Transcript Human Genetic Disorders

Human Genetic Disorders
Biology
Genetic Testing

Amniocentesis and Chronic Villi Sampling
 Sample

of amniotic fluid or placenta
Karyotyping
 Taking
a picture of the chromosomes in a cell
What Can Go Wrong?

Nondisjunction (most deadly)
 Improper
separation of homologous
chromosomes in meiosis I or chromatids in
mieosis II or mitosis (at an early embryonic
stage)
 Results in too many or too few chromosomes
in daughter cells

DNA mutations
 More
specific letter-changes in code
 Results in the inability to make certain proteins
Nondisjunction Causes:

Aneuploidy: cells that have too many or
too few chromosomes are aneuploid.
 Monosomy:
only 1 of a pair present
 Trisomy: 3 instead of 2 present
Incidence of Genetic Abnormalities

Maternal Age
 At
25 years, 17% of eggs may have
chromosomal abnormalities. At 40 years, up
to 74% may contain abnormalities.

Spontaneous Abortion (Miscarriage)
 Two-thirds
of all pregnancies are lost. These
miscarriages are called spontaneous
abortions.
 Genetic mutation causes an estimated 60% of
these spontaneous abortions.
Family Pedigrees
Down Syndrome
Caused by Trisomy 21
 Symptoms:

 Mental
retardation
 Flattened face
 Sparse, straight hair
 Short stature
 High risk of cardiac anomalies, leukemia,
cataracts, and digestive blockages
 Average life expectancy: 55 years (much
longer than it used to be even just recently)
Edward Syndrome
Caused by Trisomy 18
 Symptoms:

 Mental
and physical retardation
 Skull and facial abnormalities
 Defects in all organ systems
 Poor muscle tone
 Average life expectancy: 2-4 months
Patau Syndrome
Caused by Trisomy 13
 Symptoms:

 Mental
and physical retardation
 Skull and facial abnormalities
 Defects in all organ systems
 Cleft lip & large triangular nose
 Extra digits
 Average life expectancy: 6 months (but ½ die
in the first month)
Sex Chromosome Abnormalities

Turners Syndrome (X0 - female)
1
in 2000
 Infertile, sexually underdeveloped, short
stature, narrow aorta, normal intelligence

Klinefelter Syndrome (XXY - male)
1
in 1000
 Reduced sexual maturity, secondary sexual
characteristics (breast swelling), no sperm
production
Sex Chromosome Abnormalities

Triple X Syndrome (XXX – female)
1
in 1500
 Slight IQ reduction, menstrual irregularities

Jacob Syndrome (XYY – male)
 Incidence
unknown (lack of diagnosis)
 Tall, acne issues, speech/reading problems
 Disproportionate number incarcerated
 96% are normal (most don’t realize they have
this condition)
DNA Mutations

Cri du Chat Syndrome (cry of the cat)
 Deletion

on part of chromosome 5
Fragile X
 Repeated
sequences of CCG on X
chromosome
 Normal = 6-50 copies
 Carrier (males) = 50-230 copies
 Disorder = more than 230 copies
 Causes mental retardation (2nd behind only
Down Syndrome)
Autosomal Recessive Disorders

Cystic Fibrosis (CF)
 Mutation
on chromosome 7
 Thick mucous develops in lungs and digestive
tract
 Difficulty breathing & lung infections
 Most common lethal genetic disorder
 1 in 25 is a carrier
 1 in 2500 has disorder
More Autosomal Recessive

Tay Sachs Disease
 Fatty
substance builds up in neurons
 Gradual paralysis and loss of nervous function
by age 4-5
 Single defective enzyme
 Heterozygote carriers (Hh) do not have
disorder, but are resistant to Tuberculosis
 Especially common in Jewish population
(central and eastern European descent), up to
11% are carriers
More Autosomal Recessive

PKU (Phenylketonuria)
 Can’t
break down amino acid phenylalanine
(missing critical enzyme)
 Phenylalanine builds up and interferes with
nervous system leading to mental retardation
and even death
 Early screening  phenylalanine restricted
diet for children with disorder
More Autosomal Recessive

Sickle-Cell Anemia
 Abnormality
in hemoglobin (carries oxygen in
our red blood cells)
 Cells become sickle-shaped and clog blood
vessels (painful)
 Causes poor circulation, jaundice, anemia,
and hemorrhaging
 Heterozygote carriers (Hh) do not have
disorder and are resistant to malaria
 8-10% of Africans (or descendants) are
carriers
Sickle-Cell Anemia Photo
Autosomal Dominant Disorders

Neurofibromatosis (NF)
 Could
be “Elephant Man’s” disorder
 As mild as tan spots on skin
 Could cause severe deformities, tumors, even
death
 1 in 3000 newborns
 Mutation on chromosome 17
Autosomal Dominant Disorders

Huntington’s Disease
 Brain
cells degenerate, causing involuntary
muscle jerks, slurred speach, loss of balance,
mood swings, memory loss, incapacitation
 Progressive: eventually causes death
 Onset: 35-45 years old
 Repeated sequences of AGC on chromosome 4
 Diagnostic test available, but no cure
 Would you want to know?
X-Linked or Sex-Linked Traits
Traits located on X Chromosome
 Males have them more often than females

 They
only have one X chromosome
X-Linked or Sex-Linked Traits

Colorblindness (3 types – Red/Green most
common)
X-Linked or Sex-Linked Traits

Hemophilia
1
in 1500 males
 Lack a blood clotting factor
 Can bleed to death from wounds or bruises
(internal bleeding)

Duchenne Muscular Dystrophy
1
in 5000 males
 Muscular deterioration starts 3-5 years old
 Wheelchair by 12, rarely survive past 20