What Do We Know Now?
Trisomy 13 syndrome (Patau syndrome) is a disorder of human chromosomes which occurs in approximately 1 in 10,000-25,000 live-born infants. Trisomy refers to three copies of a chromosome instead of the normal two and in Trisomy 13 there is the presence of an extra #13 chromosome. Approximately 80% of infants with Trisomy 13 syndrome will have a full trisomy (affecting all cells) while the remainder will have a trisomy due to a rearrangement of cells called a translocation (an attachment of all or part of one chromosome to another chromosome) or have mosaicism (two different cell lines in an individual).
Most often a diagnosis of Trisomy 13 is suspected by findings seen on fetal ultrasound, or screening by maternal blood tests. Optional invasive testing, amniocentesis or chorionic villus sampling, is needed to confirm a diagnosis but carry a small risk to the fetus. A prenatal diagnosis of Trisomy 13, before 24 weeks, is often followed with an option to terminate; a decision made by 75% in the USA and 90% in Europe. A diagnosis can affect the care provided to those continuing pregnancy, their birthing options, and the care of a liveborn infant.
Infants born with Trisomy 13 have a recognizable pattern of physical features that often allows the health professional to make the diagnosis of the syndrome. Notable physical birth defects and, sometimes, anatomic changes of internal organs are present. Findings of significance include small head size (microcephaly); small eyes (microphthalmia) or sometimes an absent eye or faulty development of the retina; and failure of the forebrain to divide properly (holoprosencephaly). Cleft lip or cleft palate or both occur in about 60% of children and heart defects as described in the next paragraph. In addition, there are a number of less medically significant physical findings that are helpful in diagnosis. These include variations of ear shape, changes on the palm of the hand, and extra fingers and toes. Changes in foot development, including changes to the heel, the so-called rocker bottom foot, can occur.
Common Birth Defects seen in Trisomy 13
- Omphalocele 10%
- Holoprosencephaly 60% (an anatomic defect of the brain involving failure of the forebrain to divide properly)
- Kidney defects 30%
- Skin defects of the scalp 20%
- Cleft lip and or palate or both 60%
- Ocular (eye) abnormalities >50% such as small or absent eyes