Original Article Journal of Korean Epilepsy Society 16(2):49-55, 2012 Received December 12, 2012 Accepted December 28, 2012 1 세브란스병원소아신경과, 2 충남대학교의과대학해부학교실, 3 충남대학교병원소아청소년과 강준원 1 김동운 2 이영숙 2 이영호 2 이건수 3 Polymorphism of SCN1A and SCN2A Gene in Pediatric Refractory Epilepsy Patients Joon Won Kang, MD, PhD 1, Dong Woon Kim, PhD 2, Young Sook Lee, PhD 2, Young Ho Lee, MD, PhD 2, Keon Su Lee, MD, PhD 3 1 Division of Pediatric Neurology, Pediatric Epilepsy Clinics, Severance Children s Hospital, Pediatric Epilepsy Research Institute, Brain Research Institute, Department of Pediatrics, Yonsei University College of Medicine, Seoul; 2 Department of Anatomy, Brain Research Institute, Chungnam National University Hospital, Chungnam National University School of Medicine, Daejeon; 3 Department of Pediatrics, Chungnam National University Hospital, Chungnam National University School of Medicine, Daejeon, Korea Purpose: Epilepsy is a common chronic neurological disorder characterized by recurrent unprovoked seizures. While there have been many break throughs in development of antiepileptic medications, the cure for epilepsy still needs many answers, such as genetic aspects of the illness. Gene mutation may contribute to this situation. In this study, we have evaluated children with single nucleotide polymorphisms (SNP) of SCN1A c.3184 A G (rs2298771) and SCN2A c.56 G A (rs17183814) to analyze these genes were associated with refractory seizure. Methods: Three hundreds and eleven children who visited the outpatient clinic in Chungnam National University Hospital, were retrospectively reviewed and, the data for their demographic profiles, clinical characteristics, and the results for SNP of SCN1A and SCN2A gene were collected. We divided them into three groups of control, response, and refractory groups. Results: There was no statistical difference in demographic profiles of the patients. A variant of SCN2A c.56 G A polymorphism was associated with refractory seizure in pediatric patients with epilepsy (p=0.004; odds ratio 2.78, 95% confidence interval 1.39-5.56). Conclusions: SNP of SCN2A c.56 G A could be suggested as one of the causes of pediatric refractory epilepsy. Keywords: Refractory epilepsy, Polymorphism, Sodium channel 서론 뇌전증은전인구의 0.5-1% 에서발생하는것으로알려져있으며, 1,2 약 70% 의환자는항경련제복용으로경련이조절된다. 3,4 최근까지여러항경련제가개발되었으나여전히뇌전증환자의약 30% 정도는최고용량, 다약제투여에도불구하고항경련제에내성을가진다. 5-7 항경련제내성에연관되 는기전은체내에서약물의대사, 약물의체내이동, 약물의작용점등과관련이있다. 8-10 하지만항경련제의마지막작용점인이온통로에관련된유전자의연구는상대적으로아직많지않은실정이다. 단일염기다형성 (single nucleotide polymorphism, SNP) 은희소대립형질의빈도가최소 1% 이상인유전자변이로정의하며, 그자체가하나의표현형또는질환의독립적인원인은 Address for correspondence: Keon Su Lee, MD, PhD Department of Pediatrics, Chungnam National University School of Medicine, 282 Munwha-ro, Jung-gu, Daejeon 301-721, Korea Tel: +82-42-280-7253, Fax: +82-42-255-3158, E-mail: ksulee@cnu.ac.kr 이논문은 2010년충남대학교병원공모과제연구비에의해수행되었음. Journal of Korean Epilepsy Society Vol. 16 No. 2, 2012 49
강준원 김동운 이영숙 이영호 이건수 아니지만개체간의다양한표현형의차이를결정하는것으로알려져있다. 11,12 전압관문나트륨통로는신경전도와뇌전증기전에서의역할외에도항경련제작용에관련되는것으로알려져있으며, 12,13 나트륨통로의몇몇단일염기다형성들중에서 SCN1A c.3184 A G (rs2298771) 과 SCN2A c.56 G A (rs17183814) 유전자다형성들은신경질환들에서기능적인의미를갖는다고밝혀졌다. 14 SCN1A 결함은영아기중증근간대뇌전증, 열성경련을동반한전신경련플러스 2형과전신근간대발작을동반한소아기불응성뇌전증의원인이되며, 15,16 SCN2A c.56 G A 변이는열성경련후의국소뇌전증과열성경련을동반한전신뇌전증과연관되어있다. 17,18 이에 SCN1A c.3184 A G (rs2298771) 과 SCN2A c.56 G A (rs17183814) 단일염기다형성으로전압관문나트륨통로의약물반응성에대한개체간의차이를연관지으려는시도가있었으나아직일관된결론을이끌어내지못하였다. 19-22 본연구에서는현재까지의전압관문나트륨통로에대한이해를바탕으로항경련제에대한뇌전증의반응여부가전압관문나트륨통로와연관되어있을것으로가정하고, SCN1A c.3184 A G (rs2298771) 과 SCN2A c.56 G A (rs17183814) 단일염기다형성이소아불응성뇌전증환자에게미치는영향을알아보고자한다. 대상과방법 1. 대상 2010년 12월부터 2011년 11월까지충남대학교병원소아청소년과에서진료를받은뇌전증환아 163명과건강한어린이 148명을대상으로하였다. 연구참여자와법정대리인으로부터연구참여의사및유전자연구에따른동의를서면으로확인하고, 연구윤리심의위원회의심의를거쳤다. 경련의과거력이없는정상군과함께항경련제의사용기간과사용약제, 경련횟수에따라반응군과불응군으로구분하였다. 반응군은항경련제를최초치료약물로사용하여 1년이상발작이없는환자들로정하였다. 불응군은항경련제를허용가능한최대용량까지증량하였음에도 1달에 1회이상의확실한경련이있으며, 2개이상의항경련제를사용 함에도경련이지속되어다른항경련제를추가한환자들을포함하였다. 항경련제에의한부작용으로약물을사용할수없는경우, 금지약물에의한경련을보인경우, 약물의순응도가좋지않은경우와뇌전증발작의양상이불확실한경우등은연구대상에서제외하였다. 뇌전증환자군에서연령, 성별, 경련의양상과원인등은의무기록을후향적으로조사하여확인하였다. 2. SCN1A, SCN2A 유전자의단일염기다형성확인 1) DNA의추출환자군과정상대조군에서전혈을채취하여 3배부피의적혈구용해완충액을첨가한후 5-6회섞은후 10분간실온에서반응을시키고, 13,000 RPM에서 20초간실온에서원심분리한후상층액을버렸다. 적혈구용해과정후얻어진고형물에핵용해완충액과단백질침전액을넣은후잘섞고 13,000 RPM에서 5분간원심분리한후상층액만을취하였다. 2-propanol을첨가하여 13,000 RPM에서원심분리후상층액을버리고 70% 에탄올을넣은후 13,000 RPM에서원심분리하고상층액을버리고에탄올을말린후 DNA 재수화용액을넣어녹여 genomic DNA를얻었다. 2) 시동체 (primer) 제작본연구를위해사용한시동체는 Gene Bank로부터 SCN1A 와 SCN2A의 cdna 염기서열정보를얻어시동체를주문제작하였다. 염기배열순서는표 1과같다. 3) 중합효소연쇄반응 (polymerase chain reaction, PCR) PCR은 TaKaRa PCR Thermal Cycler DICE (TaKaRa, JP) 을이용하여 2x PCR 완충액 10 μl, 50 mm forward primer 1 μl, 50 mm backward primer 1 μl, 50 ng/μl Template genomic DNA 1 μl에멸균증류수를더하여최종반응액은 20 μl로하였다. PCR 반응액을 95 에서 5분간반응시켜두가닥 DNA를한가닥으로분리하였다. 이후 DNA 분리 (95 에서 30초 ), DNA와시동체결합 (SCN1A, SCN2A을각각 56, 55, 57 에서 30초간 ), DNA 증폭 (72 에서 1분간 ) 과정을 Table 1. Primer sequences used in the study Single nucleotide polymorphism Primer sequence Restriction enzyme SCN1A c.3184 A G (rs2298771) SCN2A c.56 G A (rs17183814) 5 -TGCACAAAGGAGTAGCTTATG-3 5 -AGTCAAGATCTTTCCCAATTTCAG-3 5 -CTGACAGCTTCCGCTTCTTT-3 5 -TTCCTGCTTCCAAGTCACTG-3 PvuII ScrFI 50 대한뇌전증학회지제 16 권제 2 호, 2012
35회반복하였다. 72 에서 7분간최종증폭하였다. PCR 산물은 ethidium bromide 를포함한 2.5% 아가로스겔에서 100 mv 로 15분간전기영동한후자외선투영기로관찰하였다. 4) 제한효소법및전기영동 PCR에서얻어진반응액 15 μl와멸균증류수 2 μl를넣고잘섞은후제한효소완충용액 2 μl와제한효소 PvuII과 ScrFI 1 μl를처리한후 2시간동안 37 의배양기에놓아두었다. Ethidium bromide 염색용액을포함한 3% 아가로스겔에서 100 mv로 20분간전기영동한후자외선투영기로관찰하고카메라로촬영하였다. SCN1A c.3184 A G 단일염기다형성은 PvuII에의한제한부위에의해확인되었다 (A 대립유전자는 198 bp; G 대립유전자는 175와 23 bp). 즉 198 bp 부위에띠가나타나면정상동형접합체 (normal homozygote, A/A), 198 bp 부위와 175 bp 부위에띠가나타나면돌연변이이형접합체 (mutant heterozygote, A/G), 175 bp 부위에만띠가나타나면돌연변이동형접합체 (mutant homozygote, G/G) 로판정하였다 (Figure 1). SCN2A c.56 G A 단일염기다형성은 ScrFI에의한제한부위의소실에의해확인되었다 (G 대립유전자는 124와 23 bp, A 대립유전자는 147 bp). 즉 124 bp 부위에띠가나타나면정상동형접합체 (normal homozygote, N/N), 124 bp 부위와 147 bp 부위에띠가나타나면돌연변이이형접합체 (mutant heterozygote, N/M), 147 bp 부위에만띠가나타나면돌연변이동형접합체 (mutant homozygote, M/M) 로판정하였다 (Figure 2). 3. 통계정상군, 반응군, 불응군사이에 SCN1A와 SCN2A 유전자의단일염기다형성의유전형과대립형질의분포를비교분석하였다. 통계분석방법은 t-test 분석법과 χ 2 -test를이용하여측정한 SNP의대립형질과유전형의빈도가 Hardy-Weinberg equilibrium 에따른분포를보이는지확인하였다. 모든통계치는 SAS version 9.2 (SAS Institute Inc., Cary, NC, USA.) 을이용하여분석하였으며유의수준은 p<0.05로하였다. 결과 1. 전체대상군의임상적특성 (Table 2) 전체 311명의환자중정상군은남자가 82명 (55.4%), 여자가 66명 (44.6%) 이었고평균나이는 12.9세였다. 환자군은 163 명으로남자가 91명 (55.8%), 여자가 72명 (44.2%) 이었고평균나이는 13.1세였다. 혈청나트륨과칼슘을포함한다른임상적특성들도양군간에유의한차이는없었다. 2. 환자군의임상적특성 (Table 3) 전체환자군의발병나이는 91.1개월이었으며부분발작이 143명 (87.7%), 전신발작이 20명 (12.3%) 이었다. 반응군은전체 163명중 110명 (67.5%) 이었고불응군은 53명 (32.5%) 이었 Figure 1. PCR analysis of the single nucleotide polymorphism of SCN1A c.3184 A G (rs2298771). A/A, normal homozygote; G/G, mutant homozygote; A/G, mutant heterozygote. Figure 2. PCR analysis of the single nucleotide polymorphism of SCN2A c.56 G A (rs17183814). N/N, normal homozygote; M/M, mutant homozygote; N/M, mutant heterozygote. Table 2. Demographic profiles of all group Control (n=148) Total epilepsy (n=163) Sex (M:F) 82:66 91:72 Age (years) 12.9±4.0 13.1±5.8 Electrolytes (serum) Sodium (mg/dl) 139.8±0.6 140.3±0.3 Calcium (mg/dl) 9.4±0.3 9.3±0.1 Journal of Korean Epilepsy Society Vol. 16 No. 2, 2012 51
강준원 김동운 이영숙 이영호 이건수 다. 반응군은평균 1.4개, 불응군은평균 3.3개의항경련제를사용하고있었다. 발병나이는반응군이평균 102.4개월, 불응군이평균 67.6개월로불응군이더빨리발병하였으며통계적으로유의하였다 (p=0.001). 뇌전증의원인을특발성, 증상성, 잠복성으로나누었을때반응군에서는특발성이, 불응군에서는잠복성원인의비율이많았다. 증상성원인의종류로는중추신경계감염, 종양, 선천성뇌기형, 혈관질환, 뇌실주위백색연화증등이있었다. Table 3. Clinical profiles of epilepsy patients Responders (n=110) Refractory (n=53) Sex (M:F) 67:43 24:29 Age (years) 12.7±5.2 14.0±6.6 Age of onset (months) 102.4±46.0 67.6±8.1 Follow up period (months) 52.5±10.7 104.1±123.8 Seizure type Partial 100 (90.9%) 43 (81.1%) Generalized 10 (9.1%) 10 (18.9%) Etiology Idiopathic 79 (71.8%) 17 (32.1%) Symptomatic 18 (16.4%) 14 (26.4%) Cryptogenic 13 (11.8%) 22 (41.5%) History of febrile seizure 25 (22.7%) 13 (24.5%) Electrolytes (serum) Sodium (mg/dl) 140.4±1.3 140.3±1.6 Calcium (mg/dl) 9.4±0.7 9.1±0.2 3. SCN1A, SCN2A 유전자의대립유전자빈도 (Table 4, 5) SCN1A의유전자형은전체대상군에서 A/A 270 (86.8%), A/G 39 (12.5%), G/G 2 (0.7%) 이었다. 정상군과환자군, 반응군과불응군에서유전자형과대립유전자빈도는각군사이에서통계적유의성이없었다. SCN2A의유전자형은전체대상군에서 N/N 244 (78.4%), N/M 63 (20.3%), M/M 4 (1.3%) 이었다. 정상군과환자군에서유전자형과대립유전자빈도는각군사이에유의성이없었다. 불응군은유전자형 (p=0.007) 과대립유전자빈도 (p=0.004) 의단일염기다형성의비율이반응군보다통계적으로유의하게높았다. 고찰뇌전증은약 70% 가소아에서발생하며대부분의뇌전증은약물치료로완치가되거나잘조절되지만, 약 20-30% 의뇌전증은약물치료로조절되지않는다. 23,24 이경우를불응성뇌전증이라하는데보통 2가지이상의약물을충분히사용하였음에도, 발작이조절되지않는경우를말한다. 25 Vigevano 26 는부분발작또는전신발작환자의약 70% 는항경련제치료로조절되지만, 나머지 30% 환자는경련이지속되며, 조절되지않는경련은소아에서발달지연이나타날수있다고보고하였다. 뇌전증은예후에따라서자연적인관해를이루는군, 항경련제를사용하여관해를이루는군 ( 반응군 ) 과항경련제를사용함에도불구하고지속적인경련을하는군 ( 불응군 ) 의셋으로나눌수있는데, 앞의두군은각각 20-30% 를차지하고, Table 4. Distribution of SCN1A rs2298771 and SCN2A rs1718314 polymorphisms; genotype and allele frequencies in epilepsy patients vs. healthy controls Controls (n=148) Patients (n=163) Odds ratio (95% CI) p-value SCN1A rs2298771 AA 128 (86.5%) 142 (87.1%) reference - AG 18 (12.2%) 21 (12.9%) 1.05 (0.54, 2.06) 0.884 GG 2 (1.4%) 0 (0.0%) - - A * 274 (92.6%) 305 (93.6%) reference - G * 22 (7.4%) 21 (6.4%) 0.86 (0.46, 1.59) 0.627 SCN2A rs1718314 NN 117 (79.1%) 127 (77.9%) reference - NM 28 (18.9%) 35 (21.5%) 1.15 (0.66, 2.01) 0.619 MM 3 (2.0%) 1 (0.6%) 0.31 (0.03, 2.99) 0.310 N * 262 (88.5%) 289 (88.7%) reference - M * 34 (11.5%) 37 (11.3%) 0.99 (0.60, 1.62) 0.957 * Alleles. 52 대한뇌전증학회지제 16 권제 2 호, 2012
Table 5. Distribution of SCN1A rs2298771 and SCN2A rs1718314 polymorphisms; genotype and allele frequencies in drugresistant vs. drug-responsive patients with epilepsy Responders (n=110) Refractory (n=53) Odds ratio (95% CI) p-value SCN1A rs2298771 AA 95 (86.4%) 47 (88.7%) reference - AG 15 (13.6%) 6 (11.3%) 0.81 (0.30, 2.22) 0.680 GG 0 (0.0%) 0 (0.0%) - - A * 205 (93.2%) 100 (94.3%) reference - G * 15 (6.8%) 6 (5.7%) 0.82 (0.31, 2.18) 0.690 SCN2A rs1718314 NN 93 (84.5%) 34 (64.2%) reference - NM 17 (15.5%) 18 (33.9%) 2.90 (1.34, 6.26) 0.007 MM 0 (0.0%) 1 (1.9%) - - N * 203 (92.3%) 86 (81.1%) reference - M * 17 (7.7%) 20 (18.9%) 2.78 (1.39, 5.56) 0.004 * Alleles. 불응군이 30-40% 를차지한다. 27 불응성뇌전증의빈도는보고에따라 10-37.5% 까지다양한데, 7,28,29 본연구에서는불응성뇌전증이전체환자군의 32.5% 로유사한양상을보였다. 본연구의불응성뇌전증의진단기준은 Hauser 등 30 과같이두가지이상의항경련제를적절한용량으로썼음에도불구하고경련의조절이안되는경우로 1달에 1회이상의경련을하거나 6-12개월동안경련이조절되지않는경우로하였다. 불응성을예측할수있는인자들에는경련의종류, 항경련제의반응정도, 나이, 뇌전증시작시의경련빈도등이있다. 30년간추적관찰을한보고에서불응성뇌전증중특발성전신발작은 13%, 특발성부분발작은없었으며, 증후성뇌전증중전신발작은드물었으나부분발작은 49% 를차지하였다. 31 본연구에서는불응군에서특발성과증후성모두부분발작이 76% 와 85% 로우세하였다. 2개이상의항경련제를사용하였음에도불구하고경련조절이되지않는다면이는불응성의중요한지표가된다. 30 경련관해율은첫번째항경련제를썼을때에 61.8% 이고, 한가지약물을쓴이후에는다음항경련제에반응하는빈도가 41.7%, 16.6% 로점차감소된다. 6 가지항경련제를사용한이후에는완벽한불응성을보인다고한다. 32 본연구의불응군에서평균 3.3±1.2개의항경련제를사용하고있었으며, 최대 6가지의항경련제를사용한경우에도불응성을보였다. 경련시작나이가어린경우불응성과관련이있다는보고가있는데, 이는미성숙한뇌에경련이지속되어신경세포의손상과갭결합 (gap junction) 의수적증가로비정상적인연결이이루어지고피질의과연결성이나타나불응성이생기는것으로추측하고있다. 33,34 본연구에서도불응군이약 67.6개월로 102.4개월의반응군에 비하여더어린나이에경련을시작하였으며, 이는통계적으로도유의성을나타내었다 (p=0.001). 소디움이온통로는막단백질로서네개의상동영역들이서로연결되어하나의펩타이드형태를이루게되는 α 아단위와보조단위인 β1, β2 아단위로구성된다. 35 소디움이온통로의기본적인기능인활동전위의발생과전파는 α 아단위만으로도가능하고, β 아단위는 α 아단위의기능을조절한다. 36 중추신경계에는 α 아단위의아형인 SCN1A, SCN2A, SCN3A, SCN8A 유전자와 β 아단위의아형인 SCN1B 유전자가가주로발현되는데, 35,37 이중 SCN1A, SCN2A, SCN1B 유전자변이가전신뇌전증에동반된열성경련플러스 (generalized epilepsy with febrile seizures plus, GEFS+) 등여러뇌전증증후군에관련되는것으로알려졌다. 35,38 단일염기다형성은대부분독립적으로특정표현형을초래할만한기능은없으나, 유전체내에서특정표현형과밀접하게연관되어있을경우질병유전자의위치를알려주는유전표지자로서의기능을하게된다. 39 Ram의연구에서는 SCN1A c.3184 A G 단일염기다형성이뇌전증환자에서정상인보다유의하게많이발견되었으며 (p=0.005, 교차비 1.76, 95% 신뢰구간 1.19-2.61), SCN2A c.56 G A 단일염기다형성은불응성뇌전증을시사한다고하였다 (p=0.03, 교차비 1.62, 95% 신뢰구간 1.03-2.56). 21 중국인들을대상으로한연구에서는비록본연구와동일한단일염기다형성은아니지만같은 SCN2A 유전자의 IVS7-32A>G (rs- 2304016) 단일염기다형성이다약제불응뇌전증과밀접하게연관되어있음이알려졌다 (p=0.007, 교차비 2.1, 95% 신뢰구간 1.2-3.7). 22 국내의연구에서 SCN1A c.3184 A G 단일염기다형성이카바마제핀의내성과는큰연관이없는것으로나 Journal of Korean Epilepsy Society Vol. 16 No. 2, 2012 53
강준원 김동운 이영숙 이영호 이건수 타났다. 국내의다른연구에서는다중인자차원감쇠의방법을통하여전압관문나트륨통로가항경련제의저항성과연관될수있음을제시하였다. 40 본연구에서는 SCN1A c.3184 A G 단일염기다형성의표현형과대립유전자빈도는정상군과환자군, 그리고반응군과불응군사이에서차이가없었다. 하지만 SCN2A c.56 G A 단일염기다형성은표현형이반응군에서 NN 84.5%, NM 15.5%, MM 0% 이고불응군에서 NN 64.2%, NM 33.9%, MM 1.9% 로통계적유의하게단일염기다형성의비율이높았다 (p=0.007, 교차비 2.90, 95% 신뢰구간 1.34-6.26). 대립유전자빈도가반응군에서 N 92.3%, M 7.7% 이고불응군에서 N 81.1%, M 18.9% 로, 불응군에서통계적유의하게단일염기다형성의비율이높았다 (p=0.004, 교차비 2.78, 95% 신뢰구간 1.39-5.56). SCN2A c.56 G A 단일염기다형성이전압관문나트륨통로의기능에영향을주어불응성을일으키는한요소로고려될수있을것이다. 결론적으로불응성뇌전증에서반응성뇌전증에비해어린나이부터경련이시작되고, SCN2A c.56 G A 단일염기다형성의표현형과대립유전자빈도가유의하게높은것을알수있었다. 하지만 SCN2A c.56 G A 단일염기다형성외에독립적인영향력이적은여러유전자의단일염기다형성간의상호작용에의해불응성이결정될가능성을배제할수없기때문에추가적으로다른유전자와의상호작용을고려하고유의한결과를위하여추가적인대단위연구와실험실연구가뒷받침되어야할것이다. REFERENCES 1. Shneker BF, Fountain NB. Epilepsy. Dis Mon 2003;49:426-78. 2. Neubauer BA, GroB S, Hahn A. Epilepsy in childhood and adolescence. Dtsch Arztebl Int 2008;105:319-28. 3. Hesdorffer DC, Logroscino G, Cascino G, Annegers JF, Hauser WA. 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