Genetic epidemiology, classification of Genetic Disorder, factor causing genetic abnormalities, difference between congenital and teratogenic abnormalities and prevention of genetic diseases

1. Genetic Epidemiology
Edenburgh International College
Mohan Bastola
BPH 5th Sem

2. Concept:
• Gene, are the unit of heredity. They contain the hereditary information
encoded in their chemical structure for transmission from generation to
generation.
• unit of hereditary information that occupies a fixed position (locus) on
a chromosome. Genes achieve their effects by directing the synthesis
of proteins.
• Genetics is the study of genes, heredity, and genetic variation in
living organisms (Hartl D, Jones E (2005).
• Each human cell nucleus contains 46 chromosomes, that carry hereditary
information and genetics is the study of how this information is
transmitted from parents to offspring.

3. Contd..
• Genetic epidemiology was defined by Newton Morton as "a science
which deals with the etiology, distribution, and control of disease in
groups of relatives and with inherited causes of disease in
populations“ (Morton, N. E.) (1982).
• Genetic epidemiology is defined as the study of the distribution of
and risk factors for diseases and genetic and environmental causes of
familial resemblance.

4. Classification of genetic disorder
• Chromosomal abnormalities
• Unifactorial (single gene or Mendelian) diseases
• Multifactorial disorder

5. Chromosomal disorder
• A chromosomal disorder, anomaly, aberration, or mutation is a
missing, extra, or irregular portion of chromosomal DNA. It can be
from a typical number of chromosomes or a structural abnormality in
one or more chromosomes.
They are of 2 types:
• Relating to sex chromosomes
• Relating to autosomes

6. Relating to sex chromosomes
1. Klinefelter’s syndrome:
• The person suffering from this syndrome are abnormal males having
two or more X chromosomes in addition to one Y chromosome (XXY,
XXXY).
• It only affects males.
• They have non-functional testes.
• Growth of hair on face, axillae and pubes is scanty.

7. 2.XYY syndrome:
• The male with an extra Y chromosome attached.
• They have anti-social, aggressive and criminal behavior.
• They appear to be exceptional height (usually 6 ft and over).

8. 3. Turner’s syndrome
• Turner syndrome is a chromosomal condition that affects
development in females.
• The most common feature of Turner syndrome is short height, which
becomes evident by about age 5.
• An early loss of ovarian function (ovarian hypo function or premature
ovarian failure) is also very common.
• They have 45 chromosome which constitute of XO instead of XX(O
represents missing chromosome)

9. 4. Super females
• They are females with 3 to 5 X-chromosomes.
• They have underdeveloped external genitalia, uterus and vagina.
• Triple X syndrome, also known as trisomy X and 47,XXX, is characterized by
the presence of an extra X chromosome in each cell of a female
Relating to autosomes:
• Down syndrome (DS or DNS), also known as trisomy 21, is a genetic
disorder caused by the presence of all or part of a third copy of
chromosome 21.
• It is usually associated with physical growth delays, mild to moderate
intellectual disability, and characteristic facial features.

10. Unifactorial (single gene or Mendelian)
diseases
• A single gene disease occurs due to a change in a gene that leads to
loss or disturbed function of that gene.
• They are:
I. Sickle cell anemia
II. Thalassaemia
III. Haemophilia
IV. Cystic fibrosis
V. phenylketonuria

11. Thalassaemias
• it is a hereditary disorder characterized by the reduction in the
synthesis of globin chain(alpha or beta).
• It causes reduced haemoglobin synthesis.
Sickle cell anemia:
• An inherited, chronic disease in which the red blood cells, normally
disc shaped, become sickle shaped.
• Mostly prevalent among blacks, especially in certain parts of Africa
and tharus community in western part of Nepal.

12. Haemophilia
• It is inherited genetic disorder in which the blood does not clot
properly.
• Also known as royal disease.
• It mostly affects men.

13. Cystic fibrosis
• Is a genetic disease which affects respiratory and gastrointestinal
tracks and sweat glands.
• The body produces thick and sticky mucus that can clog the lungs and
obstruct the pancreas.
• Cystic fibrosis (CF) can be life-threatening, and people with the
condition tend to have a shorter-than-normal life span

14. Phenylketonuria(PKU)
• It is an autosomal recessive disorder resulting in the deficiency of liver
enzyme phenylalanine hydroxylase which converts phenylaline to
tyrosine.
• It results in decreased metabolism of the amino acid phenylalanine.
• Untreated, PKU can lead to intellectual disability, seizures, behavioral
problems, and mental disorders.
• It may also result in a musty smell and lighter skin.

15. Multifactorial Genetic Disorder
• Multifactorial inheritance is also called complex or polygenic
inheritance. Multifactorial inheritance disorders are caused by a
combination of environmental factors and mutations in multiple
genes.
• For example, different genes that influence breast cancer
susceptibility have been found on chromosomes 6, 11, 13, 14, 15, 17,
and 22. Some common chronic diseases are multifactorial disorders.

16. Factor causing genetic abnormalities:
• A genetic disorder is a disease caused in whole or in part by a change
in the DNA sequence away from the normal sequence.
• Changes in the genes causes mutation, alter the structure function of
the gene product which give rise to diseases.
• Combination of gene mutations and environmental factors
• Damage to chromosomes.
• Translocation
• Inversion.

17. Difference between congenital abnormalities
and teratogenic abnormalities
• A congenital malformation is an anatomical or structural abnormality
present at birth.
• It can be caused by genetic factors or environmental insults or a
combination of the two that occur during prenatal development.
• Most of them demonstrate multifactorial inheritance with a threshold
effect and are determined by a combination of genetic and
environmental factors.
• Some birth defects are life-threatening, in which case a baby may
only live for a few months.

18. Contd..
• Teratogens are the substances that alter an environment within
womb/ fetus to cause the birth defects, e.g., alcohol, nicotine/smoke,
certain medicines, numerous industrial chemicals, etc. during
pregnancy.
• The combined consequences of consuming a harmful substance, such
as the alcohol, on a developing fetus may manifest itself as growth
deficiency and mental retardation.

19. Prevention of genetic diseases:
• avoiding harmful environmental factors which increase the mutation
frequency;
• screening all newborn infants for diseases when early treatment can
prevent the occurrence of physical and/or mental handicaps;
• early detection of couples at risk, followed by genetic counselling and
preventative measures in case of pregnancy.

20. Reference:
• K.PARK (25TH edition)
• https://www.britannica.com/science/gene
• https://www.genome.gov/For-Patients-and-Families/Genetic-
Disorders
• https://www.medicinenet.com/genetic_disease/article.htm
• https://www.yourgenome.org/facts/what-are-single-gene-disorders
• https://www.yourgenome.org/facts/what-is-a-chromosome-disorder.

21. thank You.