STUDY ON MODERN GENETICS

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STUDY ON MODERN GENETICS

• Human genetic diseases
• (Thalassaemia, Down Syndrome, G6PD)
• Genetic screening
• Genetic counseling

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Human genetic diseases-Thalassaemia (??????)

• What?
• originated over 50,000 years ago
• derived from a Greek word meaning sea
• Normal red blood cells contain haemoglobin which
  has 2 main types of molecular chain, alpha and
  beta. Production of these chains are controlled
  by genes.
• An inherited defect in one of these genes results
  in thalassaemia
• an inherited disorder in which there is an
  abnormality in one or more of the globin genes.

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Human genetic diseases-Thalassaemia

• Two forms of Thalassaemia
• Thalassaemia Major
• -not making enough haemoglobin
• -bone marrow cannot produce enough red blood
  cells.
• gtThe red blood cells that are produced are
  nearly empty

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Human genetic diseases-Thalassaemia

• Thalassaemia Minor
• -sometimes known as Trait
• -completely healthy and normal but some of them
  have slight anaemia
• -only discovered if the person has a special
  blood test

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Human genetic diseases-Thalassaemia

• Who?
• people with Mediterranean descent,
• e.g. Egypt, Greece, India, Italy,Middle East,
  Turkey and some parts of South East Asia.
• 3-5 of Malaysians are carriers

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Human genetic diseases-Thalassaemia

• Major Treatment
• Monthly Blood Transfusion
• to replace empty red blood cells with new healthy
  ones
• each time lasts about 4 to 6 hours
• Side effects Build-up iron problem
• -darker skin, muscle pain, short or delayed
  puberty

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Babies having their monthly blood transfusion to
treat their thalassaemia
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Human genetic diseases-Thalassaemia

• Major Treatment
• 2. Desferal Injection
• a drug that injected under skin very slowly
  using a special kind of pump which runs for 6 to
  7 hours.
• picks up excess iron and carries it out in the
  urine

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Desferal Injection
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Human genetic diseases-Thalassaemia

• Major Treatment
• 3. Bone Marrow Transplant
• expensive and of high risk of rejection

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Human genetic diseases-G6PD Deficiency

• What?
• Glucose-6-phosphate dehydrogenase, a cytoplasmic
  enzyme found in every cells
• most common human enzyme deficiency
• benefit of having G6PD deficiency is that it
  confers a resistance to malaria

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Human genetic diseases-G6PD Deficiency
(???-?-??????????)

• WHAT?
• some G6PD deficient individuals are also allergic
  to fava beans (??)
• more than 400 mutations of the deficiency, each
  responding differently to certain foods and drugs
  
• Sex-linked, located on the X chromosome

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Human genetic diseases-G6PD Deficiency

• Who?
• most of the affected individuals reside in
  Africa, the Middle East, and Southeast Asia.
  African Americans and some isolated tribes in
  Africa and Southeast Asia
• Symptoms?
• yellowing of the eyes

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Human genetic diseases-G6PD Deficiency

• How to treat?
• No specific treatment is needed since the
  condition is usually self limiting. Rarely blood
  transfusions are indicated

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Human genetic diseases-Down Syndrome

• What?
• a genetic condition caused by extra genetic
  material (genes) from the 21st chromosome
• causes an extra dose of some proteins
• Those proteins cause the typical features of Down
  Syndrome

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Human genetic diseases-Down Syndrome

• Some of the physical traits of people with Down
  Syndrome that are common but not always present
  are folds over the eyes, flattened bridge of the
  nose.

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Human genetic diseases-Down Syndrome

• Who?
• the chances depend upon the age of the mother

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Human genetic diseases-Down Syndrome

• More on Down Syndrome
• Do people with Down Syndrome have normal life
  expectancies?
• Generally, life expectancy is reduced by
  10-20 years. Some people with Down syndrome,
  however, have been known to live into their 80's.

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Human genetic diseases-Down Syndrome

• More on Down Syndrome
• Is there medical treatment for Down Syndrome?
• Though there have been proposed medical
  treatments for Down Syndrome, none of them have
  been proven effective.

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GENETIC SCREENING
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What is the purpose of Genetic Screening?

• to locate the defective genes in
• human body
• to discover the mystery behind genetic
• disorders genes wanted are discovered
• discover feasible methods for "cures
• help parents identify whether their babies will
• be born with defective genes

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What is Genetic Screening?

• Gene tests (also called DNA-based tests)
• --- direct examination of the DNA molecule
• What for? Patient's DNA sample for mutated
  sequences
• How? Sequence of DNA bases in a patient's gene
  compared to a normal version of the gene
• Cost? Range from hundreds to thousands of
  dollars, depending on the sizes of the genes and
  the numbers of mutations tested.

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Where is Genetic Screening mainly applied to?

• Carrier screeningidentifying unaffected
  individuals who carry one recessive gene of a
  disease while two the disease is expressed only
  in homozygous recessive condition
• Prenatal diagnostic testing
• Newborn screening
• Pre-symptomatic testingpredicting adult-onset
  disorders
• Conformational diagnosis of a symptomatic
  individual

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• GENETIC
• COUNSELING

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What is the purpose of Genetic Counseling?

• If you are planning to have a baby, it is
  recommended that you speak with a Genetic
  Counselor, if for no other reason than becoming
  informed and making intelligent decisions.

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How does Genetic Counseling develop?

• Genetic Counselors
• health professionals with specialized master's
  degrees and experience in the areas of medical
  genetics and counseling
• providing information and support to families who
  have members with birth defects or genetic
  disorders and to families who may be at risk for
  a variety
• of genetic conditions

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• identify families at risk
• investigate problems present in the family
• interpret information about the inheritance
  patterns and risks of recurrence
• review available options with the family
• engage in research activities related to the
  field of genetic counseling

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What are Genetic Counselors and what are their
works?

• A BRIEF HISTORY____
• In the early "hereditary counseling clinics,
  medical geneticists met with families, examined
  affected individuals and drew pedigrees
• Relatively common diseases and conditions such as
  sickle cell anemia
• were worked with

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• Laboratory tests for genetic diseases
• were few
• From the mid 1940's through the mid 1960's,
• medical genetics and genetic counseling was
  practiced in only a handful of
• specialty clinics

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• A giant leap forward in 1967 with the first
  amniocentesis
• WHAT IS Amniocentesis?
• Amniocentesis is a procedure which help identify
  chromosomal and genetic abnormalities which may
  be present in fetuses.

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Background of Amniocentesis

• The fetus is surrounded by amniotic fluid
• Floating in the amniotic fluid are cells that
  have washed off the baby's skin, intestines and
  urinary tract
• Each of these cells contains a complete set of
  fetal chromosomes

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How is it done?

• A long, thin needle is placed through the
  mother's abdomen, a tablespoon or two of amniotic
  fluid is removed
• The fetal cells are removed from the fluid and
  cultured in the laboratory
• Cells are treated with a chemical which halts the
  cell division process, followed by treatment with
  a hypotonic solution which causes cells to swell
• The swollen cells are then broken open
• Microscopic analysis of the slide will show the
  chromosomes which have been released from the
  cells.
• The chromosomes can then be counted and analyzed
  to give a genetic "snapshot" of the developing
  fetus

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Genetic Counseling in HK

• In Hong Kong, the Family Planning Association
  is offering a service named e-counseling.
• For reference,
• http//www.famplan.org.hk

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THE END
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(21) LAU YEUNG YEUNG