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					Genetic Counseling


Ashley Carlson
1st Year Genetic Counseling
Sarah Lawrence College
Bronxville, NY
What is a Genetic Counselor?
 A health professional with experience
  in medical genetics and counseling.
 Provides information and support to
  families who:
   – have members with genetic
     disorders or birth defects
   – may be at risk for genetic disorders
     or birth defects
 Practices non-directive counseling
  How Can I Become a Genetic
         Counselor?
 Obtain  a specialized graduate
  degree in Genetic Counseling
 Most enter the field from a variety
  of disciplines including biology,
  genetics, nursing, psychology,
  public health and social work. (NSGC
 1983)

 Havingexperience in counseling is
 very important
How Did I Become a GC?
 High school – Took Chemistry, Biology I and
  II, and Physical Science
 Undergrad – Biology, Genetics,
  Developmental Bio, Chemistry, Statistics,
  Evolutionary Bio, Genetic Technology, etc.
 Experience in a counseling-based agency –
  Worked in a Battered Women’s Shelter
 Volunteered for two prenatal Genetic
  Counselors in Wilmington, NC for one year
What Made Me Decide to Become a
      Genetic Counselor?
   Senior Exit Project
    – The idea came from my brother
 Interviewed two genetic counselors
 Personal History
    – Arnold-Chiari
    Malformation I
Chromosomes
 They   are the packages that contain
  our genetic material – our genes
 All of our cells have 46
  chromosomes
 Half (23) are inherited from each
  parent
 Chromosomes exist in pairs (23
  pairs)
Normal Appearing Female
        46,XX
Normal Male
  46,XY
Cell Division/Reproduction
Mitosis             Meiosis
 Cell division      How egg and

 All 46
                      sperm are formed
  chromosomes        One cell with 46
  copy themselves     chromosomes
 Both new cells
                      divides twice
  have the same       resulting in 4 cells
  set of 46           that each have
  chromosomes         only 23
                      chromosomes
Nondisjunction

 Failure of paired chromosomes to
  separate during meiosis in Anaphase I
 Leads to egg or sperm with extra or
  missing chromosomes
 When abnormal egg/sperm is used for
  fertilization, the result is an aneuploid
  embryo
Down syndrome
               Most common live born
                chromosome disorder
               Extra 21 chromosome
               Prevalence: 1:800 births
                – 350,000 people in USA
               Mental retardation
                – Characteristic facial
                  features
                – Heart defects
                – Vision/hearing problems
                – Increased risk of Leukemia
                  and Alzheimer's
Trisomy 18 - Edwards Syndrome
Edwards Syndrome
                1:8000 live births
                Mental deficiency
                Small jaw
                Short sternum
                Heart defects
                Malformed ears
                Rocker-bottom feet
                Characteristic
                 clenched fist
                90% die before 1 yr
Turner Syndrome
Turner Syndrome

               1:8000 live births
               Webbed neck
               Puffiness of hands
                and feet
               No sexual maturation
               Broad chest and
                widely spaced nipples
               Learning difficulties
What Are Genes?
 Genes   are the units of heredity we
  receive from our parents
 They are packaged at specific
  locations (loci) on our
  chromosomes
 Like chromosomes, they occur in
  pairs, one from each parent
 They are sequences of DNA
    Reasons for Genetic Disease
 A change in a gene from its natural state
 Changes can be inherited or acquired
 Genes themselves do not cause disease
 Mutation = gene malfunction = malformed
  or absent gene product = disease
 “She has the breast cancer gene…”
  means she has a mutated version of that
  gene
 ALL of us have some version of the
  Breast Cancer Gene or BRCA
Recessive Inheritance
Autosomal Recessive Conditions

 Cystic Fibrosis
 Xeroderma Pigmentosa
 Tay-Sachs
 Sickle Cell Anemia
Albinism
            Eyes,   hair and
             skin
            Lack of
             pigment
            25% risk to
             children of
             carriers
Dominant Inheritance
Autosomal Dominant Conditions
 Achondroplasia – dwarfism
 Familial Breast Cancer – BRCA1 and 2
 Huntington Disease
Crouzon’s Syndrome

               Premature
                fusion of the
                skull bones
               Wide, shallow
                eyes
               Hearing loss
X-Linked Inheritance
X-Linked Traits

 Color blindness
 Hemophilia
 Fragile X


 x-linked   dominant: “Incontinentia
 pigmenti” -various severity from skin
 abnormality to CNS problems
Fragile X Syndrome
          Most common cause of
           inherited mental
           impairment
          Caused by expanding
           area of DNA on
           chromosome X (CGG
           Repeat)
          Prevalence:
             – 1 in 4000 males
             – 1 in 6000 females
             – All races and ethnic groups
What Happens During a
Genetic Counseling Session?
   Family history is taken
   Discuss medical/genetic
    problems in general
   Provide risk assessment
   Discuss testing options,
    in terms of risks, benefits
    and limitations
   Consent patient for
    testing
Pedigree Construction
 Geneticists’ fundamental tool
 Allows for easy construction of a multi-
  generational family history
 Simple method for detailed
  documentation of inheritance of a
  particular trait in a family
 Can often assess the inheritance of a
  trait based on pattern of affected
  individuals
Pedigree Fundamentals
Autosomal Recessive
(it can be hidden and reappear)
What inheritance pattern?
Autosomal Dominant
What inheritance pattern?
X-Linked Dominant
(if father carries, every girl has it)
What inheritance pattern?
Y-linked
(all sons of affected fathers are
affected, ex; TDF-testes determining factor)
Any ideas on this one?
Mitochondrial Inheritance
(all children get mitochondria of
mother)
Prenatal Genetics
         Women who are at
          increased risk to have a
          child with a genetic
          disorder/ birth defect
          – Advanced maternal age
          – Family history of medical
            problem/genetic disease
          – Exposure to drugs,
            alcohol, medication
          – Prenatal sonogram
            abnormalities
     Maternal Age Effect
   As the age of the
    mother increases,
    there is an
    increased risk for
    a chromosome
    abnormality in
    their child.
      Different Prenatal Testing

   MSAFP
    – (test mother’s blood)
 Amniocentesis
 CVS
 Nuchal Fold-
    – sonogram measures amount of fluid in
      fetus’ dorsal neck
Maternal Serum Screen

                     AFP HCG uE3 Inhibin
                                 A
Down
Syndrome
Trisomy                            N/A
18
Neural Tube Defect       N/A   N/A N/A
Neural Tube Defects
Diagnostic Testing
CVS – Chorionic   Amniocentesis
Villi Sampling
Case 1

 Mother is 28 years old
 Maternal Serum Screen indicates 1/30
  for Down Syndrome
Teratogens
 Thalidomide
 Medications   for maternal illness
Osteogenesis Imperfecta
Marfan Syndrome
Ehlers-Danlos Syndrome
Neurofibromatosis
Prader-Willi Syndrome
Treacher Collins Syndrome
Case 2: Huntington Disease

 Woman is 31 years old
 Has a sister and father with HD
 Wants to be pregnant without knowing
  her HD status
 Goes through 2 rounds of
  Preimplantation Genetic Diagnosis
  (PGD)  unsuccessful
 At 34 she becomes pregnant naturally
Case 3: Cancer Genetics

 Breast cancer in a family with
  Ashkenazi Jewish heritage
 Unaffected father worried about two
  daughters: 28 and 23 yrs
Information Websites
 National Society for Genetic Counselors
http://www.nsgc.org
 The American Board of Genetic
  Counseling (ABGC)
http://www.abgc.net
 Canadian Association of Genetic
  Counsellors
http://www.cagc-accg.ca
      For more information contact:
              Caroline Lieber
Director of The Joan H. Marks Graduate Program
              in Human Genetics

             Sarah Lawrence College
                  1 Mead Way
              Bronxville, NY 10708
              Tel: 914.395.2371


  http://www.slc.edu/grad_humangenetics.php

				
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posted:9/26/2011
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