The Patau syndrome, or trisomy 13, is a rare chromosome abnormality caused by an extra copy of segments or the entire chromosome 13 in the cells.
There are three different types of trisomy 13. In the first type, an extra copy of the entire chromosome is present in every cell of the body. The second type is mosaicism: the third copy of the chromosome occurs only in some cells of the body. The third type is partial trisomy: in this case only some segments of chromosome 13 are present in three copies, not the entire chromosome. In rare cases, the extra chromosome or segment is attached to another chromosome (called translocation in the literature). The normal development of the fetus is disturbed by the amount of extra DNA.
Incidence of the Patau syndrome
Fortunately, it is a rare disease, much rarer than Down syndrome. While the latter one occurs in 1 in 700 newborns on the average, according to international literature data, the average incidence of Patau syndrome is 1 in 10,000 newborns. However, it is usually a much more severe disease than the Down syndrome: over 80% of the children with Patau syndrome die during the first month of life.
In most cases, the Patau syndrome is not hereditary. Trisomy 13 is caused by changes in the ovum or sperm, which will form the fetus.
Symptoms of the Patau syndrome
If only a segment of chromosome 13 is duplicated (partial trisomy), the variety and severity of the symptoms depends on the place on the chromosome where the changes occurred. In the case of mosaicism, that is, cases where not all, but only some cells of the body have an extra chromosome, the severity of the symptoms is influenced by the percentage proportion of cells in which this abnormality occurs.
One of the typical symptoms of the Patau syndrome is cleft palate. Extra fingers or toes may also be present, most commonly a single tiny extra finger. The disease may be associated with fusion of fingers or toes: this symptom is most commonly seen with the second and third toes.
The eyes of the newborn are closer than normal, and in some cases, they may be connected (their size is also smaller than normal). The ears are also lower than in the case of a normal newborn. Some portions of the scalp may be missing, and microcephaly may occur. In most cases, the disease is associated with severe mental retardation.
Muscle tone is usually poorer than normal and tremors may also occur. Cryptorchidism may often be present, that is, the testicles do not drop into the scrotum, and remain in the abdominal cavity.
The development of some parts of the children’s brain (especially the forebrain), their kidneys and heart may be severely hindered. The most important hereditary cardiac abnormality is the underdevelopment of the tissue separating the heart chambers from each other. This condition may affect both the ventricles and the atria. A part of the aorta, which delivers oxygen-rich blood to the body, remains open. The same thing may occur with the pulmonary artery.
Many children with Patau syndrome will not grow sufficiently and will not gain in weight in the normal pace. Severe feeding problems may occur. Breathing may temporarily stop (apnea). In most cases, life-threatening complications will occur as early as newborn age or early childhood.