Transcript Document

Chromosomal Disorders
张咸宁
[email protected]
Tel：13105819271; 88208367
Office: A705, Research Building
2012/09
Chromosome Disorders Are A Major
Category of Genetic Disease
• Large proportion of:
– Reproductive wastage (miscarriages)
– Congenital malformations
– Mental retardation
• Significant role in pathogenesis of
malignancy
Chromosome Disorders Are A Major
Category of Genetic Disease
• Specific chromosomal abnormalities are:
– Responsible for >100 identifiable syndromes
– Collectively more common than all of the
Mendelian single gene disorders together!
Chromosome Disorders Are A Major
Category of Genetic Disease
– ~ 1% of live births
– ~ 2% of prenatal diagnoses in women >35
yrs old
– 50% of all first trimester spontaneous
abortions
What are the indications for ordering
a chromosome analysis?
• Growth and
developmental
abnormalities
• Pregnancy with
“advanced maternal
age” (AMA)
• Family history of
chromosome
abnormalities
• Stillbirth/neonatal
death
• Infertility
• Infertility/history of
pregnancy loss
• Neoplasia
How is a karyotype（核型）
prepared?
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Sample: blood, skin, amnio, CVS
Cells grown in culture
Blocked in metaphase using colchicine
Spread on slide and stained
Abnormalities detected by number,
morphology and banding pattern
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Anatomy
Centromere Chromosome
placement
p (short arm)
q (long arm)
Size
Banding pattern (Giemsa stain)
– Heterochromatin 异染色质
(inactive, condensed) - dark
– Euchromatin 常染色质
(active, decondensed) - light
Interphase & Metaphase Nuclei
Giemsa Staining (G-banding)
Normal Human Male Karyotype
Individual Chromosomes Cut from Metaphase Spread
Ideogram of Human Male G-banded Metaphase Chromosomes
(400 bands per haploid karyotype)
Abnormalities of
Chromosome Number
• Heteroploid（异倍体）
– Any chromosome number other than 46
(1) Euploid （整倍体）
– An exact multiple of the haploid
chromosome number (n), where n = 23
(2) Aneuploid （非整倍体）
– Any chromosome number that is not an
exact multiple of the haploid number (n)
Triploidy（三倍性）
• Most often due to fertilization by two sperm
(dispermy) or occasionally a diploid sperm or
egg
• Partial hydatidiform moles (remnants of
placenta ± small atrophic fetus): triploid with
extra paternal set
– Mole: from the Latin mola, for false conception
• Extra maternal set: early spontaneous
abortions
Molar pregnancies
• Partial mole:
remnants of fetal
tissue (embryonic
and/or
extraembryonic)
• Triploid, paternal
• Complete mole: no
fetal tissues
• Risk for ovarian
teratoma or
choriocarcinoma
• Diploid but all
chromosomes are
maternal or paternal,
respectively
Aneuploidy（非整倍性）
• Trisomy（三体）: three copies
– 47,XY+21: Down syndrome
• Monosomy （单体） : one copy
– 45,X: Turner syndrome
• Nondisjunction（不分离）: failure of a
pair of chromosomes to separate (to
disjoin) normally in meiosis I or II
Different Consequences to the Gamete
of Nondisjunction at
Meiosis I or Meiosis II
both parental
21s present
2 copies of one
parental 21
Abnormal Male Karyotype:
47,XY +21
Down syndrome
• Most common
trisomy 1:800
in new born
• Most common
sever mental
retardation
• Related with
advanced
maternal age
Down syndrome
Down syndrome
Trisomy 18
（Edward syndrome）
• 1:7500 in liveborn
and more common
in abortion and
stillbirth
• Severe mental
retardation and
multiple structural
anomalies
Trisomy 18
Trisomy 13
（Patau syndrome）
• 1:20,000 in liveborn
and more common
in abortion and
stillbirth
• Severe structural
anomalies lead to
death in one month
Trisomy 13
Trisomy 13
Monosomy
• Almost all
monosomy for an
entire chromosome
is lethal
• Turner syndrome:
45,X, the only
monosomy can be
born and survive
Turner syndrome
XXY, Klinefelter syndrome
• 1:1,000 in male
liveborn
• Hypogonadism
• Infertility
Abnormalities of
Chromosome Structure
• Balanced: nothing gained or lost
• Unbalanced: material gained or lost
Balanced Rearrangements
（平衡性重排）
• Individuals with balanced rearrangements
appear normal
• Therefore, they may not be detected until:
– Birth of a child with an unbalanced
rearrangement
– Infertility evaluation (recurrent pregnancy loss)
Balanced and Unbalanced Translocations
（平衡易位、非平衡易位）
Translocation
• Reciprocal ~
（相互易位）
Resulted
from
breakage
of
nonhomologous chromosomes, with
reciprocal exchange of the broke-off
segments
Reciprocal Translocation (9;22)
Robertsonian Translocation
（罗氏易位）
• Two acrocentric chromosomes fuse
near the centromere region with loss
of the short arms, which carry
multiple copies of genes for rRNA.
• Only 45 chromosomes with balanced
karyotype and phenotype
45, XX, rob ( 13q14q)
Balanced translocation in meiosis
High Risk
to produce
unbalanced
offspring
Translocation Down Syndrome
• 4% of all Down cases
• One chromosome is a
Robertsonian translocation
• 21q + q of another
acrocentric chromosome,
usually 14 or 22
• 46,XX,rob(14;21),+21 or
46,XY,rob(14;21),+21
Down syndrome:21/21 t
Offsprings
Down syndrome: t
Down syndrome: t
The Tools:
Cytogenetic Analysis
Conventional
Karyotyping
SKY(spectral karyotyping)
What is FISH?
13
12
p 11.2
11.1
11.1
11.2
12
11.2 13
12
13
14
15
21.1
21.2
21.3
22.1
22. 2
q 22.3
23
24
p
q
25
26.1
26.2
26. 3
13
12
11.2
11.1
11.1
11.2
12
13
14
15
21.1
21.2
21.3
22.1
22. 2
22.3
23
24
25
26.1
26.2
26. 3
Normal ch romos ome 15
Dupli cation chro moso me 1 5
• Fluorescence in situ
hybridization
• Detects a specific
position or gene on an
intact chromosome
• Can be used to detect
numeric problems or
rearrangements –
Banding could not be
detected < 4Mb
Fluorescence In Situ Hybridization（FISH）
Cs+ Probe Co-denature
Anneal,hybridize
• Using DNA probe labeled with a certain
marker
• Hybridizing with DNA in chromosomes
and nuclei on slides
• Probes hybridized with the fragment in
chromosome are detected by signals from
the labeled markers
Down syndrome----FISH
Chromosome Painting
Specific Cytogenetic Changes in Cancer
• Association of cytogenetic changes with specific
forms of cancer
• Breakpoints may be associated with structural
rearrangements of oncogenes
• Cytogenetic changes in cancer are numerous
and diverse
– Many seen repeatedly in same type of tumor
– Evaluate by FISH and chromosomal painting
Philadelphia Chromosome in Chronic Myelogenous Leukemia
Ph Chromosome FISH
嵌合体：Mosaic and chimera
Aberration
Mosaic
Aberration
Chimera
Submicroscopic polymorphic
chromosome region copy number
variants are increasingly being
detected by high-resolution
techniques such as aCGH.
Array Comparative Genomic Hybridization (aCGH)
Suggested Readings
Acknowledge（PPT特别鸣谢！）
• UCLA David Geffen School of Medicine
• www.medsch.ucla.edu/ANGEL/
• Prof. Grody WW (Divisions of Medical
Genetics and Molecular Pathology), et al.