Patau syndrome
Patau syndrome, also known as trisomy 13, is a severe genetic disorder characterized by the presence of an extra chromosome 13 in each cell, leading to a total of 47 chromosomes instead of the typical 46. This condition arises primarily due to nondisjunction during the formation of egg or sperm cells, with advanced maternal age identified as a significant risk factor. The syndrome manifests with various physical and developmental anomalies, including microcephaly, cleft lip and/or palate, and polydactyly (extra fingers or toes). Affected individuals often have profound intellectual disabilities, heart defects, and other serious health challenges, resulting in a high mortality rate; approximately 44% of affected newborns do not survive beyond the first month, and over 70% do not survive the first year.
Diagnosis typically occurs at birth based on visible symptoms, though genetic testing is essential for confirmation. While treatment is tailored to the specific needs of the child, it often focuses on comfort and addressing immediate health issues, such as surgical interventions for heart defects. Despite the challenges, there is some evidence suggesting that early medical care can improve survival rates, with some children living beyond their early years. Genetic counseling and prenatal screening options, like amniocentesis, are recommended for expectant parents, particularly those at higher risk due to maternal age.
Patau syndrome
ALSO KNOWN AS: Trisomy 13; Patau’s syndrome; D trisomy syndrome; Bartholin-Patau syndrome
DEFINITION Patau syndrome is a severe systemic disorder that affects many essential body systems and functions. Typically, each cell in the body will have an extra copy of chromosome 13, thus yielding a total of 47 chromosomes per cell instead of the usual 46.
Risk Factors
The only consistently reported risk factor is advanced maternal age, since the extra copy of chromosome 13 most commonly arises from an error in meiosis during egg cell maturation. Sex does not appear to be a significant risk factor, with the incidence in female fetuses being 52 percent as compared to 48 percent in males, as reported in a 2012 Pediatrics study by K. E. Nelson, K. R. Hexem, and C. Feudtner.
Etiology and Genetics
The presence of an extra chromosome 13 in the cells of a developing fetus results from a type of error called nondisjunction, which can occur during (sperm or egg) production in either parent. Either the failure of chromosomes to separate from each other during the first meiotic division or the failure of sister chromatids to separate from each other during the second meiotic division will result in mature sperm cells or egg cells that have either one extra or one missing chromosome. Since each chromosome contains thousands of genes, it is not surprising that individuals with extra or missing chromosomes in all cells would have a severe imbalance of genetic information and suffer from multiple developmental anomalies. In fact, only three autosomal trisomies (conditions in which each cell has three copies of a nonsex chromosome) are generally known to be consistent with full-term delivery, and Patau syndrome is the least common and most severe of these. The most common and least severe is Down syndrome (trisomy 21). Edwards syndrome (trisomy 18), like Patau syndrome, results in affected newborns with multiple structural and developmental problems, and survival beyond the first year is rare.
Very occasionally, a case of 13 occurs in which the extra copy of chromosome 13 does not appear as a separate chromosome but rather is physically attached onto the end of another chromosome; such cases are known as Patau syndrome. While the clinical features of the affected newborn do not differ from the usual form of the syndrome, it is particularly important to identify this variety of Patau, since it may be transmitted with high frequency by a normal-appearing parent who carries the translocation chromosome.
One additional variant that is infrequently encountered is known as mosaic trisomy 13. The bodies of mosaic individuals are composed of two distinctly different cell lines, in which only some of the cells have the extra chromosome 13, while the remainder have a normal chromosome complement. The severity of the clinical presentation in these cases depends on the type and number of cells that carry the extra chromosome, but in almost all cases a less severe form of the syndrome is manifested.
Symptoms
The most consistent symptoms present at birth include microcephaly (small head), cleft lip and/or palate, and (extra fingers or toes). Ears are often low-set and malformed, and the nose can be oddly shaped or occasionally altogether absent. Most affected individuals are presumed to be hearing impaired, and many are blind as well. Other neurological problems are common, including profound intellectual disability and failure of the brain to divide into its proper hemispheres during gestation. About 80 percent of affected newborns are reported to have moderate to severe heart defects, as reported by the National Organization for Rare Diseases.
Screening and Diagnosis
According to the University of Chicago, Patau syndrome occurs in about 1 out of 5,000 live births, and diagnosis is most often immediately apparent, although there is some overlap of symptoms with Edwards syndrome. Genetic studies should be performed to confirm the diagnosis. Ultrasound examinations and imaging studies should be done to check for more extensive developmental problems. They include brain, heart, and kidney defects as well as an extra spleen, rotated intestines, and defects of the liver and pancreas. Males may have undescended testes, while females frequently have a divided uterus.
Treatment and Therapy
Because of the heterogeneous nature of each clinical presentation, treatment is usually specifically directed to the particular physical problems with which each affected child is born. As reported by the University of Chicago, about 44 percent of affected newborns die within the first month and more than 70 percent die within a year. Most die from serious heart defects or severe neurological problems. Historically, medical treatment has focused primarily on patient comfort and noninvasive symptom treatment rather than on prolonging life.
Surgery may be performed to repair heart defects or cleft lip and palate. In 2017 researchers from Stanford University and the University of Arkansas published the results of a study conducted between 2004 and 2015 on almost 1,600 patients affected by trisomy 13 or trisomy 18. The study determined that early surgical intervention to repair heart issues present in patients with Patau syndrome as well as trisomy 18 showed extended lifespans of at least one to two years. In those Patau syndrome cases where survival extends beyond one or two years, additional surgeries and physical therapy are often undertaken to allow the affected child to reach his or her full developmental potential. Nelson, Hexem, and Feudtner's study indicates that children born with Patau syndrome are surviving for increasingly longer periods and that neonatal interventions may improve survival rates.
Prevention and Outcomes
Except for the rare translocation form of Patau syndrome, there is no effective means of prevention. Genetic counseling should always be available for parents of an affected child, and amniocentesis is an option for older at-risk mothers. According to the University of Chicago, only up to 30 percent of affected newborns survive the first year of life, and survival into the teenage years is exceedingly rare.
Bibliography
Cummings, Michael R. Human Heredity: Principles and Issues. 10th ed. Belmont: Brooks/Cole, 2014. Print.
De la Rocha, Kelly. "Chromosomal Abnormalities: Trisomy 13 and 18." Health Library. EBSCO, 28 May 2014. Web. 5 Aug. 2014.
Kosiv, Katherine A. et al. "Congenital Heart Surgery on In-Hospital Mortality in Trisomy 13 and 18." Pediatrics, vol. 140, Nov. 2017, DOI: 10.1542/peds.2017-0772. Accessed 4 Sept. 2024.
Lewis, Ricki. Human Genetics. 10th ed. New York: McGraw, 2011. Print.
Nelson, Katherine E., Kari R. Hexem, and Chris Feudtner. "Inpatient Hospital Care of Children with Trisomy 13 and Trisomy 18 in the United States." Pediatrics 129.5 (2012): 1–8. PDF file.
Nussbaum, Robert L., Roderick R. McInnes, and Huntington F. Willard. Thompson and Thompson Genetics in Medicine. 7th ed. New York: Saunders, 2007. Print.
"Trisomy 18 (Edwards), Trisomy 13 (Patau)." Pediatrics Clerkship, University of Chicago. U of Chicago, 2013. Web. 13 Aug. 2014.