Transcript Chromosomal Anomalies

Categories of Factors Responsible for
Birth Defects
Abnormalities of Individual Genes
(Single Gene Defects)
Chromosomal Abnormalities
Intrauterine Injury
Multifactorial Circumstances
Chromosomal Abnormalities
Trisomy 21
Turner Syndrome
Klinefelter’s Syndrome
Chromosomal Anomalies
Result from abnormal karyotypes (physical
arrangement of chromosomes) resulting from:
Non-disjunction - occurred during meiotic
division resulting in aneuploidy or too many
chromosomes
Deletion - loss of genetic material
Translocation - relocation of a chromosome
strand on some non-homologous chromosome
Trisomy 21- Downs Syndrome
Epidemiology
1/800-1, 000 live births.
In the United States over 350,000 people have Down syndrome
At least 20 percent will be stillborn.
6-10% of all mental retardation in the U.S.
Trisomy 21- Downs Syndrome
Syndrome
Structural- facial abnormalities, floppy joints,
small stature, CV defects
Functional- Immune defects, varying degrees
of mental retardation
Trisomy 21- Downs Syndrome
RELATIONSHIP OF DOWN SYNDROME INCIDENCE TO
MOTHERS' AGE
Mothers Age
Incidence of Down Syndrome
Under 30
Less than 1 in 1,000
30
1 in 900
35
1 in 400
36
1 in 300
37
1 in 230
38
1 in 180
39
1 in 135
40
1 in 105
42
1 in 60
44
1 in 35
46
1 in 20
48
1 in 16
49
1 in 12
Trisomy 21- Downs Syndrome
Anomalies of the Sex Chromosomes
Failure of the X chromosome to separate
during meiosis
Very Common
May be asymptomatic
Wrong number of sex chromosomes
Anomalies of the Sex
Chromosomes
Most Common Possibilities:
Mom
XX
Dad
O
X
XXX
XO
Y
XXY
YO
Turner’s Syndrome XO
Syndrome:
* Morphologically female, but no functional ovaries.
Structural- Short stature, shield chest, growth delay,
prominent ears, increase risk for CVD, diabetes,
infections
Functional- carrying degrees of mental retardation,
may be very mild and imperceptible
Epidemiology: 1/2,000 live births
Treatment: Estrogen therapy, psychosocial
counseling
Klinefelter’s Syndrome XXY
Epidemiology: 1/500-1/2000 live births
Syndrome: morphologically male relatively normal
secondary sex characteristicsoften sterile due to lack
of development of germ cells in the testes
Structural- tall for age, narrow shoulders, broad
hips
Functional- intelligence is usually normal but
some developmental delays
Categories of Factors Responsible for
Birth Defects
Abnormalities of Individual Genes
(Single Gene Defects)
Chromosomal Abnormalities
Intrauterine Injury
Multifactorial Circumstances
Intrauterine Injury
Congenital abnormalities result from exposure to
teratogenic substances.
Teratogens take many forms- drugs, infectious
agents, trauma.
Generally the degree of damage is a function
of two things:
1. The amount exposure
2. The time of exposure related to gestational
age
Fetal Alcohol Syndrome
* Leading cause of preventable birth defects in
this country
Epidemiology: 3.5 per 10,000 live births
Syndrome:
Structural- Facial dismorphology, low ear set, broad
mid-facial region, narrow eye slits, microcephaly,
CV defects, postnatal growth deficiency
Functional- Attention deficits, varying degrees of
mental retardation and language deficits
Tobacco
Currently, about 13 percent of pregnant women in
the U.S. smoke during pregnancy.
In 1998, 12 percent of babies born to smokers in the
U.S. were of low birth weight, compared to 7.2
percent of babies of nonsmokers.
Studies by the American Academy of Pediatrics
(AAP) also suggest that smoking increases the risk
of preterm delivery by about 30 percent.
Cocaine
•Prematurity
•Lower birth weight, shorter
•Smaller head circumference
•A piercing cry, which is apparently indicative of
neurological dysfunction
•Lower Apgar score
•Irritability and hypersensitivity. The newborn shoots from
sleep to screaming and is inconsolable.
•Poor feeding
•High respiratory and heart rates
•Tremulousness
•Startling responses
•Poor sleep patterns
Isotretinoin (Accutane)
Accutane: a type of retinoic acid that is orally administered and
used in the treatment of acne and several other skin diseases.
Causes:
Increased risk of Spontaneous abortion
CV defects
Parathyroid hormone deficiency
CNS abnormalities including cerebral abnormalities,
cerebellar malformation, hydrocephalus, microcephaly,
cranial nerve
deficit
Rubella Syndrome
Syndrome:
Caused by the Rubella Virus
Occurs as a result of fetal viremia creating inflammation in
the arteries
Limits O2 supply to developing tissues.
Results:
Problematic if contracted during pregnancy
1st month - 50%, 1st trimester - 25%, 3rd trimester - 8%
There is a 20% chance of mortality within the first 18 months
of life
Causes:
Hearing loss, learning disabilities, growth retardation, heart
defects
Categories of Factors Responsible for
Birth Defects
Abnormalities of Individual Genes
(Single Gene Defects)
Chromosomal Abnormalities
Intrauterine Injury
Multifactorial Circumstances
Multifactorial Disorders
Abnormalities that reflect the combined effects
of multiple genes interacting with
environmental agents.
Spina Bifida- Failure of the spinal column
to close around the spinal cord
The amount left unclosed and the location
(high or low) determines the risk or
problems.
Other examples- cleft palate and club feet
Multifactorial Disorders
In general, the three types of spina bifida (from mild to severe)
are:
1. Spina Bifida Occulta: There is an opening in one or more
of the vertebrae (bones) of the spinal column without
apparent damage to the spinal cord.
2. Meningocele: The meninges, or protective covering
around the spinal cord, has pushed out through the opening
in the vertebrae in a sac called the "meningocele." However,
the spinal cord remains intact. This form can be repaired
with little or no damage to the nerve pathways.
3. Myelomeningocele: This is the most severe form of spina
bifida, in which a portion of the spinal cord itself protrudes
through the back. In some cases, sacs are covered with skin;
in others, tissue and nerves are exposed. Generally, people
use the terms "spina bifida" and "myelomeningocele"
interchangeably.
Multifactorial Disorders
cleft palate
A cleft palate is an opening in the roof of the mouth in
which the two sides of the palate did not fuse, or join
together, as the unborn baby was developing.
One of every 600 newborns is affected by cleft palate.
A child born with a cleft frequently requires several
different types of services, e.g., surgery,
dental/orthodontic care, and speech therapy, all of
which need to be provided in a coordinated manner
over a period of years.