigabine for example, specif-

ically target Kv7 channels. Retigabine acts as an activator

of neuronally expressed KCNQ-channels, thereby reduc-

ing neuronal excitability.27,28 Patients with a KCNQ2-

mediated epileptic encephalopathy may especially benefit

from this targeted therapy, as rapid control of seizures

could potentially improve developmental outcome. Spe-

cific clinical studies will be needed to test this hypothesis.

In the meantime we suggest that KCNQ2 screening

should be included in the diagnostic workup of neonatal

epileptic encephalopathies. The yield of mutation detec-

tion in this heterogeneous group is already �10%. As

our patients were not recruited in a prospective manner,

but from a preexisting database, there is an underlying

ascertainment bias in our cohort. Thus the exact preva-

lence of KCNQ2 mutations in neonatal epileptic ence-

phalopathies remains to be elucidated in larger prospec-

tive series. Nevertheless, in a more selected group of

patients with onset of epilepsy in the first month of life

and the phenotypic characteristics described above, the

yield is likely to be even higher.

Acknowledgments

The research is supported by the Fund for Scientific

Research Flanders (FWO) [PDJ], Methusalem excellence

grant of the Flemish Government [PDJ], University of

Antwerp [PDJ], the Interuniversity Attraction Poles

(IAP) program P6/43 of the Belgian Science Policy

Office (BELSPO) [PDJ], the Eurocores program Euro

EPINOMICS of the European Science Foundation

[PDJ]and National Health and Medical Research Coun-

cil of Australia. [IS and SFB]

We thank the patients and their family members

for their cooperation and participation in this study. We

also thank the VIB Genetic Service Facility (http://www.

vibgeneticservicefacility.be) for the genetic analyses. A.S.

is a postdoctoral fellow of the University of Antwerp.

D.A. is a postdoctoral fellow of the Research Foundation

– Flanders (FWO).

Authorship

S.W., S.M., A.S., I.E.S., and P.D. contributed equally to

this work.

Potential Conflicts of Interest

Nothing to report.

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Weckhuysen et al: KCNQ2 Encephalopathy