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1、Principles of Clinical CytogeneticsPost-Translation ProcessingPost-translational modifications:肽链从核蛋白体释放后，肽链从核蛋白体释放后，经过细胞内各种修饰处理成为有活性的成熟蛋白质的过程。经过细胞内各种修饰处理成为有活性的成熟蛋白质的过程。Primary translation product is folded and bonded into a specific three-dimensional structure.Two or more polypeptide chains combine
2、 to form a single mature protein complex.Cleavage of the protein The protein products may also be modified chemicallySTRUCTURE OF HUMAN CHROMOSOMES Composition of ChromatinDNAProteins (histones and nonhistone) The basic structure unit of chromatin: Nucleosome H1, (H2A, H2B, H3, H4)2(H2A,H2B,H3,H4)OR
3、GANIZATION OF THE HUMAN GENOMESingle-copy or unique DNARepetitive DNASingle-Copy DNA SequencesOnce or a few times /a genomeShort stretches (several kb)Coding portion of genes: a small proportion of all the single-copy DNARepetitive DNA FamiliesDefinition Hundreds to millions of times in the genomeRo
4、le Maintain chromosome structureCategoryClustered repeated sequencesDispersed repeated sequencesPrinciples of Clinical CytogeneticsYuxia YangDepartment of Medical Genetics, Peking University Health Science CenterIntroduction to CytogeneticsCytogenetics（细胞遗传学）Medical CytogeneticsClinical Cytogenetics
5、Introduction to CytogeneticsClinical indications for chromasome analysis Cytogenetics: the study of chromosomes and their abnormalities is called cytogenetics.Clinical Indications for Chromosome Analysis Problems of early growth and development Stillbirth and neonatal death. （死产、新生儿死亡）（死产、新生儿死亡）Fert
6、ility problems. （生育问题）（生育问题）Family history （家族史）（家族史）Neoplasia （肿瘤）（肿瘤）Pregnancy in a woman of advanced age（高龄孕妇）（高龄孕妇） The Human KaryotypeThe chromosomes are classified into 7 groups (A-G) Karyotype：是指一个体细胞中的全部染色体，按照大小、形态特征顺序排列所构成的图像Centromere: (primary constriction) 、p (short arm) 、 q (long arm) G
7、 bandingA chromosome at metaphase chromatid 染色单体染色单体 chromatid 1 chromosome p qTelomere（端粒端粒）telomereCentromere（着丝粒着丝粒）(primary constriction)topa,b: metacentric（中央着丝粒） c,d: submetacentric（亚中着丝粒） e: acrocentric（近端着丝粒） f: telocentric（端着丝粒）Chromosome Identification Identification of Human Chromosomes s
8、tained A uniform system of chromosome classification ISCN (An International System for Human Cytogenetic Nomenclature)（人类细胞遗传学国际命名体系）人类细胞遗传学国际命名体系）ISCN规定的界标：着丝粒、端粒、明显的带Arm Region Band Sub-bandXq13Chromosome IdentificationG Banding: trypsin(胰蛋白酶) 、 Giemsa(姬姆萨)Q Banding: quinacrine mustard(喹吖因氮芥喹吖因氮芥)
9、 R Banding: special treatmemt (heating) 、 staining 、 the reverse of G or Q bandingG BandingQ BandingR bandingIdeogram showing G banding patterns for human chromosomes at metaphaseChromosome Identification C Banding: staining the centromeric region、 other constitutive heterochromatin regionsHigh-Reso
10、lution Banding: chromosomes stained at the stage of prophase or prometaphase, detecting a subtle structural abnormality(前中期、晚前期的单倍染色体带纹数可达前中期、晚前期的单倍染色体带纹数可达550-850550-850条带条带; ;典型典型中期染色体，一套单倍染色体带纹数约中期染色体，一套单倍染色体带纹数约320-400320-400条带条带 )C BandingHigh-Resolution Banding Fluorescence In Situ Hybridizati
11、on (FISH:荧光原位杂交荧光原位杂交)Principles: Labeling probe with a fluorescent dye Denature of the probe and metaphase、prophase or interphase chromosomes Hybridization Visualizing the location of hybridization under a fluorescence microscopeChromosome Identification Probes: three typesgene-specific or locus-sp
12、ecific probes （单拷贝单拷贝单拷贝单拷贝） repetitive DNA probes (satellite DNA probes) （重复序列重复序列重复序列重复序列）chromosome painting probes (probes for entire chromosomes or chromosome arms) （染色体涂染染色体涂染染色体涂染染色体涂染）A single-copy DNA probe specific for the factor VIII gene on the X chromosomeMetaphase：中期中期Interphase:间期间期A
13、repetitive alpha satellite DNA probe specific for the centromere of chromosome 17MetaphaseInterphaseA whole chromosome “paint” probe specific for the X chromosomeMetaphaseInterphaseApplication: to examine the presence or absence of a particular DNA sequence to diagnose the existence of an abnormal c
14、hromosome number in clinical materialto detect chromosome rearrangements with combinations of FISH probes18-yellowY-greenX-red23,Y; 23,X 24,XX 24,XY Human Spermnormal n+1 n+113-green21-red18-aquaX-green18-aquaX-greenY-redPrader-Willi syndromedemonstrating deletion of 15q11-q13 Green：alpha satellite
15、DNA at the chromosome 15 centromereRed：SNRPN geneSpectral karyotyping (SKY：光谱核型分析)Chromosome AbnormalitiesAbnormalities of Chromosome NumberAbnormalities of Chromosome StructureAbnormalities of Chromosome Number Euploid Variation：以染色体组为单位发生的染色体成倍的增减以染色体组为单位发生的染色体成倍的增减, , 2n+n=3n; 2n+2n Aneuploid Var
16、iation：细胞内染色体数目增加或减少一条或几条细胞内染色体数目增加或减少一条或几条, , 2n+1; 2n+2Haploid (n)Euploid（整倍体整倍体） Triploid(三倍体三倍体) Definition: 3nReason: dispermy(双受精双受精) ) (most common)、 digyny(双雌受精双雌受精)Phenotypic expression: paternal-abnormal placenta; maternal-abortionkaryotypes: 69,XXX; 69,XXY; 69,XYYdispermydigyny Tetraploid
17、(四倍体四倍体)Definition: 4nReason: endoreduplication (核内复制核内复制), endomitosis (核内的有丝分裂核内的有丝分裂) Karyotypes: 92,XXXX or 92,XXYYEuploidEuploid（整倍体）（整倍体）Aneuploidy（非整倍体非整倍体）l Trisomy （三体性三体性） Definition: a trisomic cell involves a single extra chromosome; that is, the cell has three copies of a particular chr
18、omosomes and two copies of other chromosomes. A trisomic cell is 2n+1Example: trisomy 21 (karyotype: 47,XX/XY,+21) Monosomy （单体性单体性）Definition: a monosomic cell involves a loss of a single chromosome; that is, the cell is 2n-1.Example: Turner syndrome (Turner syndrome karyotype: 45, X)Mechanism- non
19、disjunctionMeiotic nondisjunction （减数分裂不分离）Mitotic nondisjunction （有丝分裂不分离）Meiotic NondisjunctionMitotic Nondisjunction 46464646464745nondisjunctionmitotic nondisjunction-mosaicismAbnormalities of Chromosome StructureMechanism: chromosome breakage 、 reconstitution in an abnormal combinationIncidence
20、: 1 in 375 newborns Types of structure rearrangementsBalancedUnbalancedUnbalanced RearrangementslDeletion (del, 缺失缺失)Definition: is a chromosomal mutation in which part of a chromosome is missingIncidence of autosomal deletions: 1/7000 live birthTypes: terminal (末端缺失末端缺失), interstitial (中间缺失中间缺失) （非
21、平衡重排）Karyotype: 46,XX,del(1)(q21) 46,XX,del(1)(pterq21:)Terminal deletionLoss常见染色体结构畸变的描述方法：常见染色体结构畸变的描述方法：按国际规定的要求，依次先写明染色体总数，性染色体组成，然后用一个字母（如t）或三联字符号（如del）说明重排染色体类型的名称，其后在括号内写明有关的染色体号数，接着在另一括号内注明区、带号以表示断裂点。简式：只用其断点来表示其断点来表示： 46, XX, del(1)(q21)；繁式：在最后括弧内，描述染色体重排的描述染色体重排的带的组成带的组成： 46, XX, del(1)(pt
22、erq21:)Karyotype: 46,XX(XY),del(3)(q21q31) 46,XX(XY),del(3)(pterq21:q31qter) LossInterstitial deletionReasons: Deletions may originate simply by chromosome breakage and loss of the acentric segment. Unequal crossing over between misaligned homologous chromosomes or sister chromatids.Deletions can al
23、so be generated by abnormal segregation from a balanced translocation or inversionDuplication (dup,重复重复)Definition: is a chromosomal mutation that results in the doubling of a segment of a chromosome.正位重复反位重复Duplication (dup)Reasons: Can originate by unequal crossing overBy abnormal segregation from
24、 meiosis in a carrier of a translocation or inversion.Ring Chromosomes(r ,环状环状)Ring Chromosome (r)Definition: deletions sometimes occur at both tips of a chromosome. The remaining chromosome ends can then fuse, forming a ring chromosome.ring chromosomelosslosslossIsochromosomes (I,等臂等臂)Definition: i
25、s a chromosome in which one arm is missing and the other duplicated in a mirror-image fashion.isochromosomereplicationafter replicationafter replicationisochromosomesIsochromosomes (i)Mechanisms: Misdivision through the centromere in meiosis II Exchange involving one arm of a chromosome and its homo
26、log (or sister chromatid) at the proximal edge of the arm, adjacent to the centromere.Isochromosomes (i)Common Isochromosomes: i(Xq) i(18p) i(12p) DicentricChromosomes (dic,双着丝粒双着丝粒)Definition: a dicentric is a rare type of abnormal chromosome in which two chromosome segments (from different chromos
27、omes or from the two chromatids of a single one), each with a centromere, fuse end to end, with loss of their acentric fragments.dicentric chromosomeBalanced RearrangementsInversions (inv, 倒位倒位)Definition: occurs when a single chromosome undergoes two breaks and is reconstituted with the segment bet
28、ween the breaks inverted.Types: Paracentric (not including centromere) Pericentric (including centromere)（平衡重排）ParacentricKaryotypes: 46,XX,inv(1)(p22p34) 46,XX,inv(1)(pterp34:p22p34:p22qter)PericentricKaryotypes: 46,XX,inv(2)(p15q21) 46,XX,inv(2)(pterp15:q21p15:q21qter)Inversion carrier: a carrier
29、of either type of inversion is at risk of producing abnormal gametes that may lead to unbalanced offspringABACDBCDThe risk that a carrier of a paracentric inversion will have a liveborn child with an abnormal karyotype is very low indeed.ABACDBCD臂间倒位携带者在形成生殖细胞的减数分裂过程中，根据在配子形成中同源染色体节段相互配对的规律，它将形成倒位圈，
30、并且，经过在倒位圈内的交换，形成4种不同的配子，一种为正常染色体，一种为倒位染色体，另外两种均带有部分重复及部分缺失的重排染色体。这两种异常重排染色体各有一个着丝粒，属于稳定性畸变而可往后传递。因此其遗传效应主要决定于重复和缺失片段的长短及其所含基因的致死效应。一般来说，其倒倒位片段越短，则重复和缺失部分越长，形成配子和合子正常发育的可能性越小，临床表位片段越短，则重复和缺失部分越长，形成配子和合子正常发育的可能性越小，临床表现为婚后不育、早期流产和死产的比例越高，娩出子女的可能性相对低现为婚后不育、早期流产和死产的比例越高，娩出子女的可能性相对低；而倒位片段越倒位片段越长长，则其重复和缺失部
31、分越短，其配子和合子正常发育的可能性越大，则其重复和缺失部分越短，其配子和合子正常发育的可能性越大，娩出畸形胎儿的娩出畸形胎儿的危险性相对较高危险性相对较高Translocations (t, 易位易位)Definition: involves the exchange of chromosome segments between two, usually nonhomologous chromosomesMain types: reciprocal (rcp,相互易位相互易位) ), Robertsonian (rob,罗伯逊易位罗伯逊易位)Reciprocal Translocations
32、 (rcp)Definition: this type of rearrangement results from breakage of nonhomologous chromosomes, with reciprocal exchange of the broken-off segments.Karyotypes:46, XX, t(2;5)(q21;q31)46, XX, t(2;5)(2pter2q21:5q315qter;5pter5q31:2q212qter)reciprocal translocationCarriers of balanced reciprocal transl
33、ocation: are associated with a high risk of unbalanced gametes and abnormal progenyFigure 9-12. A, Diagram of a balanced translocation between chromosome 3 and chromosome11, t(3;11)(q12;p15.5)平衡易位携带者在形成生殖细胞的减数分裂的前期I时，易位染色体将在联会时配对形成四射体。至后期I时，相关染色体可进行对位分离和邻位1和邻位2分离以及3:1分离。其中，仅有一种配子是正常的，一种是平衡易位的，其余都是不平
34、衡的。与正常配子受精后所形成的合子中，大部都形成单体或部分单体、三体或部分三体患胎而导致流产、死胎或畸形儿。Pairing at meiosisSegregationUnbalanced Unbalanced Normal balancedUnbalanced Unbalanced(50%)(50%)(rare)(inviable)(inviable)(viable)Robertsonian Translocations (rob)Definition: this type of rearrangement involves two acrocentric chromosomes that f
35、use near the centromere region with loss of the short arms罗伯逊易位罗伯逊易位：又称着丝粒融合。在着丝粒部位或着丝粒附近部位发生断裂后，两者的长臂在两条近端着丝粒染色体两条近端着丝粒染色体着丝粒处结合在一起，形成一条由长臂构成的衍生染色体，两个短臂则构成一个小染色体，小染色体往往在第二次细胞分裂时丢失，这可能是由于缺乏着丝粒或其完全由异染色质构成所致。lossRobertsonian translocation14p1114p1121q1121q11Two (13q14q , 14q21q ) of Robertsonian trans
36、locations are commonCarrier of Robertsonian translocation: a carrier of a Robertsonian translocation is phenotypically normal, there is a risk of unbalanced gametes and therefore offspring. 14q21q TranslocationGerm cellGameteNormal gameteZygotesBalancedNormalTrisomy 21Monosomy 21Monosomy 14Trisomy 1
37、414q21q2114Insertions (ins,插入插入)Definition: an insertion is a nonreciprocal type of translocation that occurs when a segment removed from one chromosome is inserted into a different chromosome, either in its usual orientation or inverted.insertionMosaicism (mos,嵌合体嵌合体) Definition: two or more differ
38、ent chromosome complements are present in an individual, this situation is called mosaicism Types: numerical (most common type), structuralMosaicism (mos)Examples: 46, XX/47, XX, +21 45, X/46, XXReasons: mosaicism is nondisjunction in an early postzygotic mitotic division.46464646464745nondisjunctionmitotic nondisjunction-mosaicism
