Causes of Down Syndrome
Down Syndrome Causes: Book Excerpts
Down Syndrome as a symptom:
Conditions listing Down Syndrome
as a symptom may also be potential underlying causes of Down Syndrome.
Our database lists the following as having
Down Syndrome as a symptom of that condition:
Related information on causes of Down Syndrome:
As with all medical conditions,
there may be many causal factors.
Further relevant information on causes of Down Syndrome may be found in:
Causes of Down Syndrome: Online Medical Books
16 MEDICAL BOOKS ONLINE!
Review excerpts from medical books online, free, without registration,
for more information about the causes of Down Syndrome.
Trisomy 13 syndrome:
Causes and incidence
(Professional Guide to Diseases (Eighth Edition))
Approximately 75% of all cases of trisomy 13 syndrome are caused by chromosomal nondisjunction. About 20% are due to chromosomal translocation involving a rearrangement of chromosomes 13 and 14. About 5% are estimated to be mosaics; the clinical effects in these cases may be less severe.
Incidence is estimated to be 1 in every 5,000 neonates. The risk of chromosomal abnormalities typically increases with advanced maternal age; however, the mean maternal age for this abnormality is about 31 years.
» READ BOOK EXCERPT ONLINE »
Source: Professional Guide to Diseases (Eighth Edition), 2005
Down syndrome:
Causes and incidence
(Professional Guide to Diseases (Eighth Edition))
Down syndrome usually results from trisomy 21, a spontaneous chromosomal abnormality in which chromosome 21 has three copies instead of the normal two because of faulty meiosis (nondisjunction) of the ovum or, sometimes, the sperm. This results in a karyotype of 47 chromosomes instead of the normal 46. In about 4% of patients, Down syndrome results from an unbalanced translocation in which the long arm of chromosome 21 breaks and attaches to another chromosome. Most commonly, this is a robertsonian translocation and results in an increased risk of having multiple children with Down syndrome. The disorder may also be due to chromosomal mosaicism with two cell lines — one with a normal number of chromosomes (46) and one with 47 (an extra chromosome 21).
Down syndrome occurs in 1 in 660 live births, but the incidence increases with advanced parental age, especially when the mother is age 34 or older at delivery or the father is older than age 42. At age 20, a woman has about one chance in 2,000 of having a child with Down syndrome; by age 49, she has one chance in 12. However, if a woman has had one child with Down syndrome, the risk of recurrence is 1% to 2% unless the trisomy results from translocation.
» READ BOOK EXCERPT ONLINE »
Source: Professional Guide to Diseases (Eighth Edition), 2005
Trisomy 18 syndrome:
Causes and incidence
(Professional Guide to Diseases (Eighth Edition))
Most cases of trisomy 18 syndrome are caused by spontaneous meiotic nondisjunction. The risk of chromosomal abnormalities typically increases with maternal age; however, the mean maternal age for this disorder is 32½. Incidence is 1 in 3,000 neonates, with females three times more likely to be affected than males.
» READ BOOK EXCERPT ONLINE »
Source: Professional Guide to Diseases (Eighth Edition), 2005
Down syndrome:
Causes
(Handbook of Diseases)
Down syndrome usually results from trisomy 21, a spontaneous chromosomal abnormality in which chromosome 21 has three copies instead of the normal two because of faulty meiosis (nondisjunction) of the ovum or, sometimes, the sperm. This results in a karyotype of 47 chromosomes instead of the normal 46. In about 4% of patients, Down syndrome results from an unbalanced translocation (chromosomal rearrangement) in which the long arm of chromosome 21 breaks and attaches to another chromosome. The disorder may also be due to chromosomal mosaicism, a mixture of two cell types — one with a normal number of chromosomes (46) and some with 47 (an extra chromosome 21).
Down syndrome occurs in 1 in 650 to 700 live births, but the prevalence increases with advanced parental age, especially when the mother is age 34 or older at delivery or the father is older than age 42. At age 20, a woman has about 1 chance in 400 of having a child with Down syndrome; by age 49, she has 1 chance in 12. If a woman has had one child with Down syndrome, the risk of recurrence is 1% to 2%. This risk varies according to the type of translocation the parents carry, and genetic counseling should be discussed.
» READ BOOK EXCERPT ONLINE »
Source: Handbook of Diseases, 2003
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