Connexin 26基因233delC突变与中国人先天性耳聋的研究

目的：Connexin 26基因突变是引起常染色体隐性遗传DFNB1和常染色体显性遗传DFNA3的遗传基础，其中的35delG的突变在欧美人DFNB1耳聋患者中的检出率为70－80％，但在中国耳聋人群中未检到该点突变。本文指在筛选中国人耳聋相关的Connexin 26基因的突变热点。方法：采用PCR－RFLP筛选和219例不同耳聋类型的患者和50例听力正常人的Connexin 26基因233delC的突变（21．5％）。结果：219例耳聋患者中共发现了47例Connexin 26基因233delC的突变（21．5％）。在先天性耳聋患者中233decC的突变率为33％，遗传性语前聋患者为26．7％。50例药物性致聋的患者有10例发生突变。遗传性及散发性进行性感音神经性耳聋和听力正常人未检测到233decC突变。结论：Connexin 26基因233delC突变在中国先天性耳聋人群中发生频率较高，与欧美人不同。我们的结果表明，Connexin 26基因异常导致耳聋的突变热点具有种族特异性。     

非综合征性耳聋患者连接蛋白26基因突变的研究

目的　探讨中国人非综合征性耳聋患者连接蛋白 2 6 (connexin 2 6 ,Cx2 6 )基因突变频率和特性。方法　收集中国散发先天性聋哑儿童 16例 ,常染色体隐性遗传性聋 39例 (39个家系 ) ,10岁前开始听力下降的常染色体显性遗传性聋 30例 (30个家系 )和健康对照组 10 0例。聚合酶链反应 单链构象多态 (singlestrandconformationalpolymorphismanalysisofpolymerasechainreaction ,PCR SSCP)分析初筛可疑突变者 ,SSCP分析发现异常构象带后再行DNA测序。结果　健康对照组中 15例发现 5种多态性改变 ,耳聋患者中 10例发现 6种多态性改变。散发先天性聋哑和常染色体隐性遗传非综合征性耳聋中未发现致病突变。 1个常染色体显性遗传性聋家系发现所有患者 (3例 )Cx2 6基因的编码区2 99 30 0位碱基AT杂合性缺失 ,导致移码突变 ,翻译的蛋白质截短 ,该家系听力正常者无此突变。结论　蒙古人种中常染色体隐性遗传性非综合征性耳聋的Cx2 6基因突变率可能低于其他人种。Cx2 6基因编码区 2 99 30 0位碱基AT杂合性缺失可致常染色体显性遗传性聋DFNA3型     

遗传性耳聋资源收集保存及基因定位克隆

目的建立聋病遗传资源收集网络,着重收集具有中国特色的聋病遗传资源,进行聋病基因定位克隆及相关的分子流行病学研究。方法通过遗传资源收集网络进行聋病遗传资源的收集,建立资源库进行遗传资源的表型鉴定和分析。应用微卫星标记的连锁分析及候选基因法进行家系的基因定位克隆和分子流行病学研究。结果共收集到含有多种耳聋表型的大小家系2071个,其中涵盖了单基因病孟德尔遗传的全部遗传方式:包括X-连锁遗传家系2个,Y-连锁遗传家系1个(命名为DFNY1基因座)、常染色体显性遗传性耳聋大家系12个(完成了基因定位5个)、常染色体隐性遗传性耳聋核心家系619个以及线粒体突变母系遗传性耳聋家系76个;大前庭水管综合征163例;听神经病108例;不明原因感音神经性耳聋478例;西北地区聋哑学校聋哑患者612例。对1489例散发患者进行了线粒体基因12S rRNA 1555G,缝隙连接蛋白基因(GJB2,GJB3和GJB6)以及SLC26A4基因的突变筛查与分析。其中西北地区612例聋哑人群中发现27．92％患者分别存在三个基因的突变,mtDNAA1555G平均阳性率为9．15％,GJB2为9．97％,SLC26A4为8．8％。结论遗传性听力损失是非常常见的耳聋疾病,其发病率超出原有的预测。基于大家系的基因定位研究有望发现新的基因座位及新的基因突变。分子流行病学研究发现遗传因素在先天性聋和学语后听力损失中的作用强于环境因素,并发现中国人群具有耳聋基因的高发病率和特异的突变图谱。     

一个遗传性耳聋大家系的基因突变检测

目的 :探讨中国人遗传性耳聋基因的突变热点和明确我们最近收集到的一个遗传性耳聋家系是否为已克隆的耳聋基因的突变所致。方法 :该家系 5代共 4 7人 ,其中耳聋患者 1 8人 ,从家系图分析 ,符合常染色体显性遗传 ;所有患者均为语后聋 ,从 1 6 3 0岁起病 ,为双耳对称性、进行性、高频听力下降为主的感觉神经性聋 ,不伴其它器官系统的异常 ;采用PCR 直接测序法在该家系中进行HDIA1、GJB3、GJB2、DFNA5、а tectorin(可导致DFNA8和DFNA1 2两型遗传性耳聋 )、MYO7A、POU4F3等 7个常染色体显性耳聋基因的突变检测。结果 :发现CX2 6基因有 2种核苷酸改变即A3 4 1G和GC2 5 7 2 5 8CG ;POU4F3基因有 1种核苷酸改变即T90C。分析后发现 ,上述核苷酸改变均不是该家系耳聋的致病性突变。其余 5个基因未发现突变。结论 :该常染色体显性耳聋家系由目前已克隆基因突变所致的可能性较小 ,笔者目前正在进行的全基因组扫描和连锁分析极有可能定位一个新的耳聋基因位点     

东莞户籍33810例新生儿听力筛查联合耳聋基因检测与分析

目的了解分析东莞地区新生儿常见耳聋基因的突变类型和突变携带率,并对听力筛查和耳聋基因联合检测进行评价。方法对2016年1月至2017年2月在东莞辖区内出生的33810例户籍新生儿同时进行听力筛查和耳聋基因检测,听力筛查包括耳声发射和听性脑干反应,耳聋基因检测采用耳聋基因芯片(微阵列芯片法)对我国常见的致聋基因GJB2(c.235del C,c.299_300del AT,c.176_191del16,c.35del G)、SLC26A4(IVS7-2A>G,c.2168A>G)、线粒体12Sr RNA(m.1555A>G,m.1494C>T)和GJB3(c.538C>T)进行检测。结果 33810例新生儿共检出1145个等位基因突变,突变携带率约为3.39%。其中GJB2突变661个,突变携带率约1.96%;SLC26A4突变364个,突变携带率约1.08%;线粒体DNA12Sr RNA突变74个,突变携带率约0.22%;GJB3突变46个,突变携带率约0.14%。在6242例新生儿听力筛查结果中,听力筛查未通过103例,未通过率1.65%。结论 c.235del C、IVS7-2A>G是东莞地区新生儿耳聋基因突变的主要类型。开展新生儿听力筛查与耳聋基因联合检测有助于了解本地区耳聋基因携带情况及患儿听力状况,提早发现先天性耳聋患者,高度预警药物性耳聋和迟发性耳聋,做到早发现、早诊断、早干预、早治疗,对降低耳聋发生率有重要意义。     

芜湖地区109例听障儿童及家属耳聋基因突变检测结果分析

目的应用基因芯片对先天性耳聋儿童及其家属行耳聋基因检测,了解芜湖地区耳聋儿童常见的致聋基因。方法选取来自芜湖市第二人民医院的37例非综合征型耳聋儿童及其家属(共109例),行耳聋高危因素问卷调查、耳鼻咽喉科专科检查、听力学评估及影像学检查,应用基因芯片对109例受检者行GJB2、GJB3、SLC26A4、mt DNA 4个常见基因9个热点突变点位的检测。结果 37例受检儿童,23例检测出基因突变,阳性率为62.16%,其中15例GJB2基因突变(40.54%)(235del C纯合突变6例、杂合突变4例;299del AT杂合突变1例;235del C和299del AT复合杂合突变3例;176del16和235del C复合杂合突变1例);7例SLC26A4基因突变(18.92%)(IVS7-2纯和合突变2例、杂合突变5例);1例mt DNA基因突变(2.70%)(1555A>G均质突变)。检出GJB2或/和SLC26A4突变的聋儿,其父母均检测出相应的基因突变。结论芜湖地区耳聋儿童常见的致聋基因是GJB2、SLC26A4、mt DNA,最常见的是GJB2基因235del C点位突变,GJB2及SLC26A4基因与遗传高度相关。     

新生儿听力及耳聋基因联合筛查

新生儿听力及耳聋基因联合筛查,近年来受到医学界的广泛关注。北京市新生儿耳聋基因筛查项目证明,通过基因筛查不仅可以发现先天性遗传性聋患者,更重要的是发现药物敏感性聋基因携带者和迟发性聋基因携带者。早期对耳聋患者实施干预和康复,可以使其聋而不哑;对耳聋基因携带者进行预警及耳聋防治知识的宣教,可以有效预防和减少耳聋的发生;通过进一步的耳聋遗传咨询,可以避免生育聋儿。     

福建省606例非综合征型聋患者常见聋病基因突变检测结果分析北大核心CSCD

目的分析福建省不同地区非综合征型聋患者耳聋基因突变检测结果,了解福建省聋病患者常见突变基因及突变热点。方法收集福建福州、龙岩、南平、三明地区606例非综合征型聋患者的外周血样本,采用飞行时间质谱检测技术结合毛细管电泳测序对常见的致聋基因20个常见突变位点12SrRNA基因1555A→G、1494C→T,GJB2基因35del G、167del T、176_191del 16、235del C、299_300del AT,SLC26A4基因281C→T、589G→A、IVS7-2A→G、1174A→T、1226G→A、1229C→T、IVS15+5G→A、1975GC、2027T→A、2162C→T、2168A→G,GJB3基因538C→T、547G→A进行检测。结果606例非综合征型聋患者中,共检测出耳聋基因突变140例(23.10%),其中12SrRNA基因突变40例(6.60%),GJB2耳聋基因突变67例(11.06%),SLC26A4突变患者33例(5.54%),未检测到GJB3基因突变。福州、龙岩、南平、三明地区常见耳聋基因突变检出率分别为17.89%(34/190)、22.39%(30/134)、31.06%(41/132)、23.33%(35/150),南平地区检出率高于福州地区,差异有统计学意义(P<0.05)。结论福建省非综合征型聋病患者GJB2突变检出率最高,其次为12SrRNA、SLC26A4。     

205例先天性非综合征型聋患儿GJB2基因突变分析

目的探讨先天性非综合征型聋婴幼儿的GJB2基因突变频率、突变热点和听力学表型特点。方法对来自上海及周边地区的205例先天性非综合征型聋患儿GJB2基因PCR扩增产物行酶切鉴定以及直接测序法进行突变检测,对1例GJB2基因235delC纯合突变先证者母亲再次妊娠19周时通过羊水穿刺行产前诊断。结果205例先天性非综合征型聋儿中,共发现GJB2基因移码突变49例,占23.90%（49/205）,其中46例患儿存在GJB2基因235detc突变,占93.88%（46/49）,GJB2基因突变者多为中到极重度听力损失。1例胎儿产前诊断确诊为GJB2基因235delC纯合突变。结论GJB2基因纯合或复合杂合移码突变可导致非综合征型常染色体隐性遗传性聋,听力损失程度多为中度至极重度;235delC突变占所有突变等位基因85.88%。     

非综合征型遗传性耳聋患者中GJB2基因的致病突变与多态性研究进展

目前认为60%的耳聋患者与遗传相关,而遗传性耳聋根据是否伴有全身其它症状,分为综合征型遗传性耳聋和非综合征型遗传性耳聋。现有的研究资料显示:与非综合征型遗传性耳聋密切相关的GJB2基因,不同人种突变位点不同,各个位点突变形式、频率也有所不同。     

Absence of GJB6 mutations in Indian patients with non-syndromic hearing loss

Objective

Hearing loss is the most frequent sensory defect in human being. Genetic factors account for at least half of all cases of profound congenital deafness. The 13q11-q12 region contains the GJB2 and GJB6 genes, which code connexin 26 (CX26) and connexin 30 (CX30) proteins, respectively. Mutations in the gene GJB2, encoding the gap junction protein connexin 26, are considered to be responsible for up to 50% of familial cases of autosomal recessive non-syndromic hearing loss and for up to 15-30% of the sporadic cases. It has also been reported that mutations in the GJB6 gene contribute to autosomal recessive and autosomal dominant hearing defects in many populations. The 342-kb deletion [del(GJB6-D13S1830)] of the Cx30 gene is the second most common connexin mutation after the CX26 mutations in some NSHL populations. The aim of this study was to screen GJB6 gene mutations in Asian Indian patients with autosomal non-syndromic hearing loss.

Methods

We screened 203 non-syndromic hearing loss patients, who were negative for homozygous mutations in GJB2 gene, for GJB6-D13S1830 deletion and mutations in coding regions of GJB6 using polymerase chain reaction, denaturing high performance liquid chromatography and direct sequencing.

Results

No deleterious mutation in GJB6 gene was detected in our study cohort.

Conclusion

The present data demonstrated that mutations in the GJB6 gene are unlikely to be a major cause of non-syndromic deafness in Asian Indians.     

screening of gjb2 mutations in chinese population

The GJB2 gene(connexin 26) has been shown to be responsible for DFNB1 and DFNA3. We screened the GJB2 gene in 488 patients with prelingual deafness(Group 1), 124 with postlingual deafness(Group 2), and 117 normal hearing subjects(Group 3). We found that, in Group 1, 65 patients(13.32%) were homozygotes or compound heterozygotes and 51 patients (10.45%) carried a single pathogenic mutation. The 235delC mutation was the most frequent mutation, accounting for 73.22% of the known pathogenic alleles in Group 1. No homozygotes or compound heterozygotes were detected in Group 2 or Group 3. Some postlingual deaf patients (2.42%) and normal hearing subjects(4.27%) were 235delC carriers. Our preliminary data indicate that 235delC, the most frequent mutation identified in this study, is a major cause for prelingual deafness.     

GJB2 gene mutations in newborns with non-syndromic hearing impairment in Northern China

Mutations in GJB2 account for the majority of recessive forms of prelingual hearing loss. However, in most previous studies it was not possible to distinguish between congenital (present at birth) and non-congenital prelingual hearing loss. In the present study, the frequency of GJB2 alleles in 20 newborns with bilateral severe-to-profound non-syndromic hearing impairment (NSHI) who were found at birth through newborn hearing screening and clinical examination is reported. PCR was used to amplify the coding region of GJB2 gene followed by sequencing analyses. Fifty volunteers with normal hearing were included as controls. Results showed that three cases were 235delC/235delC homozygotes; one was 235delC/605ins46 compound heterozygotes, 605ins46 mutation was a novel mutation reported in the Chinese population; another was 235delC/299-300delAT compound heterozygotes. 25% (5/20) of the deafness in newborns studied was caused by GJB2 gene mutations. The frequency of 235delC allele carrier in patients and in control group was 22.5% and 1%, respectively. One case was identified as being a 235delC heterozygote without other mutations detected. Besides, multiple polymorphisms such as V27I, V37I, E114G, T123N were also detected. In conclusion, GJB2 analysis is an important test that identifies a major cause of newborns with bilateral severe-to-profound NSHI screened by universal newborn hearing screening in Northern China. The most common pathologic mutation of GJB2 in studied cases was 235delC. Molecular analysis and genetic counseling will be extremely important for congenital deafness present at birth.     

散发性耳聋GJB2基因突变分析

目的 通过分析内蒙古鄂尔多斯和呼和浩特地区散发性耳聋患者GJB2 235delC点突变,以探讨散发性耳聋患者的分子病因学。方法 对131例(汉族92例,蒙古族39例) 散发性耳聋患者进行耳聋病因学问卷调查、纯音听阈及声导抗测试。聚合酶链反应(polymerase chain reaction PCR)扩增目的片段并用限制性内切酶对其进行GJB2 235delC基因突变检测,对酶切检测结果呈阳性的样本用直接测序法进行验证。对50例健康中国人和100例健康加拿大白种人行限制性内切酶GJB2 235delC点突变检测,作为阴性对照。结果 131例散发性耳聋患者全部为感音神经性聋。在该群体中4例(汉族3例,蒙古族1例)存在GJB2 235delC纯合性突变;3例(汉族2例,蒙古族1例)存在GJB2 235delC杂合性突变。50例健康中国人对照组中检测出1例GJB2 235delC点突变携带者,100例健康加拿大白种人中未检测到GJB2 235delC点突变。结论 GJB2 235delC点突变是中国人散发性感音神经性耳聋的分子病因学之一。内蒙古地区汉族、蒙古族GJB2 235delC突变频率无明显差异,对GJB2 235delC点突变的基因筛查可以明确一些散发性耳聋患者的病因,从而对基因突变引起的散发性耳聋的早期诊断、遗传咨询及防聋治聋起到重要作用。     

Mutationsanalyse des Connexin26-Gens bei sporadischen Fällen mittel- bis hochgradiger Schwerhörigkeit

Non-syndromic neurosensory recessive deafness (NSRD) is one of the most common human sensory disorders. Mutations in the connexin 26 gene have been established as a major cause of inherited and sporadic non-syndromic deafness in different populations. The CX26 gene encodes the gap junction protein connexin 26 (beta-2, GJB2), whose expression was shown in several tissues and in the cochlea. The 30delG mutation is the most frequent mutation in the CX26 gene. It represents a deletion of guanosine (G) in a sequence of six Gs extending from position 30 to 35 of the CX26 cDNA. The deletion creates a frameshift resulting in a premature stop codon and a non-functional intracellular domain in the protein. The 30delG mutation can be detected at the molecular level using PCR followed by BsiYI digestion. We screened 164 mainly German patients with non-syndromic sporadic deafness for this mutation to determine its distribution in the German population. The frequency of the mutation in our analyzed patients was lower than in other studies and therefore indicates its dependency on geographically distinct populations.     

中国西北地区线粒体DNA12SrRNAA1555G和GJB2基因突变

目的研究mtDNA 12SrRNA A1555G突变和GJB2突变在西北地区非综合征型感音神经性聋患者中的流行情况,探讨GJB2基因与mtDNA A1555G点突变的关系。方法收集本地区221例非综合征感音神经性聋患者的基因组DNA,多聚酶链反应扩增线粒体DNA和GJB2基因目的片断,Alw26Ⅰ限制性内切酶检测A1555G点突变,对酶切阳性病例和全部的GJB2基因的PCR产物进行DNA测序。结果21例患者检出mtDNA 12SrRNA A1555G突变;发现GJB2基因11种序列改变,有44例患者检出GJB2致病突变,235delC占携带致病突变患者的54．54％：在21例A1555G突变患者中,11例为GJB2基因多态改变,9例未检出GJB2基因序列改变,1例为109G→A（V371）突变。结论mDNA 12SrRNA A1555G在这一地区人群中有较高的发生频率．235delC是本地区GJB2基因突变的主要形式,GJB2基因突变不是mtDNA A1555G突变致聋的主要修饰因素。     

Audiological features of GJB2 (connexin 26) deafness

OBJECTIVE: The aim of the present study was to characterize audiological profiles in patients with GJB2 deafness DESIGN: We screened DNA from 399 individuals with nonsyndromic deafness for mutations in the connexin 26 gene (GJB2) by sequence analysis. A total of 77 (19%) of these deaf individuals were biallelic GJB2 mutations (either homozygous or compound heterozygous mutations) (GJB2 deafness). Using the audiological classification criteria of genetic deafness proposed by the European Workshop on Genetic Hearing Loss, we analyzed audiograms of these patients to characterize audiological features of the GJB2 deafness. In addition, we reviewed audiological data of 411 deafness cases from the literature providing details of audiological data (including 157 with GJB2 deafness). RESULTS: All categories of hearing loss severity were found, with significant differences in the findings from GJB2 cases: 1 (4.5%) of 22 individuals with mild hearing loss, 10 (13.3%) of 75 with moderate loss, 14 (14.9%) of 94 with severe loss, and 52 (25%) of 208 with profound deafness (Chi-square test, 3 df, p = 0.016). 81.6% of patients with GJB2 mutations had severe to profound loss, 18.4% with mild to moderate loss (Chi-square test, p = 0.014). The 235delC mutation was always associated with profound deafness. The main audiogram shapes found were residual/sloping (72.7%) and flat (23.4%). There were no differences in the severity and audiogram shapes of the hearing impairment between homozygous and compound heterozygous GJB2 deafness (Chi-square test, p > 0.05). CONCLUSIONS: Our study shows that the probability of finding biallelic GJB2 mutations increases with the severity of hearing loss. Audiograms associated with GJB2 deafness were usually nonspecific. Patients with unknown causes of severe or profound hearing loss should be routinely tested for GJB2 mutations, but due to the variability in hearing loss, individuals with lesser degrees of hearing loss should not be precluded from testing.     

国人conneXin 2 6基因突变与先天性感音神经性耳聋的相关性研究

目的探讨国人耳聋人群中connexm26基因的突变频率和位点.方法收集15例有遗传性耳聋家族史的病例和252例散发性先天性耳聋病例血液样本,使用PCR-SSCP方法分析connexin26基因编码区突变.同时采用PSDM和BsBsiYI酶切的方法,直接检测异常connexin26基因35delG的突变.结果检出突变样本46例,其中散发耳聋患者中38例,突变率为15.1%;有家族史的聋儿15例中8例,突变率为53.3%.46例中5份有相似的异常电泳带,PCR产物直接测序,其形式为79位G→A的突变;另外在散发耳聋患者中还发现2例251delT和233delC,PDSM分析未发现有35delG的突变.结论国人先天性耳聋患者中存在着connexin26基因的高突变率,但突变热点与国外报道的不同,推测connexin26基因突变有明显的种族特异性.     

GJB2, SLC26A4 and mitochondrial DNA A1555G mutations in prelingual deafness in Northern Chinese subjects

CONCLUSION: This genetic epidemiological study demonstrated that 26.65% of the prelingual deafness in Northern Chinese patients can be detected at younger ages by genetic testing of three common hearing loss genes (GJB2, SLC26A4 and mtDNA A1555G), and thus, early intervention measures could be undertaken to help them in language acquisition. OBJECTIVES: The GJB2, SLC26A4 and mtDNA A1555G mutations are the prevalent causes of prelingual deafness worldwide. Numerous studies have revealed that the forms and frequencies of the mutations in the three genes are largely dependent on the ethnic or geographic origins. Hence, this study aimed to characterize the mutation profiles of the three genes in prelingual deafness in Northern Chinese patients. SUBECTS AND METHODS: An investigation of 514 patients with prelingual deafness and 117 controls with normal hearing was conducted. Bidirectional sequencing (or enzyme digestion) was applied to identify sequence variations. RESULTS: This study revealed that 26.65% patients had two mutated alleles (homozygote or compound heterozygote) of GJB2 (9.14%) or SLC26A4 (8.95%) and/or an mtDNA A1555G (8.56%) mutation. In detail, 19.26% patients carried GJB2 mutations including 10.12% single mutant carriers. 235delC was the most common type, making up 69.18% of all mutants for GJB2. The mutant carrier rate for SLC26A4 was 15.2%, including 6.23% single mutant carriers. The two most common types (IVS7-2A > G and H723R) accounted for 51.61% and 33.06% mutations, respectively. Forty-five patients had mtDNA A1555G, giving a frequency of 8.75%. In the control group with normal hearing, 2.56%, 1.71% and 0% of the subjects carried a single mutant for GJB2, SLC26A4 and mtDNA A1555G, respectively.     

淮阴A1555G突变相关耳聋核心家系成员的连接蛋白26基因突变分析

目的探讨连接蛋白26（connexin 26，Cx26）基因是否是江苏淮阴A1555G突变相关母系遗传聋家系的核修饰基因。方法采用聚合酶链反应一限制片断长度多态性分析（PCR—restriction fragment length polymorphism，PCR-RFLP）和测序技术，对江苏淮阴A1555G突变相关母系遗传非综合征型聋核心家系中的26例母系成员和62例对照（包括2例父系亲属、10例配偶对照和50例当地无关对照）的Cx26基因编码区序列进行了研究，并根据孟德尔遗传规律构建了家系成员Cx26基因的单体型图。结果在26例母系成员中共发现4处杂合性碱基变化，分别为79G→A、109G→A、341G→A和235delC。其中，前3种为已知多态性差异，而235delC为已知的可引起常染色体隐性聋的致病突变。但235delC突变仅存在于1例具有中度聋表型的母系成员和其2例听力正常的子女中，并不与耳聋表型共分离。而根据遗传规律，推测该突变来源于1例配偶对照，为外来突变；同时，根据4个位点变化构建的Cx26基因单体型图也未揭示Cx26基因与A1555G突变致聋有任何相关性；另外，在62例对照中也发现1例235delC杂合性缺失突变。结论235delC杂合性突变并不加重A1555G突变的致聋效应；Cx26基因也不是江苏淮阴母系遗传聋家系A1555G突变的核修饰基因。