Genetics- Principles & Disoreders in Paediatric Dentistry

GENETICS: PRINCIPLES AND
DISORDERS IN PAEDIATRIC
DENTISTRY
PRESENTED BY:
DR. SUSMITA SHAH
MDS PART- I
DEPARTMENT OF
PAEDIATRICS & PREVENTIVE
DENTISTRY
K.M.S.D.C.H
2

CONTENT:
• History
• Introduction
• Basic Terminologies
• DNA Structure
• Karyotyping
• Chromosomal Abnormalities
• Hereditary Traits In Families
• Monogenic Traits & Polygenic
traits
• Pedigree Charting 3

• Inheritance Pattern
Autosomal
Sex Linked
Multifactorial
• Genetics Of Dental
Diseases
• Genetic Counselling
• Human Genome Project
• Conclusion
• References 4

HISTORY:
• Gregor Mendel is considered as the
‘Father of genetics’.
• Galton (1875) initiated the idea of
polygenic inheritance.
• DNA was first isolated by Friedrich
Miescher in 1869.
• Hardy and Weinberg – population genetics.
• Watson and crick Discovered the
double helix model of DNA
DEAN, MCDONALD, AVERY. DENTISTRY FOR THE CHILD AND ADOLOSCENT.9TH EDITION, NEW
DELHI, ELSEVIER, 2013
5

• Its molecular structure was identified by James
Watson and Francis Crick in 1953, whose model-building
efforts were guided by X-ray diffraction data acquired by
Rosalind Franklin.
• 20th century: Mendel’s breeding technique – found
chromosomes contains genes as a basic unit of inheritance.
666666
6

WHAT IS GENETICS ?
• A branch of biology that deals with hereditary, especially the
mechanism of hereditary transmission and the variation of
inherited characteristics among similar or related organisms.
• Gene is a Greek word : generation or origin.
• A gene is the basic physical and functional unit of heredity.
• Holds the genetic information and passes the genetic traits to
the offspring
• A portion of DNA in the cell.DEAN, MCDONALD, AVERY. DENTISTRY FOR THE CHILD AND ADOLOSCENT.9TH EDITION, NEW
7

• The Human Genome Project has estimated that
humans have between 19,000 and 20,000 genes.
• An error(mutation) in any of this gene leads to
recognizable genetic disease.
• DNA have 4 types of nitrogenous bases:
Single carbon nitrogen ring e.g. Pyrimidine= Cytosin &
Thymin & Double carbon nitrogen ring e.g. Purine=
Adenin & Guanin.
• DNA subunit – nucleotide bases – A, C, G & T
suggestive of different proteins.DEAN, MCDONALD, AVERY. DENTISTRY FOR THE CHILD AND ADOLOSCENT.9TH EDITION, NEW
8

CHROMOSOMES
• It is the Storage unit of genes
• Humans have 46
chromosomes.
• 23 pairs of chromosomes are
present
• 22 are autosomes and the
remaining pair is sex
chromosomes namely X and Y.
9

BASIC
TERMINOLOGIES
1. GENOMICS: is defined as the study of genes and their
functions, and related techniques.
2. DNA: a self-replicating material which is present in nearly all
living organisms as the main constituent of chromosomes. It
is the carrier of genetic information.
3. RNA: ribonucleic acid, a nucleic acid present in all living cells.
Its principal role is to act as a messenger carrying instructions
from DNA for controlling the synthesis of proteins, although
in some viruses RNA rather than DNA carries the genetic
information (Plant viruses & Poliomyelits).DEAN, MCDONALD, AVERY. DENTISTRY FOR THE CHILD AND ADOLOSCENT.9TH EDITION, NEW DELHI,
ELSEVIER, 2013
11

4. GENOME: Collection of the entire genetic content within the
chromosomes present within a cell or an organism.
6. CHROMOSOMES: DNA is grouped into the units
7. AUTOSOME: is any chromosome other than the sex
chromosome.
8. HOMOLOGE: each autosome has paired mate that is referred as
homologe.
9. CHROMATIN: it is the name given to the material of which
chromosomes are made.
10. TRAIT: any detectable phenotypic property or character.
11. LINKAGE: two genes situated close together on same
chromosome are said to be linked.DEAN, MCDONALD, AVERY. DENTISTRY FOR THE CHILD AND ADOLOSCENT.9TH EDITION, NEW
12

12. ALLELE: alternative forms of a gene found at same locus on
homologous chromosomes.
13. GENOTYPE: refers to the set of genes that as individual caries
and in particular, usually refers to the specific pair of alleles that
a person has given the particular location.
14. PHENOTYPE: Observable properties and physical
characteristics of an individual, as determined by the individual’s
genotype and environment in which the individual develops over
a period of time.
15. Deletion: absence of piece of chromosome.
16. Duplication: insertion of an extra fragment into chromosome.
13

17. Inversion: breaking of chromosomes in two places &
subsequent rejoining with middle piece inverted.
18. Translocation: attachment of a broken piece from one
chromosome to another, but non homologues chromosome.
DEAN, MCDONALD, AVERY. DENTISTRY FOR THE CHILD AND ADOLOSCENT.9TH EDITION, NEW DELHI,
ELSEVIER, 2013
14

19. Dominant: The trait manifests itself when the person carries
only one copy of the gene responsible for the defect along with
one normal allele.
20. Recessive: Two copies of defective genes are required for
expression of trait.
DEAN, MCDONALD, AVERY. DENTISTRY FOR THE CHILD AND ADOLOSCENT.9TH EDITION, NEW DELHI,
ELSEVIER, 2013
15

• Deoxyribonucleic acid (DNA) is the
genetic information of most living
organisms (except retroviruses, use
ribonucleic acid as genetic
information).
- DNA can be copied over
generations of cells: DNA
replication
- DNA can be translated into
proteins: DNA transcription into
RNA, further translated into
proteins)
• DNA is found in the nucleus of the
cell, but a small amount is also
present in the mitochondria.
ATLAS OF GENETICS AND CYTOGENETICS IN ONCOLOGY AND HAEMATOLOGY
16

• DNA is a polymere, made of units called
nucleotides (or mononucleotides).
- Nucleotides also have other functions:
energy carrier, cellular respiration, signal
transduction.
• The double helix is a quite rigid and viscous
molecule of an immense length and a small
diameter. It presents a major groove and a
minor groove.
• The major groove is deep and wide, the minor
groove is narrow and shallow.
• DNA-protein interactions are major/essential
processes in the cell life (transcription
activation or repression, DNA replication and
repair).
17

• Proteins bind at the floor of the DNA grooves, using specific
binding: hydrogen bonds, and non specific binding: van der
Waals interactions, generalized electrostatic interactions.
• Some proteins bind DNA in its major groove, some other in the
minor groove, and some need to bind to both.
• DNA is found in the nucleus of the cell, but a small amount is
also present in the mitochondria.
• The number of DNA copies in one given mitochondria is
variable.
18

KARYOTYPIN
G
• Karyotyping may be offered in the case of the following-
1. Confirmation of the diagnosis of a medical condition that is genetic
in nature, for a child or an adult.
2. If there is a family history of a specific disease.
3. If several members of a family present with symptoms of the same
disease.
4. If there is concern over passing a genetic disease to the next
generation.
5. If the couple are blood relatives and have entered into a
consanguineous marriage.
6. If a couple wants to start a family and one of them has a family
history of a disease, genetic testing will reveal if they are "carriers" of a
19

5. If the couple are blood relatives and have entered into a
consanguineous marriage.
6. If a couple wants to start a family and one of them has a
family history of a disease, genetic testing will reveal if they are
"carriers" of a particular illness.
7. If a women is pregnant and is above the age of 34.
8. If a woman had more than two spontaneous abortions.
9. If a couple already had a child with a genetic disease and is
planning for the next child.
20

PAEDIATRIC DENTISTRY
CONSIDERATION
If parents come with chief complain of their child’s
• Delayed eruption
• Atypical pattern of eruption
• Unusual shaped teeth
• Enamel defects
• Orthodontic problems
21

TECHNIQUE OF
KARYOTYPING
• The test can be performed on a sample of
blood, bone marrow, amniotic fluid, or
tissue from the placenta, the organ that
develops during pregnancy to feed a
growing baby.
• To test amniotic fluid, an amniocentesis is
done.
• A bone marrow specimen requires a bone
marrow biopsy.
• The sample is placed into a special dish
and allowed to grow in the laboratory. 22

• Cells are later taken from the
growing sample and stained.
• The laboratory specialist uses a
microscope to examine the size,
shape, and number of
chromosomes in the cell sample.
• The stained sample is
photographed to provide a
karyotype, which shows the
arrangement of the chromosomes.
23

• Certain abnormalities can be
identified through the number or
arrangement of the chromosomes.
• Chromosomes contain thousands of
genes that are stored in DNA, the
basic genetic material.
24

• In 1971 the Paris conference established & numbered the
bands. It involves
• 1) chromosome number
• 2) chromosome arms( p for short & q for long arm)
• 3) band number
• Ex. 13q21 – designates band 21 on long arm of chromosome
number 13
• Each chromosomes consists of thousand of genes
DEAN,MCDONALD,AVERY.DENTISTRY FOR THE CHILD AND ADOLOSCENT.9TH EDITION ,NEW DELHI
,ELSEVIER, 2013 25

TITLE
**
GENETIC PROFILE OF RETINOBLASTOMA PATIENTS
FROM A REFERRAL HOSPITAL IN GUJARAT
Authors Oza Sunil, Patel Brijesh, Parikh Niyati, Prajapati Sweta, Jadav Hrishikesh, Pensi
Aim The aim of this study was to carry out karyotypic study in Retinoblastoma cases and identifying
nature of chromosomal abnormalities in these patients to determine recurrence risks to assist
genetic counseling.
Materials &
methods
Karyotypic study was perform by Trypsin- Giemsa Banding for 17 unilateral and 8 bilateral
retinoblastoma patients (total 25) for that their blood samples were taken. A prior written consent
was taken from the parents of these patients.
Result Out of 25 cases of Retinoblastoma, one female (4%) had 13q14 deletion and 24 (96%) showed
normal chromosomal constitution and not a single case of translocation was found.
Interpretation Karyotyping is the simplest and affordable genetic test for most of the retinoblastoma families
especially in a developing country like India. Genetic testing is crucial for accurate risk prediction
for retinoblastoma in close relatives of probands and provides a basis for genetic counseling.

CHROMOSOMAL ABNORMALITIES:
By applying the karyoptyping technique:
• Lejeune and colleagues demonstrated that the fundamental
cause in down syndrome, presence of an extra specific
chromosome 21
• When extra chromosome is present, the condition is called a
trisomy.
• Monosomy – missing autosomal chromosome.
• Monosomy of the sex chromosome can be compatible with life
and typically affects the internal and external sex organs of
individuals.
• e.g. Turner syndrome 45X
DEAN,MCDONALD,AVERY.DENTISTRY FOR THE CHILD AND ADOLOSCENT.9TH EDITION ,NEW DELHI ,ELSEVIER,
2013 27

A. DISORDERS OF CHROMOSOMAL
NUMBER
• Called as ANEUPLODY occurs when an individual is missing a
chromosome from pair (monosomy) or has more than two
chromosomes of pair (trisomy, tetrasomy).
• Trisomy 13
• Trisomy 18
• Trisomy 21
• Klinfelter’s Syndrome/testicular Dysgenesis
• Triple X Syndrome
28

TRISOMY 13
• Also called as Patau Syndrome.
• caused by a chromosomal abnormality, in which
some or all of the cells of the body contain extra
genetic material from chromosome 13.
• The extra genetic material disrupts normal
development, causing multiple and complex
organ defects.
• Signs and symptoms- microcephaly, polydactyly
(extra digit), cleft palate, ventricular septal
defects, abnormal palm structure, overlapping
digits.
29

TRISOMY
18
• Also known as Edwards Syndrome.
• is a genetic disorder caused by a third copy of all
or part of chromosome 18.
• Babies are often born small and have heart defects.
• Other features include a small head, small jaw,
clenched fists with overlapping fingers, and severe
intellectual disability.
• Most cases of Edwards syndrome occur due to
problems during the formation of the reproductive
cells or during early development.
• Occasionally not all cells have the extra
chromosome, known as mosaic trisomy, and
symptoms in these cases may be less severe.
30

TRISOMY 21
• Down syndrome is a genetic disorder.
• birth defects, learning, problems, and facial
features, heart defects and problems with
vision and hearing, Blood conditions, such as
leukemia, and risk for infections.
• Down syndrome is one of the most common
genetic birth defects. It affects about 1 in 800
babies. Adults with Down syndrome may live
about 60 years, but this can vary.
• Can often be diagnosed before birth
31

KLINFELTER’S
SYNDROME
• also known as 47,XXY or XXY
• Results from two or more X chromosomes in males.
• The primary features are infertility and small testicles.
• Often, symptoms may be subtle and many people do not
realize they are affected.
• Sometimes, symptoms are more prominent and may include
weaker muscles, greater height, poor coordination, less body
hair, breast growth.
32

• Often it is only at puberty that these symptoms are noticed.
• Intelligence is usually normal; however, reading difficulties and
problems with speech are more common.
• no cure is known, a number of treatments may help.
• Physical therapy, speech and language therapy, counseling, and
adjustments of teaching methods may be useful.
33

TRIPLE X
SYNDROME
• also known as trisomy X and 47,XXX.
• It is characterized by the presence of an extra X chromosome in
each cell of a female.
• Those affected are often taller than average.
• Usually there are no other physical differences and normal
fertility.
• Occasionally there are learning difficulties, decreased muscle
tone, seizures, or kidney problems.
34

B. DISORDERS OF CHROMOSOMAL
STRUCTURE
Structural chromosome rearrangements are changes in the
physical
structure of chromosomes that may result in-:
• birth defects
• mental retardation
• increased risk for infertility
• pregnancy loss.
35

Due to-: chromosomal breakage or unequal crossing over which
result in
• Deletions
• Duplications
• Translocations
• Insertions
• Inversions.
• Isochromosomes
• Complete Aberration
36

Deletions
•Abnormalities in
which a portion of
chromatin from a
single
chromosome is
lost are called
Deletions.
Duplications
• Duplications are unbalanced
arrangements that result in
partial trisomy.
• Duplications are believed to
result primarily from unequal
crossing over especially in
regions of the genome where
repeat sequences are found
Translocation
s
• Translocations involve breaks in
two different chromosomes
with an exchange of segments.
• In humans, there are two major
types of translocation:
• Reciprocal translocations-: in
which there is no visual loss of
chromatin
• Robertsonian translocations-: in
which the long arms of two
acrocentric chromosomes are
joined with loss of the two short
arms.
37

Inversions
• Inversions are formed
by two breaks in the
same chromosome with
exchange of the two
ends.
• Types-:
• Pericentric Inversions
• Paracentric Inversions
Insertions
• an insertion is the
addition of one or more
nucleotide base pairs
into a DNA sequence
• This can often happen
in microsatellite regions
due to the DNA
polymerase slipping
39

HEREDITARY TRAITS IN FAMILIES
• Chromosomal abnormalities are an imp cause of spontaneous
abortions only 0.3 to 0.5% of all live born infants have a chromosomal
abnormality detected with standard microscopic karyotyping.
• The transmission of characters from parents to offspring by
information encoded in the parental germ cells- Heredity
• Heritability - The extent to which genetic individual differences
contribute to phenotypic individual differences (i.e. Individual
differences in observed behavior)
• Three main types of inheritance patterns:
1. MONOGENIC
2. POLYGENIC
3. MULTIFACTORIALDEAN,MCDONALD,AVERY.DENTISTRY FOR THE CHILD AND ADOLOSCENT.9TH EDITION ,NEW DELHI ,ELSEVIER, 2013
41

,ELSEVIER, 2013
42
MONOGENIC TRAITS
SINGLE GENE
EASY TO RECOGNIZE
NOT AMENABLE ON A
LARGE SCALE TO
ENVIRONMENTAL
MODIFICATIONS
RARE (1 IN 1000)
POLYGENIC TRAITS
MANY GENES
COMMON AND
ILLUSTRATED BY TRAITS
LIKE INTELLIGENCE,SKIN
COLOUR
NO CLEAR CUT
DIFFERENCES BETWEEN
AFFECTED AND NORMAL
CONTINOUS OR
QUANTITATIVE
PHENOTYPE.
MULTIFACTORIAL
TRAITS
COMBINATION OF GENETIC
AND ENVIRONMENTAL
FACTORS
NET EFFECT OF ALL GENES

PEDIGREE
CHARTING
• A diagram that shows the occurrence and appearance of
phenotypes of a particular gene/organism and its ancestors
from one generation to the next
• A pedigree is a chart of the genetic history of family over
several generations.
• Males are represented as squares and females are represented
as circles.
• Shaded symbols mean an individual is affected and unshaded
one represents unaffected individual.
,ELSEVIER, 2013
43

• It is a shorthand method of classifying the family data,
conveniently summarizes the family data for the study of
inherited traits.
• Valuable tool for the clinician who is concerned with diagnosis
of & counseling regarding hereditary traits.
DEAN,MCDONALD,AVERY.DENTISTRY FOR THE CHILD AND ADOLOSCENT.9TH EDITION ,NEW
DELHI ,ELSEVIER, 2013
44

INHERITANCE
PATTERN
,ELSEVIER, 2013 45
Autosomal
Dominant
Autosomal
Recessive
X- Linked
Dominant
X- Linked
Recessive
Multifactorial

Autosomal Dominant
FEATURES :
• Disease usually appear in each generation.
• Delayed age of onset.
• Vertical transmission.
• Mostly involve structural proteins.
• Variability in clinical expression.
• Affected individual has an affected parent.
• Male and female siblings are equally affected.
• Each child of an affected parent is at 50% risk of inheriting the abnormal gene.
DEAN,MCDONALD,AVERY.DENTISTRY FOR THE CHILD AND ADOLOSCENT.9TH EDITION ,NEW DELHI ,ELSEVIER, 2013
47

EXAMPLES
• Osteogenesis
imperfecta
• Dentinogenesis
imperfecta
• Mesiodens
• Dentine dysplasia
,ELSEVIER, 2013
48

AUTOSOMAL
RECESSIVE
FEATURES:
• Expressed only in homozygote state.
• Homozygote receives one abnormal (recessive) gene from each
parent.
• Horizontal transmission : multiple affected members in same
generation; no affected members in other generations.no
dominant trait.
• Chances of affected - children 25%
2013
50

• Males and females equally affected.
• Increased frequency in case of consanguinity.
• Heterozygote for autosomal recessive trait is called carrier.
• If both parents are affected they are homozygous for the abnormal gene,
all the children will be (homozygous) affected.
Examples
• Dentin dysplasia (coronal type)
• Hereditary amelogenesis imperfecta
• Hypophosphatasia
• In the AI pigmented hypo-maturation occurs teeth appear dark brown in
color.
DEAN,MCDONALD,AVERY.DENTISTRY FOR THE CHILD AND ADOLOSCENT.9TH EDITION ,NEW DELHI ,ELSEVIER, 2013
51

X-LINKED RECESSIVE
INHERITANCE
• Male: 1 – X & 1 – Y chromosomes & Females : 2 – X
chromosomes
• The only genes known to be active on Y – chromosome are
concerned with male reproductive system.
• Males are hemizygous for all X – linked genes.
• Female can be homo/heterozygous as having 2 X chromosomes
• All recessive genes in male in single dose express themselves
phenotypically and behave as they are dominant genes.
• XLR diseases are more common in male than female.
2013
53

• Because all XLR genes behave as dominant genes in males, the
following criteria distinguish an XLD trait in families:
1. Affected males must transmit the trait to all of their daughters
(as with XLR traits), all of them are affected.
2. Affected males cannot transmit the trait to their sons (just as
with XLR traits).
3. Heterozygous females transmit the trait on the average to 50%
of their children of both sexes, The latter situation is
exceptionally rare for a dominant trait and is practically never
observed.DEAN,MCDONALD,AVERY.DENTISTRY FOR THE CHILD AND ADOLOSCENT.9TH EDITION ,NEW DELHI ,ELSEVIER, 2013
54

• Example-
• Haemophilia A
• Blindness
55

SAMPLE FOOTER TEXT 2/7/2019 56
56

X-LINKED DOMINANT
INHERITANCE
Example :
Hypoplastic type of amelogenesis imperfecta is inherited
as sex linked dominant trait, both the dentitions are
affected.
57

MULTIFACTORIAL INHERITANCE
• Achieved through an interaction of multiple
genes and environmental factors and occurs
when a liability threshold is exceeded.
• Environmental factors - those non genetic
circumstances that render an individual more
or less susceptible to disease state.
• The change depends upon the individual’s
ability to respond to the environmental factors
which may be heavily influenced by the same
gene or other. Example : dental caries.
DEAN,MCDONALD,AVERY.DENTISTRY FOR THE CHILD AND ADOLOSCENT.9TH EDITION ,NEW
DELHI ,ELSEVIER, 2013
58

• The interaction product of three essential factors: a cariogenic
diet, a caries-producing bacterial flora, and a susceptible tooth.
• These three factors encompass a variety of biologically
complicated entities, such as saliva, plaque, tooth matrix
formation, and crystallization. It should be easy to see that the
development of these complex elements must involve a great
number of genes.
• Environmental modification, such as properly timed systemic
fluoride supplementation, produces a considerable alteration in
the phenotype without changing the genetic constitution of the
individual.
,ELSEVIER, 2013
59

MULTIFACTORIAL (COMPLEX) INHERITANCE
IN HUMAN DISEASES
• For many common disorders, such as diabetes and
hypertension, there is a definite familial tendency.
This is shown by the fact that the proportion of
affected near relatives is greater than the incidence in
the general population.
• However, this proportion is much lower than what is
expected for amonogenic trait, and the explanation
most commonly offered for major congenital
malformations is that they are multifactorial traits.
2013
60

• Characteristics:
• Each person has a liability for a given disease, and that liability
represents a sum of the genetic and environmental liabilities.
• The multifactorial-threshold model is a mathematical way of
expressing these liabilities.
• Example: CLP. Such a threshold means that all persons with
sufficient gene dosage and environmental interaction will be
above the threshold of expression and show the cleft lip.
Those with less will not show a cleft lip.
61

• Fifty years ago, dental caries was presented to dental students
as a disease that was so common that more than 99% of the
general population was afflicted by it.
• Although it is still recognized as a common disease, the use of
systemic and topical fluorides and persistence by organized
dentistry to bring about changes in dietary habits and oral
hygiene practices have contributed significantly to a remarkable
decrease in the prevalence of this disorder, especially noted in
children.
• Bretz et al.13 observed a high heritability component (h2) for
surface based caries prevalence (h2 = 64.6), lesion severity (h2
= 61.7) and sucrose sweetness preference (h2 = 55.2) in 115
pairs of twins aged 4–7 years old.
S OPAL, S GARG, J JAIN, I WALIA. GENETIC FACTORS AFFECTING DENTAL CARIES RISK. AUSTRALIAN
DENTAL JOURNAL 2015; 60: 2–11
64

S OPAL, S GARG, J JAIN, I WALIA. GENETIC FACTORS AFFECTING DENTAL CARIES RISK. AUSTRALIAN DENTAL JOURNAL
2015; 60: 2–11 65

• A group of saliva proteins designated as the proline-rich
proteins (PRPs) because of their high content of the amino acid
proline have been linked to early plaque and pellicle. PRPs are
known, and all these proteins are coded for by a block of genes
called the salivary protein complex, located on the short arm of
human chromosome 12.
• These polymorphic acidic PRPs in saliva are encoded at two loci,
PRH1 and PRH2. Pa, Db, and PIF are alleles at the PRH1 locus 52
and PRH2 codes for Pr.
• Yu and colleagues reported significant association between Pa
and Pr22 and an increase in dental caries scores in the
permanent teeth of children 6 to 15 years of age. 66

67
Title Prevalence and Heritability of Early Childhood Caries Among Monozygotic and
Dizygotic Twins
Authors Anuradha Kuppan (a1), Steven Rodrigues (a1), Victor Samuel (a2), Mahesh Ramakrishnan
Journal J of Twin Research and human gen., Volume 20, Issue 1
February 2017, pp. 43-52
Level of Evidence IV
Abstract Deciphering the relative importance of genetic and environmental factors, which play a major role in the
prevalence of early childhood caries (ECC), can help clinicians with planning a long-term preventive
treatment. The objective of the study was to determine the prevalence and heritability of
ECC among monozygotic (MZ) and dizygotic (DZ) twins in Chennai, India, in the year 2013.
A cross-sectional study was designed to estimate the prevalence of ECC among twins. Zygosity classification
for the survey framework was adapted from a highly accurate parental report questionnaire pertaining to the
physical similarity between twins. The associated heritability index was estimated. The DMFS Index was used
as the diagnostic criterion for dental caries. The prevalence of ECC was estimated at 18.7%. The
correlation coefficient between the twin pair showed significant correlation. The heritability index for
ECC was estimated at 15% higher prevalence of ECC found among children in the age group 25–36
months. The heritability estimate indicated a relatively low genetic influence for early childhood
caries among twins. There was no significant difference detected in the concordance rate
for the MZ and DZ twins.

GENETICS AND PERIODONTAL DISEASE
• Dental plaque formation is the critical step in initiation of
chronic periodontal disease and dental caries-
• Michalowicz and colleagues published a large study of adult
twins (mean age, 40 years) of which there were 63 monozygotic
and 33 dizygotic pairs. The authors stated that from 38% to
82% of the periodontal disease identified in these twins was
attributable to genetic factors.
68

• Early onset of periodontitis may occur in the primary dentition
(prepubertal periodontitis), may develop during puberty (JP), or may
be characterized by exceedingly rapid loss of alveolar bone (rapidly
progressive periodontitis)
• Prepubertal periodontitis appears to be the most commonly
encountered cause of premature exfoliation of the primary teeth,
especially in girls.
• JP has the following features:
1. An early onset of the breakdown of alveolar bone. This bone loss is
of two types:
chronic periodontitis in a generalized form affecting any dental area,
a localized form in which the molar or incisor regions of bone are the
most severely affected.
69

• Progress has been made in the study of rare
genetic conditions or syndromes that can
predispose to periodontal disease or have
periodontal disease as a relatively consistent
component of their pleiotropic effect.
Examples:
Papillon-Lefèvre syndrome
70

GENETIC AND
MALOCCLUSION
• Normal occlusion and malocclusion are dynamic concepts that
involve the interrelationships of many factors, a few of which have
been shown to be influenced by genetic factors.
• For example, (Yamaguchi and colleagues) in a study of the
association of the P56IT
• It is a variant present in the growth hormone receptor (GHR) gene,
• The GHR P56IT allele present - greater mandibular ramus length
• The GHR P56IT allele present- lesser the mandibular hieght (4.65 mm
shorter than the average for those without the GHR P56IT allele.)
71

• Lundstrom- studies of occlusion in Twins: concluded that
hereditary had significant role in determining tooth size, width and
length of dental arch, height of palate, crowding and spacing of
tooth and overbite.
• Kraus et al- Ceph. studies of Triplets: concluded morphology of
individual bones under strong genetic control
• Environment plays a major role on- how various bony elements
combined to achieve harmonious/disharmonious relationship.
• Harris has shown that the craniofacial skeletal patterns of
children with class II malocclusions are heritable and that there is
a high resemblance to the skeletal patterns in their siblings with
normal occlusion.
• From this he concluded that the genetic basis for this
resemblance is probably polygenic. Interestingly, Harris used the
72

GENETIC
COUNSELING
• DEFINITION :- Genetic counseling is communicative process
which deals with human problems associated with occurrence
and or recurrence of a genetic disorder in a family.
• Understand the medical facts including diagnosis, probable
course of disorder and available management.
73

• Understand the mode of
inheritance of the disorder and
the risk of developing and/or
transmitting it.
• Choose the course of action
which is appropriate for them.
• Make the best possible
adjustment to the disorder in an
affected family member and or to
the risk of recurrence of the
disorder
74

TYPES OF GENETIC COUNSELING
(A) Prospective genetic counseling:
• This allows for the true prevention of disease.
• This requires to identify heterozygous individuals for any
particular defect by screening.
• Explaining to them the risk of their having affected children if
they marry another heterozygote for the same gene.
• If heterozygous marriage can be prevented or reduced, the
prospects of giving birth to affected children will diminish.
75

(B) Retrospective genetic counseling:
• Most genetic counseling at present is
retrospective, (the hereditary disorder
has already occurred within the family).
Ex. Mental retardation.
76

Objective
• Provide concrete, accurate information about inherited
disorders.
• Reassure people who are concerned that their child may inherit
a particular disorder that the disorder will not occur.
• Educate people about inherited disorder and the process of
inheritance.
• Offer support by skilled health care professionals to people
who are affected by genetic disorders.
77

AREAS OF GENETIC
COUNSELING:
(A) Prenatal Genetic Counseling-
• There are several different reasons a person or couple may
seek prenatal genetic counseling.
• If a woman is of age 34 or older and pregnant, then there is an
increased chance that her foetus may have a change in the
number of chromosomes present.
• Changes in chromosome number may lead to mental
retardation and birth defects
78

PAEDIATRIC GENETIC
COUNSELING:
• Families or paediatricians seek genetic counseling when a child
has features of an inherited condition.
• Any child who is born with more than one defect, mental
retardation or dysmorphic features has an increased chance of
having a genetic syndrome.
• Task is to establish a diagnosis in a child, provide longitudinal
care for the child, and advise the parents about recurrence risk
and options to deal with that risk.
79

ADULT GENETIC COUNSELING
• Adults may seek genetic counseling
when an adult begins exhibiting
symptoms of an inherited
condition, or when there is a new
diagnosis of someone with an
adult-onset disorder in the family
In addition.
• the birth of a child with obvious
features of a genetic disease leads
to diagnosis of a parent who is
more mildly affected.
80

CANCER GENETIC
COUNSELING
• A family history of early onset breast, ovarian
or colon cancer in multiple generations of
family is a common reason a person would
seek a genetic counsellor who works with
people who have cancer.
• While most cancer is not inherited, there are
some families in which a dominant gene is
present and causing the disease
81

STEPS OF GENETIC
COUNSELING
• History & Physical examination
• Include present, past history, detailed family history, obstetric history
including still births and abortions if any and exposure to teratogen.
• Careful examination of affected and of apparently unaffected
individuals in the family.
• Pedigree - Construct a 3 generation pedigree diagram with their age,
sex and state of health.
• Risk assessment - One of the most important aspect, often called
“recurrence risk”. Requires to take into account- Mode of inheritance
Analysis of pedigree or family tree Results of various tests.
82

• Diagnosis Most crucial step, confirm the diagnosis by available
diagnostic tests.
• Communication - Transmitting the information, with ample
time for discussion and questions.
• Management - Discuss available options for treatment of
disease and prevention of known complications or prevention
of genetic disorder( medical termination of pregnancy).
• Support groups - Group of patient or parents of children with
same disorder (patient support group).
83

• The Human Genome Project (HGP) was an international scientific
research project with the goal of determining the sequence of
nucleotide base pairs that make up human DNA, and of identifying
and mapping all of the genes of the human genome from both a
physical and a functional standpoint.
• It remains the world's largest collaborative biological project.
• After the idea was picked up in 1984 by the US government when
the planning started, the project formally launched in 1990 and
was declared complete in 2003.
85

• What is the Human Genome Project?
• Human Genome: is the full complement of genetic material in a
human cell
• Locates where the DNA pairs are located in your body
• A person has between 100,000 and 300,000 genes.
• Technique-
Researchers used a technique called genetic mapping.
Genetic mapping: locates the pairs of genes on the
chromosomes.
Using genetic mapping, you can determine the genetic code that
allows our bodies to develop. 86

WHAT ARE THE OUTCOMES OF THE HUMAN
GENOME PROJECT?
• Genetically proven to have the ability to
locate genes that are responsible for locating
diseases
• Gene Therapy used today
• The HGP has been very successful.
87

CONCLUSIO
N
• Significant studies in human genetics that are now taking
place should enable screening of those individuals at risk
and help in implementation of targeted preventive measures
to provide protection from various oral diseases.
88

REFERENCES:
• Dean, Mcdonald, Avery. Dentistry for the child and adoloscent.9th edition ,New Delhi ,Elsevier, 2013.
• S Opal, S Garg, J Jain, I Walia. Genetic factors affecting dental caries risk. Australian Dental Journal
2015; 60: 2–11.
• Clinical pedodontics Finn 4th edition 2001 A.I.T.B.S
• Abecasis GR, Cardon LR, Cookson WO. A general test of association for quantitative traits in nuclear
families, Am J Hum Genet 66(1):279-292, 2000.
• Rosenberg RN, Stuve O, Eagar T. 200 years after Darwin, JAMA 301(6):660-662, 2009.
• Deeley K, Letra A, Rose EK et al. Possible association of amelogenin to high caries experience in a
Guatemalan-Mayan population, Caries Res 42(1):8-13, 2008.
• Wankhede A, Wankhede S, Wasu S. Role of Genetic in Periodontal Disease. Journal of the International
Clinical Dental Research Organization. 2017.
• Mario Taba Jr, Sergio Luis Scombatti de Souza, Viviane Casagrande Mariguela. Periodontal disease: a
genetic Perspective. Braz Oral Res., (São Paulo) 2012;26(Spec Iss 1):32-8
89

• Kenneth Lange “Mathematical and Statistical Methods for Genetic Analysis”
• Dentinogenesis imperfecta: A case report. Subramaniam P,Mathew S,Sugnani S.
N. Journal of the Indian Society of Pedodontics & Preventive Dentistry. Jun2008,
Vol. 26 Issue 2, p85-87.
• http://www.nhgri.nih.gov/DIR/VIP/Glossary/index.html
• M.D.National Human Genome Research Institute, National Institutes of Health,
Bethesda, Maryland DJ WATTENDORF and M MAXIMILIAN, American Family
Physician December 1, 2005 Volume 72. www.aafp.org/afp
• Achondroplasia and periodontal disease . Kirti Chawla , Arundeep Kaur Lamba,
Farrukh Faraz, Shruti Tandon.
• Journal of Indian Society of Periodontology - Vol 16, Issue 1, Jan-Mar 2012.
• Papillon-Lefevre syndrome: Report of two cases in the same family.
• Rosenberg RN, Stuve O, Eagar T. 200 years after Darwin, JAMA 301(6):660-662,
2009.
90

Genetics- Principles & Disoreders in Paediatric Dentistry

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Genetics- Principles & Disoreders in Paediatric Dentistry

Similar to Genetics- Principles & Disoreders in Paediatric Dentistry (20)

More from DrSusmita Shah

More from DrSusmita Shah (12)

Recently uploaded

Recently uploaded (20)

Genetics- Principles & Disoreders in Paediatric Dentistry