Content uploaded by Hayk S. Arakelyan
Author content
All content in this area was uploaded by Hayk S. Arakelyan on Aug 27, 2019
Content may be subject to copyright.
Trisomy 13 and Chromosomes.
Authors.
Prof. Hayk S. Arakelyan. Full Professor in Medicine,
Doctor of Medical Sciences, Ph.D , Grand Ph.D .
Senior Expert of Interactive Clinical Pharmacology , Drug Safety,
Treatment Tactics, General Medicine and Clinical Research.
Armenia, Yerevan State Medical University
Johnner Tan
Managing Director of Map My Gene LLC
Singapore
Hsiu-Hsien Tsai
Medical school, Taipei Medical University
Changhua County, Taiwan
“Every human being is the author of his own health or disease.”
“Buddha”
Introduction.
Trisomy 13 is a type of chromosome disorder characterized by having 3 copies
of chromosome 13 in cells of the body, instead of the usual 2 copies. In some
affected people, only a portion of cells contains the extra chromosome 13
(called mosaic trisomy 13), whereas other cells contain the normal chromosome
pair.
Other Names:
Patau syndrome; Chromosome 13, trisomy 13 complete; Complete trisomy 13
syndrome; D trisomy syndrome (formerly) .
Causes of Trisomy 13.
Most cases of trisomy 13 are caused by random events during the formation of
eggs or sperm in healthy parents (prior to conception). Trisomy 13 is typically due
to having three full copies of chromosome 13 in each cell in the body, instead of
the usual two copies. This is referred to as complete trisomy 13 or full trisomy 13.
The extra genetic materialpresent disrupts the normal course of development,
causing the characteristic features of the disorder. Trisomy 13 can also occur when
part of chromosome 13 becomes attached (translocated) to another chromosome
during the formation of eggs or sperm, or very early in fetal development. This is
referred to as translocation trisomy 13. People with this type of trisomy 13 have
the normal two normal copies of chromosome 13, plus an extra copy of
chromosome 13 that is attached to another chromosome. Translocation trisomy 13
can be inherited. Approximately 20% of cases of trisomy 13 are caused by
translocation trisomy 13. In rare cases, only part of chromosome 13 is present in
three copies in each cell (rather than the full chromosome); this is called partial
trisomy 13. In other rare cases, a person has an extra copy of chromosome 13 in
only some of the body's cells; this is called mosaic trisomy 13. The severity of
mosaic trisomy 13 depends on the type and proportion of cells that have the extra
chromosome. Most cases of Patau syndrome are not inherited, but occur as random
events during the formation of reproductive cells (eggs and sperm). An error in cell
division called non-disjunction can result in reproductive cells with an abnormal
number of chromosomes. For example, an egg or sperm cell may gain an extra
copy of the chromosome. If one of these atypical reproductive cells contributes to
the genetic makeup of a child, the child will have an extra chromosome 13 in each
of the body's cells. Mosaic Patau syndrome is also not inherited. It occurs as a
random error during cell division early in fetal development.
Signs and symptoms of Trisomy 13.
Trisomy 13 is associated with severe intellectual disability and physical
abnormalities in many parts of the body. People with this condition often
have congenital heart defects, brain or spinal cord abnormalities, very small
or poorly developed eyes (microphthalmia), extra fingers and/or toes
(polydactyly), cleft lip or palate, and decreased muscle tone (hypotonia). Many
infants with trisomy 13 fail to grow and gain weight at the expected rate
(failure to thrive); have severe feeding difficulties; and episodes in which there
is temporary cessation of spontaneous breathing (apnea). Other features or
trisomy 13 may include:
Clenched hands (with outer fingers on top of the inner fingers),Close-set eyes,
Hernias: umbilical hernia, inguinal hernia,A hole, split, or cleft in the iris of
the eye (coloboma), Low-set ears, Scalp defects such as missing skin, Seizures,
Single palmar crease, Skeletal (limb) abnormalities,Small head
(microcephaly), Small lower jaw (micrognathia), Undescended testicle
(cryptorchidism).
Diagnosis of Trisomy 13.
While most cases of trisomy 13 occur randomly, a few cases are due to the
presence of a translocation involving chromosome 13 in a parent. Parents who are
at risk to have a translocation due to their family history can have a blood test
called a karyotype, which can determine if a translocation is present. Prenatal
testing or screening (such as maternal blood screening, fetal
ultrasound, chorionic villus sampling, or amniocentesis) is also available to
determine if a current pregnancy is at risk for, or is affected by, trisomy 13 or
other chromosome disorders.
People with a family history of trisomy 13 who are interested in learning
about genetic screening or testing for themselves or family members are
encouraged speak with a genetic counselor or other genetics professional.
Diagnosis is usually based on clinical findings, although fetal chromosome
testing will show trisomy 13. While many of the physical findings are similar to
Edwards syndrome there are a few unique traits, such as polydactyly. However,
unlike Edwards syndrome and Down syndrome, the quad screen does not provide a
reliable means of screening for this disorder. This is due to the variability of the
results seen in fetuses with Patau.
If you have any questions concerning ’Trisomy 13 and
Chromosomes. ’,interactive clinical pharmacology , or any other questions, please
inform us.
Prof. Hayk S. Arakelyan
Johnner Tan
Managing Director of Map My Gene LLC
Hsiu-Hsien Tsai
Medical school, Taipei Medical University
Changhua County, Taiwan