These problems are all caused by an extra chromosome, specifically an
extra copy of chromosome number 13. Chromosomes, which normally come in pairs (one in each pair from the mother, and one from
the father), are the packages of genetic material which give the baby instructions for growth and development. The extra genetic
material that the baby receives interferes with these instructions. The extra chromosome was present in either the sperm or
the egg which went to form the baby, and this mistake occurred either prior to or just at conception. Many parents wonder
why Trisomy 13 occurred, but we know of nothing that either parent could have done that would have caused or prevented this
written by Karen Taylor-Good
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Trisomy 13 Facts
Infants affected with Trisomy 13 tend to be small at birth. Spells of interrupted breathing (apnea) in early infancy
are frequent, and mental retardation is usually severe. Many affected children appear to be deaf. A moderately
small head (microcephaly) with sloping forehead, wide joints and openings between parietal bones of the head are present.
Gross anatomic defects of the brain, especially failure of the forebrain to divide properly (holoprosencephaly) are common.
A hernial protrusion of the cord and its meninges through a defect in the vertebral canal (myelomeningocele) is found in almost
50% of cases.
The entire eye is usually small (microphthalmia),
and a defect of the iris tissue (coloboma), and faulty development of the retina (retinal dysplasia) occur frequently.
The supraorbital ridges are shallow and palapebral fissures are usually slanted. Cleft lip, cleft palate, or both are
present in most cases. The ears are abnormally shaped and unusually low-set.
A single transverse crease on
the palm, extra fingers and toes (polydactyly) and hyperconvex, narrow fingernails are common. The fingers tend to flexed,
but not in the same manner seen in Trisomy 18 Syndrome. The feet show posterior prominence of the heel, and there may
be a rocker-bottom foot.
Approximately 80% of cases show the following additional congenital anomalies.
Ventricular Septal Defect - A hole between the lower chambers of the heart which prevents the
heart from pumping blood correctly; a heart murmur is generally heard with this congenital defect.
Atrial Septal Defect - A hole between the two upper chambers of the heart which makes it difficult
for the heart to pump sufficient oxygen-rich blood to the body's tissues; a heart murmur can be heard.
Patent Ductus Arteriosus - A congenital heart defect in which closure of a duct fails to occur,
resulting in abnormal direction of blood flow.
Dextrocardia - Location of the heart in the right side of the chest.
Tumors made up of newly formed
capillary blood vessels (capillary hemangiomes) especially on the forehead in the midline, may also be present. Other
midline defects include dermal sinuses on the scalp and loose folds of skin over the back of the neck.
The genitalias are frequently abnormal in both sexes. Failure of the testes to descend into the scrotum
(cryptorchidism) and abnormally developed scrotum may occur in males. A uterus with horn-shaped branches (bicornuate)
sometimes occurs in females.
Hemotologically, there is an increased
frequency of nuclear projection in polymorphonuclear leukocytes and a persistence of fetal hemoglobin.