This document provides an overview of genetics and genetic abnormalities relevant to hematology. It begins with definitions of key genetic terms. It then discusses chromosomal abnormalities associated with hematological conditions like hemoglobinopathies, leukemias, and bleeding disorders. Specific examples of genetic abnormalities are described, such as translocations in CML and AML. The document outlines various genetic tests used in hematology and stresses the importance of genetic studies in disease classification and management. It emphasizes the role of genetics in understanding inherited hematological diseases.

1. Prepared by:
Col (Dr) Amir Muhriz Abdul
Latiff M.D (USM) Mpath
(Haematology)
Senior Lecturer and
Haematologist
Medical Faculty UiTM
1

2. LEARNING OBJECTIVES
1. Describe gene & chromosome abnormalities in
haemoglobinopathies, leukaemias, (Philadelphia
chromosome and other related chromosomal
abnormalities) & bleeding disorders
2. Interpret the chromosome and gene nomenclature in
relevant diseases.
3. Relate the importance of genetic studies in the
classification and management of disease.
4. List common test used in the detection of genetic
abnormalities in haematology
5. Discuss the importance of carrier detection in
haematological diseases.
2

3. Contents
1. Important definitions
2. Chromosomal and molecular abnormalities
in
a. Haemoglobinopathy and thalassaemia
b. Leukaemia
c. Bleeding disorders
3. Importance of genetic and chromosomal
studies in haematology
4. common test used in the detection of genetic
abnormalities in haematology
5. Importance of carrier detection in
haematological diseases
11/27/2012 3

4. Important definition
Genetics:
The branch of science concerned with the means and
consequences of transmission and generation of the
components of biological inheritance.
(Stedman, 26th ed)
Molecular genetics:
The study of the molecular constitution of genes and
chromosomes (World English Dictionary)
Chromosomes:
any of several threadlike bodies, consisting of chromatin, that
carry the genes in a linear order: the human species has 23
pairs, designated 1 to 22 in order of decreasing size and
X and Y for the female and male sex chromosomes
respectively.
(dictionary.com)
4

5. Importance of genetics
 The only way to understand hereditary
diseases
 What we are begins with our genetic heritage
and is modified by our environment and
experiences
 Our genetic heritage determines susceptibility
to multifactorial diseases such as:
◦ Hypertension Diabetes
◦ Vascular disease Cancer
◦ Osteoarthritis Autoimmune diseases
 Critical to developing new disease treatments
◦ Statins tPA EPO

6. The scope of genetics
 The human genome has been sequenced!
 Approximately 35,000 genes, most of which
encode a protein, in a haploid genome of 3 X
9
10 base pairs
 Only about 1.5 % of the DNA actually encodes
functional genes
 All living organisms are remarkably similar at
the genetic level
◦ Same genetic code
◦ About 50 % of genes comparable between us and
plants
 All nucleated somatic cells have a complete
set of genes
◦ Only a small fraction of genes are active in a single
cell
◦ Enables cloning

7. The burden of Mendelian (single gene)
disorders
 Although individually rare, genetic diseases
collectively constitute a major health problem
 About 5 - 8 % of admissions to a pediatric hospital
and about 1 % of admissions to an adult hospital
are for Mendelian disorders
 9 % of pediatric deaths are due to Mendelian
disorders
 About 1- 2 % of the population has a Mendelian
disorder
 Most Mendelian disorders are apparent by
childhood
 Life span is reduced in about 60 % of these
disorders
 Each person is estimated to have 1 - 5 lethal

8. From cellular to molecular biology

9. Genetic terminology
 Gene: The fundamental unit of heredity.
About 35,000 in the human genome. A
typical gene:
5’ 3’
enhancer promoter repressor
intron
exon
5’ UTR 3’ UTR
AAAAAAAAA mRNA
coding domain (ORF)

10. Exons, introns and alternative splicing
 Most genes have introns
 Alternative splicing is common
 Many alternate proteins can be generated
from a single gene, each of which can have a
unique function

11. Transcription and translation
 Transcription: Generation of an RNA copy of a
single gene
 Translation: Synthesis of a protein using the
mRNA as a template

12. Important definitions
 Alleles: Alternative forms of a gene that can be
distinguished by their alternate phenotypic effects or
by molecular differences; a single allele for each locus
is inherited separately from each parent
 Autosome: One of chromosomes 1 - 22
 Dominant allele: An allele whose phenotype is
detectable (even if only weakly) in a single dose or
copy
 Recessive allele: An allele whose phenotype is
apparent only in the homozygous or hemizygous
state.
 Heterozygous: Having a normal allele on one
chromosome and a mutant allele on the other

13. More terms to know
 Hemizygous: Having half the number of alleles
(e.g. males are hemizygous for all X chromosome
genes)
 Expressivity: The severity or intensity of the
phenotype of an allele.
 Penetrance: The degree to which a gene
expresses any observable phenotype
 Locus (pl. loci): The position on a chromosome of a
gene or other chromosome marker; also, the DNA
at that position.
 Proband: The first affected individual who comes to
clinical genetic evaluation. Indicated by an arrow on
the pedigree diagram.

14. Major mutation types
 Single base substitutions that cause premature
termination of protein synthesis, change of amino
acid, suppress termination of protein translation, alter
level of gene expression, or alter patterns of mRNA
splicing
 Translocations, that bring disparate genes or
chromosome segments together
 Deletions of a few nucleotides up to long stretches of
DNA
 Insertions and duplications of nucleotides up to long
stretches of DNA
 Many different mutations can occur within a given
gene, although it appears that genes have different
degrees of mutability
 Different mutations affecting a gene can result in
distinct clinical syndromes

15. Types of mutations
 Point mutations: Change of the normal
base to another
◦ Possible consequences:
 Silent mutation: No consequence
 Missense mutation: changes the codon to one
encoding a different amino acid
 Nonsense mutation: Changes codon from one
encoding an amino acid to a stop codon
 Splice site alteration: can abolish or create a
splice site
 Regulatory region mutation: Can result in net
increased or decreased gene expression

16. Location, location, location

17. Small mutations can have subtle or drastic
effects
In frame deletion of one codo:
No frameshift
Deletion of one
base: Frameshift Out of frame deletion of
three bases:
Frameshift

18. Clues that suggest a Mendelian
disease
 Positive family history
 Characteristic syndrome
 Unusual syndrome (e.g. progressive
neurologic deterioration, multiple organ
system abnormalities, intermittent
neurologic symptoms) at any age
 Common syndrome at unusually early age
 Lack of environmental or other primary
cause of symptoms and signs

19. Taking a family history
 Inquire about the health of each family member
through second degree relatives
(grandparents, first cousins)
 Pay special attention to any signs or symptoms
related to your patient’s condition in relatives
 Inquire about causes of any deaths, including
any stillbirths or early deaths,
institutionalizations
 Obtain medical (and death) records of relatives
as well as of proband
 Inquire about any possible consanguinity
 Recognize that false paternity does occur

20. Some essential nomenclature for chromosomal notations
Comma (, ) Separates chromosome numbers, sex chromosomes and
chromosome abnormalities.
del Deletion denotes both terminal and interstitial deletion
inv Inversion of a part of a chromosome
Minus ( -) Chromosome loss, monosomy
p Short arm of chromosome
q Long arm of a chromosome
Ph Philadelphia chromosome
t translocation
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21. Pedigree symbols

22. Constitutional karyotype
There is a role of constitutional karyotype that predispose to malignancy.
e.g.
Down syndrome, trisomy 21- increased risk of developing acute
leukaemia.
Klinefelter’s syndrome 47, XXY.
Bloom’s syndrome
Fanconi’s anaemia.
11/27/2012 22

23. Chromosomal and molecular
abnormalities in leukaemia
Disease genes Correspondin Method of
g protein activation
AML t(8;21) (q22;q22) ETO AML-1 fusion
AML, M3 t(15,17) (q22;q21) PML PML-RARA fusion
AML M4 inv (16) (p13q22) MYH-11 CBF fusion
CML t (9,22) (p34q11) ABL Bcr-abl fusion
11/27/2012 23

24. Philadelphia chromosome
Partial karyogram of chromosomes 9 and 22 from a
patient with CML, showing t(9;22). The normal chromosome of
each pair is on the left and the abnormal (translocated)
chromosomes are on the right (arrowed)
11/27/2012 24

25. The most consistent chromosomal abnormality
associated with a haematological malignancy is the
Philadelphia chromosome (Ph).
1. CML, this translocation is found in 92% of patients.
2. BCR–ABL fusion gene.
3. Breakpoints within BCR occur within a 5.8-kb region,
termed the major breakpoint cluster region (M- BCR),
4. This transcribes an aberrant 8.5-kb mRNA, encoding
a chimeric p210 protein with enhanced tyrosine
kinase activity.
11/27/2012 25

26. AML t(8;21)
1. Good-risk cytogenetic groups
2. This translocation occurs
predominantly in FAB type M2
(acute myeloid leukaemia with
granulocytic maturation at or
beyond promyelocyte stage) and
M4 (myelomonocytic leukaemia).
3. It fuses the core binding factor alpha gene (CBFα, AML1 or RUN1) on
chromosome 21 with ETO on chromosome 8 to produce a novel
chimeric gene.
11/27/2012 26

27. AML – inv (16)
1. These abnormalities of chromosome 16
are found in AML M4 and are notable for
their association with abnormal
eosinophilia (M4Eo) and a good
prognosis.
2. Fusion of the smooth muscle myosin
heavy-chain gene, MYH11, normally on
16p13 and CBFβ, normally on 16q22.
3. FISH and RT- PCR have become routine
detection methods.
11/27/2012 27

28. PML-RARA fusion gene
11/27/2012 28

29. AML – t(15,17)
1. The translocation
t(15;17)(q22;q21) (is specific for
AML M3 and M3v (acute
promyelocytic leukaemia).
2. APML patients has a tendency to
develop bleeding tendencies
because of the presence of
promyelocytes.
3. patients < 35 years old.
4. Rearrangement of the retinoic acid receptor alpha
(RARα) gene, located at 17q21, which is fused to the
PML gene on chromosome 15, a gene which is
transcribed in normal haemopoietic cells.
11/27/2012 29

30. 5. PML-RARA fusion transcript blocks the differentiation.
6. The prognosis in these patients is good.
7. Response to treatment with all-trans-retinoic acid (ATRA). This
acts by converting the PML–RAR-α fusion protein from a
transcriptional repressor to a transcriptional activator, thus
inducing terminal differentiation of the leukaemic clone. (i.e.
Maturation of promyelocytes)
8. ATRA has now been adopted as a component of first-line
therapy for this disease, highlighting the importance of
accurate identification of this chromosomal abnormality.
9. FISH and RT-PCR
11/27/2012 30

31. Other techniques: FISH
FISH (fluorescence in situ
hybridization).
Four interphase nuclei showing
individual signals specific for the
ABL (red) and BCR (green) genes
on the normal chromosomes 9 and
22 respectively and the BCR/ABL
fusion (red/green collocalized
signals appearing yellow) indicating
the
presence of the Philadelphia
chromosome.
11/27/2012 31

32. Other techniques: multiplex FISH
Karyogram of a
normal
male painted in
seven colours in
such
a way as to
produce coloured
bands
along the
chromosome arms
(Rx-FISH)
allowing
identification of the
individual
chromosome pairs.
11/27/2012 32

33. Beta Thalassaemia
Definition: Thalassemia is inherited disorders
characterized reduced or absent amounts of hemoglobin,
the oxygen-carrying protein inside the red blood cells.

34. Two Basic Groups of Thalassemia
Disorder
 Alpha Thalassemia
 Beta Thalassemia: A person with this
disorder has two mutated genes

35. There are 3 types of Beta
Thalassemia
 Thalassemia Minor
 Thalassemia Intermediate.
 Thalassemia Major or Cooley's
Anemia

36. Thalassemias
In the case of beta thalassemias, in
contrast to alpha -thalassemias, the
most frequently encountered molecular
abnormalities are point mutations and
short insertions or deletions limited to a
few nucleotides
chain is still synthesized. The quantity of
Two situations have clearly to be globin chain, which is made, varies largely
distinguished: from one molecular defect to another, this
In beta + thalassemias, the mutated chain may be structurally normal or
gene encodes for a small amount of abnormal
In beta 0 thalassemias , the gene is
normal mRNA and, thus, a low amount
unable to encode for any functional mRNA
of and therefore there is no beta chain
synthesize

37. Beta Thalasemia
 It is caused by a change in the gene for the beta
globin component of hemoglobin
 It can cause variable anemia that can range from
moderate to severe.
 Beta thalassaemia trait is seen most commonly in
people with the following ancestry: Mediterranean
(including North African, and particularly Italian and
Greek), Middle Eastern, Indian, African, Chinese,
and Southeast Asian (including Vietnamese,
Laotian, Thai, Singaporean, Filipino, Cambodian,
Malaysian, Burmese, and Indonesian

38. Symptoms of Beta
Thalassemia
 It is characterize by severe anemia that can
begin months after birth
 Paleness
 Delays in growth and development
 Bone marrow expansion.
 Untreated Beta Thalassemia major can lead
to child death due to heart failure.

39. Alpha and Beta Thalassemias
 The thalassaemia are, therefore,
considered quantitative hemoglobin
diseases.
 Because all types of thalassaemia
are caused by changes in either the
alpha- or beta-globin gene. These
changes cause little or no globin to be
produced.

40. 11/27/2012 40

41. Types of mutation that can occur in globin
genes and adjoining sequences.
 Point mutations -Within coding sequence, i.e. within an exon
 Within non-coding sequence, i.e. In an intron
 Mutation 5’ or 3’ to the gene (i.e. outside the gene)
 Deletion or duplication of one or more genes
 Deletion of genes with downstream enhancer being juxtaposed to remaining
gene
 Duplication of a gene
 Triplication of entire a globin gene cluster
 Abnormal cross-over during meiosis leading to gene fusion
 Deletion of DNAsequences but without a frame shift in coding sequence
 Deletion plus inversion
 Deletion plus insertion
 Frame shift mutation
 Types of mutation that can occur in globin genes and adjoining sequences.
11/27/2012 41

42. A famous pedigree

43. A nicer pedigree

44. A modest pedigree

45. X linked recessive, normal father,
carrier mother
1 carrier daughter
1 normal daughter
1 affected son
1 normal son

46. Clotting cascade

47. Hemophilia A
 Clinical syndrome
◦ Easily prone to hemorrhage from minor trauma
◦ Hemarthroses common - result in degenerative joint disease
◦ Ecchymoses, but not petechiae
 Laboratory
◦ Prolonged PTT, normal PT & bleeding times
◦ Normal platelet function
 A treatable genetic disease: Plasma (90 % of those
treated with donor blood products developed AIDS in
the 1980’s), recombinant factor 8 (10 -15 % develop
antibodies)
 Over 620 different mutations known to affect the factor
VIII clotting factor gene (allelic heterogeneity)
 Gene lies at Xq28

48. One common Factor VIII
mutation

49. Knowing genetic syndromes
can help prevent treatable
complications of untreatable
diseases

50. Ethnic background and
geographic origins are
important risk factors for some
genetic conditions

51. Glucose-6-phosphate dehydrogenase
deficiency
 Common among Africans, Asians and around
the Mediterranean
 Discovered that about 10 % of African
American servicemen during WWII
developed hemolytic anemia when given
certain drugs, such as sulfonamides,
antimalarials or when they ate fava beans
 Caused by deficiency of the enzyme, which
is needed to generate NADPH

52. G6PD deficiency
 Affects the G6PD gene at Xq28
 Many mutations and polymorphisms
have been discovered
 Heterozygosity (technically
hemizygosity) in women appears to
confer resistance to malaria

53. Prevalence of G6PD

54. Old World Malaria prevalence

55. X linked recessive, affected
father
2 carrier
daughters
2 normal sons:
Never any Male-
to-
Male
transmission!