Human%20Genetic%20Disorders

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Human Genetic Disorders
Every cell in the human body has 46 chromosomes
except for gametes, egg sperm cells, which
contain 23 or the haploid number. Human genetic
disorders can result from the inheritance of a
single gene, or an entire chromosome.
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Autosomal disorders
The following diseases are known as autosomal,
because their inheritance is based on a single
gene, dominant or recessive, and is not linked to
the sex of the individual.
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Albinism
Absence of skin pigment, sensitive to light,
need to avoid sunlight 1 in 17,000 in US
Recessive trait Visual impairment Diagnosis
made by blood test
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Cystic Fibrosis
Second most common childhood onset disorder in
US 1 in 3,200 whites, 1 in 14,000 African
Americans Recessive trait Mucus builds up in
respiratory tract Treatment includes antibiotics,
breathing treatments Mothers can be pre-screened
prior to birth. Sweat test used in older
patients Survival rates have risen to average of
33 years of age
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Huntingtons Disease
Autosomal dominant Symptoms develop between 30-50
years of age Lack of concentration, loss of
muscle control, clumsiness No treatment exists,
death is certain 1 in 10,000 Americans Gene
testing done to diagnose May consider genetic
counseling if it runs in the family
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PKU (Phenylketonuria)
Recessive trait Inability to utilize
phenylalanine, an enzyme 1 in 10,000
births Diagnosed at birth with blood test Treated
with diet to avoid phenylalanine Mental
retardation may result without treatment
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Polycystic Kidney Disease
1 in 500,000 in US Dominant trait May live for
decades without symptoms Urinary tract
infections, high blood pressure, kidney stones,
enlarged kidneys Diagnosed by family history and
ultrasound Treatment is dialysis and kidney
transplant
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Tay Sachs
Recessive trait Carried by 1 in 30 Jewish
Americans Fatal disease Healthy at birth, quickly
develop symptoms, nervous system breaks
down Death by age 5
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Sex-linked traits
Sex-linked traits are those that are linked or
occur on the X chromosome. Since females are XX
and males are XY, the male need only inherit one
gene for the trait in order to have the trait.
This is why these disorders are more common in
males and rare in females
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Muscular Dystrophy
Sex-linked, recessive disease More common in
males On set varies Life expectancy varies Causes
muscle weakness, loss of mobility,
speech Diagnosed by blood test Treatment involves
crutches, wheelchairs, orthotics, possibly
surgery Occurs in 1 in 3,500 males
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Color blindness
Sex-linked recessive 1 in 12 men, 1 in 200
women Severity of colorblindness varies No
treatment Diagnosed with color blot tests
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Hemophilia
Sex-linked recessive Results in the lack of
clotting factor in the blood Diagnosed by blood
test, genetic screening Treated by blood
transfusions 1 in 7,500 males 1 in 25,000,000
females!
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Chromsomal Disorders
In some cases, an entire chromosome can be
missing, or there can be an extra chromosome.
These types of disorders usually result in more
severe defects.
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Human Karotyping
Human chromosomal disorders can be diagnosed
through a karyotype. This involves removing
amniotic cells from the mother, taking an x-ray
of the chromosomes, cutting them out an counting
them up. If the number of chromosomes is not 46,
there is a chromosomal defect
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Down Syndrome
Result of an extra 21st chromosome (trisomy 21),
random 1in 700 births Wide range of
symptoms Slower developmental process, some
learning impairment Physical features, shape of
face, eyes Life expectancy 50-60 years
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Edward syndrome
Trisomy 18- extra 18th chromosome, random 50 of
babies die by one week of age Growth deficiency,
feeding and breathing difficulty, mental
retardation Can be detected by amniocentesis No
treatment 1 in 6,000 live births many fetuses
self-terminate
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Sex Chromosomal Disorders
A handful of chromosomal disorders occur
involving the sex chromosomes. Since a normal
female is XX and a normal male is XY, inheriting
an extra sex chromosome, or missing one can have
effects upon the sexual development of individuals
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Turner Syndrome
Occurs when an X chromosome is damaged or missing
(X_) Diagnosed with a karyotype Occurs in 1 of
2,500 females Treatment involves hormone
therapy Females may be of short stature and have
delayed puberty if untreated Random inheritance
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Klinefelter Syndrome
Caused by the inheritance of an extra X
chromosome by a male (XXY) Results in breast
development, sparse facial hair, inability to
produce sperm Occurs in 1 in 1,000 male
births Treatment may include testosterone
injections Diagnosed prior to birth by
amniocentesis Random inheritance
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Trisomy X
Effects females who inherit 3 x chromosomes
(XXX) Occurs 1 in every 1,500 births Many have no
symptoms Diagnosed by amniocentesis May have
infertility, tall stature, increased space
between eyes Random inheritance