Etiology and genetic mechanisms
The development of Syndromum Patau is based on an alteration in the child's karyotype, specifically trisomy 13. This means that instead of a normal pair at the 13th position of the karyotype, there are three homologous chromosomes.
The primary pathogenetic mechanism underlying this anomaly is chromosomal nondisjunction. This failure occurs during cell division—meiosis—in the germ cells of one of the parents. As a result, a gamete is formed with extra genetic material, which is transmitted to the zygote upon fertilization, triggering a cascade of severe embryonic developmental disorders.
Epidemiology
Although chromosomal abnormalities are generally not rare, Patau syndrome occurs with a specific frequency in the population. According to statistical data, this rate ranges from 1:5,000 to 1:7,000. This makes this pathology one of the classic trisomies requiring close attention during prenatal screening.
Clinical presentation (phenotype)
The phenotypic manifestations of the syndrome are caused by a global disruption of organogenesis during embryogenesis. The clinical picture consists of multiple developmental malformations. The most severely affected systems include:
- Brain: gross structural anomalies develop.
- Facial skeleton: marked deformations are observed.
The most typical visual sign associated with this trisomy is a cleft upper lip combined with a cleft palate. This defect severely affects the newborn's appearance and serves as one of the markers during the initial examination.
Prognosis for patients
Due to the severity of combined malformations, the prognosis for Patau syndrome is assessed as extremely unfavorable.
The absolute majority of infants with this diagnosis die in the early neonatal period—in the first weeks or months of life. Only in extremely rare cases, with less pronounced damage to vital systems, can patients live somewhat longer; however, as a rule, their life expectancy is no more than one year. Reaching adolescence or, moreover, adulthood in true complete trisomy 13 is excluded.
Briefly: answers to topical questions
What ocular changes are characteristic of the Patau syndrome phenotype?
The phenotype of Patau syndrome is characterized by multiple severe developmental malformations, including impaired development of the eyeballs.
The following ocular abnormalities have been described:
- microphthalmia;
- retinal dysplasia;
- colobomas of the iris and choroid;
- lens malformations;
- cartilage ectopia.
What cytogenetic variants (forms) of Patau syndrome exist besides simple complete trisomy?
In addition to simple complete trisomy 13, there are forms of Patau syndrome associated with Robertsonian translocations.
In these cases, the development of the pathology is caused by the transmission of an additional chromosome (or its long arm) as a result of D/13 and G/13 Robertsonian translocations. Simple complete trisomy 13 (as a consequence of meiotic nondisjunction) accounts for 80–85% of all cases, while translocation variants account for the remaining 15–20%.
Patau = 13 (associate with the "devil's dozen", i.e., 13 — an extremely unfavorable prognosis).
Class and exam questions
Which chromosomal abnormality is associated with Patau syndrome?
The disease is caused by trisomy 13 (unlike, for example, trisomy 21 in Down syndrome or trisomy 18 in Edwards syndrome).
What is the underlying cause of the extra chromosome?
The cause lies in a meiotic disturbance in one of the parents, when chromosomal nondisjunction occurs, and extra genetic material enters the germ cell.
Which facial defect is considered the most typical for this syndrome?
The most characteristic phenotypic feature is the presence of a cleft upper lip and cleft palate.
Do patients with Patau syndrome survive into adolescence?
No, the prognosis is extremely unfavorable. Children generally live no more than one year; the majority die in the first weeks or months of life.
What else to study on this topic
- Mechanisms of chromosomal nondisjunction in meiosis I and meiosis II
- Comparative characteristics of trisomies: chromosomes 13, 18, and 21
- Embryogenesis of the facial skeleton and causes of cleft lip and palate formation
- Specific brain malformations in Patau syndrome
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