Title: Developmental Pathology
1Developmental Pathology
- Thursday, 10-1-07
- Michelle Dolan, M.D.
- dolan009_at_umn.edu
2Cytogenetics
- Examination of chromosomes under the microscope
- Necessary to induce cells to undergo mitosis in
order to see individual chromosomes - Molecular cytogenetic techniques (e.g., FISH) can
be performed on interphase cells (cells that are
not actively dividing)
3Reasons to do a cytogenetic study
- Diagnose constitutional disorders
- I.e., disorders present at birth -- classic
example is trisomy 21 (Down syndrome) - Typically involve more than one cell line
- Add further diagnostic or prognostic information
to a diagnosis of an acquired disorder - I.e., diseases that are NOT constitutional --
these are most commonly malignancies - Typically involve only the cell line or tissue
involved by the malignancy
448-hour culture overnight exposure to colcemid
572-hour culture several hours
colcemid ethidium bromide added
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8Basic Terminology
- Constitutional Chromosomal Abnormalities
- Acquired Chromosomal Abnormalities
- Numerical abnormalities
- Structural abnormalities
- Balanced
- Unbalanced
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10Karyotype -- Blood
11Karyotype -- Marrow
12FISH diagram (scanned)
13Fluorescence in situ hybridization (FISH)
- Specimen is collected as previously described for
each tissue type - Indications for FISH include
- Microdeletions (e.g., Prader-Willi, Angelman and
DiGeorge syndromes) - Cryptic translocations (e.g., t(1221))
- Cancer translocations (e.g., BCR-abl, PML-RARA)
and rearrangements (e.g., MLL) - Enumeration of chromosomes or detection of
translocations or rearrangements in interphase
nuclei
14Clinical History
- Approximately 32 weeks gestation
- Abnormalities detected on ultrasound
- Abnormal head shape
- Frontal bossing
- Clenched fists
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19Newest method -- array-based Comparative Genomic
Hybridization
- DNA is extracted from patient
- DNA from patient and sex-matched control are
labeled in different colors - Labeled DNA is hybridized to a chip (microarray)
on which are oligonucleotides spaced across the
genome (density or spacing of oligos depends on
platform) - Results in ratio of patient to control at these
loci
20Array CGH
- Used to detect abnormalities too small to be seen
under the microscope (each G-band can contain
hundreds of genes) - Can detect only unbalanced rearrangements (e.g.,
deletions, duplications) - Balanced rearrangements (e.g., inversions,
insertions) will NOT be detected by array-CGH
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23Specimen to draw for a cytogenetic study?
- SODIUM heparin tube
- Recommend at least 1 ml (3 if poss)
24Trisomy (one extra chromosome)
- Typically arises from a nondisjunction error in
either meiosis I, meiosis II or mitosis (if due
to amitotic error, the trisomy is mosaic) - Most autosomal trisomies arise from maternal
nondisjunction errors - Strong correlation between increasing maternal
age and risk for nondisjunction - Advanced Maternal Age (AMA) is the most common
reason for referral for a prenatal chromosome
study - 95 of trisomy 21 is due to maternal
nondisjunction errors
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27Major viable trisomies
- Chromosome 13 (obsolete name, Patau synd)
- Chromosome 18 (obsolete name, Edward synd)
- Chromosome 21 (Down synd)
- All other chromosomes have been reported in
trisomic state unless mosaic, virtually
uniformly fatal in utero or shortly after birth
28Trisomy 21 (1 in 800 live births incidence
greater if mat. age gt35)
- Hypotonia
- Short neck with loose skin at nape
- Flat nasal bridge
- Brushfield spots around edge of iris
- Epicanthal folds
- Short, broad hands with single transverse palmar
crease - Congenital heart disease
- Mental retardation
- Increased risk for leukemia
29Thompson Thompson, Genetics in Medicine, 7th
ed, p. 91
30Trisomy 13 (1 in 15-25000 live births)
- Growth retardation
- Severe central CNS malformations (e.g.,
holoprosencephaly) - Microcephaly
- Cleft lip, cleft palate
- Polydactyly
- Congenital heart, renal and genitourinary
malfomations
31Thompson Thompson, Genetics in Medicine, 7th
ed, p. 95
32Trisomy 18 (1 in 7500 live births)
- Severe cardiac malformations
- Low-set, malformed ears
- Characteristic clenched fist (2nd and 5th digits
overlap) - Rocker-bottom feet
- Mental retardation
- Increased maternal age is a risk factor
33Thompson Thompson, Genetics in Medicine, 7th
ed, p. 94
34Sex chromosome numerical abnormalities
- Male
- Klinefelter (47,XXY) 1/1000 males
- 47,XYY 1/1000 males
- 46,XX males 1/20,000 males
- Female
- Turner (45,X) 1/5000 females
- Trisomy X (47,XXX) 1/1000 females
- 46,XY females 1/20,000 females
- Androgen insensitivity (testicular feminization)
1/20,000 females
35Klinefelter syndrome
- Tall, thin body habitus long legs
- Signs of hypogonadism at puberty
- Small testes, underdeveloped secondary sex
characteristics - May have gynecomastia
- Almost always infertile
- May be mosaic for a normal (or other abnormal)
cell line
36Thompson Thompson, Genetics in Medicine, 7th
ed, p. 106
37Turner syndrome
- Approx. 99 of 45,X conceptions die in utero
livebirth approx 1/4000 females - Approx. 50 cases 45,X remainder are mosaic for
another cell line, either 46,XX or with a
structurally abnormal X (e.g., isochromosome Xq)
38Turner syndrome
- Short stature
- Broad chest with widely spaced nipples
- Gonadal dysgenesis (e.g., streak gonads)
- Webbed neck (from lymphedema during fetal life)
- Lymphedema of dorsum of feet
- Low posterior hairline
- Renal and cardiovascular abnls, incl. coarctation
of aorta
39Thompson Thompson, Genetics in Medicine, 7th
ed, p. 108
40Microdeletion/microduplication syndromes
- Very small (sometimes visible by G-banding,
sometimes not) deletions - Result from unequal crossing over between
homologous regions on chromosomes during meiosis - Typically confirmed by FISH
41Thompson Thompson, Genetics in Medicine, 7th
ed, p. 97
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43Microdeletion syndromes
Thompson Thompson, Genetics in Medicine, 7th
ed, p. 96
44DiGeorge/velocardiofacial syndromes
- Characteristic craniofacial features
- Varying degrees of mental retardation may be a
feature - Conotruncal heart defects (e.g., tetralogy of
Fallot, pulmonary atresia, absent pulmonary
valve) - Over 30 different genes in this region, so
phenotype dependent on size of deletion
45Prader-Willi/Angelman syndromes
- Both due to a deletion within the proximal long
arm of a chromosome 15 - Manifestations depend on which chromosome 15 is
deleted the 15 that came from the patients
mother or the 15 that came from the patients
father - IMPRINTING
- Need specialized molecular studies to determine
which homolog is deleted
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48Cassidy SB et al, 2000, Am J Med Genet 97136
49Prader-Willi
- Severe hypotonia in infancy
- Hypogonadism
- Feeding difficulties in infancy
- Over time, feeding difficulties resolve and
hyperphagia ensues --gt extreme food-seeking
behavior - Obesity
- Mild mental retardation, learning difficulties,
behavioral issues
50Angelman
- Severe mental retardation and developmental delay
- Jerky, ataxic gait (puppet-like) together with
characteristic arm position - Paroxysms of inappropriate laughter
- Virtually absent speech
51Marfan syndrome
- Autosomal dominant connective tissue disorder due
to mutations in fibrillin 1 (FBN1) gene - FBN1 encodes an extracellular matrix glycoprotein
- Wide-ranging systemic effects
- Skeletal, ocular, pulmonary, skin
- Clinical diagnosis heterogeneity of gene makes
identification of causative gene extremely
difficult
52Marfan
- Tall stature, arachnodactyly
- Pectus excavatum
- Joint laxity
- Narrow palate
- Ectopia lentis
- Mitral valve prolapse
- Aortic dilatation, dissection
- Pulmonary blebs, pneumothorax
- Striae
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57Cystic Fibrosis
- Autosomal recessive patients have mutations in
both CFTR (CF transmembrane conductance regulator
gene) alleles - Predominantly dz of northern Europeans, with
carrier rate approx 1 in 29 (incidence of dz
approx 1/2500) - Lungs and exocrine pancreas primarily affected
- Increased sweat chloride concentrations
58CF Clinical Features
- Pulmonary findings
- Very thick secretions, recurrent infections, COPD
and bronchiectasis - Pancreatic findings
- Decreased secretion of pancreatic enzymes such as
trypsin and lipase (pts can take supplements) - Other features meconium ileus in 10-20 newborns
with CF - CBAVD Congenital bilat absence of vas deferens
(some pts with absent to very mild features of CF
may present with infertility)
59Fragile X syndrome
- X-linked mental retardation syndrome due to
unstable CGG repeats in promoter region of FMR1
gene on very distal long arm of X chromosome - Prevalence 16-25/100,000 in gen pop most common
cause of inherited mental retardation
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61Fragile X
- Due to expansion of repetitive sequences (similar
disorders Huntington, myotonic dystrophy,
various ataxias) - CGG repeat in 3 untranslated region of FMR1
gene - 5-40 repeats normal
- 41-58 repeats gray zone
- 59-200 repeats premutation
- gt200 repeats full mutation
- This expansion occurs during maternal meiosis (so
mothers of Fragile X pts have premutations) risk
of expansion to full mutation increases with size
of premutation
62Fragile X clinical features
- Both males and females can manifest features
(usually more pronounced in males as no other
copy of normal X) - Moderate mental retardation (usu. milder in
females) - Hyperactivity, hand flapping or biting, temper
tantrums - Post-pubertal males long face, prominent jaw and
forehead, large ears, large testes (FMR1 is
normally expressed in testes)
63From geneticsmodules.duhs.duke.edu
64Duchenne Muscular Dystrophy
- X-linked progressive myopathy due to mutations or
deletions within the DMD gene - Incidence approx 1/3500 male births
- DMD encodes dystrophin, expressed in muscle
(smooth, cardiac and skeletal) - Mutations lead to partially functional or
nonexpressed dystrophin (severity of disease
based in part on expression status of dystrophin)
65DMD clinical features
- Progressive muscle degeneration and weakness
- Begins with hip girdle and neck flexors, begins
to spread distally - Usually manifests by age 5 (Gowers maneuver) and
have calf pseudo-hypertrophy - Cardiac findings present in approx 95 pts
chronic heart failure in 50 - Confined to wheelchair by age 12 or so
- Median age at death is 18 years
66From medgen.genetics.utah.edu
67References
- Nussbaum RL, McInnes RR, Willard HF. Thompson
Thompson Genetics in Medicine (7th ed). Elsevier
Saunders, 2007. - Excellent in-depth introduction to clinical
genetics. - Jones KL. Smiths Recognizable Patterns of Human
Malformation. Elsevier Saunders, 2006. - Outstanding guide, with many pictures and
differential diagnoses, of many genetic syndromes
and abnormalities. Lists of syndromes associated
with various clinical findings (e.g., dental and
maxillofacial abnormalities). - www.genetests.org
- Very well-written and updated reviews under the
section, GeneReviews.