Title: Genetic Diseases
1Genetic Diseases
- Dr. Joseph de Nanassy
- Associate Professor, PALM, uOttawa
- Chief of Anatomical Pathology, CHEO
- Site Chief of Laboratory Medicine, CHEO
- jdenanassy_at_cheo.on.ca
- 613-737-7600 x 2897
2Objectives
- Develop a basic understanding of the genetic
apparatus - Comprehend definitions of major genetic
abnormalities - Correlate molecular abnormalities and genetic
defects
3Outline
- I. Definitions
- Genetic code
- Chromosomes, Genes, Cell Division
- Molecular mechanisms
- II. Abnormal fetal development
- Malformations, deformations, dysplasias,
disruptions - III. Perinatal pathology
- Birth defects
- Metabolic disorders
4The Cell
5Nucleus
- DNA arranged in chromosomes
- (network of granules nuclear chromatin)
- RNA spherical intranuclear structure(s)
- - nucleolus / nucleoli
6Genetic Code
- A series of messages contained in the
chromosomes - This code regulates cell functions by way of
directing the synthesis of cell proteins - The code corresponds to the structure of the
DNA - The code is transmitted to new cells during
cell division
7DNA structure
8DNA replication
9mRNA and tRNA
10Chromosomes
- ? Exist in pairs homologous 22a 1s
- ? Composed of double coils of DNA
- ? Basic unit nucleotide
- phosphate group
- deoxyribose sugar
- base purine (A, G)
- pyrimidine (T, C)
11Genes
- ? A locatable region of genomic sequence,
corresponding to a unit of inheritance - ? A union of genomic sequences encoding a
coherent set of potentially overlapping
functional products i.e. genes are one long
continuum (2007) - ? Determine cell properties, both structure and
functions unique to the cell
12Genome
- ? Sum total of all genes contained in a cells
chromosomes - ? Identical in all cells
- ? Not all genes are expressed in all cells
- ? Not all genes are active all the time
- ? May code for enzymes or other functional
proteins, structural proteins, regulators of
other genes
13Gene Product
- ? A protein or RNA specified by a gene
- ? Transcribed into mRNA in the nucleus
- ? Translated through tRNA and cytoplasmic
ribosomes into protein
14Human Genome
- ? 3 billion pairs of DNA nucleotides
- ? 50,000 100,000 genes
- ? Protein-coding Genes lt10 (2) of human
genome - ? Exons parts of the DNA chain that code for
specific proteins - ? Introns the parts in-between the exons
- ? Both exons and introns are transcribed but
only the exons are translated (introns are
removed from mRNA before leaving nucleus) - ?Junk DNA no obvious function but 80
expressed
15Sex chromosomes
- ? Genetic sex composition of X and Y
- ? Large X many genes, many activities
- ? Small Y almost entirely male sexual diff.
- ? Female XX, male XY
- ? One X randomly inactivated and nonfunctional
after first week of embryonic development - ? Same inactivated X in descendant cells
16(Mary) Lyon Law
17(Murray) Barr body
18Y chromosome
- ? Stains with some fluorescent dyes
- - bright fluorescent spot in the nucleus
- ? Normal female sex chromatin body
- but no fluorescent spot
- ? Normal male fluorescent spot
- but no sex chromatin body
19Cell Division
- ? Mitosis somatic cells (PMAT)
- Daughter cells have the same number of
chromosomes as the parent cell. - ? Meiosis gametogenesis (1st and 2nd div)
- Number of chromosomes reduced by half.
20Chromatids
- ? Before mitosis, the DNA chains duplicate to
form new chromosome material. - The duplicated chromosome material lies side by
side two sister chromatids. - Mitosis the process by which conjoined
chromatids separate into sister chromatids and
move into new daughter cells.
21Mitosis
- ? Interphase DNA duplication to form
chromatids just before mitosis - ? Prophase centriole migration, mitotic
spindle - ? Metaphase chromosomes line up in centre,
chromatids still joined at centromere - ? Anaphase chromosomes separate into sister
chromatids - ? Telophase sister chromatids form new
chromosomes, new nuclear membranes form,
cytoplasm divides
22Mitosis
23Meiosis
- ? First meiotic division interphase
duplication of chromosomes to form paired
chromatids - ? Prophase 1 of meiosis homologous chromosomes
lie side by side over entire length synapse. - Interchange of segments of homologous
chromosomes crossover. - 2 Xs side by side just like the autosomes.
- X and Y end-to-end no crossover.
24Meiosis
- ? Metaphase 1 paired homologous chromosomes
align at the equatorial plate - ? Anaphase 1 homologous chromosome pairs
migrate to opposite poles of the cell - each chromosome is composed of two chromatids,
the chromatids are not separated - ? Telophase 1 two new daughter cells form
- each contains half the chromosome number
reduction of chromosomes by half interchange of
genetic material occurred during synapse
25Meiosis
- ? Second meiotic division mitotic division
- Prophase 2 DNA does not replicate
- Metaphase 2 chromosomes align at the equatorial
plate - Anaphase 2 sister chromatids migrate separately
- Telophase 2 four haploid cells (half the normal
number of chromosomes)
26Meiosis
27Gametogenesis
- ? Gonads testes, ovaries contain
- ? Precursor cells or germ cells mature into
- ? Gametes sperm, ova in gametogenesis
- ? Spermatogenesis, oogenesis
28Gametogenesis
29Primary follicles
30Oogenesis vs. spermatogenesis
- ? One ovum ( 3 polar bodies) vs. four
spermatozoa - ? Oocytes formed before birth vs. continuous
spermatogenesis (fresh sperm) - Prolonged Prophase 1 until ovulation
- more frequent congenital abnormalities in ova of
older women (longer exposure to potentially
harmful environmental influences until meiotic
division resumes at ovulation)
31Chromosome Analysis
32Karyotype
33Genes and Inheritance
- ? Locus specific site of a gene on the
chromosome. Since the chromosomes exist in
pairs, genes are also paired. - ? Alleles alternate forms of a gene can occupy
the same locus (homozygous, heterozygous) - ? Recessive gene expressed only when homozygous
- ? Dominant gene expressed whether homozygous or
heterozygous, both
expressed when co-dominant - ? Sex-linked gene only X-linked in males,
most are recessive, hemizygous (no allele on Y)
34Gene Imprinting
- ? Genes occur in pairs on homologous
chromosomes, one from each parent - ? Different effects of gene whether ? or ?
- ? Genes modified during gametogenesis
- ? Gene imprinting additional methyl groups
added to DNA molecules - ? Basic structure unchanged
- in some diseases different expression
(behaviour) depending on parent of origin - hereditary disease as a result of imprinting
35Genetic Engineering
- ? Insertion of a gene encoding a desired product
(e.g. insulin) into a bacterium - ? Bacterial gene spliced enzymatically,
recombinant DNA inserted into plasmid (circular
DNA segment in bacterium), dividing bacterial
population produces desired protein
36Gene Therapy
- ? Normal gene inserted into defective cell
- ? Compensates for the missing or dysfunctional
gene, in somatic cells only - ? Can be inserted into mature cell (ly)
- ? Can be inserted into stem cell (bone marrow)
- ? Used to treat e.g. ADA deficiency, CF,
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38Congenital / Hereditary Diseases
- ? Congenital present at birth
- ? Hereditary (genetic) result of chromosome
abnormality or - defective gene
39Causes of malformations
- Chromosomal abnormalities
- Gene abnormalities
- Intrauterine injury (e.g. drugs, radiation,
infection, environmental, etc) - Environmental effect on genetically predisposed
embryo
40Chromosomal abnormalities
- ? Nondisjunction failure of homologous
chromosomes in germ cells to separate from one
another during 1st or 2nd meiotic division - ? Sex chromosomes or autosomes
- ? Extra chromosome trisomy (24 or 47)
- Absent chromosome monosomy (22 or 45)
41Nondisjunction in meiosis
42- ? Chromosome Deletion Broken piece of
chromosome is lost from cell - ? Translocation Not lost, just misplaced and
attached to another chromosome - - reciprocal between two nonhomologous
chromosomes (no loss or gain of genetic material
- no loss of cell function) - - in germ cells deficient or excess chromosome
material abnormal zygote
43Translocation in gametes
44Sex chromosome abnormalities
45Turner syndrome
46Klinefelter syndrome
47Autosomal abnormalities
- ? Loss of genetic material aborted embryo
- ? Deletion of gene congenital anomalies
- ? Trisomy syndromic, e.g. 21, 18, 13
48Trisomy 21 (Down)
49T21 causes
- Nondisjunction during gametogenesis (95)
- Translocation (few)
- Nondisjunction in zygote (rare)
50Translocation T21
51Zygote nondisjunction T21- Mosaic
52Abnormal gene diseases
- ? Individual gene abnormalities
- ? Hereditary diseases transmitted mostly on
autosomes, only a few on sex chromosomes. - ? Gene mutation spontaneous
- environmental
- ? Minor structural change may result in major
functional abnormality (e.g. SCD HgbSA,
co-dominant, Hgb beta gene)
53Modes of Inheritance
- ? Autosomal dominant (a dominant gene expressed
in the heterozygous state) - ? Autosomal recessive (expressed only in
homozygous individual, disease only if both
alleles are abnormal, carrier if only one abN) - ? Codominant (full expression of both alleles in
heterozygous state) - ? X-linked (usually affects male offspring the
abnormal X-linked gene acts as dominant gene when
paired with the Y chromosome)
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55Intrauterine Injury
- 1. Drugs thalidomide (phocomelia), DES (cervical
cancer), street drugs (IUFD), smoking (IUGR),
alcohol (FAS), etc - 2. Radiation x-rays
- 3. Maternal infections
- - Rubella virus (CVS, CNS, chr. infection)
- - CMV (microcephaly, chronic infection)
- - Toxoplasma gondii (hydrocephalus,
systemic infection)
56Thalidomide baby
57Prenatal CMV infection
58Multifactorial Inheritance
- ? Combined effect of multiple genes interacting
with environmental agents, - e.g. cleft palate, cardiac malformations, club
foot, hip dislocation, spina bifida, etc - ? Cause developmental sequence fails to reach a
certain point at an appropriate time (threshold)
59Genetically determined variationin rate of
development
60Effect of harmful environmental agents on
susceptibility for congenital malformations
61Interaction of genetic predisposition and
environmental factors in cleft palate
62Prenatal Diagnosis of Congenital Abnormalities
- Examination of fetal cells for chromosomal,
genetic or biochemical abnormalities - Examination of amniotic fluid for products
secreted by the fetus - Ultrasound of the fetus to detect malformations
(NTD, hydrocephalus, PCKD, etc)
63Prenatal Diagnosis of Congenital Abnormalities
64Main indications for amniocentesis
- Maternal age (gt35)
- Previous infant with T21 or other chromosomal
abnormality - Known translocation T21 carrier
- Other chromosomal abnormality in either parent,
e.g. t(721) - Risk of genetic disease in the fetus that can be
detected prenatally (thalassemia) - Previous infant born with neural tube defect
(multifactorial inheritance, 5)
65Methods of fetal DNA analysis
- Enzyme analysis of DNA resultant
- DNA fragments different in health and disease,
e.g. sickle cell anemia - 2. DNA probes same complementary nucleotide
arrangement as in defective DNA gene binds to
mutant gene
66Molecular Genetics of Solid Pediatric Tumors
- ? Mechanisms for tumor development
- 1. Creation of novel fusion proteins
- 2. Loss of tumor suppressor genes
- 3. Activation of proto-oncogenes
67Translocations, Oncogenes, Tumor suppressor genes
68NB MYCN amplification and 1p deletion by FISH
69NB Double-minute chromosomes by FISH
70RB MYCN probe to detect homogeneously staining
region in metaphase spread and interphase nuclei
71Ewing sarcoma t(1122) EWS green, FLI-1 pink, t
yellow
72E-RMS Spectral karyotypet(13), t(115), t(121)
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74Abnormal Fetal Development
- ? Malformation
- ? Deformation
- ? Dysplasia
- ? Disruption
75Prenatal development, pre-embryonic
76Prenatal development, early embryonic
77Prenatal development, late embryonic
78Fetal development
79Normal gametogenesis
80Meiosis
81Abnormal gametogenesis
82? ? gametes
83Sperm penetrating oocyte
84Fertilization
85Causes of human congenital anomalies
86Malformations
- ? Intrinsic abnormalities of blastogenesis and
organogenesis affecting the morphogenetically
reactive fields of the embryo developmental
field defects - ? Occur alone or in combination (syndromes or
associations) - ? Severe (spina bifida aperta) or
- mild (spina bifida occulta)
87Malformations
- ? Causally heterogeneous
- ? Intrinsic causes mendelian mutations,
chromosome abnormalities, - environmental interactions (multifactorial),
mitochondrial mutations
88Disruptions
- ? Environmental (exogenous) causes producing
abnormalities of morphogenetic field dynamics - ? E.g. rubella, thalidomide, isotretinoin,
alcohol, etc
89Rubella embryopathy
90Diabetic embryopathy
91Dysplasias
- ? Disturbances of histogenesis, occurring later
and somewhat independently of morphogenesis - ? Morphogenesis is prenatal,
- histogenesis continues postnatally in all
tissues that have not undergone - end differentiation
- ? Dysplasias may predispose to cancer
92Neurofibromatosis
93Tuberous sclerosis
94Deformities
- ? Secondary changes in form or shape of
previously normally formed organs or body parts - ? Caused by extrinsic forces (e.g. Potter
syndrome) or intrinsic defects (e.g. - fetal akinesia syndrome with congenital
arthrogryposis)
95Oligohydramnios (Potter) sequence
96Arthrogryposis
97Sequences
- ? Secondary consequences of malformations,
disruptions, dysplasias, or deformities - ? E.g. renal adysplasia leads to Potter
oligohydramnios sequence - DiGeorge anomaly leads to tetany,
hypoparathyroidism, heart failure, conotruncal
congenital heart defect
98Minor Anomalies
- ? Disturbance of phenogenesis in fetal life
- ? Phenogenesis the process of attaining final
quantitative anthropometric traits of the race
and family (variant familial developmental
pattern) - ? Causes
- intrinsic (chromosome imbalance)
- extrinsic (teratogens)
99Syndromes
- ? Patterns of anomalies proven or presumed
causally related - ? Causes
- - chromosome mutations
- - imprinting defects
- - aneuploidy
- - multifactorial disorders
- - teratogenic sequences
100Treacher-Collins syndrome(mandibulofacial
dysostosis) AD
101Leprechaunism(defective insulin binding) AR
102Associations
- ? Idiopathic multiple congenital anomalies of
blastogenesis - Vertebral anomalies V
- Anorectal anomalies A
- TracheoEsophageal defects TE
- Radial and Renal defects R
- ? Single hit during gastrulation affecting
multiple, morphogenetically closely related
structural primordia -
103Metabolic Disorders
- ? Most are inherited as AR, some are
- X-linked, a few are AD.
- ? Great variability in presentation
- ? Some present with dysmorphic features
- ? Storage material in RES and other tissues
104Storage Diseases
- ? Lysosomal Lipid Storage Diseases
- Nieman-Pick sphyngomyelin
- Gaucher disease glucocerebrosidase
- Tay-Sachs disease Gangliosidoses
- Metachromatic leukodystrophy
- ? Mucopolysaccharidoses (I, II, III, VII)
- glycosaminoglycans and glycolipids
105Hurler syndrome (MPS 1A) AR
106COH Disorders
- ? Glycogen Storage Diseases
- ? Galactosemia
107Glycogen storage disease type II
108Amino Acid Disorders
109Misc.
- ? Fatty Acid Beta-Oxidation Defects (LCAD,
MCAD, SCAD) - ? Organic Acidemias
- ? Defects in Purine Metabolism
- ? Carnitine Deficiency
- ? Peroxisomal Disorders
- ? Disorders in Metal Metabolism
- ? Defects in Copper Metabolism
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111References
- ? Wigglesworth Textbook of Fetal and Neonatal
Pathology - ? Moore, Persaud The Developing Human
- ? Perspectives in Pediatric Pathology, Volume
21, Society for Pediatric Pathology - ? Gilbert-Barness Potters Atlas of Fetal and
Infant Pathology - ? Crowley An Introduction to Human Disease,
Pathology and Pathophysiology
112Thank you
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