Patau syndrome: trisomy 13

Sometimes, even the smallest modifications in genetic code can have serious consequences on human health. One of these anomalies is Patau syndrome (trisomy 13), which manifests before birth and is characterized by severe clinical progression.

What is Patau syndrome?

Patau syndrome is a rare genetic anomaly that occurs when an extra copy of chromosome 13 appears in every cell of the organism. Instead of two copies, there are three. Normally, humans have 46 chromosomes (22 pairs of autosomes and one pair of sex chromosomes), but in the case of trisomy 13, the total number increases to 47.

There are different forms of trisomy 13:

• Complete form: each cell contains an extra chromosome 13.
• Mosaic form: only a portion of the cells contain the trisomy, while the others have a normal number.
• Translocation form: the extra genetic material from chromosome 13 is attached to another chromosome.

The extra chromosome typically arises from errors during the division of sex cells (egg or sperm). As a result, the gamete receives an additional chromosome and transmits it to the embryo.

According to clinical observations, Patau syndrome is more frequent in the case of natural conception than in the case of in vitro fertilization (IVF). This can be explained by the possibility of performing preimplantation genetic testing (PGT-A) as part of an IVF procedure, which allows for the exclusion of embryos with chromosomal abnormalities before their transfer into the uterine cavity.

The disease was first described in 1960 by American geneticist Klaus Patau. His work established a direct link between severe congenital malformations and the presence of an extra chromosome 13.

Differences between trisomy 13 and other chromosomal anomalies

Patau syndrome: Chromosome 13 Appearance frequency: 1 in 7,000–14,000 Common severe malformations: microphthalmia, heart, brain, and kidney malformations frequent and severe, unfavorable prognosis

Edwards syndrome: chromosome 18, appearance frequency 1 in 6,000 Micrognathia, low-set ears, heart malformation, digestive tract malformations, intellectual disabilities, life expectancy up to 1 year

Down syndrome: chromosome 21, frequency 1 in 700–1,000 flat face, narrow eye openings, heart, thyroid malformations, possible learning, life expectancy often into adulthood

Main symptoms of Patau syndrome

• Heart malformations — congenital anomalies in the structure of the heart that prevent normal blood circulation.
• Phenotypic signs: cleft eyes, cleft lips and palates, abnormal ear structure.
• CNS lesions: fusion of brain hemispheres, microcephaly, seizures, poor response to stimuli.
• Skeletal anomalies: polydactyly, dislocations, limb deformities, hernias.
• Gastrointestinal and internal organ disorders: including the absence of communication between the esophagus and stomach.
• Genitourinary system anomalies: congenital pathologies in boys and girls.

In the mosaic form, symptoms are less pronounced, and the child may survive longer while retaining some functions.

Causes of Patau syndrome

Genetic factors

The primary cause is an accidental mutation during meiosis or mitosis, leading to the formation of gametes with an extra chromosome 13. Most cases are not hereditary but occur spontaneously.

Mother's age and risks

With age (especially after 35), the risk of chromosomal abnormalities increases. In rare cases, parents may have a balanced translocation that causes no symptoms in them but increases the risk of passing the pathology to the child.

How to detect trisomy 13?

Prenatal diagnosis and screening before birth

Prenatal diagnostic methods allow the assessment of the probability of trisomy 13 during pregnancy. One of the first steps is biochemical screening, which involves analyzing hormone and specific protein levels in the woman's blood. These markers can indicate the presence of chromosomal abnormalities in the fetus.

It is also important to perform an ultrasound during the first and second trimesters. It allows for the detection of characteristic anatomical anomalies: disorders of brain development, heart malformations, shortening of the limbs. At an early stage, cleft lips and palates may be invisible, but they are easier to detect at a later stage.

Modern technologies allow for a non-invasive prenatal test (NIPT), in which fragments of fetal DNA are isolated from maternal blood. This is a safe and highly accurate method that can suspect trisomy 13 before invasive procedures are prescribed.

Invasive diagnosis includes procedures such as amniocentesis (sampling of amniotic fluid), chorionic villus sampling (sampling of placental tissue), and cordocentesis (sampling blood from the umbilical cord). These methods allow for accurate examination of the fetus's karyotype and confirmation of the diagnosis.

Postnatal diagnosis and examination after birth

If the newborn shows characteristic external signs of trisomy 13, such as microcephaly, polydactyly, cleft lip, or palate, a physical examination is performed. The diagnosis is confirmed by a cytogenetic analysis of the blood, which allows for the detection of the extra chromosome. Imaging methods are also used: ultrasound, neurosonography, echocardiography, to assess the degree of damage to internal organs and systems.

Treatment and care for children with Patau syndrome

The treatment of Patau syndrome cannot aim to eliminate the cause of the disease, as it is of genetic origin. However, modern medicine offers several approaches to improve the child's quality of life and prolong it as much as possible.

Supportive treatment includes a set of measures. Among these are physiotherapy, which helps maintain motor activity and prevent complications. Massages, passive exercises, breathing techniques, and sensory stimulation methods that promote the development of perception of the surrounding world are used.

If necessary, medications are prescribed. These may include sedatives if the child experiences seizures or significant excitability, as well as medications to support heart activity and relieve pain.

In some cases, doctors may consider surgical intervention. Operations are performed to correct potentially life-threatening congenital malformations, for example, in cases of complex heart anomalies, severe digestive tract malformations, or severe hydrocephalus. The decision is made on a case-by-case basis, taking into account the child's general condition and the expected tolerance to anesthesia.

Prognosis

The prognosis is extremely unfavorable: up to 80 to 90% of children with complete trisomy 13 die in the first months of life. Only 5 to 10% survive to the age of one, mainly in the mosaic form. Even if they survive, the children exhibit severe mental and physical disabilities and require constant care.

Current research

According to the American Journal of Medical Genetics, in 75% of cases, complete trisomy 13 is diagnosed, and in other cases, a mosaic form or translocations. These forms differ in the severity of symptoms.

Ongoing research contributes to a better understanding of genetic anomalies, helps improve early diagnostic methods, and approaches to pregnancy planning.