Trisomy 13 Syndrome (Patau Syndrome)

What is Trisomy 13 Syndrome?
Trisomy 13 syndrome, also known as Patau Syndrome is a very rare and the most severe of the possible autosomal trisomies. Most of the cases have seen survival for not more than 3 days. Initially In 1960, it was identified as a Cytogenetic Syndrome. The cause of Patau syndrome is abnormal presence of an extra copy of chromosome 13, acrocentric chromosome of a medium-length. The extra chromosome 13 disturbs the normal course of development, causing the characteristic features of Patau syndrome.

Chronic mental deficiency is a regular characteristic found in children born with Patau Syndrome although; many of the clinical features are highly variable. Polydactyly, Holoprosencephaly, flexion of the fingers, facial clefting, rocker-bottom feet, and heart defects also are frequent clinical symptoms. Patau syndrome is generally diagnosed at the time of birth by the presence of structural birth defects and poor neurological performance. The probability ratio is around 1:5000 in live births.

Physiology and Pathology
The main cause of the most cases of Patau syndrome is trisomy 13. In this case, each cell in the body has three copies of chromosome 13 instead of the usual pair. There is also a small probability when only some of the body's cells have an extra copy of chromosome 13, which leads to a mixed group of cells with a differing number of chromosomes; such cases are known as Mosaic Patau.

Also, when part of chromosome 13 translocated to another chromosome before or at the time of conception, then Patau syndrome can occur. The persons suffering Trisomy 13 syndrome have two copies of chromosome 13, plus extra material from chromosome 13 attached to another chromosome. With a translocation, the person is considered to have a partial trisomy for chromosome 15. The physical symptoms of the syndrome vary from the typical one in such cases.

Generally, it has been observed that, most cases of Patau syndrome are not related with inheritance parameter, but usually occur as random events during the process of formation of reproductive cells like ova and sperms. During the stage of cell division, an error occurs called as non-disjunction results in production of reproductive cells carrying an additional number of chromosomes. For example, an ova or sperm cell may get an extra chromosome attached to the original pair of chromosome 13. If any of these abnormal reproductive cells play a role in the genetic makeup of a fetus then the child will carry an extra number of chromosomes 13 in each of its body cells.

Other cases like of Mosaic Patau syndrome is also not related with inheritance. As mentioned earlier, it occurs as a random error during cell division early in fetal development. As a result, some of the body's cells have the usual two copies of chromosome 13, and other cells have three copies of the chromosome.

But, Patau syndrome due to a translocation can be a typical case of inheritance. People who carry this type of balanced translocation previously are at great risk of having their children born with this condition.

In fact, trisomy 13 is the biggest sustained autosomal imbalance by the embryo. Complex physiologic structures found in the Central Nervous System and heart, are particularly sensitive to this chromosomal imbalance.

Prognosis
Average survival period for children with Patau syndrome is 2.5 days, with a possibility of only 1 child out of 20 surviving more than 6 months. Reports of adults with Patau syndrome are rare.

Holoprosencephaly, a brain malformation associated with Patau syndrome, is characterized by chronic neurological impairment, and disruption of the development of structural features of the mid face. It is also found associated with cardiac anomalies. Studies have shown that deaths occur due to cardiopulmonary arrest (70%), congenital heart disease (13%), and pneumonia (4%). Survivors experience severe mental retardation and developmental delays. They are highly exposed to risk for malignancy.

Symptoms
Newborns with Patau syndrome typically present in the neonatal period with low Apgar scores and may have the symptoms like Polydactyly (postaxial), Cleft lip, Cleft palate, Microcephaly, Microphthalmia, Rocker-bottom feet, Scalp defects (cutis aplasia) Hernias.

Physical symptoms include Cardiac defects occur in 80% of cases, accompanied by the conditions like Patent ductus arteriosus, Dextrocardia, Ventricular septal defect, Atrial septal defect. Holoprosencephaly, in which the brain is not divided into halves, is often present and is generally signaled by the presence of midline facial defects like Hypotelorism, Anophthalmia, and Microphthalmia, Absent or malformed nose or proboscis, severe clefting of the lip and/or palate. Also symptoms like Capillary hemangiomata, polycystic kidneys or other renal malformations are found

Diagnosis
1. Gastrointestinal x-rays or ultrasound can reveal abnormal rotation of the internal organs.
2. MRI or CT scans of the head may reveal Holoprosencephaly, where the 2 cerebral hemispheres are fused.
3. Chromosome studies show trisomy or translocation

Treatment
Surgical treatments are generally suspended for the first few months of life because of the high mortality rates of babies associated with Patau syndrome. Physicians have to carefully judge about extraordinary life-prolonging measures against the severity of the neurological and physical defects that are present and the likelihood of post surgical recovery or prolonged survival.