Patau syndrome is a genetic disorder in which a persons chromosome thirteen appears three times instead of twice.
Defining Patau Syndrome
Patau syndrome, also referred to as, 'Trisomy 13,' is a form of genetic disorder in which all or a portion of the person's chromosome thirteen appears three times instead of twice in the cells of their body. In some people who are affected by the syndrome, only a percentage of the cells may contain the extra thirteenth chromosome, referred to as, 'mosaicism,' whereas additional cells do contain the average chromosomal pair. The extra material interferes with the person's regular process of development, which leads to severe intellectual disability and physical abnormalities in a number of parts of their body.
A syndrome caused by a chromosomal abnormality, in which some or all of the cells of the body contain extra genetic material from chromosome 13. This can occur either because each cell contains a full extra copy of chromosome 13 (a disorder known as trisomy 13 or trisomy D), or because each cell contains an extra partial copy of the chromosome (i.e., Robertsonian translocation) or because of mosaic Patau syndrome.
Patau syndrome occurs in approximately one out of every ten-thousand to sixteen-thousand infants. The majority of people with Patau syndrome have not inherited it, instead receiving the syndrome as a result of random events during the formation of eggs and sperm in healthy parents. Due to the presence of a number of life-threatening medical issues, many babies with Patau syndrome die in the first few days or weeks of their lives. Five to ten-percent of children with Patau syndrome live past their first year of life.
Babies who are born with Patau syndrome present with a recognizable pattern of physical features which many times permit medical professionals to make a diagnosis of the syndrome. Physical birth defects that are notable and at times, anatomical changes to the baby's internal organs are present. Significant findings include a small head size, referred to as, 'microcephaly,' small eyes or, 'microphthalmia,' and at times, the absence of an eye or a fault in the development of the child's retina. Approximately sixty-percent of children with Patau syndrome present with either a cleft palate or cleft lip. Additional findings can include variations in the child's ear shape, extra toes or fingers, and changes in the palm of the child's hand. Changes may occur in the child's heel or foot development, and they may present with, 'rocker-bottom foot.' Additional names for Patau syndrome include:
Symptoms of Patau Syndrome
People affected by Patau syndrome many times have heart defects, small or poorly developed eyes, spinal cord or brain abnormalities, cleft lip or palate, extra toes or fingers, and decreased muscle tone. Numbers of babies with Patau syndrome do not grow or gain weight at the rate they are expected to, experience difficulties with feeding, as well as episodes where they have a temporary cessation of spontaneous breathing or, 'apnea.' Additional features of Patau syndrome can include:
Approximately eighty-percent of babies with Patau syndrome will experience a congenital heart defect. The forms of heart defects children with this syndrome may experience can include ventricular septal defect, which involves and opening between the lower chambers of their heart and prevents their heart from pumping blood correctly. They may experience atrial septal defect, and opening between the two upper chambers of their heart that makes it difficult for their heart to pump sufficient oxygen-rich blood to their body tissues. 'Patent ductus arteriosis,' is another form of heart defect children with Patua syndrome may experience, it involves a defect where the lack of closure of the channel that usually closes near the time of birth. They may also experience dextrocardia, location of the child's heart on the right side of their chest, or on occasion - more serious heart defects. Common and important birth defects associated with Patau syndrome include:
Common disorders among both infants and young children with Patau syndrome include difficulties with feeding, slow post natal growth, gastroesophageal reflux, seizures, apnea, kidney defects, and hypertension. Infants and children may also experience scoliosis and developmental disabilities.
Causes of Patau Syndrome
Patau syndrome happens when an extra DNA from chromosome thirteen appears in some or all of the cells in a person's body. 'Mosaicism,' is a condition where the presence of an extra chromosome thirteen is present only in some of the person's cells. A, 'partial trisomy,' occurs when the presence of a part of an extra chromosome thirteen exists in the person's cells. The extra materials interferes with the person's normal development. Most people with Patau syndrome have not inherited the syndrome. Events that have lead to the syndrome happened in either the sperm or the egg which formed the fetus.
The majority of people with Patau syndrome have three copies of chromosome thirteen in each cell of their body, instead of the usual two copies. The excess genetic material is disruptive to their course of development, leading to the characteristic features of Patau syndrome. The physical features of people with mosaic Patau syndrome are many times milder than persons with full Patau syndrome.
Diagnosing Patau Syndrome
Infants with Patau syndrome may present with a single umbilical artery at birth. Many times there are signs of congenital heart disease, such as atrial septal defect, abnormal placement of their heart towards the ride side of their chest, ventricular septal defect, or patent ductus arteriosus. Ultrasound or gastrointestinal X-rays might display rotation of the infant's internal organs.
CT or MRI scans of the infant's head can show a problem with the structure of their brain. The problem is referred to as, 'holoprosencephaly,' and involves the joining together of both sides of the infant's brain. Chromosome studies, in addition to these tests, can help to make a definitive diagnosis of Patau syndrome, as well as differentiating between Patau syndrome, mosaicism, and partial Patau syndrome.
Treatment of Patau Syndrome
Treatment of children with Patau syndrome involves planning on a case-by-case basis. The forms of treatment a particular person receives is dependent upon the person's particular condition. Intervention through surgical means are commonly withheld for the first few months of the person's life due to the high mortality rate of children with Patau syndrome. Both parents and health care workers have to weigh decisions concerning extraordinary life-prolonging measures against the severity of the physical and neurological defects the child is experiencing and the likelihood of the child's post-surgical recovery, or prolonged survival.
Patau syndrome involves many abnormalities that are not compatible with life. Greater than eighty-percent of infants with the syndrome do not live past their first month. Complications due to the syndrome start nearly immediately, with many infants experiencing heart disease. Complications of Patau syndrome can include feeding problems, breathing difficulties or lack of breathing, deafness, heart failure, seizures, and vision problems.
Patau syndrome (also known as trisomy 13) is considered the 3rd commonest autosomal trisomy. This along with Down syndrome (T21) and Edward syndrome (T18) are the only three trisomies to be compatible with extra-uterine life. However few infants live more than a few days. The estimated incidence is at ~1:6000. There can be an increased incidence with advanced maternal age.
Most conditions of Patau Syndrome cannot be inherited. During the formation of the sperm or egg, a problem with cell division can cause an extra chromosome 13 in the cells. This is not the fault of the parent, but rather a random occurrence. Another type of Patau Syndrome can be inherited. Translocation trisomy 13 can happen when an unaffected parent carries a rearrangement of genetic material from chromosome 13 and another chromosome and passes this material on to the child.
Note: This extrapolation calculation uses the incidence statistic: 1-in-5000 approximately.