|
Diagnosis: Down Syndrome
ISCN: 47,XY,+21
Discussion:
This child presented with many of the common clinical findings of a newborn
child with Down syndrome. Some of the most common clinical findings in
children with Down syndrome include mental retardation, hypotonia, congenital
heart disease, upslanting palpebral fissures, epicanthal folds, iris Brushfield
spots, flat facial profile, protruding tongue, small ears, Simian creases,
brachycephaly, congenital malformations of the GI tract, and short stature.
The majority of patients has hearing loss and is at an increased risk
of early-onset Alzheimer disease and has an increased risk of leukemia.
Down syndrome is seen in about 1/800 livebirths. The majority of cases
of Down syndrome occur because of meiotic nondisjunction during maternal
meiosis I. Most of the Down syndrome conceptions (~80%) abort spontaneously,
however many (~20%) survive to childbirth. The risk of having a child
with Down syndrome increases with maternal age, going from approximately
1/1500 for women between the ages of 15-29 to approximately 1/50 for women
over the age of 45. About 90-95% of patients with Down syndrome have an
extra free copy of chromosome 21 (+21), about 2-4% are mosaic for trisomic
(+21) and normal cell lines, and about 3-5% have a Robertsonian translocation.
The recurrence risk depends upon the maternal age and the mode of inheritance.
As the newborn in this example had an extra free chromosome 21, resulting
from nondisjunction, karyotyping of the parents is not indicated. Genetic
counseling of the parents would be recommended to explain the cause of
this infant's chromosomal abnormality and the recurrence risk for future
preganancies.
Web Links:
Additional information can be obtained at the Online Mendelian Inheritance
in Man (OMIM) web site and/or the National
Down Syndrome Society's web site.
Metaphase/
Karyotype/ Answer/
Discussion/ Case Studies/ Home
Page
|
