Patau syndrome

Introduction

Patau syndrome, also known as Trisomy 13, is a genetic disorder characterized by the presence of an extra copy of chromosome 13 in some or all of an individual's cells. Normally, individuals have two copies of each chromosome, one inherited from each parent. However, in Patau syndrome, individuals have three copies of chromosome 13. This extra genetic material disrupts normal development, leading to a range of severe physical and intellectual abnormalities.

Child with trisomy 13

Trisomy13

HandTrisomy13

Genetics of Patau Syndrome

The extra copy of chromosome 13 in Patau syndrome usually results from a process called nondisjunction, where cellular mechanisms fail to properly separate the chromosomes during the formation of reproductive cells (gametes). This results in an egg or sperm cell with an extra copy of chromosome 13. If such a cell contributes to the formation of an embryo, the resulting individual will have three copies of chromosome 13 in each cell.

Less commonly, Patau syndrome can result from a translocation, where a piece of chromosome 13 becomes attached to another chromosome. In such cases, individuals may have two normal copies of chromosome 13, but they also have additional material from chromosome 13 attached to another chromosome.

Clinical Manifestations

Patau syndrome leads to a wide array of abnormalities that can affect almost every part of the body:

• Neurological and Craniofacial Features: These include intellectual disability, microcephaly (a smaller than normal head size), and structural brain abnormalities. Facial features may include close-set eyes, small eye openings, a small mouth, and low-set ears.
• Eye Abnormalities: Structural defects such as microphthalmia (abnormally small eyes), anophthalmia (absence of one or both eyes), and retinal dysplasia are common.
• Limb and Digit Abnormalities: Individuals may have extra fingers or toes (polydactyly) and other limb abnormalities including a notable decrease in muscle tone (hypotonia).
• Other Features: Heart defects are common, as are abnormalities of the kidneys and other organs.

Diagnosis and Management

Patau syndrome is often diagnosed prenatally through screening tests such as ultrasound and amniocentesis, which can detect the presence of an extra chromosome 13. After birth, the diagnosis can be confirmed through a blood test called a chromosomal karyotype, which can visualize the presence of trisomy 13.

Management of Patau syndrome focuses on supportive care and addressing the individual's specific symptoms, as there is no cure for the condition. Children with Patau syndrome often need a team of specialists to address their complex medical needs.

Prognosis

Patau syndrome is typically associated with severe health problems and a shortened lifespan. Many affected individuals do not survive past the first few weeks or months of life due to the serious health problems associated with the condition. However, some individuals with less severe forms of the condition can live into adolescence or adulthood with appropriate supportive care.

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References

• Cereda A, Carey JC. The trisomy 13 syndrome. Orphanet Journal of Rare Diseases. 2012;7:74.
• Parker SE, Mai CT, Canfield MA, et al. Updated National Birth Prevalence estimates for selected birth defects in the United States, 2004-2006. Birth Defects Res A Clin Mol Teratol. 2010;88(12):1008-1016.