This document discusses genetic disorders, including: - Genetic disorders are caused by abnormalities in DNA and genes, and can be heritable or non-heritable. - There are three main types of genetic disorders - single gene, chromosomal, and multifactorial. Examples are provided for each type, including cystic fibrosis, Down syndrome, and Alzheimer's disease. - The history of understanding genetic disorders is explored, from Mendel's work in genetics to modern discoveries like the structure of DNA and genetic coding. Classification and examples of different genetic disorders are provided.

1. Genetic Disorder
- Chhabi Acharya
Sunandan Poudel
HOPE Int’l College

2. Content:
• Introduction
• History
• Types
- Discussion
- Examples

3. Introduction:
• A genetic disorder is an illness caused
by one or more abnormalities in the
genome, especially a condition that is
present from birth (congenital).
• Most genetic disorders are quite rare and
affect one person in every several
thousands or millions.
• Genetic disorders may or may not be
heritable, i.e., passed down from the
parents' genes.

4. Contd..
• In non-heritable genetic disorders, defects
may be caused by new mutations or
changes to the DNA.
• The defect will only be heritable if genetic
disorder occurs in the germ line.

5. History:
• 1866 - First there was
Gregor Mendel, who
studied inherited
characteristics.
• This was followed by
Francis crick and James
Watson who unraveled
the DNA molecule.
• This has led us to
understanding the
human genome
sequence.

6. Contd..
• 1950’s - Maurice
Wilkins, Rosalind
Franklin, Francis H. C.
Crick of Britain and
James D. Watson of
the U.S. discover
chemical structure of
DNA, starting a new
branch of science -
molecular biology.

7. Contd..
• 1957- Arthur
Kornberg of the
U.S. produced
DNA in a test tube.
• 1966 - The Genetic
code was
discovered.

8. Contd..
• 1983 – “Genes are able to change
position on chromosomes” - Barbara
McClintock
• Late 1980's - An international team of
scientists began the project to map the
human genome.
• 1990 - Gene therapy, first used for patient

9. • Earliest Evidence Of Hereditary Genetic
Disorder Discovered :
The fossil is dated as 1.5 million years old and is from a two-year-old
Homo erectus child. Homo erectus was a precursor of modern man.
Facts

10. Classification:
• Single gene disorder
• Chromosomal genetic disorder
• Multifactorial genetic disorder

11. 1. Single gene disorder
• These disorders involve mutations in the
DNA sequences of single genes. As a
result, the protein the gene codes for is
either altered or missing.
• Over 4000 human diseases caused by
single gene defects.
• Some Example : Adenosine deaminase
deficiency, Alpha-1 Antitrypsine
deficiency, Cystic fibrosis, Galatosemia,
Huntington’s disease, Maple syrup urine
disease, Phenylketonurimea c, Severe
combined immunodeficiency, Sickle cell
disease, Smith-Lemil-Optiz Syndrome

12. 1-a. Cystic Fibrosis:
• Cystic fibrosis is a genetic disorder
that affects the respiratory and
digestive systems.
• People with cystic fibrosis inherit a
defective gene on chromosome 7
called CFTR (cystic fibrosis
transmembrane conductance
regulator).
• The protein produced by this gene
normally helps salt (sodium chloride)
move in and out of cells.

13. Contd..
• If the protein doesn't work correctly, that
movement is blocked and an abnormally
thick sticky mucus is produced on the
outside of the cell.
• The cells most seriously affected by this
are the lung cells. This mucus clogs the
airways in the lungs, and increases the
risk of infection by bacteria.
• The thick mucus also blocks ducts in the
pancreas, so digestive enzymes can't get
into the intestines.

14. 1-b. Galactosemia:
• Galactosemia is a rare disorder that
affects the body's ability to break down
a food sugar called galactose.
• The body breaks down lactose into
galactose and glucose and uses these
sugars for energy.
• Most people with galactosemia are
missing an enzyme (called GALT) that
helps further break down galactose.
• Defects in galactose metabolism
cause toxic chemicals to build up in
cells of the body.

15. 1-c. Severe Combined
Immunodeficiency (SCID)
• SCID is a group of very rare-and
potentially fatal-inherited disorders
related to the immune system.
• People with SCID have a defect in
their immune system that leaves
them vulnerable to potentially
deadly infections.
• The most common form is caused
by a mutation in the SCIDX1 gene
located on the X chromosome.

16. Contd..
• This gene encodes a protein that is
used to construct a receptor called
IL2RG (interleukin-2 receptor).
• These receptors reside in the plasma
membrane of immune cells.
• Their job is to allow two types of
immune cells - T cells and B cells - to
communicate.
• When the gene is mutated, the
receptors cannot form and are absent
from immune cells.

17. Contd..
• As a result, the immune cells can't
communicate with one another about
invaders in the environment. Not
enough T and B cells are produced to
fight off the infection, and the body is
left defenseless.
• Some of infections including
pneumonia (lung infection), meningitis
(brain infection), and sepsis (blood
infection).

18. 1-d. Sickle Cell Disease
• Sickle cell disease is a disorder that
affects the red blood cells, which use a
protein called hemoglobin to transport
oxygen from the lungs to the rest of the
body.
• Normally, red blood cells are round and
flexible so they can travel freely through
the narrow blood vessels.

19. Contd..
• The hemoglobin molecule has two parts:
an alpha and a beta.
• Patients with sickle cell disease have a
mutation in a gene on chromosome 11
that codes for the beta subunit of the
hemoglobin protein.
• As a result, hemoglobin molecules don't
form properly, causing red blood cells to
be rigid and have a concave shape (like a
sickle

21. World’s rarest diseases (Its a genetic disease)
Fibrodysplasia
Ossificans
Progressiva
(FOP)
:Sometimes
called “stone
man” syndrome,
is extremely rare
genetic disease
causes soft
tissue to turn
into bone.
Oh My God!!!

22. 2. Chromosomal Genetic Disorder
• In these disorders, entire chromosomes,
or large segments of them, are missing,
duplicated, or otherwise altered.
• Can be organized into two basic groups:
1) Numerical Abnormalities: When an
individual is missing either a
chromosome from a pair (monosomy) or
has more than two chromosomes of a
pair (trisomy)
2) Structural Abnormalities: When the
chromosome's structure is altered.

23. Contd..
• Some Examples: Cri-Du-Chat Syndrome,
Down Syndrome, 47 XXY Klinefelter
Syndrome, Turner Syndrome
(Monosomy), William Syndrome

24. 2-a. Cri-du-cat Syndrome
• The name of this syndrome is French for
"cry of the cat," referring to the distinctive
cry of children with this disorder.
• The cry is caused by abnormal larynx
development, one of the many symptoms
associated with this disorder.
• Cri-du-chat is caused by a deletion (the
length of which may vary) on the short
arm of chromosome 5.
• Multiple genes are missing as a result of
this deletion, and each may contribute to
the symptoms of the disorder.

25. Contd..
• Babies with cri-du-
chat are usually
small at birth, and
may have
respiratory
problems.
• Often, the larynx
doesn't develop
correctly, which
causes the signature
cat-like cry.

26. 2-b. Down Syndrome
• Down syndrome is a developmental
disorder caused by an extra copy of
chromosome 21 (which is why the
disorder is also called "trisomy 21").
• Having an extra copy of this chromosome
means that individuals have three copies
of each of its genes instead of two,
making it difficult for cells to properly
control how much protein is made.
• Producing too much or too little protein
can have serious consequences.

27. Contd..
• People with Down syndrome have very
distinct facial features: a flat face, a small
broad nose, abnormally shaped ears, a
large tongue, and upward slanting eyes
with small folds of skin in the corners.
• People with Down syndrome have an
increased risk of developing a number of
medical problems: respiratory infections,
gastrointestinal tract obstruction,
leukemia, heart defects, hearing loss,
hypothyroidism, and various eye
abnormalities.

28. Contd..
• No cure exists for
Down syndrome.
• But physical
therapy and/or
speech therapy
can help people
with the disorder
develop more
normally.

29. 2-c. 47, XXY
(Klinefelter syndrome)
• Males (46, XY) and females (46, XX).
• 47, XXY (or XXY) is a genetic condition
caused when someone has two X
chromosomes and one Y chromosome.
• Because people with an XXY
chromosome arrangement have a Y
chromosome, they are considered genetic
males.
• Most XXY individuals develop as males,
often not knowing they have an extra
chromosome.

30. Contd..
• XXY is usually caused by what is called
nondisjunction.
• Nondisjunction happens when a pair of
sex chromosomes fails to separate during
egg (or sperm) formation.
• The XXY chromosome arrangement
affects primarily sexual development.
• Typically, testes don't fully develop, and
the levels of the hormone testosterone
(important for male sexual development)
are lower than average.

31. Contd..
• As adults, nearly all XXY males are
unable to make sperm and so cannot
have biological children.
• Many men discover their condition only
after they seek medical help for infertility.
• Changes that appear at puberty can
include low growth of facial and body hair,
development of breast tissue, and small
testes.

32. 2-d. Turner Syndrome
• Turner syndrome is caused by a missing
or incomplete X chromosome.
• People who have Turner syndrome
develop as females.
• The genes affected are involved in growth
and sexual development, which is why
girls with the disorder are shorter than
normal and have abnormal sexual
characteristics.

33. 2-e. Williams Syndrome
• Williams syndrome is a
rare genetic disorder
that affects a child's
growth, physical
appearance, and
cognitive development.
• People who have
Williams syndrome are
missing genetic material
from chromosome 7,
including the gene
elastin.

34. Colorblindness:
• Mutated
genes are
located on
the X-
chromoso
me (for
red/green
color
blindness)
or both the
X and Y
chromoso
mes (for
total color
blindness).
- What about
you? Try it:

35. 3. Multifactorial Disorder
• These disorders involve variations in
multiple genes, often coupled with
environmental causes.
• Some example: Alzheimer's Disease,
Breast/Ovarian Cancer, Colon Cancer,
Hypothyroidism. Asthma, cancers, cleft
palate, diabetes, heart disease,
hypertension, inflammatory bowel
disease, mood disorder, obesity,
refractive error, infertility

36. 3-a. Alzheimer's Disease
• Alzheimer's is a disease that
causes dementia, or loss of brain
function. It affects the parts of the
brain that deal with memory,
thought, and language.
• The brain of a person with
Alzheimer's contains abnormal
clumps of cellular debris and
protein(plaques) and collapsed
microtubules (support structures of
the cell).

37. Contd..
• Microtubule disintegration is
caused by a malfunctioning
protein called tau, which
normally stabilizes the
microtubules.
• In Alzheimer's patients, tau
proteins instead cluster
together to form disabling
tangles.
• These plaques and tangles
damage the healthy cells
around them.

38. Contd..
• Because Alzheimer's
destroys brain cells,
people who have the
disorder slowly lose their
ability to think clearly.
• At first, they may forget
words or names, or have
trouble finding things.
• As the disorder worsens,
they may forget how to
do simple tasks.
*

39. References:
• Genetics Science learning center, University of UTAH – Health
Science
http://www.learn.genetics.com
• National human genome research institute
http://www.genome.gov/11508982
• http://www.narragansett.k12.ri.us
• http://faculty.ccc.edu/jminarcik
• http://www.medicalschoolpathology.com
• http://www.fnhk.cz/fs392/14geneticdiseases.ppt
• Day in Health by Lisa Collier Cool,
http://health.yahoo.net/experts/dayinhealth/worlds-rarest-diseases